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Posted on May 15, 2018
A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to temporarily store electrical energy in an electric field. The forms of practical capacitors vary widely, but most contain at least two electrical conductors (plates) separated by a dielectric (i.e. an insulator that can store energy by becoming polarized). The conductors can be thin films, foils or sintered beads of metal or conductive electrolyte, etc. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.
When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of the capacitor, a displacement current can flow.
An ideal capacitor is characterized by a single constant value, its capacitance. Capacitance is defined as the ratio of the electric charge Q on each conductor to the potential difference V between them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F).
The larger the surface area of the "plates" (conductors) and the narrower the gap between them, the greater the capacitance is. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance.
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow,
capacitor start motor
A motor capacitor, such as a start capacitor or run capacitor (including a dual run capacitor) is an electrical capacitor that alters the current to one or more windings of a single phase AC induction motor to create a rotatingmagnetic field.
Troubleshooting single-phase refrigeration compressors requires a technician to have a proficient understanding of capacitors. The start capacitor is one of two types of capacitors that can be found on single-phase compressors. Understanding how to troubleshoot and replace a defective starting capacitor is essential when working with these compressors.
The start capacitor is used to boost the starting torque of a compressor’s motor. This is done by placing the start capacitor in series with the start winding during the starting of the compressor. As current flows through the start capacitor and the start winding, the capacitor causes the start winding to become out of phase with the run winding.
This causes the motor to start with a higher torque than would normally be possible. The addition of a start capacitor increases the starting torque of the compressor by 300% to 500%. The start capacitor is designed to stay in the circuit only until the compressor reaches 2/3 to 3/4 of its operating speed. If left in longer, the start capacitor could be damaged. It is not designed to dissipate the heat that will build up from continuous operation.
Defective start capacitors can and will lead to problems with the operation of single-phase compressors. A start capacitor can be damaged by a sticking relay, which will cause it to stay in the circuit longer than normal and overheat. A start capacitor can also overheat from rapid cycling of a compressor. It is recommended that a start capacitor be limited to a maximum of 20 starts per hour.
capacitor start capacitor run motor
The most complicated and expensive single-phase motor is the Capacitor-Start/Capacitor-Run Motor. These motors contain both a starting and running capacitor. Smaller sizes will generally have two capacitor enclosures on the top of the motor, while larger sizes may have both capacitors in a large housing on the side of the motor. Capacitor-start/capacitor-run motors are used over a wide range of single-phase applications primarily for starting hard loads. They are available in sizes ranging from ½ to 25 horsepower; however, common sizes are between 3-and-10 horsepower. Maximum sizes allowed are generally dictated by the electrical power supplier. The speed of this motor varies about 10% from no load to fully loaded conditions. Some capacitor-start/capacitor-run motors are available as multi-speed motors with two-or-three fixed operating speeds when appropriate control equipment is used.
Capacitor-start/capacitor-run motors have moderate-to-high starting torque compared to other types of single-phase motors. Starting torque generally ranges from 200%-350% of normal full-load torque. Their main advantage over the capacitor-start motor is their lower starting-torque that results in lower starting current. Because of the lower starting current, they are generally used for most single-phase applications between 3-and-10 horsepower due to their lower starting current. Common applications include: larger single-phase compressors, pumps, grinders, conveyors, and larger single-phase air-conditioning compressors.
Capacitor-start/capacitor-run motors require less running current and are therefore more energy efficient than capacitor-start motors; however, they cost more to purchase than many other motors. Capacitor-start/capacitor-run motors typically cost from 100%-to-115% of the cost of a comparable 3-Phase Induction Motor.
These motors have two capacitors in series with the main stator winding. The starting capacitor is connected in series with the centrifugal switch, while the running capacitor is NOT. The starting capacitor optimizes starting-torque during the starting period, while the running capacitor optimizes the motor's current flow leading to better energy efficiency when operating at running speed.
When the motor initially starts with the centrifugal switch in the closed position, both capacitors are functional. Once the motor gets to about 70%-to-80% of normal operating speed, the switch disconnects the starting capacitor. Since the run capacitor is NOT wired in series with the switch, the run capacitor remains functional to optimize the motor's performance. This design provides optimum levels of both starting-torque and efficient running characteristics. The motor will have starting problems if the centrifugal switch sticks open or closed which can be relatively common in dirty environments. If the switch sticks closed, it will cause the starting winding to burn out of the motor. If the switch sticks in the open position, the motor will NOT start the next time, while sitting there making a humming sound.
Capillary tube is one of the most commonly used throttling devices in the refrigeration and the air conditioning systems. The capillary tube is a copper tube of very small internal diameter. It is of very long length and it is coiled to several turns so that it would occupy less space. The internal diameter of the capillary tube used for the refrigeration and air conditioning applications varies from 0.5 to 2.28 mm (0.020 to 0.09 inches). Capillary tube used as the throttling device in the domestic refrigerators, deep freezers, water coolers and air conditioners.
How Capillary Tube Works?
When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary. In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary.
The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary. Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it.
In the normal working conditions of the refrigeration plant there is drop in pressure of the refrigerant across the capillary but when the plant stops the refrigerant pressure across the two sides of the capillary equalize. Due to this reason when the compressor restarts there won’t be much load on it. Also, due to this reason one cannot over-charge the refrigeration system with the refrigerant and no receiver is used.
The capillary tube is non-adjustable device that means one cannot control the flow of the refrigerant through it as one can do in the automatic throttling valve. Due to this the flow of the refrigerant through the capillary changes as the surrounding conditions changes. For instance as the condenser pressure increases due to high atmospheric pressure and the evaporator pressure reduces due to lesser refrigeration load the flow of the refrigerant through the capillary changes. Thus the capillary tube is designed for certain ambient conditions. However, if it is selected properly, it can work reasonably well over a wide range of conditions.
The length of the capillary of particular diameter required for the refrigeration applications cannot be found by fixed formula rather it is calculated by the empirical calculations. Some approximate length required for certain application is found out and it is then corrected by the experiments.
When the refrigerant leaves the condenser and enters the capillary tube its pressure drops down suddenly due to very small diameter of the capillary. In capillary the fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of the capillary. The decrease in pressure of the refrigerant through the capillary depends on the diameter of the capillary and the length of the capillary. Smaller is the diameter and more is the length of the capillary more is the drop in pressure of the refrigerant as it passes through it.
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Carbon monoxide (CO) is a deadly, colorless, odorless, poisonous gas. It is produced by the incomplete burning of various fuels, including coal, wood, charcoal, oil, kerosene, propane, and natural gas. Products and equipment powered by internal combustion engines such as portable generators, cars, lawn mowers, and power washers also produce CO.
On average, about 170 people in the United States die every year from CO produced by non-automotive consumer products. These products include malfunctioning fuel-burning appliances such as furnaces, ranges, water heaters and room heaters; engine-powered equipment such as portable generators; fireplaces; and charcoal that is burned in homes and other enclosed areas. In 2005 alone, CPSC staff is aware of at least 94 generator-related CO poisoning deaths. Forty-seven of these deaths were known to have occurred during power outages due to severe weather, including Hurricane Katrina. Still others die from CO produced by non-consumer products, such as cars left running in attached garages. The Centers for Disease Control and Prevention estimates that several thousand people go to hospital emergency rooms every year to be treated for CO poisoning.
What are the symptoms of CO poisoning?
Because CO is odorless, colorless, and otherwise undetectable to the human senses, people may not know that they are being exposed. The initial symptoms of low to moderate CO poisoning are similar to the flu (but without the fever). They include:
Shortness of breath
High level CO poisoning results in progressively more severe symptoms, including:
Loss of muscular coordination
Loss of consciousness
Symptom severity is related to both the CO level and the duration of exposure. For slowly developing residential CO problems, occupants and/or physicians can mistake mild to moderate CO poisoning symptoms for the flu, which sometimes results in tragic deaths. For rapidly developing, high level CO exposures (e.g., associated with use of generators in residential spaces), victims can rapidly become mentally confused, and can lose muscle control without having first experienced milder symptoms; they will likely die if not rescued.
How can I prevent CO poisoning?
Make sure appliances are installed and operated according to the manufacturer's instructions and local building codes. Most appliances should be installed by qualified professionals. Have the heating system professionally inspected and serviced annually to ensure proper operation. The inspector should also check chimneys and flues for blockages, corrosion, partial and complete disconnections, and loose connections.
Never service fuel-burning appliances without proper knowledge, skill and tools. Always refer to the owners manual when performing minor adjustments or servicing fuel-burning equipment.
Never operate a portable generator or any other gasoline engine-powered tool either in or near an enclosed space such as a garage, house, or other building. Even with open doors and windows, these spaces can trap CO and allow it to quickly build to lethal levels.
Install a CO alarm that meets the requirements of the current UL 2034 safety standard. A CO alarm can provide some added protection, but it is no substitute for proper use and upkeep of appliances that can produce CO. Install a CO alarm in the hallway near every separate sleeping area of the home. Make sure the alarm cannot be covered up by furniture or draperies.
Never use portable fuel-burning camping equipment inside a home, garage, vehicle or tent unless it is specifically designed for use in an enclosed space and provides instructions for safe use in an enclosed area.
Never burn charcoal inside a home, garage, vehicle, or tent.
Never leave a car running in an attached garage, even with the garage door open.
Never use gas appliances such as ranges, ovens, or clothes dryers to heat your home.
Never operate unvented fuel-burning appliances in any room where people are sleeping.
Do not cover the bottom of natural gas or propane ovens with aluminum foil. Doing so blocks the combustion air flow through the appliance and can produce CO.
During home renovations, ensure that appliance vents and chimneys are not blocked by tarps or debris. Make sure appliances are in proper working order when renovations are complete.
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What CO level is dangerous to my health?
The health effects of CO depend on the CO concentration and length of exposure, as well as each individual's health condition. CO concentration is measured in parts per million (ppm). Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible.
What should I do if I am experiencing symptoms of CO poisoning and do not have a CO alarm, or my CO alarm is not going off?
If you think you are experiencing any of the symptoms of CO poisoning, get outside to fresh air immediately. Leave the home and call your fire department to report your symptoms from a neighbor’s home. You could lose consciousness and die if you stay in the home. It is also important to contact a doctor immediately for a proper diagnosis. Tell your doctor that you suspect CO poisoning is causing your problems. Prompt medical attention is important if you are experiencing any symptoms of CO poisoning. If the doctor confirms CO poisoning, make sure a qualified service person checks the appliances for proper operation before reusing them.
Are CO alarms reliable?
CO alarms always have been and still are designed to alarm before potentially life-threatening levels of CO are reached. The safety standards for CO alarms have been continually improved and currently marketed CO alarms are not as susceptible to nuisance alarms as earlier models.
How should a consumer test a CO alarm to make sure it is working?
Consumers should follow the manufacturer's instructions. Using a test button tests whether the circuitry is operating correctly, not the accuracy of the sensor. Alarms have a recommended replacement age, which can be obtained from the product literature or from the manufacturer.
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How should I install a CO Alarm?
CO alarms should be installed according to the manufacturer's instructions. CPSC recommends that one CO alarm be installed in the hallway outside the bedrooms in each separate sleeping area of the home. CO alarms may be installed into a plug-in receptacle or high on the wall. Hard wired or plug-in CO alarms should have battery backup. Avoid locations that are near heating vents or that can be covered by furniture or draperies. CPSC does not recommend installing CO alarms in kitchens or above fuel-burning appliances.
What should you do when the CO alarm sounds?
Never ignore an alarming CO alarm! It is warning you of a potentially deadly hazard.
If the alarm signal sounds do not try to find the source of the CO:
Immediately move outside to fresh air.
Call your emergency services, fire department, or 911.
After calling 911, do a head count to check that all persons are accounted for. DO NOT reenter the premises until the emergency services responders have given you permission. You could lose consciousness and die if you go in the home.
If the source of the CO is determined to be a malfunctioning appliance, DO NOT operate that appliance until it has been properly serviced by trained personnel.
If authorities allow you to return to your home, and your alarm reactivates within a 24 hour period, repeat steps 1, 2 and 3 and call a qualified appliance technician to investigate for sources of CO from all fuel burning equipment and appliances, and inspect for proper operation of this equipment. If problems are identified during this inspection, have the equipment serviced immediately. Note any combustion equipment not inspected by the technician and consult the manufacturers’ instructions, or contact the manufacturers directly, for more information about CO safety and this equipment. Make sure that motor vehicles are not, and have not been, operating in an attached garage or adjacent to the residence.
What is the role of the U.S. Consumer Product Safety Commission (CPSC) in preventing CO poisoning?
CPSC staff worked closely with Underwriters Laboratories (UL) to help develop the safety standard (UL 2034) for CO alarms. CPSC helps promote carbon monoxide safety by raising awareness of CO hazards and the need for correct use and regular maintenance of fuel-burning appliances. CPSC staff also works with stakeholders to develop voluntary and mandatory standards for fuel-burning appliances and conducts independent research into CO alarm performance under likely home-use conditions.
Do some cities require that CO alarms be installed?
Many states and local jurisdictions now require CO alarms be installed in residences. Check with your local building code official to find out about the requirements in your location.
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In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal.
A centrifugal compressor is a type of dynamic compressor, or turbocompressor, with a radial design. Unlike displacement compressors that work at a constant flow, dynamic compressors work at a constant pressure and the performance is affected by external conditions such as changes in inlet temperatures.
So, how does a centrifugal compressor work?
Air is drawn into the center of a rotating impeller with radial blades and is pushed toward the center by centrifugal force. This radial movement of air results in a pressure rise and the generation of kinetic energy. Before the air is led into the center of the impeller, the kinetic energy is also converted into pressure by passing through a diffuser and volute.
Each stage takes up a part of the overall pressure rise of the compressor unit. Depending on the pressure required for the application, a number of stages can be arranged in a series to achieve a higher pressure. This type of multi-stage application is often used in the oil and gas and process industries. Alternately, in wastewater treatment plants, low pressure, single-stage applications are used to achieve the desired pressure ratio.
In modern configurations of centrifugal air compressors, ultra-high speed electric motors are used to drive the impellers. This results in a compact compressor without a gearbox and associated oil-lubrication system, thus making it oil-free and appropriate for applications that require 100 percent oil-free air.
Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits.
Common uses include water, sewage, petroleum and petrochemical pumping; a centrifugal fan is commonly used to implement a vacuum cleaner. The reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy.
A centrifugal switch is an electric switch that operates using the centrifugal force created from a rotating shaft, most commonly that of an electric motor or gasoline engine. The switch is designed to activate or de-activate as a function of the rotational speed of the shaft,
CFM refers to the method of measuring the volume of air moving through a ventilation system or other space, also known as "Cubic Feet per Minute." This is a standard unit of measurement found in many forms of ventilation, both in vehicle and in home heating, ventilation and air conditioning systems. a home air conditioner moves roughly 400 cubic feet of air per minute. For metric measurements, 1 cubic foot of air equals approximately 28.31 liters. Professionals measure this rate using a tool known as an anemometer, which measures both the volume of air and the rate at which it moves.
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change of state
A material will change from one state or phase to another at specific combinations of temperature and surrounding pressure. Typically, the pressure is atmospheric pressure, so temperature is the determining factor to the change in state in those cases.
Names such as boiling and freezing are given to the various changes in states of matter. The temperature of a material will increase until it reaches the point where the change takes place. It will stay at that temperature until that change is completed.
All air conditioners and refrigerators rely on the correct charge, or amount of refrigerant gas in their systems, to work correctly. Refrigerant charging refers to the replenishment of these gases when system repairs or leaks have caused depleted levels. Refrigerant charging may be carried out using bulk refrigerant containers or charging kits which generally only hold enough gas for one charge. In either case, a refrigerant charging manifold with its associated hoses, valves, and gauges is needed to complete the operation. Recharging of refrigerant gas is typically carried out via a non-return service port or valve fitted to the system.
Air conditioning units and refrigerators are designed to operate correctly with a predetermined charge of refrigerant gas. Under perfect operational conditions, air conditioners and refrigerators would never require recharging but leaks do sometimes develop which deplete refrigerant charges. Repairs to these systems also require the draining and subsequent recharging of the refrigerant. There are several quick pointers during normal operation which indicate a depleted refrigerant charge. These include low system efficiency, noticeably lower temperatures from the condenser fan, icing up of the coils, and localized oily residue on pipes which may indicate a leak
If a depleted refrigerant charge is suspected, the condition should be verified using a set of system pressure gauges; this verification procedure may have to be carried out by a qualified technician. If the result is positive, the system should be recharged as soon as possible because low refrigerant charges place excessive loads on the compressor. Most refrigeration and air conditioning systems will feature a service valve to facilitate recharging the system. These valves are typically of a Schraeder non-return design which allow for refrigerant charging without any loss of system pressure. The recharging process is carried out from a cylinder or recharge kit of relevant refrigerant via the manifold and gauge assembly.
Refrigerant charging is carried out with the compressor running to ensure even charging. The system should also be given time to warm up to normal operational temperatures before recharging commences. When recharging, refrigerant gas should be added in small increments to avoid overloading the system. Between each gas input, the system should be allowed to run for a short time to allow the gas charge to settle and the pressure checked. When the pressure is within the manufacturers operation specifications, the supply valve on the cylinder can be closed and the manifold removed from the system.
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When the maintenance of some devices, such as domestic refrigerators, window blocks, packing unit, ice machines, and automotive Air conditioning there can be no guesses as to how much refrigerant should be in the squad. There is a certain amount of refrigerant used in this type of equipment and the manufacturer places that amount on the data plate. The amount necessary in these units, as a rule, is given in pounds and ounces. When using small quantities such as this, one of the ways that it could be handled very fine adjustment of the scale or thecharging cylinder. In cylinder it is a valuable tool that should be part of your inventory tool, if you are working on this type equipment.
Operation of the charging cylinder extremely simple once you understand procedure.A tube where you place the amount of refrigerant is located in the center of the cylinder.
This refrigerant charging scale is used for charging and recovery of commercial, automotive and refrigeration A/C systems, large weight platform to easely accomodate 30lb tanks.
A check valve , also called a non-return valve, is a mechanical device that normally allows fluid to flow through it in only one direction. The force of upstream fluid creates high differential pressure across the interior valve body, and it then allows forward streams to pass through, An important concept in check valves is the cracking pressure, which is the minimum upstream pressure required for the valve to operate. Typically, the check valve is designed for a specific cracking pressure. Check valves are useful in several different types of devices. They stop flooding in water-related devices such as sump pumps and water heaters. They also protect equipment that can be harmed by the reverse flow of material, such as control valves, strainers and flow meters. In addition, check valves can stop material from constantly flowing backwards when a device is off, which can save power and protect the parts of the device.
There are several types of check valves. Some of the more popular include ball check valves, diaphragm check valves, dual-door check valves and clapper check valves. Most of these valves work in a similar way, but no one type of valve is good for all applications. Each of these check valve types has its advantages and disadvantages depending on the application.
chilled water system
There are three types of HVAC systems that utilize water as a heat transfer medium. The first system,
which is used for cooling in dry climates, is called the “Swamp Cooler.” This system employs a fan that
blows outdoor air or return air over a revolving drum. The drum is covered with a sponge-like material and
the lower portion of the drum is immersed in water. As the air passes over the drum, the air temperature is
lowered, and the relative humidity of the air is increased as water on the drum evaporates. This
evaporation process will remove 760 BTU per pound of water evaporated. However, as mentioned earlier,
the process only works in dry climates where the air has a moisture content that is low enough to allow it to
accept the additional moisture from the evaporation process.
The second water-based system uses a constant source of water at a temperature of 80°F or less to condense
the refrigerant vapor in a standard mechanical refrigeration circuit. This water is called condenser water.
This type of unit is known as a packaged water-cooled air conditioner. Condenser water is normally
provided by a mall or a large building for use by its tenants. The building then maintains a cooling tower
that is used to cool the condenser water and pumps that are used to circulate the water. This type of system
is used where there is limited access to outdoor areas such as roofs for placement of outdoor equipment.
We will deal with water-cooled systems in detail in a future article.
The third type of water based air conditioning system is called a chilled water system. Chilled water
systems utilize a constant source of water at a temperature of approximately 45°F. This water can be
provided by a central building chilled water plant, an off-site utility that sells chilled water, or by the
tenant’s own packaged chiller. Most retail stores with less than 40,000 square feet of floor space do not
have their own chillers and depend on Landlord furnished chilled water
Chilled water system description and operation:
For our purposes, let’s assume that the Landlord is providing an uninterruptable source of 45°F chilled
water to the building. This water is distributed throughout the building via a piping network. The large
horizontal pipes are called mains, the small piping leading to each tenant space are called branches, and the
vertical runs are called risers. The chilled water piping is heavily insulated and the insulation is covered
with a vapor barrier, which is impervious to moisture. These pipes are carrying a low temperature liquid,
and if they were left uninsulated, moisture from the air would condense on the outside of the pipes and drip
onto anything below the piping. In addition, heat would be transferred to the piping from the air resulting
in wasted energy and a rise in the chilled water temperature.
One or more air handlers serve each tenant. An air handler is a sheet metal box that contains a fan and a
cooling coil. The cooling coil is made of copper tubing bent into a serpentine shape with aluminum fins
bonded to the copper tubing to increase the heat transfer area. The air handler also contains air filters that
remove impurities from the air that is being drawn over the coil by the fan. The fan is also called a blower.
A motor drives the blower via a drive belt that has a V section. The air handler may also be furnished with
a heating coil that adds heat to the air when heat is required.
Most chilled water air handlers contain a section called a mixing box. The mixing box is a sheet metal
section with two openings in it. There is a duct connected to each opening and a damper located within
each opening. One duct is used to bring return air from the conditioned space back to the air handler. The
second duct is connected to the outdoors and is used to introduce outdoor air for ventilation purposes.
Operation of a system like this is simple. The fan runs continuously, drawing a mix of outdoor air and
return air through the air filters. The air is then heated or cooled as it passes over hot coils or cold coils.
Chilled water flow to the cooling coil is controlled by a motorized valve. If the space temperature is at or below the setpoint of the thermostat, the motorized valve closes. If the thermostat is not satisfied, the
motorized valve opens causing chilled water to flow through the coil.
If the air handler is equipped with a hot water heating coil and a chilled water-cooling coil the system is
known as a four-pipe system. In some buildings, the same coil is used for both heating and cooling.
During the cooling season, chilled water is circulated through the piping system that serves the air handlers
and during the heating season, hot water is circulated through the system. This is known as a two-pipe
system. Sometimes heat is provided by an electric resistance coil, a steam heating coil, or a gas fired duct
furnace instead of being provided by hot water.
Most chilled water air handlers are installed with outdoor air ducts that can deliver the full volume of air
the unit is designed to circulate. This oversized outdoor air duct, the mixing box, and the addition of
certain controls, forms the components required for an economizer cycle. When outdoor air temperatures
are below a threshold value of approximately 55°F, outdoor air may be used for cooling in lieu of using
chilled water. This is an energy saving device in four pipe systems and a necessity in two pipe systems. In
buildings with two-pipe systems, the building may be circulating hot water in an attempt to provide heat,
while some spaces with high internal loads require cooling. Under these circumstances, outdoor air is the
only medium available to provide cooling,
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A chimney is a structure that provides ventilation for hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the stack, or chimney, effect. The space inside a chimney is called a flue. Chimneys may be found in buildings, steam locomotives and ships. In the United States, the term smokestack (colloquially, stack) is also used when referring to locomotive chimneys or ship chimneys, and the term funnel can also be used.
The height of a chimney influences its ability to transfer flue gases to the external environment via stack effect. Additionally, the dispersion of pollutants at higher altitudes can reduce their impact on the immediate surroundings. In the case of chemically aggressive output, a sufficiently tall chimney can allow for partial or complete self-neutralization of airborne chemicals before they reach ground level. The dispersion of pollutants over a greater area can reduce their concentrations and facilitate compliance with regulatory limits.
For matters of this discussion, chimney draft is usually thought of as the speed at which the vented gasses travel up the stack, or pressure of the gasses. This can also be referred to as the stack effect. A common question might be “how strong is the stack effect?” Good draft conditions mean that the vented gasses are traveling up the chimney quickly rather than slowly or not at all.
The reason smoke (or other flue gas) goes up the chimney at all is because of the vacuum in the chimney. The question you should ask now is “a vacuum relative to what?” The general answer is that it’s relative to the air in the house. Don’t read too much into that because it gets tricky (for example, how does replacement air get into the house?- because the house environment is a relative vacuum to the outside. Yet the inside of the house is not a vacuum compared to the chimney.) Let’s keep this simple and just talk about the chimney. The pressure in the chimney is typically less than that inside the house. Thus, the draft effect is caused by air inside the chimney being pushed up the chimney by the house air.
And why is there a difference in pressure in and out of the house, or in and out of the chimney? There can be a few reasons, but the biggest and most important reason is the temperature difference from one place to another. Remember that when air is heated it expands? The same amount of air occupies a larger space, or you could say the same amount of space has less air (fewer molecules of air.)
The air outside the house in the winter is colder and heavier than the warmer air in the house. It pushes its way into the house (or is it pulled, depending on how confused you want to be.) The air in the chimney just came from a fire so it’s really hot and expanded and being pushed up the chimney to the cooler air outside where warm air rises, right? That’s buoyancy. Problems occur when these processes don’t happen correctly.
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Co indicator provides a simplified method for centering a workpiece or fixture on HORIZONTAL or VERTICAL machines, EXTERNAL or INTERNAL diameters -also with N/C, EDM and other hard to turn spindles.
The face of the indicator remains stationary in any desired position while the machine spindle rotates, thus leaving the operator with both hands free to accurately position the machine table by coordinated movement of the table positioning controls while observing the indicator hand reaction. (Indicator hand travel diminishes as location error is reduced to a point where the hand stands still, indicating coaxial alignment of the diameter being checked with the spindle axis)
By using the CO-AX INDICATOR with the machine spindle running exact operating conditions are more nearly simulated for the centering operation since the influence of power transmission, lubricant flow, bearing characteristics and torque are integrated into the indicator reading.
When two molecules meet under the right circumstances, they may exchange electrons in ways that change both molecules into new kinds of molecules. While they're doing that - reacting to each other - they may also release some electrical energy in the form of heat or light. This is what happens whenever there is a fire. The earliest fires were stars, where when hydrogen atoms meet under a lot of pressure from gravity, they merge together into helium atoms and let off some extra energy - that's the sunshine we get from our Sun.
The same kind of thing happens in a forest fire, or when you light a candle or a match. Candles are made of hydrocarbon molecules (sometimes oil, sometimes beeswax, sometimes tallow from animal fat), and matches are made from hydrocarbon molecules (wood). When they get hot enough, these hydrocarbon molecules react with the oxygen in the air. The heat can come from friction, like when you strike a match, or from another fire, like when you hold the match to the candle, or from lightning that starts a forest fire, or from focused sunlight. When the hydrocarbon molecules reach 300 degrees Fahrenheit (150 degrees Celsius), the reaction begins.
reaction, the molecules come apart and recombine into carbon, carbon dioxide, smoke, and water. But the reaction leaves a little energy left over, and that's the heat and light of the fire.
Anything made of hydrocarbons, like wood, charcoal, alcohol, leaves, people, oil, gas, or plastic, will burn. A few other things, like magnesium metal, will also burn.
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Combustion air is necessary for burning fuel such as gas, oil and wood. For a furnace to work properly, it must have an adequate supply of combustion air. The fire triangle calls for fuel, oxygen and an ignition source to have successful combustion.In this discussion, our focus is on gas furnaces that are obtaining combustion air from inside the home. These would include natural draft and induced draft furnaces. For simplicity, we will use the example of a conventional gas furnace, even though these systems have not been installed in a very long time. Any of these you see in the field are typically near or past their life expectancies.
Burners in conventional gas furnaces are natural draft. This means that we are not blowing any air into the combustion chamber to create an artificial draft condition (this is forced draft), nor are we pulling air through the combustion chamber on the exhaust side, again creating an artificial draft condition (this is induced draft).
Need 30 Feet of Air For Every Foot of Gas
Furnaces need both combustion air and dilution air. The requirements are about 15 cubic feet of combustion air and 15 cubic feet of dilution air for every cubic foot of gas burned. Since a cubic foot of natural gas contains about one thousand BTUs, a furnace that fires at the rate of 120,000 BTUs per hour would use 120 cubic feet of gas if it fired constantly for 60 minutes. This means that it would use two cubic feet of gas per minute.
We need about 60 cubic feet of air per minute (30 x 2) to ensure proper operation of this furnace. This is similar to the capacity of a typical bathroom exhaust fan. If we put the furnace in a closet and seal it off, it won’t have enough air to work properly.
Not Enough Air
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The available air in a closed room 5 feet by 5 feet by 8 feet tall is 200 cubic feet. This would be consumed very quickly by a furnace firing at this rate. If the room could not easily replace the air, the room and the furnace would be under negative pressure, relative to the chimney.
The implications of inadequate air are significant. The incomplete combustion process will generate carbon monoxide (the poisonous gas). Further, the lack of dilution air is likely to result in backdraft. This means that combustion products can’t go up the chimney but are dumped back into the room, which is under low pressure (since it’s starved for air, because we’ve pulled all the air into the furnace for the combustion and dilution process). Some people call backdrafting spillage.
Strategy for Checking for Spillage
When a furnace is operating, it’s easy to look for spillage or backdrafting through the draft hood. Some people use a match or smoke candle. However, in most cases you can tell simply with your hand. When you put your hand into the base of the draft hood, you should feel cool room air being drawn in. If you feel hot, wet exhaust air coming down onto your hand, spillage is taking place. With a little bit of practice, you can readily identify this. Don’t mistake the radiant heat from the hot flue as a downdraft.
Spillage on Start Up Normal
It’s normal to have a little bit of spillage when an appliance starts up. The heavy column of cool air in the chimney has to be overcome for the appliance to vent properly. Until the chimney is warmed by the exhaust products, spillage may occur. This should be overcome within the first minute or two of operation.
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Another indication of spillage is condensation. Because one
of the products of combustion is water vapor, the exhaust products will condense as they come back into the room. The dew point of combustion products is around 125°F. As the gas is cooled, it may cause quite a bit of condensation. Rust around the draft hood may indicate a chronic spillage (backdrafting) problem. Corrosion is a common result of condensation.
Slow Exhaust Movement
Condensation may also occur if the draft is marginally adequate. If the gases don’t move quickly enough through the vent connector and up the chimney, they may cool below their dew point and condense although the exhaust products eventually get out of the building. This is usually the result of a furnace too small for the chimney or an appliance firing at too low a rate to have the venting system work properly.
Poor Draft or Obstructed Chimney
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Both a blocked chimney and a downdraft in an open chimney will create spillage when the appliance is running. Using this test when the appliance is off, you can get an idea of which condition is causing the problem. In some cases, you can look up or down the chimney and see an obstruction. The obstruction may be in the vent connector (the pipe leading from the furnace to the chimney).
Combustion air is usually considered readily available from the house air as long as the furnace is not in a small enclosed space. Where the furnace is so enclosed, openings in the room should be provided to ensure there is adequate air.
What’s an Enclosed Space?
When a furnace is in a room that has less than 50 cubic feet of air for every cubic foot of gas (1,000 BTU/hr), vents are needed in the room. The openings have to allow access to a space that has an adequate volume of air. It does little good to add openings to an adjacent small space. You have to consider the sum of the BTU/hr of all the appliances within the space.
Opening to Outdoors
One of the other ways to get adequate combustion air to the burner is with an opening to the outdoors from the furnace room or enclosure. Where the furnace is in a basement, crude ductwork typically runs from the screened hole in the outside wall down to near the floor level, close to the burner. In some cases, a trap is created to minimize the cold draft. In this case, one square inch of opening is required for every 4,000 BTU.
he causes of inadequate combustion air include the following circumstances:
The furnace is in a small enclosure that cannot provide adequate combustion and dilution air.
The house is too tight.
There are too many other pieces of equipment exhausting air (kitchen and bathroom exhaust fans, clothes dryers, water heaters or fireplaces, for example) to provide adequate combustion and dilution air for the furnace.
The implication is incomplete combustion and carbon monoxide entering the house. This is a life-safety issue.
We have briefly introduced the topic of combustion air requirements for gas furnaces. More information is in the ASHI@HOME training program, with in-depth discussions on specific combustion air requirements for other types of appliances, as well as implications and strategies for inspection.
Comfort (or being comfortable) is a sense of physical or psychological ease, often characterized as a lack of hardship. Persons who are lacking in comfort are uncomfortable, or experiencing discomfort. A degree of psychological comfort can be achieved by recreating experiences that are associated with pleasant memories, such as engaging in familiar activities, maintaining the presence of familiar objects, and consumption of comfort foods. Comfort is a particular concern in health care, as providing comfort to the sick and injured is one goal of healthcare, and can facilitate recovery. Persons who are surrounded with things that provide psychological comfort may be described as being "in their comfort zone". Because of the personal nature of positive associations, psychological comfort is highly subjective.
The use of "comfort" as a verb generally implies that the subject is in a state of pain, suffering or affliction, and requires alleviation from that state. Where the term is used to describe the support given to someone who has experienced a tragedy, the word is synonymous with consolation or solace. However, comfort is used much more broadly, as one can provide physical comfort to someone who is not in a position to be uncomfortable. For example, a person might sit in a chair without discomfort, but still find the addition of a pillow to the chair to increase their feeling of comfort. Like certain other terms describing positive feelings or abstractions (hope, charity, chastity), comfort may also be used as a personal name.
One of the critical parameters in compressor design and selection is the compression ratio, often denoted as r. The compression ratio is simply the ratio of the absolute stage discharge pressure to the absolute stage suction pressure. an air conditioning compressor’s re-expansion gas directly affects its volumetric efficiency at different system operating conditions. The volumetric efficiency of a reciprocating (piston) compressor can vary over a wide range, depending on the compressor design and the compression ratio.
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HV AC stands for heating ventilation and air conditioning. The compressor pumps the refrigerant through the refrigerant circuit so that it can absorb and reject heat. An air conditioner is merely a refrigeration system designed to operate under particular conditions. All refrigeration systems must be capable of absorbing heat, moving it and rejecting it. The refrigerant pressure is manipulated to allow it to absorb heat and turn into vapor. The compressor sucks the vapor in, raises the pressure and pushes it out as a high pressure, high temperature vapor. The hot vapor then rejects the heat into the outdoor air and condenses back into a liquid. Liquid refrigerant feeds from the outdoor unit to the indoor unit. The liquid refrigerant is then fed through a metering device and the pressure is dropped substantially. The liquid will then boil at a low temperature and absorb more heat from the indoor air. The cycle continues until the operating controls are satisfied. The compressor is typically the single most expensive component on the system. It draws the greatest portion of power consumed. Compressors come in a variety of designs. Reciprocating compressors have pistons that move up and down in cylinders like an automobile engine. Scroll compressors use a different method and are slightly more efficient. There are also screw types, gear types and centrifugal types though they are primarily used in commercial applications. Compressors are either hermetic or semi-hermetic. Hermetic compressors are completely sealed inside a metal housing and are not serviceable. They are often referred to as throw aways. Semi-hermetic compressors are serviceable. They can be completely disassembled, repaired and returned to service. The vast majority of comfort cooling compressors are fully hermetic.
The system refrigerant starts its cycle in a gaseous state. The compressor pumps the refrigerant gas up to a high pressure and temperature. From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses energy (heat) to the outside, cools, and condenses into its liquid phase.
Causes of High Head Pressure at an Air Conditioner, Heat Pump or other Refrigeration System
Below we list a dozen causes of high head pressure in an air conditioner or heat pump compressor motor. Of these, debris clogging or malfunctioning TXVs seem to be the most common problems.
Air contamination in the refrigerant system
Air flow blocked across the condensing coil. Low condenser airflow will show up as high head pressure, normal suction line pressure, normal superheat, and normal to high sub-cooling
Air flow across the cooling coil: blocked air flow in the air handler, causing the TXV and its temp sensor to remain closed
Check valve inoperative on the refrigerant line at the condenser (look for "fluttering" pressure on the suction side)
Clogged filter drier. Check suction line temperatures across the filter/drier at the start of an on-cycle. If the filter is not clogged the temperatures will be the same.
REFRIGERANT DRIERS & FILTERS
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Contaminants on the compressor valves can cause both low suction pressure and high head pressure.
Crimp or block in the refrigerant piping on the high side or low side. (Symptoms similar to an improperl-set or debris-clogged TXV that is not passing enough refrigerant to the low side. In turn, dirt or debris in the system can clog the TXV (aka TEV) or cap tube.
Debris clogging or crimped refrigerant line at the condensing coil - Tim this would support your HVAC tech's insistence on replacing the condensing coil
High outdoor ambient temperature
Overcharging of refrigerant, liquid slugging of the compressor, oil contamination and other sources can damage compressor valves. Refrigerant overcharging will show up as high head pressure, normal suction line pressure, normal superheat, high sub-cooling.
See OVER CHARGED of REFRIGERANT, EFFECTS
TXV (or in some texts TEV) - Thermostatic Expansion Valve - improperly set, iced, contaminated, or clogged or crimpled capillary tube, or having lost power to a TXV power head can cause high pressure and can also cause valve damage by flooding the compressor if instead the valve sticks wide open.
THERMOSTATIC EXPANSION VALVES, REFRIGERANT
Water (moisture) contamination in the refrigerant system. Air or water contamination in an HVACR system are referred to as "non-condensibles"
Note: air or water contamination in HVACR systems is common and can be introduced by a tech who does not purge air from gauge hoses before attaching the refrigerant gauge or by failure to evacuate the system when refrigerant has been lost and the system is to be repaired and re-charged. Installation of a filter/drier should also always be included in such repairs. Experts note that the symptoms of air contamination and refrigerant overcharge can be similar. ACHR NEWS calls these "non-condensibles" in the refrigeration system.
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Condensation is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds. These clouds may produce precipitation, which is the primary route for water to return to the Earth's surface within the water cycle. Condensation is the opposite of evaporation.
You don't have to look at something as far away as a cloud to notice condensation, though. Condensation is responsible for ground-level fog, for your glasses fogging up when you go from a cold room to the outdoors on a hot, humid day, for the water that drips off the outside of your glass of iced tea, and for the water on the inside of the windows in your home on a cold day.
The phase change that accompanies water as it moves between its vapor, liquid, and solid form is exhibited in the arrangement of water molecules. Water molecules in the vapor form are arranged more randomly than in liquid water. As condensation occurs and liquid water forms from the vapor, the water molecules become organized in a less random structure, which is less random than in vapor, and heat is released into the atmosphere as a result.
Even though clouds are absent in a crystal clear blue sky, water is still present in the form of water vapor and droplets which are too small to be seen. Depending on weather conditions, water molecules will combine with tiny particles of dust, salt, and smoke in the air to form cloud droplets, which grow and develop into clouds, a form of water we can see. Cloud droplets can vary greatly in size, from 10 microns (millionths of a meter) to 1 millimeter (mm), and even as large as 5 mm. This process occurs higher in the sky where the air is cooler and more condensation occurs relative to evaporation. As water droplets combine (also known as coalescence) with each other, and grow in size, clouds not only develop, but precipitation may also occur. Precipitation is essentially water in its liquid or solid form falling from the base of a cloud. This seems to happen too often during picnics or when large groups of people gather at swimming pools.
HOW DOES CONDENSATE PUMPS WORK
So it looks like you are curious about how does condensate pump work, right? Well if so then you are on the right page to explain you how these devices works.
You should have already an idea of what a condensate pump is, especially if you read the information available in this section, so I’m not going to repeat that to avoid to bore you too much (after all is just a pump right? . Anyway check the relevant voice in the menu above if you want to find out more about this.
But let’s continue talking about how a condensate pump works. If you read our previous page about this argument you probably know already that a condensate pump has three main components:
A floating switch
A tank reservoir
And the pump to remove the water, accumulated in the tank reservoir
The working principle behind these kind of pumps is quite simple: the water originating from the other systems connected to the pump (like your AC system as an example) will fill the tank reservoir up to a limit. When the limit is reached the floating switch will activate the pump which will remove (suck out) the water from the reservoir until the water level is insufficient to keep the floating switch at the level required to activate the pump. The pump extracts the water via a common plastic tube connected to a sink or a drain in your house or in your garden,
Nonetheless there are some more complicated systems out there, like for example condensate pumps equipped with two pumps and a two-stages switch. The working system is similar as in the case of less complicated devices of this type with the first pump activated when the water reach the first stage of the switch. However if the water keep raising instead being extracted (this can happen if the first pump is not working properly or the drainage system – that tube connecting the tube to your drain – is blocked) then the second pump is activated by the switch when the water reaches the second stage.
In some cases this second stage may also switch off the system producing the condensation water (the AC equipment) in order to prevent the production of further condensate, trigger an alarm, or both. You should know also that systems having two pumps are also configured to share the work run-time between the two pumps; in this way a backup pump is always available in case one pump fails to function as designed.
The more complicated type of condensate pump (like those equipped with two pumps) are hard to find on the online market. However there is a number of accessories that can be bought together with a “normal” condensate pump that can be used to add the “switch off” or alarm functionality. You will find more details about this product in the “condensate pumps for sale” section of this web site if you are interested,
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In systems involving heat transfer, a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, by cooling it. In so doing, the latent heat is given up by the substance, and will transfer to the condenser coolant. Condensers are typically heat exchangers which have various designs and come in many sizes ranging from rather small (hand-held) to very large industrial-scale units used in plant processes. For example, a refrigerator uses a condenser to get rid of heat extracted from the interior of the unit to the outside air. Condensers are used in air conditioning, industrial chemical processes such as distillation, steam power plants and other heat-exchange systems. Use of cooling water or surrounding air as the coolant is common in many condensers.
A surface condenser is an example of such a heat-exchange system. It is a shell and tube heat exchanger installed at the outlet of every steam turbine in thermal power stations. Commonly, the cooling water flows through the tube side and the steam enters the shell side where the condensation occurs on the outside of the heat transfer tubes. The condensate drips down and collects at the bottom, often in a built-in pan called a hotwell. The shell side often operates at a vacuum or partial vacuum, often produced by attached air ejectors. Conversely, the vapor can be fed through the tubes with the coolant water or air flowing around the outside.
In chemistry, a condenser is the apparatus which cools hot vapors, causing them to condense into a liquid. See "Condenser (laboratory)" for laboratory-scale condensers, as opposed to industrial-scale condensers. Examples include the Liebig condenser, Graham condenser, and Allihn condenser. This is not to be confused with a condensation reaction which links two fragments into a single molecule by an addition reaction and an elimination reaction.
In laboratory distillation, reflux, and rotary evaporators, several types of condensers are commonly used. The Liebig condenser is simply a straight tube within a cooling water jacket, and is the simplest (and relatively least expensive) form of condenser. The Graham condenser is a spiral tube within a water jacket, and the Allihn condenser has a series of large and small constrictions on the inside tube, each increasing the surface area upon which the vapor constituents may condense. Being more complex shapes to manufacture, these latter types are also more expensive to purchase. These three types of condensers are laboratory glassware items since they are typically made of glass. Commercially available condensers usually are fitted with ground glass joints and come in standard lengths of 100, 200, and 400 mm. Air-cooled condensers are unjacketed, while water-cooled condensers contain a jacket for the water.
Larger condensers are also used in industrial-scale distillation processes to cool distilled vapor into liquid distillate. Commonly, the coolant flows through the tube side and distilled vapor through the shell side with distillate collecting at or flowing out the bottom.
A condenser unit used in central air conditioning systems typically has a heat exchanger section to cool down and condense incoming refrigerant vapor into liquid, a compressor to raise the pressure of the refrigerant and move it along, and a fan for blowing outside air through the heat exchanger section to cool the refrigerant inside. A typical configuration of such a condenser unit is as follows: The heat exchanger section wraps around the sides of the unit with the compressor inside. In this heat exchanger section, the refrigerant goes through multiple tube passes, which are surrounded by heat transfer fins through which cooling air can move from outside to inside the unit. There is a motorized fan inside the condenser unit near the top, which is covered by some grating to keep any objects from accidentally falling inside on the fan. The fan is used to blow the outside cooling air in through the heat exchange section at the sides and out the top through the grating. These condenser units are located on the outside of the building they are trying to cool, with tubing between the unit and building, one for vapor refrigerant entering and another for liquid refrigerant leaving the unit. Of course, an electric power supply is needed for the compressor and fan inside the unit.
Direct contact condenser
In this type of condenser, vapors are poured into the liquid directly. The vapors lose their latent heat of vaporization; hence, vapors transfer their heat into liquid and the liquid becomes hot. In this type of condensation, the vapor and liquid are of same type of substance. In another type of direct contact condenser, cold water is sprayed into the vapour to be condensed.
Flooded condensers are the prime tower pressure-control methods for total condensers that generate only liquid products, and although these control methods can be troublesome, a good understanding of their principles will help achieve improved, trouble-free operations Pressure is the most important variable for controlling distillation columns (Figure 1) because pressure affects every aspect of a distillation system: vaporization, condensation, temperature, volatility and so on. An unsteady pressure typically results in an unsteady column. There are several ways to control tower pressure, depending on how the tower is configured. If a tower has an overhead vapor product, manipulating the vapor flowrate usually controls pressure. If the tower has no vapor product (it has a total condenser and produces only liquid), tower pressure can be controlled by partially flooding the condenser and manipulating the liquid level in the condenser. Another alternative for either vapor or liquid products is to manipulate the coolant flowrate (or temperature) to control the tower pressure. Coolant manipulation is popular in refrigerated towers, but is usually avoided in cooling-water condensers, as it can cause accelerated fouling and corrosion.
A pressure-actuated holdback valve is installed at the condenser outlet. This valve is often referred to as an ORI (Open on Rise of Inlet) valve. The valve will throttle shut when the condenser pressure reaches a preset minimum pressure in a cold ambient condition (Figure 1). This throttling action will back up liquid refrigerant in the bottom of the condenser, causing a flooded condition. The condenser now has a smaller internal volume, which is what is needed for a colder ambient condition. The condenser pressure will now rise, giving sufficient liquid line pressures to feed the expansion valve. Larger receivers are needed for these systems to hold the extra refrigerant for condenser flooding in the summer months.
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While the condenser is being flooded with liquid refrigerant, a CRO (Close on Rise of Outlet) valve, located between the compressor’s discharge line and the receiver inlet, will bypass hot compressor discharge gas to the receiver inlet when it senses a preset pressure difference between the discharge line and the receiver (Figure 1). The ‘T’ symbol means the valve comes with a built-in pressure tap for ease in taking a pressure reading for service purposes and for setting the valve. The pressure difference is created from the reduced flow of refrigerant to the receiver because of the throttling action of the ORI valve. The bypassed hot gas through the CRO valve serves to warm up any cold liquid coming from the ORI valve at the receiver’s inlet, and it will also increase the pressure of the receiver so metering devices will have the proper liquid line pressure feeding them.
One of the main advantages of condenser flooding is to keep consistent liquid pressure feeding the metering device in low ambient conditions. Manufacturers do supply technical information on how much extra refrigerant is needed for flooding a condenser for a certain low ambient condition. However, in extreme low ambient conditions, it may be necessary to flood 80 to 90 percent of the condenser. On larger systems, this could mean several hundred pounds of refrigerant. This is the main disadvantage of flooding a condenser for low ambient operations. With the rising price of refrigerant and the environmental concerns of global warming and ozone depletion, condenser flooding can become quite expensive and environmentally unsound if not managed and serviced properly.
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As mentioned above, the main disadvantage of condenser flooding is that larger refrigeration systems may hold hundreds of extra pounds of refrigerant needed to properly flood a condenser at extremely low ambient conditions. One way to reduce the amount of extra refrigerant charge needed for condenser flooding is to split the condenser into two separate and identical condenser circuits . This method is referred to as condenser splitting. The splitting of the condensers is done with the addition of a pilot-operated, three-way solenoid valve installed in the discharge line from the compressors (Figure 3). The splitting of the identical condensers is done in such a way where only one-half of the condenser is used for winter operation, and both halves are used for summer operation. The top half of the condenser is referred to as the summer-winter condenser, and the bottom half of the condenser is referred to as the summer condenser. The three-way solenoid valve controlling the splitting of the condensers can be energized and de-energized by a controller sensing outside ambient conditions, an outdoor thermostat, or a high-side pressure control.
During summertime operations, the added surface area and volume of both condensers are needed to maintain a reasonable head pressure at higher ambient conditions. The pilot-operated, three-way solenoid valve is then de-energized. This positions the main piston inside the valve to let refrigerant flow from the compressor’s discharge line to the three-way valve’s inlet port, and then equally to the valve’s two outer ports. In other words, the flow of refrigerant will flow to both of the condenser halves equal
The splitting of the condensers is done with the addition of a pilot-operated, three-way solenoid valve installed in the discharge line from the compressors.
In low ambient conditions, the summer portion of the condenser can be taken out of the active refrigeration system by the three-way valve. When the coil of the pilot-operated, three-way solenoid valve is energized, the sliding piston inside the valve will move and close off the flow of refrigerant to the port on the bottom of the valve that feeds the summer condenser. This action will render the summer condenser inactive or idle, and the minimum head pressure can be maintained by flooding the summer-winter half of the condenser with conventional refrigerant-side head pressure control valves, as explained in the condenser flooding section of this column.
In fact, during winter operations, the system’s head pressure is best maintained with a combination of condenser splitting, refrigerant-side head pressure controls, and air-side controls like fan cycling or fan variable-speed devices. This combination of refrigerant-side and air-side controls will minimize the refrigerant charge even more while splitting the condenser. These combinations will also maintain the correct head pressure for better system efficiencies.
The refrigerant that is trapped in the idle summer condenser during low-ambient conditions will flow back into the active system through a bleed hole in the piston of the three-way valve. This trapped refrigerant will flow through the piston’s bleed hole, into the valve’s pilot assembly, and back to the suction header through a small copper line which feeds all parallel compressors (Figure 2). Another scheme to rid the idle summer condenser of its refrigerant is to have a dedicated pump-out solenoid valve, which will open when energized and vent the trapped refrigerant to the common suction header through a capillary tube restriction. Both the bleed hole in the piston or the capillary tube ensure that the refrigerant experiences a restriction, and is mostly vaporized before reaching the common suction header which is under low side (common suction) pressure.
A check valve is located at the summer condenser’s out- let to prevent any refrigerant from entering it while it is idle and under a low pressure condition. While not needed for backflow prevention, a check valve is also located at the outlet of the summer/winter condenser simply to make the pressure drops equal in both halves of the condenser when both are being used simultaneously in summertime operations.
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The term ‘condensing boiler’ refers to the fact that the boilers produce condense from time to time.
Condensing boilers use heat from exhaust gases that would normally be released into the atmosphere through the flue. To use this latent heat, the water vapour from the exhaust gas is turned into liquid condensate.
In order to make the most of the latent heat within the condensate, condensing boilers use a larger heat exchanger, or sometimes a secondary heat exchanger.
Due to this process, a condensing boiler is able to extract more heat from the fuel it uses than a standard efficiency boiler. It also means that less heat is lost through the flue gases.
Worcester’s Greenstar condensing boilers are at least 90% efficient, meaning that they turn 90% of the fuel they use into heat.
The official rating for boiler efficiency is the ‘SEDBUK’ scale. SEDBUK stands for ‘Seasonal Efficiency of a Domestic Boiler in the UK’.
Greenstar condensing boilers achieve the highest possible efficiency category – SEDBUK Band ‘A’.
What is SEDBUK?
The SEDBUK rating was developed under the UK Government’s ‘energy efficiency best practice programme’ with the co-operation of boiler manufacturers, including Worcester. It provides a basis for fair comparison of different models of boilers.
The SEDBUK rating is the average annual efficiency achieved in typical domestic situations. It takes into account sensible assumptions about climate, control, pattern of usage and other similar factors.
The rating is calculated from laboratory tests together with other important factors such as boiler type, fuel used, ignition type, UK climate, boiler water content and typical domestic usage patterns.
So, for estimating annual fuel running costs SEDBUK is a better guide than laboratory test results alone.
The boiler’s performance is scored, enabling the boiler to be placed in a banding system using a scale from ‘A’ to ‘G’. ‘A’ rated boilers are the most efficient.
SEDBUK was introduced in 1999 and has undergone a number of changes since then, the latest being from SEDBUK(2005) to SEDBUK(2009). Where boiler efficiency is quoted simply as ‘SEDBUK’ it should be assumed this refers to SEDBUK(2005).
Condensing boiler regulations
Building regulations that have come into force since 1st April 2005 state that any replacement or new gas or oil boiler must be a condensing boiler. Rare exceptions may apply.
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If you’re serious about investing in a high efficiency heating system, a condensing furnace is one of your best options. Condensing furnaces come with the highest AFUE ratings available for gas furnaces and can save St. Louis area homeowners a lot of money over the lifespan of the units. So what exactly is a condensing furnace and what makes it more efficient than a traditional unit,
What is a condensing furnace
Traditional furnaces are built with just one heat exchanger. During the combustion process that takes place inside of this heat exchanger, a certain amount of the heat that is produced is lost up the chimney in the form of water vapor. What this means is that traditional furnaces lose a significant percentage of the heat that they use energy to produce.
Condensing furnaces have a second heat exchanger that is able to extract extra heat from that water vapor that would normally be vented out of your home. This allows them to make more use of the energy that they consume and can significantly reduce their operating costs.
How does a condensing furnace work?
At the beginning of the heating process, a condensing furnace works similar to a traditional furnace. Gas burners deliver heat into the first heat exchanger and the combustion process leaves a byproduct of hot water vapor. That water vapor is next sent to the second heat exchanger where it is condensed and turned into a liquid.
When a gas turns into a liquid, it releases heat. Your furnace is able to use that extra heat to warm your home. The resulting liquid is then drained out of your home through a PVC pipe.
How efficient is a condensing furnace?
Because condensing furnaces are able to do more with the fuel that they consume, they come with higher AFUE ratings than traditional furnaces. In fact, condensing furnaces have AFUE ratings of at least 90 percent, with higher-efficiency models reaching AFUE ratings in the upper 90 percentiles.
Condensing Pressure. The condensing pressure is the pressure at which the refrigerant is phase changing from a vapor to a liquid. This phase change is referred to as condensation. Thus the term condensing pressure,
Condensing Temperature Clues
Condensing temperatures often give technicians valuable hints as to what the problem may be within a refrigeration system. The high side of the refrigeration system offers valuable information to the wise technician.
Most technicians would rather troubleshoot the refrigeration system's high side than the low side. This is because almost all the heat absorbed in the system is rejected in the condenser. All the heat absorbed in the evaporator and the suction line is rejected in the condenser.
Also, the compressor's motor heat and heat generated in the compression stroke, often referred to as the heat of compression, has to be rejected in the condenser
What The Condenser Does
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The three functions of the condenser are desuperheating, condensing, and subcooling the refrigerant.
Desuperheating: The compressor delivers high-pressure, superheated vapor to the condenser through the discharge line. The first passes through a standard condenser's tubes desuperheat the discharge line gases. This prepares the high-pressure, superheated vapors for condensation (phase changes from vapor to liquid), because it takes the sensible (measurable) heat away from them and shrinks their volume.
Remember, these superheated gases must lose all of their superheat before reaching the condensing temperature for a certain condensing pressure. Once the initial passes of the condenser have rejected enough superheat and the condensing temperature or saturation temperature have been reached, these gases are referred to as 100-percent saturated vapor.
When the refrigerant has reached the 100-percent saturated vapor point in the condenser , this is the end of the desuperheating process.
Condensation: Now the vapor is ready to condense if any more heat is lost. Indeed, condensation (changing vapor to liquid) is the main function of the condenser. Condensing is system dependent and usually takes place in the lower two-thirds of the condenser.
Once the saturation or condensing temperature is reached in the condenser and the refrigerant gas has reached a 100-percent saturated vapor state, condensation can take place. As more heat is taken away from the 100-percent saturated vapor, it forces the vapor to a liquid state; it condenses.
The condensation process happens between Points 2 and 3 in Figure 1. When condensing, the vapor gradually changes its state to liquid until all that remains is 100-percent liquid. This phase change, or change of state, is an example of a latent heat rejection process. The heat being removed during this phase change is latent heat, not sensible heat. This change from vapor to liquid happens at one temperature; the temperature remains constant while phase changing, even though heat is being removed. (Note: An exception to this occurs in the 400 series refrigerant blend, which has a temperature change [glide] when phase changing.)
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This one temperature is the saturation temperature. It corresponds to the saturation pressure in the condenser. Remember, only at saturation in a phase-changing region is there a pressure-temperature relationship and the technician can use a pressure-temperature chart. This pressure can be measured anywhere on the high side of the refrigeration system as long as line and vapor pressure drops and losses are negligible.
Subcooling: The last function of the condenser is to subcool the liquid refrigerant. Subcooling can be defined as any sensible heat taken away from the 100-percent saturated liquid. Technically, subcooling is the difference between the measured liquid temperature and the liquid saturation temperature at a given pressure.
Once the saturated vapor in the condenser has changed its phase to saturated liquid, and the 100-percent saturated liquid point has been reached, if any more heat is removed, the liquid will go through a sensible heat rejection process. Its temperature will drop as it loses heat. The liquid that is cooler than the saturated liquid in the condenser is called subcooled liquid. The condenser subcooling process starts at Point 3 and continues to the end of the condenser.
Subcooling is an important process, because it starts to lower the liquid temperature closer to the evaporating temperature before the refrigerant reaches the metering device. This reduces flash loss in the evaporator, so more of the vaporization of the liquid in the evaporator can be used for cooling the product load. In other words, the net refrigeration effect is increased.
Splits, Swings, And Loads
In air-cooled condensers, the temperature difference between the ambient and the condensing temperature is referred to as the condenser split. For example, if the condensing temperature is 110 degrees F and the ambient is 80 degrees, the condenser split would be 30 degrees.
(The condensing temperature in any system is figured off of the condensing pressure using a pressure-temperature chart.)
Condenser splits can range from 15 degrees to 30 degrees, depending on whether the condenser is a standard-, mid-, or high-efficiency unit. The higher the efficiency, the more coil surface area there will be, thus the lower the condenser split will be.
In this article we will discuss a standard-efficiency condenser that normally runs a 25 degree to 30 degree split. Note that condenser splits are not affected by ambient temperature changes. If there is an increase in the ambient temperature, there will also be an increase in the condensing temperature, but the condenser split (difference between the two temperatures) will remain the same.
On the other hand, condensing temperatures for a single condenser can vary depending on two factors: the ambient swing and the evaporator heating load.
As the ambient temperature increases, less heat can be rejected from the air-cooled condenser to the hotter ambient. Therefore, more of the heat absorbed by the evaporator and suction line, as well as the heat of compression generated by the compressor, will remain in the condenser. This increases the condenser's internal temperature and pressure. The condenser is now operating at an elevated condensing temperature for the elevated ambient; the difference between the condensing temperature and the ambient (condenser split) remains the same.
On the other hand, if the evaporator sees more of a heat load, more heat has to be rejected to the condenser; its condensing temperature increases. With an increased condensing temperature, the condenser split is increased because the ambient temperature remained the same.
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High And Low Splits
If you find a low condenser split, say 7 degrees, you will immediately know that not much heat is being absorbed in the evaporator. The low split tells you that the refrigerator or freezer is not working very hard. This is true no matter what the ambient or condensing temperatures are.
If you measure a low condenser split, potential system problems could include:
Frosted evaporator coil.
Malfunctioning evaporator fan.
High superheat condition in the evaporator (from undercharge or starving metering device).
On the other hand, if you find a high condenser split, you will immediately know that the refrigerator or freezer is rejecting a lot of heat out of the condenser. There must be a lot of heat being absorbed in the evaporator. Causes could include:
A door opening.
Warm products in the box.
A recent defrost period.
What happens in the condenser is a direct reflection of what is happening in the rest of the refrigeration system. Never ignore troubleshooting the high side of the refrigeration system.
condensing oil furnace
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Condensing-type furnaces, particularly those fired with gas, are becoming accepted in the heating equipment marketplace. Fifteen percent of the gas fired furnaces installed today are condensing-type furnaces. With the U.S. Department of Energy standards set to take effect in 1992, minimum AFUE’s (Annual Fuel Utilization Efficiencies) will be in the low 80% range.
This means that furnaces in this seasonal efficiency range will no longer be considered “high efficiency” models, but will become “basic” models will become unacceptable and the customer who wants a “premium” model must look at the condensing-type furnace. These points were made clear at a recent conference on condensing heat exchangers sponsored by DOE and the Gas Research Institute.
This Technical Bulletin will discuss briefly the challenges and future of oil-fired condensing furnaces and boilers.
Condensing” furnaces and boilers are so named because they utilize an added “secondary” (typically finned tube) heat exchanger to extract additional heat from the flue gases, reducing flue gas temperature from a typical 500-600°F to around 100°F, and removing the “latent heat of vaporization”, which is the heat required to hold liquids as vapor in the flue gas.
When the latent heat of vaporization is extracted, water vapor condenses and drops out of the flue gas. This condensation occurs at a temperature known as the “dew point”, which for water is about 120°F. Condensation occurs in the secondary heat exchanger and is collected for disposal. Flue gases are typically vented through a plastic flue pipe, assisted by an induced draft fan. Proper heat exchanger design in a condensing-type furnace can result in AFUE’s in the 92-96% range.
Especially in oil-fired appliances, the proper design of a condensing-type furnace or boiler requires much more than proper sizing of a secondary heat exchanger. A number of problems exist peculiar to the oil combustion process in contrast to the gas combustion process, which makes condensing oil furnace design extremely difficult.
Corrosion is a major concern when operating in the condensing mode. Along with the condensation of water, ions of sulfur (from the fuel oil) and chloride (especially from indoor combustion air) condense and form acids which will corrode carbon steel and most “common” stainless steels. This process is even more destructive in the heat exchanger zones that go through wet and dry cycles. Proper design of the secondary fin tube heat exchanger requires fairly “exotic” stainless steels, and the future may see ceramic or even high temperature plastic heat exchangers.
Accumulated condensate, which contains the same sulfuric and hydrochloric acids, must be disposed of properly. The effect of condensate on residential plumbing materials must be determined, building code restrictions must be considered and condensate drains must be kept from freezing.
The secondary heat exchanger adds restriction to the furnace or boiler, and requires very careful oil burner design and application to minimize rough starts and stops and optimize efficiency . Start and run instability can cause premature and critical sooting of the burner and heat exchanger.
Condensing boilers are being used in Europe, but require extended radiation/convection surface to provide return water at a temperature low enough to cause condensation.
Finally, venting of a condensing furnace (or a conventional-type high efficiency furnace operating at near-condensing conditions) through a masonry chimney can cause damage as condensed water and acids will attack the brick and mortar.
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The condensing unit (sometimes incorrectly referred to as compressor) is usually located outside. Its main function is that of a heat exchanger, in which it condenses a substance (refrigerant) from it's gaseous to liquid state. From there, the latent heat is given up by the substance, and will transfer to the condenser coolant. In the refrigeration cycle, a heat pump transfers heat from a low temperature heat source into a higher temperature heat sink. Heat naturally flows in the opposite direction because of the second law of thermodynamics. The most common of the refrigeration cycles uses an electric motor to drive a compressor (located inside the condensing unit). Because evaporation occurs when heat is absorbed, and condensation occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively pump refrigerant around. Inside the condenser, the refrigerant vapor is compressed and forced through a heat exchange coil, condensing it into a liquid and rejecting the heat previously absorbed from the cool indoor area. The condenser's heat exchanger is generally cooled by a fan blowing outside air through it.
THE 2-STAGE CONDENSER
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This condensing unit offers one of the highest operating efficiencies possible and whisper quiet operation. The two-stage condenser works as follows: During off-peak times, including morning and evening times in the summer, the unit will typically run in low-stage approximately 70% lower capacity. This offers greater, cost-efficiency and allows the unit to cycle long enough to properly dehumidify the home. During peak load times the unit will cycle into high-stage to maintain the temperature set point. For aggressive humidity control and during high demand periods, the units will be able to produce high speed cooling using the full tonnage. These condensing units used in conjunction with our custom, two-stage evaporator coils offer maximum cooling and dehumidification in both low and high-stage operation.
Our Conditioned space is the area we live in. We will modify the environment with mechanical systems such as heating and cooling in these areas. Our inside conditioned space includes floors walls windows doors and ceilings are all contained within this envelope. It provides a barrier to the outside and is the shelter we live in.
Our Unconditioned Space is within our building shell but not in Conditioned space. This includes attics garages unfinished basements walls etc. So our house has many areas that are unconditioned. For example in our walls we have many layers. We have the inside wall typically drywall which is connected to the framing studs Everything from the drywall to the inside space is our conditioned space. There is a cavity between the inside wall and the outside wall which often has insulation. This area between the outside wall and the inside wall is considered unconditioned space. Likewise for our attic which we consider open to the outside. Our garage is also unconditioned space and should be kept separate from the conditioned space. In many homes we have chases and mechanical closets that are connected to unconditioned space
We want to separate these spaces as much as we possibly can for health safety and energy efficiency. We do this by performing air sealing. When we perform air sealing to separate conditioned space from unconditioned space we reduce infiltration improve comfort and IAQ. Contact us for your free energy evaluation Red E3 is San Diego's Energy Efficiency Experts and we want to help you be safer more comfortable and naturally energy efficient.
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Contactors are useful in commercial and industrial applications, particularly for controlling large lighting loads and motors. One of their hallmarks is reliability. However, like any other device, they are not infallible. In most cases, the contactor does not simply wear out from normal use. Usually, the reason for contactor failure is misapplication. That's why you need to understand the basics of contactors.
When someone uses a lighting contactor in a motor application, that's a misapplication. The same is true when someone uses a "normal operation" motor contactor for motor jogging duty. Contactors have specific designs for specific purposes.
When selecting contactors, you'll use one of two common standards: NEMA or IEC. Both match a contactor with the job it has to do, but they do so in different ways.
The NEMA selection process always results in a choice of a contactor you can use over a broad range of operating conditions. For example, you could use a NEMA Size 5 contactor to run a 50-hp motor operating at 230V or a 200-hp motor at 460V.
Using IEC standards, however, you can size contactors very close to their ultimate capabilities. In many cases, this precision allows you to predict how long they'll last. For example, an IEC-rated contactor may run a motor that draws 40A at full load. In that duty, it should last for more than two million operations. But, if you used it for consistent jogging and plugging, you'd have to replace it after just a few thousand operations.
Since a contactor should last for years, don't automatically replace one that fails with an identical unit. Instead, take a few moments to see if there is an obvious problem. A contactor really has only two basic parts: the contacts and the coil. The coil energizes the contactor, moving the contacts into position. The contacts transmit the current from the source to the load. Heat can destroy either of them, so take a good look at both.
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Contacts will overheat if they transmit too much current, if they do not close quickly and firmly, or if they open too frequently. Any of these situations will cause significant deterioration of the contact surface and the shape of that surface. Erratic operation and failure will be quick. To check the contacts, just look at them. Some minor pitting (seen near the thumb in Photo 1) as well as a black oxide coating is normal, but severe pitting or any melting or deforming of the contact surface is a sure sign of misapplication. Replace contacts with such symptoms.
Coils can overheat if operating voltages are too low or too high; if the contacts fail to open or close because of dirt or misalignment; or if they have suffered physical damage or experienced an electrical short. Coil insulation degrades quickly when it gets too hot. When it degrades, it will short out (and blow a fuse) or just open and stop operating.
To check a coil, stick an ohmmeter across the coil leads (Photo 2). Infinite resistance means the coil is open. A shorted coil will usually register significant resistance, like a good coil. If you happen to have a matching contactor nearby, compare the two coils. The shorted coil will usually have significantly higher or lower resistance than the good one. If the difference is significant, replace it. Replacing the contacts or coil often means replacing the whole contactor. But no matter what you replace, compare the NEMA or IEC rating with the job the contactor will really be doing. If you match it to the application, it should last a long time.
One of the most common microbiological contaminants is the Escherichia coli bacteria, or E. coli. Certain varieties of E. coli exist naturally in the body, but the strain known as E. coli O157:H7 causes severe vomiting, diarrhea and abdominal cramps. Infections from E. coli O157:H7 occur from consuming contaminated food or water. Microbiological infections must be treated immediately with antibiotics or antiviral medications. Failure to do so can result in life-threatening conditions, such as kidney failure and liver damage.
A control system is a device, or set of devices, that manages, commands, directs or regulates the behaviour of other devices or systems. Industrial control systems are used in industrial production for controlling equipment or machines.
There are two common classes of control systems, open loop control systems and closed loop control systems. In open loop control systems output is generated based on inputs. In closed loop control systems current output is taken into consideration and corrections are made based on feedback. A closed loop system is also called a feedback control system.
The cooling system is a system of parts and fluid that work together to control an engine’s operating temperature for optimal performance. The system is made up of passages inside the engine block and heads, a water pump and drive belt to circulate the coolant, a thermostat to control the temperature of the coolant, a radiator to cool the coolant, a radiator cap to control the pressure in the system, and hoses to transfer the coolant from the engine to the radiator.
The liquid that flows through a cooling system, antifreeze, or commonly referred to as coolant, withstands extreme hot and cold temperatures and contains rust inhibitors and lubricants to keep the system running smoothly.
Coolant follows a circulation path that begins with the water pump. The water pump’s impeller uses centrifugal force to draw coolant from the radiator and push it into the engine block. Pumps are usually fan, serpentine timing belt, or timing chain driven. Nowadays, they may even be driven electrically. If the water pump experiences a leak from the seal, a cracked housing, broken impeller or a bearing malfunction, it can compromise the entire cooling system, causing the vehicle to overheat.
As coolant flows through the system, it picks up heat from the engine before arriving at the thermostat. The thermostat is a valve that measures the temperature of the coolant and opens to allow hot fluid to travel to the radiator. If the thermostat becomes ‘stuck’ and quits working, it will affect the entire cooling system.
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Once released by the thermostat, hot coolant travels through a hose to be cooled by the radiator. The antifreeze passes through thin tubes in the radiator. It is cooled as air flow is passed over the outside of the tubes. Depending upon the speed of the vehicle, airflow is provided by the vehicle’s movement down the road (ram air effect) and/or cooling fans. Radiator restrictions can compromise its ability to transfer heat. These can be either external air flow or internal coolant flow restrictions. A malfunctioning electric cooling fan or fan clutch can limit air flow across the radiator. Check/replace the fan clutch…the life expectancy of water pumps and fan clutches are about the same and share a common shaft. A failed fan clutch can cause severe damage to the water pump.
As coolant temperature increases, so does the pressure in the cooling system. This pressure is regulated by the radiator cap. Correct system pressure is required for proper water pump seal lubrication. Increasing the cooling system pressure raises the boiling point of the coolant. Each one pound of increased pressure raises the boiling point by 3ËšF. If the pressure builds up higher than the set pressure point, a spring-loaded valve in the cap will release the pressure. If an engine has overheated, the radiator cap and thermostat should be replaced.
It is important to regularly inspect the condition of your cooling system’s belts and hoses. Soft hoses, oil soaked belts or cracked belts and hoses can have dire effects on the entire cooling system. Proper belt tension is also important.
Always refer to your manufacturer’s manual to determine the recommended coolant type for your vehicle. This and the proper mixture of coolant and distilled water are the lifeblood towards keeping your system running cool. Most parts retailers now offer a solution of premixed coolant and distilled water. While it may seem like an unnecessary added expense, the cleanliness of the premixed solution will pay off over time.
Mineral deposits and sediments from corroded or malfunctioning parts accumulate in the cooling system. Before performing a cooling system repair, it is recommended to flush the cooling system prior to installing any new parts. This is a task made even easier by using a flush-fill kit. Failure to flush the system will contaminate the new parts being installed and could lead to premature component failure.
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A cooling tower is a specialized heat exchanger in which air and water are brought into direct contact with each other in order to reduce the water's temperature. As this occurs, a small volume of water is evaporated, reducing the temperature of the water being circulated through the tower.
Water, which has been heated by an industrial process or in an air-conditioning condenser, is pumped to the cooling tower through pipes. The water sprays through nozzles onto banks of material called "fill," which slows the flow of water through the cooling tower, and exposes as much water surface area as possible for maximum air-water contact. As the water flows through the cooling tower, it is exposed to air, which is being pulled through the tower by the electric motor-driven fan.
When the water and air meet, a small amount of water is evaporated, creating a cooling action. The cooled water is then pumped back to the condenser or process equipment where it absorbs heat. It will then be pumped back to the cooling tower to be cooled once again.
Types of cooling towers
Not all towers are suitable for all applications. Cooling towers are designed and manufactured in several types, with numerous sizes available. Understanding the various types, along with their advantages and limitations, is important when determining the right tower for a project. The product list provides an overview of towers to help you determine which is right for your application.
Crossflow cooling towers
In crossflow towers the water flows vertically through the fill while the air flows horizontally, across the flow of the falling water. Because of this, air does not have to pass through the distribution system, permitting the use of gravity flow hot water distribution basins mounted at the top of the unit above the fill. These basins are universally applied on all crossflow towers.
In transport engineering nomenclature, a counterflow lane or contraflow lane is a lane in which traffic flows in the opposite direction of the surrounding lanes. Contraflow lanes are often used for bicycles or bus rapid transit on what are otherwise one-way streets.
Coupling is the act of joining two things together. In software development, coupling refers to the degree to which software components are dependant upon each other. For instance, in a tightly-coupled architecture, each component and its associated components must be present in order for code to be executed or compiled. In a loosely-coupled architecture, components can remain autonomous and allow middleware software to manage communication between them. In a decoupled architecture, the components can operate completely separately and independently.
A crankcase heater is an electrical component in a compressor in an air-conditioning system, heat pump system, or chiller system. The crankcase heater is normally on all the time, even when the unit is not running, though temperature sensors and set points may turn it off when not needed. A crankcase heater's sole purpose is to prevent refrigerant migration and mixing with crankcase oil when the unit is off, and to prevent condensation of refrigerant in the crankcase of a compressor. The crankcase heater keeps refrigerant at a temperature higher than the coldest part of the system. A crankcase heater generally has the same electrical symbol as a resistor because it converts electricity directly into heat via electrical resistance. The resistance in the heater coil determines the heat it produces when voltage is applied,
HVAC CURB ADAPTORS
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When an existing rooftop HVAC unit needs be replaced there are 2 options for the building owner;
1) remove the unit and the unit's roof curb – then install a new curb, transition the duct work to attach to the new curb, and then set the unit. There is significant downtime and expense in removing the existing curb and re-roofing the new one, and of course there is always the risk of creating roof leaks.
2) remove the existing unit, but leave the existing curb in place, then set a MicroMetl curb adaptor on the existing curb that allows the new HVAC unit to transition through the existing duct and curb. This option will save both time and money.
Having the curb adaptor on the job site as quickly as possible is critical to maintaining building comfort, which is why MicroMetl ships from all 3 strategically located manufacturing plants. Many curb adaptors are available in 24 hours and almost all are offered with a standard 3 day maximum lead time. Hundreds of curb adaptor models are available to all existing HVAC unit curbs. Curb adaptors are available for 2 ton 100 ton units and are design for both constant and multi-zone applications.
Curb adaptors are constructed of welded heavy gage galvanized steel, ship fully assembled where practical and include duct transitions for easy installation. Curb adaptors are internally insulated and gasket seals are provided for the unit-to-adaptor seal and the adaptor-to-existing curb seal.
Current starting relays consist of a low resistance coil and a set of normally open contacts. The coil is wired between terminals L and M. The contacts are wired between terminals L and 2 when a start capacitor is used.
current sensing relay
A range of manufacturing and production processes rely on current-operated relays to provide a continuously adjustable trip-current setting. They are able to protect mechanical apparatus from jam-up or other overloading conditions that result in measurable increases in motor current. Functionally, they sense current levels and provide an output signal when a specified current level is reached. Current-sensing relays are used to:
Signal high-current conditions, such as a clogged grinder.
Identify low-current conditions, such as a pump that has encountered a low-water condition. Sense the current a motor is drawing to feed the current to a programmable logic controller (PLC).
To meet the unique requirements of a diverse set of applications, a wide range of devices and options is currently available to designers, installers, and maintenance professionals, including plug-in style, base-mounted, DIN-rail mount, and donut-style. These types of devices offer the following capabilities:
Sensing both AC and DC current — from milliamperes to several amperes.
Sensing thousands of AC amperes with a current transformer (CT).
Current setpoints can be fixed or adjustable.
Input AC or DC.
Analog output — voltage or current — or contact closure.
Self- or looped-power units.
Fixed or adjustable internal time delays.
cut in cut out temperature control
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The use of a low-pressure control to maintain box temperature on commercial medium-temperature applications has been a common practice for many years. It allows remote condensing units to be controlled without any additional control wiring between the refrigerated box and its compressor.
It works on the principle that there is a direct relationship between the pressure of the saturated refrigerant in the evaporator and its temperature.
A typical low-pressure control has two setpoints: its cut-in and its differential. In order for the control to work properly, both the cut-in and differential setpoints need to be set properly.
Most manufacturers have stated values for the proper setpoints for their systems. However, these values usually only work well on self-contained or close-coupled systems. If the condensing unit is remotely located, the stated values may cause problems with the cooler.
Setting The Cut-In
ystems where the condensing unit is located a considerable distance away from the evaporator, it is more accurate to first set the cut-in setpoint. The cut-in setpoint should be set to a pressure (temperature) that will allow the evaporator to completely defrost during the off cycle.
Since most commercial refrigeration systems work with a coil temperature below 32Â°F (usually between 20Â° and 25Â°), frost will develop on its coils. If this frost is not removed and continues to form, it will eventually completely block the airflow through the evaporator coil, causing the unit to malfunction.
The cut-in value needs to be set to a pressure (temperature) that will not allow the compressor to come on until the coil is completely defrosted.
Typically, if the coil temperature is above 33Â°F, no frost should be on the coil. However, that is usually too close for comfort. Most system designers recommend that the coil rise to a temperature between at least 36Â° to 39Â° before allowing the compressor to cycle on. This will ensure that the coil has been completely defrosted.
Setting The Differential
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Once the cut-in pressure has been set, the differential setting must then be set. The differential setting is used to cycle the compressor off at the lowest possible box temperature. The differential setting represents the difference between the cut-in pressure and the cut-out pressure.
For example, if the cut-in pressure is set at 40 psig and you want the compressor to cycle off at 15 psig, the differential setting would need to be set at 25 psig (40 psig – 15 psig = 25 psig). The exact cut-out pressure needed to correctly cycle off the compressor may be different from unit to unit. One of the reasons for this is that the pressure drop from the evaporator to the compressor may be different on each unit.
Here’s an easy way to correctly set the differential pressure:
1. Set the differential pressure to an extremely high value. This is a value the suction pressure should never reach under normal operating conditions. A 30-psig setting should suffice.
2. Allow the system to run while monitoring the box temperature. Once the box reaches its lowest desirable temperature, slowly adjust the differential counter-clockwise until the compressor cycles off.
Using this procedure will ensure that the cut-in and differential settings have been properly set and the system will function as intended.
Design pressure is the maximum pressure a pressurized item can be exposed to. Due to the availability of standard wall thickness materials, many components will have a MAWP higher than the required design pressure.
When the desuperheater is operational, a measured amount of water is added to the superheated steam via a mixing arrangement within the desuperheater. As it enters the desuperheater, the cooling water evaporates by absorbing heat from the superheated steam. Consequently, the temperature of the steam is reduced.
detector carbon monoxide
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Carbon monoxide is an odorless, colorless, and tasteless gas that is near impossible to identify without a proper detector. It is caused by fuels not burning completely, including wood, gasoline, coal, propane, natural gas, gasoline, and heating oil.
dew point temperature
Most people are comfortable with a dew-point temperature of 60 degrees Fahrenheit (16 degrees Celsius) or lower. At a higher dew point of, for example, 70 F (21 C), most people feel hot or "sticky" because the amount of water vapor in the air slows the evaporation of perspiration and keeps the body from cooling
Diaphragm valves (or membrane valves) consists of a valve body with two or more ports, a diaphragm, and a "weir or saddle" or seat upon which the diaphragm closes the valve. The valve is constructed from either plastic or metal. Originally, the diaphragm valve was developed for use in industrial applications.
The term "differential pressure" refers to fluid force per unit, measured in pounds per square inch (PSI) or a similar unit subtracted from a higher level of force per unit. This calculation could be taken for pressures inside and outside a pipe or simply in different places along a flow path. This calculation has applications in the drilling industry,
Measuring differential pressure along a line helps drilling professionals identify the precise point of a blockage or to determine whether reservoir fluids are about to start backing into a wellbore, which can interfere with drilling operations. Keeping an eye on pressure at various points along a fluid line is vital for operational safety.
Vent diffusers disperse pressurized air exiting heating ventilation and air conditioning (HVAC) ductwork and provide a decorative finish over the grill box hole holding the ductwork in place. Without an air diffuser, the air exiting the HVAC system would travel in a straight direction. This causes a concentration of conditioned air in one section of the room while the rest of the room remains unconditioned. The direction that a vent diffuser sends flowing air depends on the direction of the diffuser fins.
Air diffusers with stationary fins come in one-, two-, three- or four-way blows. The amount of blows that an air register uses depends on its location in relation to walls or other obstructions. A one-way blow vent diffuser has one direction to move air. This is a common air register found in directing air flow through an HVAC exhaust system.
Four-way blow vent diffusers sit in the center of rooms and disperse air across a large area of the room. Movable vent fins allow the air flow direction to change as needed. Another factor in vent diffuser selection involves the finish of the diffuser flanges and fins.
Commonly white, vent diffusers can vary in finish and material to either blend into the area surrounding the diffuser or contrast with the surrounding area to provide a unique look for a room. Brass- and copper-clad vent diffusers provide a contrast to wall, floor and ceiling finishes while matching the décor of early Victorian style homes. This allows for the comfort of central air conditioning without looking out of place in historic homes. Another option for home vent diffusers hides neatly out of sight.
Linear diffusers use a long, slim opening to disperse air from an HVAC system. The narrow opening reduces the visibility of the vent cover, allowing it to blend into the surrounding area. Typically, linear vent diffusers sit along the edges of walls or above door and window openings. After they have been installed, they are unnoticeable from a distance and provide a clean look to both historic and industrial-style homes.
Regardless of the type and style of a vent diffuser, the diffuser location has the greatest impact on the efficiency of an HVAC system. Placing a four-way blow diffuser in a location where two blows face walls will cause the air to deflect and remain stuck in one corner of a room. Pre-planning the location and type of each vent diffuser before purchasing ensures that each room of a house remains comfortable.
direct drive compressor
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The basics of piston-type pump operation
Most air compressors are reciprocating or piston-type air compressors. Their operation is similar to an automotive engine. Inside the pump, a crankshaft moves a set of pistons up and down. On the down-stroke, air is drawn into the compression chamber through a one-way valve; as the rising piston on the up-stroke compresses the air, a second one-way valve opens to force the air into a pressure tank. As more air is forced into the tank, the pressure inside the tank rises.
Most pumps are either single-stage or two-stage. The difference refers to the number of times intake air is compressed in a pump. A single stage compressor compresses intake air one time before sending the air into a storage tank. Single-stage air compressors can have one, two, or four cylinders, but the air is only compressed once. Most single-stage air compressors have a maximum pressure of 125 PSI. Two-stage air compressors compress air twice before sending it into a storage tank. A two-stage compressor has a minimum of two cylinders: a low-pressure cylinder (largest) and a high-pressure cylinder (smallest). Air is compressed once in the large cylinder and then sent through an air cooling tube, which reduces discharge air temperatures.
Lower temperatures improve operating durability and efficiency. In most lower horsepower compressors, the interstage coolers use the same airflow that cools the rest of the compressor pump structure. In larger compressors, as well as in some special applications, water cooled interstage coolers may be used.
Upon reaching the small cylinder, the air is compressed again. Two-stage air compressors produce a larger volume of air at higher pressures than smaller single-stage compressors. Two stage air compressors have a maximum pressure of 175 PSI.
direct drive motor
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development of direct drive technology, and today offers the broadest range of direct-drive motors in the industry. Direct drive motors offer industry-leading performance, zero maintenance, clean mechanical assembly, improved accuracy, higher throughput, better reliability, and smooth, quiet operation to suit a wide variety of machine design needs.
Mechanical transmission, such as gearboxes, timing belts, pulleys or lead screws, introduce backlash, mechanical losses and objectionable audible noise that can reduce machine performance, increase machine size and weight.
Direct Drive motors, either housed rotary (DDR), cartridge rotary (CDDR) or frameless (KBM high-voltage rotary or TBM low-voltage rotary or DDL linear motors) directly mount to the load to be driven thereby eliminating the transmission, providing a much more robust alternative. System maintenance is greatly reduced as mechanical parts prone to wear are removed, dramatically improving MTBF. Also improved are load acceleration, lower power consumption, reduced system inertia, and higher precision are major advantages that direct drive solutions can provide.
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direct expansion system
Condensing Air: The ambient condensing air enters the condenser at ≈ 95ºF and leaves at ≈ 115ºF.
Compressor: Moves the refrigerant through the system.
Condenser Fans: Draw ambient air across the condensing coil.
Condenser Coil: Rejects heat absorbed from the air along with the heat added to the system
during the compression process.
Expansion Device: Causes expansion cooling by creating a pressure loss between the high
and low side of the system.
Sight Glass / Moisture Indicator: Provides a view into the system. Indicator is green normally, yellow when high in moisture.
Evaporator Coil: The evaporator coil transfers heat from the warm air
to the cool refrigerant.
Supply Air: Enters the evaporator coil warm and leaves cool. Design condition for outdoor air is 95ºF dry bulb 75ºF wet bulb. Typical leaving air design condition is 55ºF dry bulb, 54ºF wet bulb.
Filter-Dryer: Removes water, debris and other contaminants from the refrigerant
Hot Gas Bypass
Hot gas bypass consists of a pressure-operated valve located on the discharge line and additional refrigerant piping from the valve to the evaporator(DX) coil. Hot refrigerant vapor enters the hot gas bypass valve from the compressor and is routed to the DX coil inlet as suction line pressure decreases. Suction line pressure decreases as the cooling load decreases (indicating a part-load condition). Benefit: Prevents the DX coil from freezing and reduces compressor cycling at part-load conditions. Availability: Standard on all MPX, ERCH and VER models with packaged DX cooling.
Hot Gas Reheat
Hot gas reheat includes a condenser coil (located in the supply airstream) and a modulating refrigerant valve to control the supply air temperature and relative humidity. Benefit: Hot gas reheat controls the supply air temperature and relative humidity without the need for auxiliary post heat (i.e. an electric heater). Hot gas reheat is often referred as “free reheat” as the refrigeration system needs to reject the heat absorbed by the refrigerant to the ambient air or supply air for proper operation. This configurationprovides a means to provide dehumidified air without overcooling the space. Availability: Optional on all MPX, ERCH and VER models.
Digital Scroll Compressors
Digital scroll compressors adjust to the cooling demand by separating (engaging and disengaging) the compressor’s scrolls. When the scrolls are separated, or disengaged, no thermodynamic work is done on the refrigerant. The compressor resumes the normal cooling cycle when the scrolls are engaged. Cycle times between the disengaged and engaged states are varied by a controller and pressure valve to adjust the compressor output to meet the cooling demand. Benefit: Digital scrolls offer capacity control from 10 to 100% of the rated compressor capacity. This turndown provides leaving coil temperature control as precise as 0.5°F. Digital scrolls also save energy by eliminating hot gas bypass as the compressor output can be adjusted to meet cooling demands at part load conditions. Availability: Optional on the MPX, ERCH, and VER models (up to 30 tons),
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Direct-Fired Absorption Chillers
Direct-fired absorption chillers offer you a choice in how energy is consumed to produce chilled water. The chiller uses natural gas or other fuels to fire the absorption refrigeration cycle.
Direct-fired absorption chillers can be used as a primary component for hybrid plants or other applications where electrical demand and consumption are expensive or in short supply.
The efficiency of the double-effect cycle used in these direct-fired absorption chillers makes them competitive with electric chillers in many regions of the world where electricity prices have risen dramatically over the last decade. All sizes can act as a chiller and/or heater to supply cold or hot water to condition the building during the summer or winter.
direct geoexchange systems
DEFINITION. GeoExchangeSM is the system also referred to as ground source or geothermal heating and cooling.1 It is an electrically powered system that transfers the natural heat of the earth to heat your home or office, and it operates in reverse to cool and dehumidify your space in summer. An optional heat reclaim device can provide virtually free water heating in summer, and proprietary technology now permits year-round integrated water heating from the same appliance. "Direct GeoExchange" is the newer technology discussed later in this Article.
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COMFORT. Heat from the sun is stored in the upper surface of the earth. The amount of that heat released into the surrounding air is determined by the local median air temperature. At the northern U.S. boundary, the ground temperature below 5 feet in depth is approximately 42oF, and at the southern extreme, is about 75oF. Because the ground temperature is almost constant throughout the seasons, it provides a far higher temperature source in the winter and a cooler source in summer than does the constantly changing ambient air. GeoExchange systems utilize this advantage to deliver more uniform comfort and savings than are possible with a "high efficiency" air source heat pump. They maintain system capacity and efficiency even when outside air temperatures reach their extremes. Air source heat pumps, however, lose capacity and efficiency when the most heat is needed because the outside air is then coldest. And when cooling is most needed they again are less efficient because the air is hottest. Surveys of GeoExchange system owners consistently show that owners rank their systems higher in comfort than do the owners of any other technology, and more than 95% of those surveyed stated they would recommend such systems to friends and family members.2
IMPROVED INDOOR AIR QUALITY. GeoExchange systems improve the quality of indoor air by eliminating the combustion of fuel and its byproducts, including carbon monoxide and odors. Greater filtration is the result of longer run cycles as compared to other space heating methods, and the system maintains more comfortable humidity levels because of the absence of a furnace.
SAFETY. Without the need for combustion of fuels, there is no flame, no furnace, no fumes, no harmful emissions, and no explosive hazard. A comforting peace of mind comes with confidence in safety.
TROUBLE-FREE RELIABILITY. Without dependence upon outside air for their heat source, GeoExchange systems do not need to expose equipment to the weather, debris, pests or vandals. Elimination of the outside fan, coil, motor, and the thermal extremes experienced by the air source heat pump results in longer equipment life and less maintenance. Eliminating dependence upon fossil fuel firing to create heat in the conditioned space, the GeoExchange system is not subjected to the thermal stresses of a furnace, requires no fuel storage, and only the air filters require cleaning.
SAVINGS TO YOU AND THE ENVIRONMENT. By transferring renewable energy, GeoExchange systems reduce heating and cooling costs an average of 30-60% and reduce the cost of water heating by 70% as compared to electric resistance water heating. GeoExchangers are the most energy efficient means of heating and cooling buildings in most areas of the United States, and they are the most environmentally clean conditioning system, according to the U.S. Environmental Protection Agency and the Department of Energy. They reduce energy consumption by as much as 44% compared to air source heat pumps and by as much as 72% compared with electric resistance and standard air conditioning.3 Utility tests have shown that the greatest savings are provided by the Direct GeoExchange systems discussed later in this article.
MARKET BARRIERS. Although GeoExchangers have doubled in sales in recent years, they have not been prevalent in the marketplace. The major limitation on their success has been the high cost of installing the intermediate heat transfer loop. High cost limits market success, which, in turn, limits public awareness. A cost breakthrough has been needed to bring GeoExchange within the budget of the general population.
TECHNOLOGY ADVANCES CREATE DIRECT GEOEXCHANGE. Innovation is the result of building upon previous knowledge. To develop the next generation of simpler technology with a lower installed cost and increased performance, intensive research began in 1980 on Direct GeoExchange, which was the method initiated in that first system installed in 1945.4 Mechanical simplicity is the objective of good engineering design. The goal was to eliminate the intermediate ground loop. The first step was to create optimized refrigerant flow controls to make it possible to extend the evaporator and condenser of the refrigerant circuit into direct contact with its heat source in the earth. This eliminates the need for the intermediate plastic loop, heat exchanger and circulating pump. In 1983, this was accomplished. Work proceeded with testing multiple loop sizes and configurations for lower cost and ease of installation.
Aggressive research and field demonstrations have made these technology advances possible. Research on metallurgy, coatings, and environmental issues was conducted at the University of South Florida, resulting in system approvals by the Florida Department of Environmental Protection. Proprietary Direct GeoExchange systems were subsequently safety-certified by national testing laboratories. Monitoring has been conducted in 12-month projects from 1986 to the present by six electric utilities, the University of Central Florida, and the University of Tennessee. Coated earth loops are appropriate where sulfur or highly acidic soils may attack the copper loops. Coated loops were successfully demonstrated and tested with funding by the National Rural Electric Cooperative Association beginning in 1996.
Direct GeoExchange is the newer technology for today and tomorrow. Dramatic progress has been made to provide the simplest available means of accessing the energy stored in the earth. By taking the refrigerant circuit into direct contact with the energy source, Direct exchange eliminates the inefficiency of an intermediate heat exchanger, an auxiliary circulating pump for antifreeze fluid, and the power to operate the pump.
ECR Technologies, Inc. began the development of DIRECT AXXESS®, the modern direct GeoExchange system, in 1980, and has pioneered more innovations for GeoExchange systems than any other company. Eight U.S. patents and ten international patents have been granted to ECR. Its utility-sponsored demonstration projects are more numerous, diverse, and show higher efficiencies than any others.
Field tests of DIRECT AXXESS® systems by electric utilities in hot and cold climates began in 1986. A Michigan utility that had tested 20 systems reported that the DIRECT AXXESS® unit was 25% more efficient than systems relaying upon the plastic intermediate loop.5 A one-year test in Florida led to a Governor's Energy award for Direct exchange technology in 1988. The system also operated the most energy efficient water heater tested by the Florida Solar Energy Center (75% savings compared to electric), including comparison with solar water heaters that used electric resistance back-up heating,
Because DIRECT AXXESS® systems place copper tubes in the ground in small bore holes (2" compared to 6" diameter), they disturb less than 15% of the volume of earth and are easier to install as compared to systems that use an intermediate loop to circulate an antifreeze fluid. Without an intermediate loop the installer does not need plastic fusing tools, pumps to add antifreeze or training to assemble the loop. ECR loops are factory assembled. Because the heat transfer is more efficient, the Direct method uses shorter and smaller loops, and the appliance is smaller because no auxiliary heat exchanger or circulating pump is required. Therefore, costs of both installation and operation are reduced. The options of vertical, diagonal or horizontal loops of the Direct method make it possible to install retrofit units in existing homes and in the smaller lots of some newer homes. Shallow horizontal loops are often the economic choice where available land area is greater.
The cost of loop installation is substantially less with a Direct system. A 4-ton vertical Direct GeoExchange loop, for example, can be installed for approximately $1,000 less than a vertical intermediate loop system. Even greater savings are realized with a horizontal pit installation for a Direct system. Simplifying GeoExchange with the Direct exchange method reduces costs, while also increasing the performance of GeoExchange systems in the same manner as the phenomenon experienced with the progression of hand-held calculator technology in the 1980's.
The simple, state-of-the-art DIRECT AXXESS® system has the ability to consistently move three to four BTU's from the earth for each BTU equivalent of energy used to operate the system and to deliver all of those BTU's into the building. This is an efficiency of 300-400%. The Direct GeoExchange system delivers improved performance to people concerned with energy costs, the environment, quality of life, and natural resources. It is the natural choice space conditioning system for living and working environments for the twenty-first century.
Equivalence of direct radiation (EDR) is a standardized comparison method for estimating the output ability of space-heating radiators and convectors.
Measured in square feet, the reference standard for EDR is the mattress radiator invented by Stephen J. Gold in the mid 19th century.
One square foot of EDR is able to liberate 240 BTU per hour when surrounded by 70 °F (21 °C) air and filled with steam of approximately 215 °F (102 °C) temperature and 1 psi of pressure.
EDR was originally a measure of the actual surface area of radiators. As radiator (and later convector) design became more complicated and compact, the relationship of actual surface area to EDR became arbitrary. Laboratory methods based on the condensation of steam allowed for very accurate measurements.
While now somewhat archaic, EDR is still computed and used for sizing steam boilers and radiators, and for modifying and troubleshooting older heating systems using steam or hot water. However, In a hot water system, one square foot of EDR is able to liberate 170 BTU per hour, depending on the temperature of the water.
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direct spark ignition
Electronic Ignition Gas Furnaces Types - Gas furnaces, boilers, and water heaters have evolved from the basic standing pilot ignition system to the state of the art electronic ignition models. Standing pilot gas furnaces relied on keeping a pilot flame lit for the furnace, boiler, or water heater to function. The advent of electronic ignition has made it possible to prove a flame without keeping a pilot light lit 24/7 and thereby saving money because electronic ignition only needs to have a flame when there is a call for heat from the thermostat. There are different types of electronic ignition gas furnaces.
Electronic Ignition Gas Furnaces Types
Typically, electronic ignition is comprised of a manufacturers OEM circuit board or an after-market ignition control module located near the gas valve of the furnace, boiler, or water heater. The gas valve is controlled directly by this circuit board or ignition module whereby the standing pilot gas valve is usually controlled by the thermostat. There are different versions of gas furnace electronic ignition systems but they all serve the same purpose and function and that is to safely heat your dwelling. Among these types of gas furnace electronic ignition systems there are:
Electronic Ignition Gas Furnace can be Direct Spark Ignition – this version has no pilot light at all. It lights the main burners on a call for heat and a state of the art flame sensor detects a flame. If no flame is detected on a try for ignition the gas valve closes. After a specified amount of time, usually seconds, the ignition module will try ignition again. Again, if the flame sensor detects no flame a delay before trying again will occur. Typically after three failed trials for ignition with the flame sensor not detecting a flame the ignition module will go into a lock-out mode for at least an hour (most models). This is a safety measure to prevent a dangerous build-up of gas. If the module endlessly tried for ignition the un-ignited gas could build up to dangerous levels and an explosion could occur. *The spark coming from the gas furnace circuit board or ignition control module can exceed 10,000 volts so caution is advised.
Electronic Ignition Gas Furnace can be Intermittent Pilot Ignition – this version has a pilot light which only lights on a call for heat. The pilot light is located near the main burner and on a call for heat the ignition module or gas furnace circuit board opens the pilot valve inside the gas valve and initiates a spark at the head of the pilot assembly to light the pilot light. The flame sensor is also located at the pilot assembly and as soon as the flame is detected the gas furnace circuit board or ignition control module opens the main valve inside the gas valve. The pilot light then lights the main burners. When the thermostat is satisfied all gas control components & shuts off until the next call for heat. If a flame is not sensed then a trial for ignition will repeat itself for up to four trials and then the gas controls will be locked out for a specified period of time (a minimum of an hour depending the gas furnace or gas controls manufacturer)when a new sequence will start over again. *The spark coming from the gas furnace circuit board or ignition control module can exceed 10,000 volts so caution is advised.
Electronic Ignition Gas Furnace can be Hot Surface Ignition – hot surface ignition can be either direct fire or indirect fire to a pilot (Honeywell Smart Valve is an example of indirect fire to a pilot). The igniter is a silicon carbon element which glows red hot when the voltage is applied to it. On a call for heat, the gas furnace circuit board or ignition module sends a specified amount of voltage to the igniter. After a small timed delay and after the igniter is glowing red hot, the main valve opens in the gas valve. The gas strikes the silicon carbon element and ignition occurs. A flame sensor located near the burners detects the flame and the main burners remain lit and the voltage is taken away from the hot surface igniter. If a flame is not sensed then a trial for ignition will repeat itself for up to four trials and then the gas controls will& be locked out for a specified period of time (a minimum of an hour depending on the gas furnace or gas control manufacturer) when a new sequence will start over again.
Electronic Ignition Gas Furnace can be Mercury Bulb – this system uses a mercury switch to prove there is a flame on a pilot light. Mercury bulb systems usually use spark ignition to light a pilot and the mercury switch proves the flame. Once the switch proves the flame the main valve in the gas valve opens and the pilot lights the main burners. Mercury is very hazardous to the environment and not many manufacturers use this type of electronic ignition.
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Electronic Ignition Gas Furnaces Types - Conclusion
It is important to note that all these electronic ignition systems work in a furnace sequence of operation as determined by the electronic ignition controller. If the furnace safety controls detects a problem with any of the safeties, including the furnace flame sensor, the furnace sequence of operation will be interrupted on a lock-out. Furnace sequence of operation varies from gas furnace to gas furnace and it is important to know the gas furnace sequence of operation to troubleshoot the system if a problem exists and the furnace is locking out the ignition of the furnace. The electronic ignition gas systems can also be used on boilers.
Direct Vent and Power Vent Water Heaters
At Haley Mechanical, we understand that given the various terms used to describe them, choosing the right water heater can be difficult. There are several variations, and determining which is best for your situation can seem like an overwhelming task.
Two of the most popular types of water heaters today include the direct vent and power vent. Basically, the difference between the two is that the power vent water heater removes combustion gases from the atmosphere via a powered venting fan, while a direct vent water heater vents these gases into the outdoor atmosphere using a chimney or exhaust pipe.
Direct Vent Water Heater
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When using a direct vent water heater, water is heated by the heat of fuel combustion. A direct vent system typically results in lower water heating costs, because the exhaust gases are vented vertically, with no extra power required as is the case with the power vent water heater.
Power Vent Water Heater
A power vent water heater uses a blower or fan to exhaust gases by pushing them through vent pipes that are horizontal. In some situations, this may be the only type of water heater that makes sense, because a chimney or vertical vent is not necessary. Some locations don’t have access to a chimney or vertical vent, so your options are limited.
The primary advantage of a power vent is that the water heater can be located in any area and does not require a vertical vent or chimney. It could be that the location where you want to install your hot water heater is not near the chimney, or your home does not have a chimney. Either way, a power vent can be vented by simply running inexpensive pipe horizontally. However, the drawback to this type of water heater is the total cost considering the blower/fan portion of the vent requires electricity to operate, the cost of the actual blower or fan, and running a power line to the fan. Essentially, because the power vent requires a fan/blower to operate, the costs of heating water will be higher over the power vent’s life span.
Noise is another disadvantage with a power vent, as there is a slight sound some homeowners notice when the blower or fan runs as the hot water heater is operating. For most people, the noise is not that noticeable or distracting, however it’s something you should be aware of should you consider this type of vent. When installed properly, the noise can be minimized or nearly eliminated.
There are several differences between a power vent and direct vent hot water heater, and it’s obvious a power vent will result in higher cost – but sometimes it simply cannot be avoided. When you don’t have access to a vertical vent or chimney, a power vent may be the right solution for you.
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Temperature and Pressure (T&P) relief valves
Temperature and pressure (T&P) relief valves used on residential water heaters are typically designed and manufactured to relieve on pressure at 150 psig and on temperature at 210 degrees F. These ASME, ANSI and CSA (AGA) approved relief valves protect the water heater from excess pressures and temperatures by discharging water.
In normal operation of the water heater and T&P valve, no water should be discharged from the valve. A T&P valve that discharges is an indication of an abnormal condition in the system and by discharging, the T&P valve is meeting its designed safety purpose. The causes of discharge can be thermal expansion, excess system pressure, low temperature relief, too high a setting on the water heater, or something in the water heater causing excess temperatures in the heater.
Thermal Expansion: When water is heated it expands. In a 40 gallon water heater, water being heated to its thermostat setting will end up expanding by approximately 1/2 gallon. The extra volume created by this expansion has to go somewhere or pressure will dramatically increase, such as when water is heated in a closed system.
A good indication of thermal expansion is when the T&P valve releases about one cup of water for each 10 gallons of heater capacity with each heating cycle. The T&P valve is functioning properly when it relieves pressure caused by thermal expansion, but frequent relief can build up natural mineral deposits on the valve seat, rendering the valve inoperative. This condition can be addressed by the installation of a Watts thermal expansion tank or other Watts thermal expansion device to protect your system from overpressure caused by thermal expansion. If there is no discharge from the valve, there is no need to replace the valve.
System Pressure: If installation of a thermal expansion device does not relieve occasional dripping from the T&P valve, then the system pressure should be checked. If system pressure is excessive (typically more than 75 PSI), a Watts pressure regulator should be installed on the incoming water line.
Warning: The discharge from a T&P valve can be very hot. It is very important that all T&P valves be installed properly with a discharge line piped downward to an adequate drain to avoid property damage and to minimize possible human contact. Please read and follow the instructions on the warning tag attached to your T&P valve.
Correct Installation of T&P Relief Valves
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Important Instructions: Relief Valves and Automatic Gas Shut-Off Devices Combination temperature and pressure relief valves with extension thermostats must be installed so that the temperature-sensing element is immersed in the water within the top 6" (152mm) of the water storage tank. They must be installed either in the hot outlet service line or directly in a tank tapping. Combination temperature and pressure relief valves that do not have extension elements must be mounted directly in a tank tapping located within the top 6" (152mm) of the water storage tank. Valves must be located so as to assure isolation from flue gas heat or other ambient conditions that are not indicative of stored water temperature.
WARNING: To avoid water damage or scalding due to valve operation, discharge line must be connected to valve outlet and run to a safe place of disposal. Discharge line must be as short as possible and be the same size as the valve discharge connection throughout its entire length. Discharge line must pitch downward from the valve and terminate at least 6" (152mm) above a drain where any discharge will be clearly visible. The discharge line shall terminate plain, not threaded. Discharge line material must conform to local plumbing codes or ASME requirements. Excessive length over 30' (9.14m), or use of more than four elbows or reducing discharge line size will cause a restriction and reduce the discharge capacity of the valve.
No shut-off valve shall be installed between the relief valve and tank, or in the discharge line. Valve lever must be tripped at least once a year to ensure that waterways are clear. When manually operating lever, water will discharge through discharge line and precautions must be taken to avoid contact with hot water and to avoid water damage. This device is designed for emergency safety relief and shall not be used as an operating control. If discharge occurs, a licensed contractor must evaluate the system and determine the cause for discharge and correct the cause immediately.
To ensure proper operation, this valve must be installed by a qualified service technician or licensed plumbing contractor in accordance with these instructions and the local plumbing codes and standards. Repair or alteration of valve in any way is prohibited by national safety standards/local codes.
For Heaters with Direct Top Tapping:
Always use an extension type thermostat T&P relief valve which permits the end of the thermostat to extend into the top 6" of the tank.
Direct Side Tapping:
FOR EXTERNAL FLUE HEATERS: Use extra length extension thermostat to extend into water storage tank. FOR INTERNAL FLUE HEATERS: Use short or standard length thermostat. Vertical discharge line must be installed with its direction downward.
"Alternate" ONLY when the tappings are not provided:
Use standard or extra length extension thermostat which permits the end of the thermostat to extend into the top 6" of the tank.
Important: A relief valve functions, in an emergency, by discharging water. Therefore it is essential that a discharge line be piped from the valve in order to carry the overflow to a safe place of disposal. The discharge line must be the same size as the valve outlet, and must pitch downward from the valve.
ANNUAL OPERATION OF T&P RELIEF VALVES:
WARNING: Following installation, the valve lever MUST be operated AT LEAST ONCE A YEAR by the water heater owner to ensure that waterways are clear. Certain naturally occurring mineral deposits may adhere to the valve, blocking waterways, rendering it inoperative. When the lever is operated, hot water will discharge if the waterways are clear. PRECAUTIONS MUST BE TAKEN TO AVOID PERSONAL INJURY FROM CONTACT WITH HOT WATER AND TO AVOID PROPERTY DAMAGE. Before operating lever, check to see that a discharge line is connected to this valve, directing the flow of hot water from the valve to a proper place of disposal. If no water flows when the lever is operated, replacement of the valve is required. TURN THE WATER HEATER “OFF” (see your water heater instruction manual) AND CALL A PLUMBER IMMEDIATELY.
REINSPECTION OF T&P RELIEF VALVES:
WARNING: Temperature and Pressure Relief Valves should be inspected AT LEAST ONCE EVERY THREE YEARS, and replaced, if necessary, by a licensed plumbing contractor or qualified service technician, to ensure that the product has not been affected by corrosive water conditions and to ensure that the valve and discharge line have not been altered or tampered with illegally. Certain naturally occurring conditions may corrode the valve or its components over time, rendering the valve inoperative. Such conditions can only be detected if the valve and its components are physically removed and inspected. Do not attempt to conduct an inspection on your own. Contact your plumbing contractor for a reinspection to assure continuing safety. FAILURE TO REINSPECT THIS VALVE AS DIRECTED COULD RESULT IN UNSAFE TEMPERATURE OR PRESSURE BUILD-UP WHICH CAN RESULT IN SERIOUS INJURY OR DEATH AND/OR SEVERE PROPERTY DAMAGE.
If discharge occurs, CALL A PLUMBER IMMEDIATELY. Discharge may indicate that an unsafe temperature or pressure condition exists which requires immediate attention by a qualified service technician or licensed plumbing contractor.
Caution: Valve must be installed so that temperature sensing element is immersed in the water within the top 6" (152mm) of the tank.
No valve may be placed between the relief valve and water tank.
Install in hot water outlet or in extra side relief valve tapping if one is provided.
To avoid water damage, discharge line must be run to a safe place of disposal and must pitch downward.
Do not install a shut-off valve, plug, or cap in the valve discharge line.
Follow local codes where they vary from these instructions.
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Copeland Discus™ with CoreSense™ Protection
Copeland Discus™ semi-hermetic compressors have, for years, been the choice and the standard in the refrigeration industry.
Discus compressors are refrigeration compressors used in supermarkets, walk-in coolers and freezers, and industrial applications. They range in horsepower from 5 to 60-hp. Discus compressors are available with capacity modulation from 10 to 100 percent. This provides the ability to match capacity to the desired load of refrigeration equipment. Capacity modulation reduces the suction pressure and temperature variation of the refrigerated space and provides for a decrease in the compressor’s cycling rate. A reduced cycling rate increases the compressor reliability.
The Discus compressor has been used in the refrigeration industry for years. Its valve design allows for less-clearance-volume vapors to be trapped when the piston is at top dead center.
Less-clearance-volume discharge gas will be re-expanded on the down stroke of the piston. In fact, re-expansion is almost zero, allowing for the suction valve to open sooner, letting new refrigerant gases in from the suction line. This gives the system a greater volumetric efficiency. The Discus valve arrangement also has larger openings that will allow more mass flow rate of refrigerant through the opening in a shorter period of time. Modulation is accomplished with a blocked suction technology by feeding a variable voltage to a solenoid for its open and close intervals.
Discus compressor technology also offers onboard diagnostics. This technology provides real-time intelligence monitoring, letting the service technician know the status of what is happening inside the compressor before any major problems develop. Compressor monitoring operations can now become centralized. This allows service technicians to systematically troubleshoot compressor problems before arriving at the site.
It also improves troubleshooting accuracy and speed of service. It gathers data, transmits operating information, and visually displays compressor status and alarm codes on the front control box. It also records and retains a history of compressor operating information and past alarms. This technology allows service technicians to be dispatched automatically if an alarm problem exists.
A modern discus compressor (Figure 1) incorporates on-board diagnostics. This new technology has the following advantages:
• Monitors compressor’s discharge temperature
• Provides contactor protection
• Enables remote diagnostics
• Integrates the compressor’s system electronics including high- and low-pressure controls, compressor cooling and temperature control, oil pressure monitoring, motor protection devices, and input/output (I/O) boards
• Reduces the number of brazed joints on the compressor that can develop leaks
• Allows consistent field in-stallations because of less wiring with fewer components.
The Copeland Discus compressor with CoreSense™ Protection saves energy – and money. Why? Because it’s the most energy-efficient compressor available for your refrigeration needs. In fact, Discus™ compressors have led the industry in energy efficiency for decades, delivering up to 12.2% more energy efficiency than any reed compressor technology. And our Discus valve technology is designed to meet a broad range of application requirements.
Copeland Discus compressors with CoreSense Protection are also built to last, saving you even more money in maintenance and service calls. Engineered for high quality and outstanding reliability, each Discus model passes a grueling series of performance and durability tests. Rigorous testing, combined with more than 25 years of field experience, makes reliability a hallmark of Discus compressor technology.
The refrigerant distributor is a device connected to the outlet of a thermostatic expansion valve (TEV). The out- let of the distributor is machined to accept tubing which connects the distributor to each evaporator coil circuit,
Draft diverters, or draft hoods, gather the exhaust gases from the flue(s) of a water heater in order to be safely vented to the exterior. It's important to use the draft diverter that was made for the tank, along with vent piping of the proper diameter in order to ensure that the tank doesn't soot up, or that poisonous exhaust gases don't backdraft into the water heater closet. The one at left is on a commercial tank, while the one right is on a residential heater.
downflow gas furnace
The most common terms used to describe the air flow configuration are: upflow, downflow, and horizontal.
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An upflow furnace may draw cool air through either its top or its base. The identifying feature of this furnace is that it pushes warm out out through the top of the furnace. An upflow configuration is typically selected when the ductwork is located above the furnace, such as in a home's basement.
Upflow furnaces can also be described as a "highboy" or a "lowboy". For the homeowner, the important distinction between the two is that the lowboy is shorter -- typically around 4 feet in height. The lowboy can be installed in low-ceiling basements. A highboy furnace is typically around 6 feet in height.
There is a second distinction between the two: the blower is installed below the heat exchanger in a highboy furnace and behind / next to the heat exchanger in a lowboy furnace.
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A downflow furnace takes cool air from the top and discharges warm air from the bottom. A downflow furnace is typically installed when the ductwork is located below the furnace.
Downflow furnaces are sometimes called "counterflow" or "downdraft" furnaces.
A horizontal furnace lies on its side, pulling cool air from one side and pushing warm air out of the other. You will occasionally see a distinction between a "horizontal left side" and a "horizontal right side" furnace. This refers to configuring a furnace to discharge warm air from the right side (in a horizontal right furnace), or the left side (in a horizontal left furnace).
Because they don't require much vertical clearance, horizontal furnaces are used in locations where space is limited, such as in a basement or attic crawl space.
Upflow / Horizontal
An upflow / horizontal furnace can be configured as either an upflow furnace, or a horizontal (left or right) furnace. It cannot be installed as a downflow furnace.
Downflow / Horizontal
A downflow / horizontal furnace can be configured as either a downflow furnace, or a horizontal (left or right) furnace. It cannot be installed as an upflow furnace.
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A "multipoise" or "multi-positional" furnace can be configured by the installing contractor in upflow, downflow, horizontal left or horizontal right positions. For this reason, some people refer to it as a "universal" air flow configuration.
A modified U-tube manometer used to measure draft of low gas heads, such as draft pressure in a furnace, or small differential pressures, for example, less than 2 inches (5 centimeters) of water.
A hydrostatic depth indicator, installed in the side of a vessel below the light load line, to indicate amount of submergence.
A draft hood is critical to the operation of a gas water heater. (It is attached between the heater's .ue outlet and the vent pipe.) When properly installed, the draft hood cools the combustion products and allows them to .ow safely from the building.
IT'S NOT THE FREON!! It's the oil in the refrigerant that absorbs moisture and holds debris in the system. Replacing the drier / accumulator, in addition to evacuation, will assure better performance.
Why Replace the Receiver-Drier?
The receiver-drier must be changed each time a system is empty regardless of the reason for loss of refrigerant. It should also be changed every three years, because the desiccant pellets will break down and clog the expansion valve. This will in turn cause the system to become inoperable and May damage the compressor.
The receiver-drier is strictly a disposable item and is thought of in the same terms as a fuel, oil, or air filter. In fact, if any component fails or is replaced for any reason, the receiver-drier must also be replaced to prevent corrosion and moisture in the system.
The receiver-drier performs three functions:
-It filters the system of non-condensables.
-It receives the liquid refrigerant and maintains a certain level of liquid at the bottom at all times in a properly charged system.
-It contains a stack of pellets called desiccant (drying agent) to trap and absorb moisture. NOTE that moisture is the most harmful enemy of the air conditioning system. If any moisture is in the system, it will combine with the refrigerant to form hydrochloric acid which is extremely corrosive to metal components.
Replacing the receiver-drier is essential when servicing the A/C system. Whenever you replace a component of the A/C system you must also replace the receiver-drier. If you do not change the receiver-drier there could be serious damage to the other parts of the system, which could be very costly. You must also have proof of changing the receiver-drier in order to receive a compressor warranty.
Definition of drip pan. 1 usually drip pan : a container for catching material that drips from above (as from the burners of a gas range or a piece of oily machinery) 2 usually dripping pan : a usually shallow rectangular metal pan used especially for baking and roasting.
drop off voltage
Voltage drop describes how the supplied energy of a voltage source is reduced as electric current moves through the passive elements (elements that do not supply voltage) of an electrical circuit. Voltage drops across internal resistances of the source, across conductors, across contacts, and across connectors are undesired as the supplied energy is lost (dissipated). Voltage drops across loads and across other active circuit elements are desired as the supplied energy performs useful work.
For example, an electric space heater may have a resistance of ten ohms, and the wires which supply it may have a resistance of 0.2 ohms, about 2% of the total circuit resistance. This means that approximately 2% of the supplied voltage is lost in the wire itself. Excessive voltage drop may result in unsatisfactory operation of, and damage to, electrical and electronic equipment.
National and local electrical codes may set guidelines for the maximum voltage drop allowed in electrical wiring, to ensure efficiency of distribution and proper operation of electrical equipment. The maximum permitted voltage drop varies from one country to another. In electronic design and power transmission, various techniques are employed to compensate for the effect of voltage drop on long circuits or where voltage levels must be accurately maintained. The simplest way to reduce voltage drop is to increase the diameter of the conductor between the source and the load, which lowers the overall resistance. In power distribution systems, a given amount of power can be transmitted with less voltage drop if a higher voltage is used. More sophisticated techniques use active elements to compensate for the undesired voltage drop.
dry bulb temperature
The dry-bulb temperature (DBT) is the temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. DBT is the temperature that is usually thought of as air temperature, and it is the true thermodynamic temperature.
dual pressure control
The HVACR industry has traditionally used mechanical pressure switches for system control and the protection of refrigeration equipment. These switches regulate critical functions within a refrigeration system and are essential to its proper operation. Low-pressure switches are commonly used to control compressor operation or act as a low-limit control.
High-pressure controls sense compressor discharge pressure and can stop the compressor in case of excessively high pressures. Dual-pressure controls are comprised of low pressure and high-pressure controls mounted in a single housing, with a single switch operated by either control. Other functions of mechanical pressure switches include condenser fan cycling and oil pressure safety control.
While mechanical pressure switches have served the industry well for many years, and seasoned technicians are comfortable with them, technology advancements are beginning to phase them out in favor of electronic controls. This shift mirrors advancements across dozens of other industries, where electronic technology has repeatedly replaced mechanical components or operations,
With electronics offering increased reliability, simplified servicing, and greater operating flexibility, it’s simple to understand why wholesalers and technicians in the HVACR field are making the switch to electronic controls.
This transition can be seen in changes being made in product manufacturing. For example, Emerson Climate Technologies began transitioning from mechanical controls to the electronic version in refrigeration equipment in 2012. That’s when the company began integrating electronic controllers onto Copeland condensing units.
In fact, Emerson reports there are more than 60,000 of its electronic controllers in the field today and contractors are beginning to realize the benefits of this change.
Technicians, in particular, benefit from the ease of set-up. Dan Whitten of Rosetown Central Refrigeration & Air Conditioning Ltd. has experience with electronic controllers and says he understands the time savings it can yield. “Our technician was very impressed by the accuracy of the pressure readings compared to his service gauges.”
Rosetown, located in Brampton, Ontario, Canada, is a diversified HVACR contractor with extensive experience (since 1966) in system design, project management, installation, and service to heating, air conditioning and refrigeration systems for commercial and industrial businesses.
Whitten says he sees this move as a way to help contractors be more productive. He explains that mechanical pressure controls require around 30 minutes for set-up and can be complicated with set point drift and difficult-to-read settings. An electronic control requires one minute or less to set up. In addition to the obvious time-savings, the device can be programmed with the touch of a button, rather than using cumbersome tools or gauges.
For wholesalers or distributors, inventory levels are improved because the electronic controller makes it possible to provide a single condensing unit that operates with multiple refrigerants. Spokespeople at Emerson say the integration of electronic controls across its condensing unit line reduced the number of models by 45% — alleviating inventory burden for wholesalers without impacting their service levels or the range of product available to support customers.
Whitten adds that contractors who install refrigeration systems that include these electronic controllers will find them to be more reliable due to fewer components. They even help reduce the chance of refrigerant leakage, he adds.
This shift in technology is quickly affecting the industry as it moves towards electronics, and technicians in the field should be prepared to manage these changes. Technicians can begin by educating themselves about the technology and learning how to install condensing units equipped with electronics. Contractors can also contact their nearest wholesaler or distributor to learn more about these types of electronics.
Ducts are used in heating, ventilation, and air conditioning (HVAC) to deliver and remove air. The needed airflows include, for example, supply air, return air, and exhaust air.Ducts commonly also deliver ventilation air as part of the supply air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as thermal comfort.
A duct system is also called ductwork. Planning (laying out), sizing, optimizing, detailing, and finding the pressure losses through a duct system is called duct design.
Ducts can be made out of the following materials:
Galvanized mild steel is the standard and most common material used in fabricating ductwork because the zinc coating of this metal prevents rusting and avoids cost of painting. For insulation purposes, metal ducts are typically lined with faced fiberglass blankets (duct liner) or wrapped externally with fiberglass blankets (duct wrap). When called for, a double walled duct is used. This will usually have an inner perforated liner, then a 1–2" layer of fiberglass insulation contained inside an outer solid pipe.
Rectangular ductwork commonly is fabricated to suit by specialized metal shops. For ease of handling, it most often comes in 4' sections (or joints). Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suite, but the most common stock sizes range evenly from 4" to 24" with 6"-12" being most commonly used. Stock pipe is usually sold in 10' joints. There are also 5' joints of non-spiral type pipe available, which is commonly used in residential applications.
Aluminium ductwork is lightweight and quick to install. Also, custom or special shapes of ducts can be easily fabricated in the shop or on site.
The ductwork construction starts with the tracing of the duct outline onto the aluminium preinsulated panel. The parts are then typically cut at 45°, bent if required to obtain the different fittings (i.e. elbows, tapers) and finally assembled with glue. Aluminium tape is applied to all seams where the external surface of the aluminium foil has been cut. A variety of flanges are available to suit various installation requirements. All internal joints are sealed with sealant.
Aluminum is also used to make round spiral duct, but it is much less common than galvanized steel.
Polyurethane and phenolic insulation panels (pre-insulated air ducts)
Traditionally, air ductwork is made of sheet metal which was installed first and then lagged with insulation. Today, a sheet metal fabrication shop would commonly fabricate the galvanized steel duct and insulate with duct wrap prior to installation. However, ductwork manufactured from rigid insulation panels does not need any further insulation and can be installed in a single step. Both polyurethane and phenolic foam panels are manufactured with factory applied aluminium facings on both sides. The thickness of the aluminium foil can vary from 25 micrometres for indoor use to 200 micrometres for external use or for higher mechanical characteristics. There are various types of rigid polyurethane foam panels available, including a water formulated panel for which the foaming process is obtained through the use of water and CO2 instead of CFC, HCFC, HFC and HC gasses. Most manufacturers of rigid polyurethane or phenolic foam panels use pentane as foaming agent instead of the aforementioned gasses.
A rigid phenolic insulation ductwork system is listed as a class 1[clarification needed] air duct to UL 181 Standard for Safety.
Fiberglass duct board (preinsulated non-metallic ductwork
Fiberglass duct board panels provide built-in thermal insulation and the interior surface absorbs sound, helping to provide quiet operation of the HVAC system.
The duct board is formed by sliding a specially-designed knife along the board using a straightedge as a guide. The knife automatically trims out a groove with 45° sides which does not quite penetrate the entire depth of the duct board, thus providing a thin section acting as a hinge. The duct board can then be folded along the groove to produce 90° folds, making the rectangular duct shape in the fabricator's desired size. The duct is then closed with outward-clinching staples and special aluminum or similar metal-backed tape.
Flexible ducts (also known as flex) are typically made of flexible plastic over a metal wire coil to shape a tube. They have a variety of configurations. In the United States, the insulation is usually glass wool, but other markets such as Australia, use both polyester fibre and glass wool for thermal insulation. A protective layer surrounds the insulation, and is usually composed of polyethylene or metalised PET. It is commonly sold boxes containing 25' of duct compressed into a 5' length. It is available in diameters ranging from as small as 4" to as big as 18", but the most commonly used are even sizes ranging from 6" to 12".
Flexible duct is very convenient for attaching supply air outlets to the rigid ductwork. It is commonly attached with long zip ties or metal band claps. However, the pressure loss is higher than for most other types of ducts. As such, designers and installers attempt to keep their installed lengths (runs) short, e.g. less than 15 feet or so, and try to minimize turns. Kinks in flexible ducting must be avoided. Some flexible duct markets prefer to avoid using flexible duct on the return air portions of HVAC systems, however flexible duct can tolerate moderate negative pressures. The UL181 test requires a negative pressure of 200 Pa.
This is actually an air distribution device and is not intended as a conduit for conditioned air. The term fabric duct is therefore somehow misleading; fabric air dispersion system would be the more definitive name. However, as it often replaces hard ductwork, it is easy to perceive it simply as a duct. Usually made of polyester material, fabric ducts can provide a more even distribution and blending of the conditioned air in a given space than a conventional duct system. They may also be manufactured with vents or orifices.
Fabric ducts are available in various colours, with options for silk screening or other forms of decoration, or in porous (air-permeable) and non-porous fabric. The determination which fabric is appropriate (i.e. air-permeable or not) can be made by considering if the application would require an insulated metal duct. If so, an air-permeable fabric is recommended because it will not commonly create condensation on its surface and can therefore be used where air is supplied below the dew point. Material that eliminates moisture may be healthier for the occupants. It can also be treated with an anti-microbial agent to inhibit bacterial growth. Porous material also tends to require less maintenance as it repels dust and other airborne contaminants.
Fabric made of more than 50% recycled material is also available, allowing it to be certified as green product. The material can also be fire retardant, which means that the fabric can still burn, but will extinguish when the heat source is removed.
Fabric ducts are not rated for use in ceilings or concealed attic spaces. However, products for use in raised floor applications are available. Fabric ducting usually weighs less than other conventional ducting and will therefore put less stress on the building's structure. The lower weight allows for easier installation.
Fabric ducts requires a minimum of certain range of airflow and static pressure in order for it to work.
The finish for external ductwork exposed to the weather can be sheet steel coated with aluminium or an aluminium/zinc alloy, a multilayer laminate, a fibre reinforced polymer or other waterproof coating.
Duct system components
A duct system often begins at an air handler. The blowers in the air handler can create substantial vibration, and the large area of the duct system would transmit this noise and vibration to the inhabitants of the building. To avoid this, vibration isolators (flexible sections) are normally inserted into the duct immediately before and after the air handler. The rubberized canvas-like material of these sections allows the air handler to vibrate without transmitting much vibration to the attached ducts. The same flexible section can reduce the noise that can occur when the blower engages and positive air pressure is introduced to the ductwork.
Downstream of the air handler, the supply air trunk duct will commonly fork, providing air to many individual air outlets such as diffusers, grilles, and registers. When the system is designed with a main duct branching into many subsidiary branch ducts, fittings called take-offs allow a small portion of the flow in the main duct to be diverted into each branch duct. Take-offs may be fitted into round or rectangular openings cut into the wall of the main duct. The take-off commonly has many small metal tabs that are then bent to attach the take-off to the main duct. Round versions are called spin-in fittings. Other take-off designs use a snap-in attachment method, sometimes coupled with an adhesive foam gasket for improved sealing. The outlet of the take-off then connects to the rectangular, oval, or round branch duct.
Ducts, especially in homes, must often allow air to travel vertically within relatively thin walls. These vertical ducts are called stacks and are formed with either very wide and relatively thin rectangular sections or oval sections. At the bottom of the stack, a stack boot provides a transition from an ordinary large round or rectangular duct to the thin wall-mounted duct. At the top, a stack head can provide a transition back to ordinary ducting while a register head allows the transition to a wall-mounted air register.
Ducting systems must often provide a method of adjusting the volume of air flow to various parts of the system. Volume control dampers (VCDs; not to be confused with smoke/fire dampers) provide this function. Besides the regulation provided at the registers or diffusers that spread air into individual rooms, dampers can be fitted within the ducts themselves. These dampers may be manual or automatic. Zone dampers provide automatic control in simple systems while variable air volume (VAV) allows control in sophisticated systems.
Smoke and fire dampers
Smoke and fire dampers are found in ductwork where the duct passes through a firewall or firecurtain.
Smoke dampers are driven by a motor, referred to as an actuator. A probe connected to the motor is installed in the run of the duct and detects smoke, either in the air which has been extracted from or is being supplied to a room, or elsewhere within the run of the duct. Once smoke is detected, the actuator will automatically close the smoke damper until it is manually re-opened.
Fire dampers can be found in the same places as smoke dampers, depending on the application of the area after the firewall. Unlike smoke dampers, they are not triggered by any electrical system (which is an advantage in case of an electrical failure where the smoke dampers would fail to close). Vertically mounted fire dampers are gravity operated, while horizontal fire dampers are spring powered. A fire damper's most important feature is a mechanical fusible link which is a piece of metal that will melt or break at a specified temperature. This allows the damper to close (either from gravity or spring power), effectively sealing the duct, containing the fire, and blocking the necessary air to burn.
Turning vanes inside of large fire-resistance rated Durasteel pressurisation ductwork
Turning vane close-up.
Turning vanes are installed inside of ductwork at changes of direction (e.g. at 90° turns) in order to minimize turbulence and resistance to the air flow. The vanes guide the air so it can follow the change of direction more easily.
Plenums are the central distribution and collection units for an HVAC system. The return plenum carries the air from several large return grilles (vents) or bell mouths to a central air handler. The supply plenum directs air from the central unit to the rooms which the system is designed to heat or cool. They must be carefully planned in ventilation design.[why?]
While single-zone constant air volume systems typically do not have these, multi-zone systems often have terminal units in the branch ducts. Usually there is one terminal unit per thermal zone. Some types of terminal units are VAV boxes (single or dual duct), fan-powered mixing boxes (in parallel or series arrangement), and induction terminal units. Terminal units may also include a heating or cooling coil.
Air terminals are the supply air outlets and return or exhaust air inlets. For supply, diffusers are most common, but grilles, and for very small HVAC systems (such as in residences) registers are also used widely. Return or exhaust grilles are used primarily for appearance reasons, but some also incorporate an air filter and are known as filter returns.
The position of the U.S. Environmental Protection Agency (EPA) is that "If no one in your household suffers from allergies or unexplained symptoms or illnesses and if, after a visual inspection of the inside of the ducts, you see no indication that your air ducts are contaminated with large deposits of dust or mold (no musty odor or visible mold growth), having your air ducts cleaned is probably unnecessary." A thorough duct cleaning done by a professional duct cleaner will remove dust, cobwebs, debris, pet hair, rodent hair and droppings, paper clips, calcium deposits, children's toys, and whatever else might collect inside. Ideally, the interior surface will be shiny and bright after cleaning. Insulated fiber glass duct liner and duct board can be cleaned with special non-metallic bristles. Fabric ducting can be washed or vacuumed using typical household appliances.
Duct cleaning may be personally justifiable for that very reason: occupants may not want to have their house air circulated through a duct passage that is not as clean as the rest of the house. However, duct cleaning will not usually change the quality of the breathing air, nor will it significantly affect airflows or heating costs.
Signs and indicator
Cleaning of the duct system may be necessary if:
Sweeping and dusting the furniture needs to be done more than usual.
After cleaning, there is still left over visible dust floating around the house.
After or during sleep, occupants experience headaches, nasal congestion, or other sinus problems.
Rooms in the house have little or no air flow coming from the vents.
Occupants are constantly getting sick or are experiencing more allergies than usual.
There is a musty or stale odor when turning on the furnace or air conditioner.
Occupants are experiencing signs of sickness, e.g. fatigue, headache, sneezing, stuffy or running nose, irritability, nausea, dry or burning sensation in eyes, nose and throat.
In commercial settings, regular inspection of ductwork is recommended by several standards. One standard recommends inspecting supply ducts every 1–2 years, return ducts every 1–2 years, and air handling units annually. Another recommends visual inspection of internally lined ducts annually Duct cleaning should be based on the results of those inspections.
Inspections are typically visual, looking for water damage or biological growth. When visual inspection needs to be validated numerically, a vacuum test (VT) or deposit thickness test (DTT) can be performed. A duct with less than 0.75 mg/100m2 is considered to be clean, per the NADCA standard. A Hong Kong standard lists surface deposit limits of 1g/m2 for supply and return ducts and 6g/m2 for exhaust ducts, or a maximum deposit thickness of 60 µm in supply and return ducts, and 180 µm for exhaust ducts. Another UK standard recommends ducts cleaning if measured bacterial content is more than 29 colony forming units (CFU) per 10 cm2; contamination is classified as "low" below 10 CFU/cm2, "medium" at up to 20 CFU/cm2, and "high" when measured above 20 CFU/cm2
Air pressure combined with air duct leakage can lead to a loss of energy in a HVAC system. Sealing leaks in air ducts reduces air leakage, optimizes energy efficiency, and controls the entry of pollutants into the building. Before sealing ducts it is imperative to ensure the total external static pressure of the duct work, and if equipment will fall within the equipment manufacturer's specifications. If not, higher energy usage and reduced equipment performance may result.
Commonly available duct tape should not be used on air ducts (metal, fiberglass, or otherwise) that are intended for long-term use. The adhesive on so called duct tape dries and releases with time. A more common type of duct sealant is a water-based paste that is brushed or sometimes sprayed on the seams when the duct is built. Building codes and UL standards call for special fire-resistant tapes, often with foil backings and long lasting adhesives.
Signs of leaks
Signs of leaky or poorly performing air ducts include:
Utility bills in winter and summer months above average relative to rate fluctuation
Spaces or rooms that are difficult to heat or cool
Duct location in an attic, attached garage, leaky floor cavity, crawl space or unheated basement
The Inductor 8 in. In-Line Duct Fan is an energy efficient way to circulate heated or cooled air around a room in your home. This duct booster fan is made of out corrosion-resistant metal.
An ECM motor is some times referred to an a variable speed motor. In one sense, this is true, it does vary its RPM of the motor, but only in response to changing conditions in the system. But in the truest sense, all it trying to do is maintain a programmed CFM. ECM stands for Electronically Commutated Motor.
Today’s higher efficiency equipment, both furnaces and A/C, are now using new higher efficiency motors to reduce the total electrical consumption of the system thus raising the efficiency. They also help with the efficiency by maintaining the proper air flow (CFM) across components like evaporator coils, heat exchangers, and even condenser coils. As you know from past postings, air flow is critical to proper operation, but, the use of ECM motor technology, also help raise efficiencies of the equipment.
So, what is an ECM motor? An ECM motor is some times referred to an a variable speed motor. In one sense, this is true, it does vary its RPM of the motor, but only in response to changing conditions in the system. But in the truest sense, all it trying to do is maintain a programmed CFM. ECM stands for Electronically Commutated Motor,
The ECM motor has 3 components:
The motor — which does not have any “windings” in it. The stator is driven by magnetic fields. The motor operates off DC voltage. When it first starts, it will actually rock back and forth before starting as it aligns the magnetic fields to drive the motor. The same motor will operate on both 110 volts and 220 volts, depending how the 5 pin power plug is configured. Rarely, does this go bad. The most common failure is due to someone “dropping” the module while it is plugged into the motor and breaking the wires going into the motor.
The module or ECM Microprocessor — or the “brains” of the motor. It receives the programming information from the board via a 16 pin harness and “translates” it so the motor produces the CFM desired. It mounts on end of the motor or can be remotely mounted and stores the “relationship” between “speed, torque, & airflow”. It is programmed at the factory to match a given unit Each module is “specific” to a model and are not interchangeable.
Lastly, there is some sort of control board where you can set the desired CFM for each application and that is connected to the module with the 16 pin harness.
The way I explain it in my training classes is this. An ECM motor maintains a programmed CFM in response to changes in torque. When the sensed torque changes, the RPM of the motor either ramps up or down to maintain the programmed CFM. Sounds confusing, doesn’t it?
Let me put it to you this way. Let’s compare how an ECM motor works to cruise control on a car. When you are using cruise control, you “program” how fast you want the car to go and set that speed (MPH). The RPM’s of the engine run at a certain level to maintain that speed. Now, you car starts to go up a hill. The cruise control senses a change in torque, so it needs to “rev” up the engine so it can maintain your “programmed speed”. Likewise, when you go down a hill, there is less torque on the engine so the RPM’s are reduced and, again, you are maintaining the programmed speed.
The same thing is occurring with an ECM motor. It works on a relationship between RPM, torque, and CFM (instead of MPH). Instead of a control on the steering column, there is a board in the unit that you need to set up with the “cool”, “adjust”, “heat”, and “delay” profiles (switches, jumpers, etc, depending on manufacturer). Once you have programmed the desired CFM for a particular application, the motor and module do the rest.
Let’s say you have a 3 ton air conditioner. So we need 400 CFM per ton or 1200 CFM to work properly. You use the programming board and set BOTH the cool and adjust profiles for as close to 1200 CFM as you can. (Always use the manufacturer’s tables for setting up an ECM motor). Now, on a call for cooling, the motor turns on and is going to try to maintain your programmed CFM. Here is where added efficiency comes in because we are maintaining ideal CFM across a range of operating conditions. Of course, as an air conditioner runs, the evaporator is going to get “wet” since we are removing latent heat and humidity. When the coil gets wet, the static pressure of the system goes up. As the static goes up, the motor senses a change in torque (like the car going uphill) and starts to increase the RPM of the motor in order to maintain the CFM of the system. Same thing occurs as a filter gets dirty, return static increases and the motor revs up the RPM to maintain the CFM. Now, as the latent heat decreases and there is less humidity or water on the coil, or someone changes the dirty filter, there is less static, a reduction in torque, so the RPM’s decrease, all the time maintaining CFM.
The same thing occurs in heating mode. You have programmed the motor to maintain a desired “temperature rise” for the system. The motor will deliver that CFM to maintain that rise. But, again, if the filter is gettng dirty, the motor’s RPM will increase, to maintain the CFM and temperature rise.
Lastly, you can also program a DELAY profile on the CFM board. This function is only for cooling but it allows you to further “fine tune” how the motor ramps up and down at the start and end of a call for cooing. You can set a “Normal, Humid, Dry, or factory default profile through the control.
By maintaining proper CFM in cooling, and temperature rise in heating, we get the maximum efficiency out of the furnace and air conditioner. This, coupled with the fact that an ECM motor uses less wattage than a PSC motor, you can see why these motors are becoming more and more popular as part of a total energy-efficient system.
The function of the economizer is, as its name implies, to "economize" or save on cooling costs. Obviously, it costs money to operate the compressor. If the compressor can be shut down and the system still provide adequate cooling, energy savings can be realized.
Heat internal to the building, such as people, lights, computers, copy machines, motors, and other machines, causes the temperature inside a structure to increase. Heat soaked up by the building structure may also continue to heat the building long after the temperature outside the building has dropped. There are times when the temperature outside a building is lower than the temperature inside.
Whenever the HVAC system is calling for cooling and the temperature outside is cool enough, it is economical to shut off the compressor and bring in cool outside air to satisfy the cooling needs of the building. Such is the function of an air economizer system.
There is one drawback to this type of control system. Even though the thermostat acknowledges that the outside air temperature is low enough to cool the building, the outside air may be too humid to provide adequate comfort for the building occupants. The occupants will feel cool but clammy. The solution is an economizer that adds a second control, which works in harmony with the outdoor thermostat and measures the outdoor air humidity. Such a control is called an enthalpy control. The term enthalpy means total heat. The enthalpy control measures both sensible and latent heat in the air and only allows outside air to be used for cooling if the air is both cool and dry enough to satisfy the space conditions.
If the indoor thermostat calls for cooling and the outside air enthalpy (total heat) is low enough, then the economizer brings in this cooler and less humid air and uses it for cooling instead of operating the compressor. Using the outside air for cooling is less expensive than operating the compressor to provide cooling.
So an enthalpy control is a control which checks to see if both the temperature (sensible heat) and the humidity (latent heat) are low enough to be used for cooling. This combination provides for the greatest comfort at the least cost.
Not all economizers use enthalpy controls. Some just check the outside air temperature and do not check the outside air humidity. Those controls do not provide the same levels of comfort as enthalpy controlled economizers.
Economizers can save a great deal of energy. They can also waste energy if they are not operating properly or are improperly adjusted. For example, if the outside air dampers are not closing properly when the outside air temperature is high, then hot air is unnecessarily entering the building and causing the air conditioning compressor to operate longer and under higher loads, thus consuming a great deal more energy than necessary.
If the dampers are open too far during the heating season, the heating system must heat the extra outside air entering the structure. Such extra heating and cooling costs can be quite high. The cost of a service call to repair such a problem is often less than the cost of one or two months of energy wasted.
Many economizers are not functioning at all or are out of service because they are not well understood by some service technicians. In fact, some service technicians simply disable them. It is essential that economizers are working properly and saving energy rather than increasing costs.
Since air economizers control and vary the amount of outside (fresh) air brought into a structure, they play an integral role in maintaining the quality of indoor air. A properly operating economizer can greatly improve indoor air quality (IAQ) and reduce air quality-related illnesses. Therefore, it is important for the service technician to have at least some knowledge of indoor air quality and its relationship to heating and cooling system operation.
Air economizers are available for residential and commercial systems and can be retrofitted to most systems as energy conserving devices. Most packaged light commercial systems (rooftop systems) have an economizer add-on package as an option which can be installed when the system is new or added to the system later.
The following items should be checked at least annually to ensure the air economizer is operating properly:
Setting and operation of the outdoor thermostat or enthalpy control;
Condition of the outdoor thermostat or enthalpy control;
Proper setting and operation of the economizer mixed air thermostat;
Proper damper operation and lubrication;
Minimum damper position adjustment;
Correct operation of the system when a call for cooling comes from the thermostat;
Function and condition of the economizer damper motor; and
Condition of the wiring and electrical terminations.
Since the enthalpy control is located in the outdoor air airstream and is a relatively sensitive control, it is not uncommon to have to replace it every few years depending upon the location of the equipment and the weather extremes in the area. The cost of a replacement control is usually recovered quickly through the energy saved. Economizer service should be a part of the scheduled maintenance performed at least on a yearly basis.
Just as our automobiles need regular service, so do residential and commercial heating and cooling systems. Like automobiles, the frequency of service depends upon how it is operated, how often and long it operates, and the environment where it operates. Like automobiles, well-maintained systems operate more efficiently, last longer, and fail less often.
electric forced air furnace
An electric forced air furnace works on the same principle as other types of forced air furnaces, but it has electric elements to heat the air, a circulating fan driven by a motor to blow the warm air, and a thermostat to regulate the temperature. The fan forces the heated air into a network of ducts that deliver the heated air to each room of the house.
An electric forced air furnace is a single, closed and compact unit that can be placed in any convenient location in the house. It has the following components:
Air filter control box
When the electric forced air furnace is switched on, the heating elements, which are made of high resistance metals become hot. The circulation fan draws in cold air from the room. The air is then passed over the hot heating elements, which warms up the air through the process of convection. The circulation fan then blows the heated air into the ducts that provide a passage to each room. Since warm air from the same source is forced into each room, all the rooms become evenly warm.
Installing the electric furnace
Place it in a convenient location, usually a room which is not occupied. Once installed, the furnace works with very little intervention and rarely breaks down when maintained as per manufacturer’s specifications
For an electric air furnace to keep working efficiently, it needs to be maintained regularly. The purpose of the air filter is to collect dust and other particulates, so it needs to be cleaned or replaced regularly. The fan blades can also become heavy with dust after months of use, so they should be wiped clean regularly (electric power should be turned off when doing any maintenance). Changing the air filter can be done by the homeowner.
The cost of operating an electric forced air furnace depends on several variables, including the utility rates, thermostat setting, size of the system, home insulation, ductwork insulation, outdoor temperature, leakage from air ducts and maintenance. An electric furnace is a good option for areas where natural gas or propane are not readily available options.
In some regions or circumstances, electricity is the preferred energy source for a forced-air heating system—though electric furnaces are quite uncommon because of the high cost of electricity as a furnace fuel in most regions.
An electric furnace is similar to a conventional gas forced-air furnace except that it produces heat with electric heating elements instead of gas burners. Circuit breakers that control the heating elements may be either inside or outside the cabinet.
An electric-resistance furnace works like a big hair dryer. As with a gas forced-air furnace, it has a blower that draws air into the cabinet through a cold-air return and then pushes the air through the heat exchanger. There, electric heating elements heat the air, and the blower pushes the warmed air back into rooms through a system of duct work.
One advantage of electric heating over gas and other combustion fuels is that electric heating doesn’t give off carbon monoxide. This is good for the environment and makes the unit easier to install because it doesn’t require a flue to carry combustion gases outside. But again, the big downside is the high cost of electricity in most regions. For this reason, heat pumps make more sense if you want to use electricity as a fuel.
Baseboard heaters are one type of electric resistance heaters. | Photo courtesy of Â©iStockphoto/drewhadley
Baseboard heaters are one type of electric resistance heaters. | Photo courtesy of ©iStockphoto/drewhadley
Electric resistance heating is 100% energy efficient in the sense that all the incoming electric energy is converted to heat. However, most electricity is produced from coal, gas, or oil generators that convert only about 30% of the fuel's energy into electricity. Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in homes or businesses that use combustion appliances, such as natural gas, propane, and oil furnaces.
If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating. The exception is in dry climates with either hot or mixed (hot and cold) temperatures (these climates are found in the non-coastal, non-mountainous part of California; the southern tip of Nevada; the southwest corner of Utah; southern and western Arizona; southern and eastern New Mexico; the southeast corner of Colorado; and western Texas). For these dry climates, there are so few heating days that the high cost of heating is not economically significant.
Electric resistance heating may also make sense for a home addition if it is not practical to extend the existing heating system to supply heat to the new addition.
TYPES OF ELECTRIC RESISTANCE HEATERS
Electric resistance heat can be supplied by centralized forced-air electric furnaces or by heaters in each room. Room heaters can consist of electric baseboard heaters, electric wall heaters, electric radiant heat, or electric space heaters. It is also possible to use electric thermal storage systems to avoid heating during times of peak power demand.
Electric furnaces are more expensive to operate than other electric resistance systems because of their duct heat losses and the extra energy required to distribute the heated air throughout your home (which is common for any heating system that uses ducts for distribution). Heated air is delivered throughout the home through supply ducts and returned to the furnace through return ducts. If these ducts run through unheated areas, they lose some of their heat through air leakage as well as heat radiation and convection from the duct's surface.
Blowers (large fans) in electric furnaces move air over a group of three to seven electric resistance coils, called elements, each of which are typically rated at five kilowatts. The furnace's heating elements activate in stages to avoid overloading the home's electrical system. A built-in thermostat called a limit controller prevents overheating. This limit controller may shut the furnace off if the blower fails or if a dirty filter is blocking the airflow.
As with any furnace, it's important to clean or replace the furnace filters as recommended by the manufacturer, in order to keep the system operating at top efficiency.
ELECTRIC BASEBOARD HEATERS
Electric baseboard heaters are zonal heaters controlled by thermostats located within each room. Baseboard heaters contain electric heating elements encased in metal pipes. The pipes, surrounded by aluminum fins to aid heat transfer, run the length of the baseboard heater's housing, or cabinet. As air within the heater is warmed, it rises into the room, and cooler air is drawn into the bottom of the heater. Some heat is also radiated from the pipe, fins, and housing.
Baseboard heaters are usually installed underneath windows. There, the heater's rising warm air counteracts falling cool air from the cold window glass. Baseboard heaters are seldom located on interior walls because standard heating practice is to supply heat at the home's perimeter, where the greatest heat loss occurs.
Baseboard heaters should sit at least three-quarters of an inch (1.9 centimeters) above the floor or carpet. This is to allow the cooler air on the floor to flow under and through the radiator fins so it can be heated. The heater should also fit tightly to the wall to prevent the warm air from convecting behind it and streaking the wall with dust particles.
The quality of baseboard heaters varies considerably. Cheaper models can be noisy and often give poor temperature control. Look for labels from Underwriter's Laboratories (UL) and the National Electrical Manufacturer's Association (NEMA). Compare warranties of the different models you are considering.
ELECTRIC WALL HEATERS
Electric wall heaters consist of an electric element with a reflector behind it to reflect heat into the room and usually a fan to move air through the heater. They are usually installed on interior walls because installing them in an exterior wall makes that wall difficult to insulate.
ELECTRIC THERMAL STORAGE
Some electric utilities structure their rates in a way similar to telephone companies and charge more for electricity during the day and less at night. They do this in an attempt to reduce their "peak" demand.
If you are a customer of such a utility, you may be able to benefit from a heating system that stores electric heat during nighttime hours when rates are lower. This is called an electric thermal storage heater, and while it does not save energy, it can save you money because you can take advantage of these lower rates.
The most common type of electric thermal storage heater is a resistance heater with elements encased in heat-storing ceramic. Central furnaces incorporating ceramic block are also available, although they are not as common as room heaters. Storing electrically heated hot water in an insulated storage tank is another thermal storage option.
Some storage systems attempt to use the ground underneath homes for thermal storage of heat from electric resistance cables. However, this requires painstaking installation of insulation underneath concrete slabs and all around the heating elements to minimize major heat losses to the earth. Ground storage also makes it difficult for thermostats to control indoor temperatures.
Any type of energy storage systems suffers some energy loss. If you intend to pursue an electric thermal storage system, it would be best for the system to be located within the conditioned space of your home, so that any heat lost from the system actually heats your home, rather than escaping to the outdoors. It would also be best to know how quickly heat will escape from the system. A system that leaks too much heat could cause control problems, such as the accidental overheating of your home.
All types of electric resistance heating are controlled through some type of thermostat. Baseboard heaters often use a line-voltage thermostat (the thermostat directly controls the power supplied to the heating device), while other devices use low-voltage thermostats (the thermostat uses a relay to turn the device on and off). Line-voltage thermostats can be built into the baseboard heater, but then they often don't sense the room temperature accurately. It's best to instead use a remote line-voltage or low-voltage thermostat installed on an interior wall. Both line-voltage and low-voltage thermostats are available as programmable thermostats for automatically setting back the temperature at night or while you're away.
Baseboard heaters supply heat to each room individually, so they are ideally suited to zone heating, which involves heating the occupied rooms in your home while allowing unoccupied area (such as empty guest rooms or seldom-used rooms) to remain cooler. Zone heating can produce energy savings of more than 20% compared to heating both occupied and unoccupied areas of your house.
Zone heating is most effective when the cooler portions of your home are insulated from the heated portions, allowing the different zones to truly operate independently. Note that the cooler parts of your home still need to be heated to well above freezing to avoid freezing pipes.
electric hydronic boiler
An electric hydronic boiler transfers heat by running water or vapor through a closed pipe system. A network of baseboards, radiant tubing and radiators transmits heat through an entire house or other type of building.FULL ANSWER
Because the heat comes through radiant delivery rather than through the transmission of forced air, distribution is even within a space. The heated water or vapor runs through a network in the entire house. Once the water returns to the boiler, it is continuously heated again until the temperature inside the designated zone reaches the level on the thermostat. Also, the issue of air blowing dust around does not arise, and homes using this type of system do not need ductwork unless it is necessary for the cooling system. The use of heating zones allows for the boiler to provide heat just to those spaces that the homeowner is using at a given time.
Having a unified system allows the electric hydronic boiler to heat water for use as well as the space inside the house. Depending on its location, the boiler can also melt snow or heat a pool. People who choose to have radiant heating installed in the floor have the bonus of warm floors.
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Electric power is usually produced by electric generators, but can also be supplied by sources such as electric batteries.
An electric shock occurs when a person comes into contact with an electrical energy source. Electrical energy flows through a portion of the body causing a shock. Exposure to electrical energy may result in no injury at all or may result in devastating damage or death.
Burns are the most common injury from electric shock.
Electric Shock Causes
Adolescents and adults are prone to high voltage shock caused by mischievous exploration and exposure at work. About 1,000 people in the United States die each year as a result of electrocution. Most of these deaths are related to on-the-job injuries.
Many variables determine what injuries may occur, if any. These variables include the type of current (AC or DC), the amount of current (determined by the voltage of the source and the resistance of the tissues involved), and the pathway the electricity takes through the body. Low voltage electricity (less than 500 volts) does not normally cause significant injury to humans. Exposure to high voltage electricity (greater than 500 volts) has the potential to result in serious damage.
If you are going to help someone who has sustained a high voltage shock, you need to be very careful that you don't become a second victim of a similar electrical shock. If a high voltage line has fallen to the ground, there may be a circle of current spreading out from the tip of the line. Your best bet may be to call 911. The electric company will be notified so that the power can be shut off. A victim who has fallen from a height or sustained a severe shock causing multiple jerks may have a serious neck injury and should not be moved without first protecting the neck.
Children are not often seriously injured by electricity. They are prone to shock by the low voltage (110-220 volts) found in typical household current. In children aged 12 years and younger, household appliance electrical cords and extension cords caused more than 63% of injuries in one study. Wall outlets were responsible for 15% of injuries.
Electro-mechanical control typically consists of multiple Relays, Timers, and/or Counters wired together on an enclosure panel. Electro-mechanical Control is also referred to simply as "Relay Control" perhaps a more accurate term, since solid state Relays, Timers, and Counters have become very common. Today this approach is common with very simple and small applications.A variety of simple electromechanical devices are available for applications such as comfort heating control, outdoor freeze protection, heat trace cable, and corrosive or hazardous environments.
electronic air filter
The first electrostatic or Electronic Air Cleaner was developed by Westinghouse in 1935. The “Precipitron”, came out of "a successful failure" in research, and a hopeful house-cleaning experiment in Pittsburgh. By the 1940s, the Precipitron was used in homes, offices, hospitals and factories, literally electrocuting dust and dirt out of the atmosphere. Westinghouse eventually left this industry and Electronic Air Cleaners continued to evolve over the years.
Electro-Air of Canada introduced its first Electronic Air Cleaner nearly 50 years ago and our history of performance and reliability have made us the #1 manufacturer for many of the world’s largest heating and air conditioning OEM’s (original equipment manufacturers).
Electronic Air Cleaners to this day are still the tried and true method of cleaning the air and offer benefits over other air purification technologies. Their operating costs are lower, using less energy than a 40 watt light bulb. They operate with a very low static “pressure drop” otherwise known as airflow resistance, which helps reduce unit and system operating costs. And they are “Earth Friendly” as the filters can be washed and re-used over and over again, for many years.
A study by the Canada Mortgage and Housing Corporation testing a variety of forced-air furnace filters found that Electronic Air Cleaners provided the best, and most cost-effective means of cleaning the air using a forced-air system. In other words, Electronic Air Cleaners are able to produce the most amount of clean air, at a lower cost than other air cleaning methods.
Powerful 4-Stage Filtration System
4-Stage-Filtration-DiagramElectronic Air Cleaners work on the principle of Electrostatic Precipitation. Millions of airborne pollutants are carried through the return air ducts of the heating/cooling system in your home and are treated through four stages of filtration.
Washable Permanent Prefilters (2) capture large particles of dirt, lint and hair. Simply wash clean with DAX Air Cleaner Detergent.
Lifetime, Environmentally-Friendly, Two-Stage Electronic Filters (2) first give a powerful positive electrical charge to incoming dirt particles by the ionizing wires. Charged particles then move into the collecting area where they are attracted to a series of grounded plates. Pollutants are held in this section like a magnet until washed away during cleaning with DAX Detergent. Removes airborne contaminants such as dust, mites, pollen, mold, bacteria, viruses, pet dander, tobacco smoke particles, cooking smoke and grease and more down to 0.01 micron (1/2,540,000 of an inch). At that size, it would take 100,000 particles to cover the head of a pin. Such particles are 500 times smaller than the smallest grains of dust trapped by conventional furnace filters. With over 8000 volts, bacteria, viruses, mold and pollen either die or become completely neutralized. No contaminants can possibly live or grow on these collecting plates.
electronic expansion valve
The subject of energy savings has become a fundamental aspect in the field of commercial refrigeration & air conditioning.This is true above all for supermarket chains, as the reduction of energy wastage represents the most
effective way to save costs and achieve better competitiveness.Furthermore, the adoption of techniques and methods aimed at saving energy in the installation also means embracing a socially responsible policy in relation to all the stakeholders that interact with the supermarket: shareholders, workers, customers, suppliers, the environment and society.
Business people who are sensitive to environmental issues and the notion of energy savings have made these concepts an integral part of their corporate Identity, with the conviction that the sustainable business model offers greater guarantees of long-term development, the opportunity to enjoy the advantages of eco-efficiency in terms of its competitiveness, as well as to share in the benefits of “territorial competitiveness”.
The traditional solution: - TEV
A conventional thermostatic expansion valve (TXV or TEV) is controlled by springs, bellows, and push rods. (Graphics courtesy of Sporlan Valve Co.)
The function of the thermostatic expansion valve (TXV or TEV) is to hold a constant evaporator superheat. When set and operating properly, the TXV will keep the evaporator active throughout its entire length.
The conventional TXV is controlled by springs, bellows, and push rods. (See Figure 1.) The spring force is a closing force on the TXV. The evaporator pressure, which acts under the thermostatic element's diaphragm, is also a closing force. An opening force is the remote bulb force, which acts on top of the thermostatic element's diaphragm.
There is also a liquid force from the liquid line, which acts on the face of the needle valve and has a tendency to open the valve. However, this force is cancelled out when using a balanced port TXV. Working together, these forces maintain a constant evaporator superheat in a refrigeration system. There are no electronic devices associated with a conventional TXV.
The SEH-100 EEV from Sporlan Valve Co.
The electronic expansion valve (EEV) operates with a much more sophisticated design. EEVs control the flow of refrigerant entering a direct expansion evaporator. They do this in response to signals sent to them by an electronic controller. A small motor is used to open and close the valve port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them by the electronic controller. The step motor is driven by a gear train, which positions a pin in a port in which refrigerant flows. A cutaway of an EEV with step motor and drive assembly is shown in Figure 2.
Step motors can run at 200 steps per second and can return to their exact position very quickly. The controller remembers the number of step signals sent by the controller. This makes it possible for the controller to return the valve to any previous position at any time. This gives the valve very accurate control of refrigerant that flows through it. Most of these EEVs have 1,596 steps of control and each step is 0.0000783 inches.
A cutaway of an electronic expansion valve (EEV) with step motor and drive assembly.
The electronic signals sent by the controller to the EEV are usually done by a thermistor connected to discharge airflow in the refrigerated case. A thermistor is nothing but a resistor that changes its resistance as its temperature changes. Other sensors are often located at the evaporator inlet and outlet to sense evaporator superheat. This protects the compressor from any liquid floodback under low superheat conditions.
Pressure transducers can also be wired to the controller for pressure/temperature and superheat control. Pressure transducers generally have three wires. Two wires supply power and the third is an output signal. Generally, as system pressure increases, the voltage sent out by the signal wire will increase. The controller uses this voltage to calculate the temperature of the refrigerant with the use of a pressure/temperature table programmed into the controller.
A combination of compressor floodback protection and the ability to maintain refrigerator case discharge air temperature set point control makes the EEV useful in many diverse applications. Some EEV controllers can also be programmed for custom control applications.
The controller may open the EEV too much and cause an overcooling condition. The sensors connected to the refrigeration system and wired to the controller will sense this overcooling condition and feed this information to the electronic controller and the EEV. This will cause the step motor to move in the closing direction and close the valve more.
All refrigeration units, whether developed for the air-conditioning or refrigeration market, commonly use a traditional thermostatic expansion valve as the expansion device: this is the standard component fitted with a
sensor bulb and, in more advanced models, a pressure fitting for external compensation.
This expansion device, hereinafter called the TEV (Thermostatic Expansion Valve), despite being functional and generally able to make the unit it is installed in “operational”, has a number of characteristics that in many aspects limit the versatility of the installation and the performance that can be achieved.
Obviously, some categories of installation are more sensitive to the negative aspects of TEV control, due to the specifications of the installation, the operating parameters and/or the distribution of the load throughout the year.
The innovation: - EEV
A solution to most, if not all of the shortfalls resulting from TEV control is the electronic expansion valve, hereinafter EEV (Electronic Expansion Valve). This servo-controlled electro-mechanic device, which has for the last few years been widely available on the market, expands the flow of refrigerant in a variable manner, using commonly a pressure sensor and a temperature sensor (corresponding to the pressure fitting for compensation and the sensor bulb in the TEV). Both these sensors are fitted to the evaporator outlet, and the measurements are read and processed by a controller that decides the best degree of opening of the valve in real-time.
The electronic valves have such a wide control capacity that they allow the
compressors to always operate in the optimum conditions (according to the outside environmental conditions). Like, in winter, the circuit can operate with a very low condensing pressure, thus improving the efficiency of the compressors and reducing power consumption.
The electronic valve allows more effective temperature control, ensuring a lower operating temperature by better exploiting the surface of the evaporator.
The system consequently does not require future adjustments, as the electronics continuously implement the control action based on the parameters read by the transducers located at the evaporator outlet, maintaining the super-heat values at the optimum levels for which a self-adapting algorithm is used.
electronic programmable thermostat
A programmable thermostat is a thermostat which is designed to adjust the temperature according to a series of programmed settings that take effect at different times of the day. Programmable thermostats may also be called setback thermostats or clock thermostats.
Heating and cooling losses from a building (or any other container) become greater as the difference in temperature increases. A programmable thermostat allows reduction of these losses by allowing the temperature difference to be reduced at times when the reduced amount of heating or cooling would not be objectionable.
For example, during cooling season, a programmable thermostat used in a home may be set to allow the temperature in the house to rise during the workday when no one will be at home. It may then be set to turn on the air conditioning before the arrival of occupants, allowing the house to be cool upon the arrival of the occupants while still having saved air conditioning energy during the peak outdoor temperatures. The reduced cooling required during the day also decreases the demands placed upon the electrical supply grid.
Conversely, during the heating season, the programmable thermostat may be set to allow the temperature in the house to drop when the house is unoccupied during the day and also at night after all occupants have gone to bed, re-heating the house prior to the occupants arriving home in the evening or waking up in the morning. Since most people sleep better when a room is cooler and the temperature differential between the interior and exterior of a building will be greatest on a cold winter night, this reduces energy losses.
Similar scenarios are available in commercial buildings, with due consideration of the building's occupancy patterns.
While programmable thermostats may be able to save energy when used correctly, little or no average energy savings has been demonstrated in residential field studies. Difficulty with usability in residential environments appears to lead to lack of persistence of energy savings in homes. According to the US EPA regarding residential programmable thermostat, "Available studies indicate no savings from programmable thermostat (PT) installation. Some studies indicate slight increased consumption." This is supported with studies by Nevius and Pigg, Cross and Judd and others and Peffer et al. has a recent review of the topic.
In addition to potential increased energy consumption, digital programmable thermostats have been criticised for their poor usability. Several studies have found that digital programmable thermostats are difficult for users to programme and older people in particular can struggle to use them (see Combe et al.). If the desired energy savings are to be achieved by these types of products then systems need to be simple, intuitive and effective to use by a wide range of people.
The most basic clock thermostats may only implement one program with two periods (a hotter period and a colder period), and the same program is run day after day. More sophisticated clock thermostats may allow four or more hot and cold periods to be set per day. Usually, only two distinct temperatures (a hotter temperature and a colder temperature) can be set, even if multiple periods are permitted. The hotter and colder temperatures are usually established simply by sliding two levers along an analogue temperature scale, much the same as in a conventional (non-clock) thermostat.
This design, while simple to manufacture and relatively easy to program, sacrifices comfort on weekends since the program is repeated each of the seven days of the week with no variation. To overcome this deficit, a push-button is sometimes provided to allow the user to explicitly switch (once) the current period from hot period to a cold period or vice versa; the usual use of this button is to over-ride a "set back" that takes place during the workday when the home is normally unoccupied.
The clock mechanism is electrical. Two methods have commonly been used to operate it:
A separate, continuous source of 24 volts alternating current (24 VAC) is provided to the thermostat.
A rechargeable battery in the thermostat operates the clock. This battery charges when the thermostat is not calling for heat and 24 VAC is available to it. It discharges to operate the clock when the thermostat is set for heating or cooling.
Digital thermostats may implement the same functions, but most provide more versatility. For example, they commonly allow setting temperatures for two, four, or six periods each day, and rather than being limited to a single "hotter" temperature and a single "colder" temperature, digital thermostats usually allow each period to be set to a unique temperature. The periods are commonly labeled "Morning", "Day", "Evening", and "Night", although nothing constrains the time intervals involved. Digital thermostats usually allow the user to override the programmed temperature for the period, automatically resuming programmed temperatures when the next period begins. A function to "hold" (lock-in) the current temperature is usually provided as well; in this case, the override temperature is maintained until the user cancels the hold or a programmed event occurs to resume the normal program. More-sophisticated models will allow for the release of the hold to take place at a set time in the future.
As with clock thermostats, basic digital thermostats may have just one cycle that is run every day of the week. More-sophisticated thermostats may have a weekday schedule and a separate weekend schedule (so-called "5-2" setting) or separate Saturday and Sunday schedules (so-called "5-1-1" settings), while other thermostats will offer a separate schedule for each day of the week ("7 day" settings). The selection of which days are defined as the "weekend" is arbitrary, depending on the user's heating and cooling schedule requirements. Often, a manufacturer will sell three similar thermostats offering each of those levels of functionality, and there is no obvious difference in the thermostats other than the factory programming and the price.
Most digital thermostats have separate programs for heating and cooling, and may feature a digital or manual switch to turn on the furnace blower for air circulation, even when the system isn't heating or cooling. More-sophisticated models may be programmed to run the circulating fan for a brief 5- to 10-minute period in the event a heating or cooling cycle has not taken place during the previous hour. This is particularly useful in buildings subject to stratification where without frequent air circulation, hot air rises and separates from the cooler air that falls.
Digital thermostats may also have a user-programmable air filter change reminder; this counts the accumulated run-time of the heating/cooling system and reminds the user when it is time to change the filter. The feature often displays the accumulated run-time either as an aggregate of both heating and cooling or displaying each time separately.
Some digital thermostats have the capability of being programmed using a touch-tone telephone or over the Internet, such as the Nest Learning Thermostat.
Digital thermostats are usually powered one of three ways:
A sophisticated power circuit operates from the 24 VAC supply when the thermostat is not calling, and operates from the current flowing in the thermostat circuit when the thermostat is calling. A battery is used to provide back-up during power failures.
A rechargeable battery operates the thermostat just as in the clock thermostat, charging when the thermostat is not calling and discharging while the thermostat is calling.
A non-rechargeable battery always powers the thermostat. To limit the amount of power drawn from the battery, such thermostats use an impulse relay that does not require the continuous application of power to the relay's coil. These thermostats can be used on millivolt circuits, as well as conventional 24 VAC circuits. Battery life is typically one to two years.
energy efficiency ratio
Room air conditioners can be an affordable way to cool a limited space, rather than using a central cooling system to cool a whole home or office building, particularly if there is unused space.While less efficient than central air, they can be significantly cheaper to operate.
Energy Efficiency of Air Conditioners
A room air conditioner's efficiency is rated according to the Energy Efficiency Ratio (EER).
This is the ratio of cooling capacity to the power input, or how well it cools compared to how much energy it needs. The ratio is measured in British thermal units (Btu) per hour. The higher the EER, the more efficient the unit. If you're shopping for a new air conditioner, look up its EER.
How to Select an Air Conditioner
The required cooling ability and strength of the air conditioner you need us based on the size of the room you plan to use it in. Getting a big, overly strong air conditioner can actually be a bad idea for a smaller room. It can cause the unit to work incorrectly, causing the room to feel damp or spotty. A smaller unit intended for that space works consistently and will dehumidify the room like it's supposed to.
Based solely on size, a good rule of thumb to follow is the unit will need 20 Btu for every square foot of space. But if you have a room with a vaulted ceiling or are located in an especially hot climate, you will need to go a bit higher to get a good air conditioner.
Before purchasing, make sure your home or business has the ability to run the unit. Room units usually run on 115-volt or 230-volt circuit.
Additionally, consider what extra features are important to you. Some units are programmable, cooling more at certain times of the day and letting the room get warmer at different times, when no one is in the room.
This automatic feature can help save you money. Also look for units with an easily removed filter, to make cleaning more simple and convenient. A digital readout can also help you set the unit to the precise temperature for efficiency, usually around 78 degrees Fahrenheit.
Operating the New Unit
Position the new air conditioner away from other appliances, such as lamps or the television. These devices can give off heat and trick the unit into working harder than it needs to, using up more energy.
Set the unit to a temperature that is as high as you can comfortably handle. Going below 78 degrees makes your unit have to work much harder, which can greatly increase your electricity bill.
By understanding what to look for when shopping for an air conditioner, you can make an informed choice that fits your needs and your budget. Consider the unit Energy Efficiency Ratio, voltage and Btu in order to get the best air conditioner for you. By using an energy efficient air conditioner strategically, you can stay comfortable while keeping your electric costs down.
Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure. Evaporation is a fundamental part of the water cycle and is constantly occurring throughout nature,
evaporative condenser cooling tower
The principle underlying evaporative cooling is the fact that water must have heat applied to it to change from a liquid to a vapor. When evaporation occurs, this heat is taken from the water that remains in the liquid state, resulting in a cooler liquid.
Evaporative cooling systems use the same principle as perspiration to provide cooling for machinery and buildings. A cooling tower is a heat-rejection device, which discharges warm air from the cooling tower to the atmosphere through the cooling of water. In the HVAC industry, the term “cooling tower” is used to describe both open- and closed-circuit heat-rejection equipment.
In an HVAC system, heat is generated by the sun shining on the building, the computers, and people. The heat is picked up in the air handlers which are indirectly tied to the refrigerant through several heat exchangers. The heat boils the refrigerant from a liquid to a vapor. Cooling Tower water is circulated through a heat exchanger where refrigerant vapor is condensed and heat is transferred to the water. The purpose of the cooling towers is to cool the warm water returning from the heat exchanger so it can be reused. In the open cooling tower, the warm return water from the heat exchanger is sprayed over the “fill”. The fill provides the surface area to enhance the heat transfer between the water and air, causing a portion of the water to evaporate. That cool water then loops back to the beginning of the process, to absorb more heat from the heat exchanger.
In a closed circuit cooling tower, cold water or a solution of ethylene or propylene glycol is used to provide cooling. Unlike in an open cooling tower, the fluid used to provide cooling is enclosed in a coil and is not exposed directly to the air. Cold water is recirculated over the outside of the coil, which contains the fluid that has been heated by the process. During operation, heat is transferred from the fluid through the coil to the spray water and then to the atmosphere as a portion of the water evaporates. The cool fluid in the coil then loops back to the beginning of the process, to be reused in the process.
A ton of air-conditioning is the rejection of 12,000 BTUH. A cooling tower ton actually rejects about 15,000 BTUH due to the heat-equivalent of the energy needed to drive the chiller’s compressor. A cooling tower ton is defined as the heat rejection in cooling 3 GPM of water entering at 95°F and leaving the cooling tower at 85°F, with an entering wet bulb temperature of 78°F, which amounts to 15,000 BTUH.The figure below shows the relationship between water and air as they pass through a cooling tower. The curve indicates the drop in water temperature (point A to B) and the rise in the air wet bulb temperature (Point C to D) in their respective passages through the cooling tower.
From a heat transfer standpoint, a cooling tower’s performance while cooling a given quantity of water is influenced only by the wet bulb temperature of the entering air. This is clearly indicated in the psychrometric analysis of the air path in a cooling tower as indicated below. The true path is approximated by the dotted curved line from Point A to Point C. To simplify the air path for purposes of explanation, it is broken down into Line AB and BC. In the analysis, air enters the tower at an unsaturated condition (Point A). Before reaching the fill, it is saturated adiabatically as it travels to point B. Passing through the fill, it absorbs heat from the falling water, thereby increasing the total heat content of the air. Since the air is continually being washed with falling water, the process follows the saturation line to the final temperature of the air leaving the tower, Point C.
During the adiabatic change, Point A to Point B, there is no cooling of the water. In this stage there is only a conversion of air sensible heat into latent heat as the air dry bulb temperature drops to that of the wet bulb temperature. The effective heat removal takes place between Points B and C where the saturated air is at the wet bulb temperature. The wet bulb temperature of the air is the only air condition influencing the performance of the tower.
Evaporative cooling is a process that uses the effect of evaporation as a natural heat sink. Sensible heat from the air is absorbed to be used as latent heat necessary to evaporate water. The amount of sensible heat absorbed depends on the amount of water that can be evaporated.
Evaporative cooling can be direct or indirect; passive or hybrid. In direct evaporative cooling, the water content of the cooled air increases because air is in contact with the evaporated water. In indirect evaporative cooling, evaporation occurs inside a heat exchanger and the water content of the cooled air remains unchanged. Since high evaporation rates might increase relative humidity and create discomfort, direct evaporative cooling can be applied only in places where relative humidity is very low.
Where evaporation occurs naturally it is called passive evaporation. A space can be cooled by passive evaporation where there are surfaces of still or flowing water, such as basins or fountains. Where evaporation has to be controlled by means of some mechanical device, the system is called a hybrid evaporative system.
Evaporative cooling is based on the thermodynamics of evaporation of water, i.e. the change of the liquid phase of water into water vapor. This phase change requires energy, which is called latent heat of evaporation- this is the energy required to change a substance from liquid phase to the gaseous one without temperature change. When non- saturated air (i.e. air that does not contain liquid water but only water vapor) comes in direct contact with water evaporation occurs. It is obvious that during this process the moisture content of air is increased. This process is represented on the psychometric chart by a displacement along a constant wet bulb line, AB. The air to be cooled is initially at point A. The air, as a result of the direct evaporative cooling process, reaches point B. This is a constant wet bulb temperature process and therefore line AB is parallel to the wet bulb temperature lines.
When evaporation occurs in the primary circuit of a heat exchanger, while the air to be cooled circulates in the secondary circuit, the air temperature decreases but its humidity ratio remains constant. It must be noted that since the air temperature drops, its relative humidity will increase, but less than during the direct evaporative cooling process. Since the humidity ratio of the air does not change, this process is represented on the psychometric chart by a displacement along a constant humidity ratio line CD. In this figure, the air to be cooled, initially at point C is sensibly cooled by the indirect evaporative cooler until it reaches point B.
Evaporative cooling uses large volumes or air. Forcing this volume of air through small ducts, around sharp corners, and out of small outlets, involves ducting costs. In some cases the best duct system is none. Just blow the air into a large daytime occupancy rooms.
If not properly designed direct type evaporative coolers may pose the following problems:
The cooled air may be excessively humid.
The high rate of air flow and large number of air changes, which are necessary for effective cooling, cause large variation in the air speed and the associated thermal sensation within the cooled space. This results in a waste of energy, which has been used to cool the discharged air.
Indirect type evaporative coolers try to overcome these defects. Since the air in these types of coolers gets cooled without coming in direct contact with water, the problem of excessive humidity in the room air gets automatically solved. Simultaneously the required number of air changes also gets reduced.
The important advantages of the indirect type evaporative cooling are as follows:
Depending upon the performance of the system used, the operating cost gets reduced by 20% - 60% below that of refrigerant air conditioning. Of course, the temperature achieved by evaporative cooling is higher and varying unlike air conditioned system.
Power consumption is less resulting in a sharp reduction in the running costs. Because of this reason, the indirect evaporative coolers can also be used where electricity is expensive or scarce.
It can be used as a precooler for refrigerant air conditioning systems.
In this type of cooling, the exhaust room air can be delivered to the cooling tower as a result of which the lower water temperature is obtained. This in turn, produces more cooling.
Evaporative Cool Mist: With our evaporative cool mist humidifiers, humidity is produced by a fan that draws the air in from the room and blows it over or through a moistened wick in water. Some of this water evaporates and this water vapor is added to the air which increases its humidity.
Evaporative Cool Mist: With our evaporative cool mist humidifiers, humidity is produced by a fan that draws the air in from the room and blows it over or through a moistened wick in water. Some of this water evaporates and this water vapor is added to the air which increases its humidity.
An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. The liquid is evaporated, or vaporized, into a gas.An evaporator is used in an air-conditioning system to allow a compressed cooling chemical, such as R-22 (Freon) or R-410A, to evaporate from liquid to gas while absorbing heat in the process. It can also be used to remove water or other liquids from mixtures. The process of evaporation is widely used to concentrate foods and chemicals as well as salvage solvents. In the concentration process, the goal of evaporation is to vaporize most of the water from a solution which contains the desired product. In the case of desalination of sea water or in Zero Liquid Discharge plants, the reverse purpose applies; evaporation removes the desirable drinking water from the undesired product, salt.
One of the most important applications of evaporation is in the food and beverage industry. Foods or beverages that need to last for a considerable amount of time or need to have certain consistency, like coffee, go through an evaporation step during processing.
In the pharmaceutical industry, the evaporation process is used to eliminate excess moisture, providing an easily handled product and improving product stability. Preservation of long-term activity or stabilization of enzymes in laboratories are greatly assisted by the evaporation process.
Another example of evaporation is in the recovery of sodium hydroxide in kraft pulping. Cutting down waste-handling cost is another major reason for large companies to use evaporation applications. Legally, all producers of waste must dispose of waste using methods compatible with environmental guidelines; these methods are costly. By removing moisture through vaporization, industry can greatly reduce the amount of waste product that must be processed.
How an evaporator works
The solution containing the desired product is fed into the evaporator and passes across a heat source. The applied heat converts the water in the solution into vapor. The vapor is removed from the rest of the solution and is condensed while the now-concentrated solution is either fed into a second evaporator or is removed. The evaporator, as a machine, generally consists of four sections. The heating section contains the heating medium, which can vary. Steam is fed into this section. The most common medium consists of parallel tubes but others have plates or coils typically made from copper or aluminium. The concentrating and separating section removes the vapor being produced from the solution. The condenser condenses the separated vapor, then the vacuum or pump provides pressure to increase circulation.
Natural/forced circulation evaporator
Natural circulation evaporators are based on the natural circulation of the product caused by the density differences that arise from heating. In an evaporator using tubing, after the water begins to boil, bubbles will rise and cause circulation, facilitating the separation of the liquid and the vapor at the top of the heating tubes. The amount of evaporation that takes place depends on the temperature difference between the steam and the solution.
Problems can arise if the tubes are not well-immersed in the solution. If this occurs, the system will be dried out and circulation compromised. In order to avoid this, forced circulation can be used by inserting a pump to increase pressure and circulation. Forced circulation occurs when hydrostatic head prevents boiling at the heating surface. A pump can also be used to avoid fouling that is caused by the boiling of liquid on the tubes; the pump suppresses bubble formation. Other problems are that the residing time is undefined and the consumption of steam is very high, but at high temperatures, good circulation is easily achieved.
An evaporator fan draws air from the refrigerator and blows it over the evaporator coils. The liquid refrigerant absorbs heat from the air and the air blows back into the refrigerator at a lower temperature, cooling the refrigerator. The liquid refrigerant starts to vaporize as it heats up and moves to the compressor.
evaporator pressure regulator
Evaporator pressure regulator (EPR) of low-limit device that prevents the evaporator pressure because of reduction below set value. It supports diis low-limit set point, regardless of how low pressure die suction line may fall due to the actions of the compressor. Evaporator pressure regulator is not designed to maintain constant pressure in the evaporator, as CPXV. Instead, it is intended to limit the minimum pressure in the evaporator and performs no action when the pressure drop exceeds this limit. Evaporator pressure regulators are used in installations in which die evaporator pressure or temperature must remain above the minimum value. They are widely used with coolers of water and brines to prevent the freezing periods of reduced load. They are also used for air cooling applications where appropriate humidity control requires a minimum limit temperature of the evaporator.
EPR is working pressure control in die evaporator. As approaches the low-limit set in paragraph EPR, its plug connector begins to modulate closed, reducing the weight of the refrigerant flow to the evaporator.
Because the rate of refrigerant flow to the evaporator from the metering device does not affect the EPR, the evaporator pressure starts to increase. When the evaporator pressure increases beyond the low-limit set point, EPR plug departs from the chair. EPR-port remains open until die pressure falls below the lower limit set point.
EPRs are available with two positions, or of the modulation frequency response. In two-position of regulatory bodies control, differential exists between the opening and closing action of the valve. It is equal to the sum of changes die pressure in the evaporator, which should happen before tne EPR can open or close. This control differential prevents two positions EPR from rapidly Cycling pressure in the evaporator is within a few units of its lower limit set point. When the evaporator pressure drops below the lower limit set point, valve closes the port. It remains closed until the evaporator pressure increases above the value of the set point plus control of the differential. If the evaporator load remains light, EPR will continuously cycle until the thermostat opens the compressor circuit. If the load increases, the EPR will remain fully open to reduce the pressure, it adds to the low side ofthe system.
Modulating a regulator of pressure in the evaporator. Unlike two-position valve port a modulating EPR never totally closed during operation of the compressor. As evaporator pressure drop in response to the reduced load, EPR modulates connect it to the seat. This action reduces die suction flow of steam leaving the evaporator, supporting the evaporator pressure above its low-limit set point. Conversely,
What is excess air
There is a theoretical amount of fresh air that when mixed with a fixed amount of fuel, and burnt will result in perfect combustion. In this situation all of the fuel will have been properly burnt and all of the oxygen in the air will have been consumed. In this circumstance there will be no excess air and combustion efficiency will be maximised.
In the real world, perfect combustion is not possible. The theoretical amount of fresh air would provide insufficient oxygen for complete combustion and some of the carbon in the fuel would be converted into carbon monoxide rather than carbon dioxide. A lack of air can lead to dangerous levels of carbon monoxide being formed and smoke being produced.
Therefore it is usual to adjust the combustion process so that a level of excess air is present to give margin safety. This level is set to account for any likely process variable, e.g. The variability of the fuel supply, changes in atmospheric pressure, changes in wind direction etc.
. exhaust valve - a valve through which burned gases from a cylinder escape into the exhaust manifold. exhaust system, exhaust - system consisting of the parts of an engine through which burned gases or steam are discharged. valve - control consisting of a mechanical device for controlling the flow of a fluid.
A thermal expansion valve (often abbreviated as TEV, TXV, or TX valve) is a component in refrigeration and air conditioning systems that controls the amount of refrigerant flow into the evaporator thereby controlling the superheat at the outlet of the evaporator.
An external hard drive is a portable storage device that can be attached to a computer through a USB or FireWire connection, or wirelessly. External hard drives typically have high storage capacities and are often used to back up computers or serve as a network drive.
external equalizer txv
An internally equalized TXV uses evaporator inlet pressure to create the 'closing' force on the valve. An externally equalized valve uses the evaporator outlet pressure' thereby compensating for any pressure drop through the evaporator.
An external hard drive is a portable storage device that can be attached to a computer through a USB or FireWire connection, or wirelessly. External hard drives typically have high storage capacities and are often used to back up computers or serve as a network drive.
external heat defrost
Understanding Defrost Cycle
During winter months many heat pumps will need to go through a “defrost” cycle during operation. Often this has not been explained well before installation, which leads to a lot of confusion about why the heat pump is not working. This document is provided to help users understand the defrosting cycle and address any concerns.
What is a “defrost cycle”?
In heating mode a heat pump extracts heat from the outside air and transfers it inside your premises to warm it. When the ambient temperature outside gets very cold (close to 0°C or below) the moisture in the air freezes on the outdoor unit’s heat exchanger as the fan blows the air across it. A defrost cycle is simply the system recognising that ice has formed or begun to form and automatically fixing this.
Why does my unit have to do a defrost cycle?
Any ice building up on the outside heat exchanger reduces the airflow across it, which will effect the efficiency, sometimes reducing it dramatically. In extreme cases this can also cause damage to the outdoor unit.
How do I tell if my unit is in a defrost cycle?
Inside you will notice the unit will stop heating, the indoor fan will stop and depending on the model there will usually be some form of visual indication like a light on the unit (usually the “run” light) will blink continuously. Outside, the outdoor fan will also have stopped and the compressor will be running.
How often will my unit go in to defrost mode?
There are a number of factors that influence how often a unit will go in to defrost mode. Some of these include:
The outdoor temperature and humidity
The amount of heating load the unit is trying to deliver
The condition of the heat pump system.
There are timers built in to the computer control of the unit that restrict how often defrosting can occur. Generally a unit must run for a minimum of around 35 minutes after starting up before completing its first defrost. From there defrosts should occur no more frequently than approximately every 35 minutes.
Once my unit is defrosting how long will it take?
Either of two factors can bring the unit out of a defrost cycle. Firstly, if the sensors on the outdoor unit detect that it’s heat exchanger temperature has risen enough, the unit will stop defrosting. Secondly, if the sensors do not stop it beforehand, the maximum time a unit will be in defrost cycle is around 10 minutes.
It is important not to stop the unit before the defrost cycle has ended, because if the unit is restarted shortly afterwards it will run very inefficiently and may cause damage to itself.
My unit is defrosting frequently / not delivering enough heat – what could be wrong?
Regular defrosting, or a lack of heat could be caused by a number of factors.
If the unit has operated like this since it was first installed (first cold snap), you may be operating it incorrectly or it may be undersized for the space it is trying to heat. Initially you should consult your instruction manual to ensure you are operating the unit correctly. If this doesn’t remedy the problem you should consult your installer or another reputable heat pump installer. They can assist you to ensure correct operation, and correct sizing.
If the unit is undersized for the space it is not faulty. The responsibility for correctly sizing the unit initially rests with the installing company – they will need to remedy the situation if the unit is too small.
A recently developed problem may be an indication of a fault or maintenance required. You can perform some basic maintenance yourself by cleaning the filters on your indoor unit, and ensuring that your outdoor unit is clear of foliage and the heat exchanger is not blocked. If this doesn’t remedy the problem you should consult your installer or another reputable heat pump installer.
Is there any way I can help to reduce defrosting?
Yes there certainly is. Keep your unit well maintained (as above) and ensure you are operating it correctly. This will help a lot.
Of course the less load you place on the unit the less frequently it will need to defrost in cold conditions. Ultimately permanent fixes such as installing insulation in ceilings, walls and under floors will help reduce your heating requirement (and ultimately save you money). More immediately, keeping doors closed and curtains drawn will also help to reduce your heating required.