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Fahrenheit is a temperature scale that bases the boiling point of water at 212 and the freezing point at 32. It was developed by Daniel Gabriel Fahrenheit, a German-born scientist who lived and worked primarily in the Netherlands. Today, the scale is used primarily in the United States and some Caribbean countries. The rest of the world uses the Celsius scale.

 

Fahrenheit: Facts, History & Conversion Formulas

In the Fahrenheit scale, water boils at 212 degrees.

Credit: Shane Trotter | Shutterstock

Fahrenheit is a temperature scale that bases the boiling point of water at 212 and the freezing point at 32. It was developed by Daniel Gabriel Fahrenheit, a German-born scientist who lived and worked primarily in the Netherlands. Today, the scale is used primarily in the United States and some Caribbean countries. The rest of the world uses the Celsius scale.

 

In 1714, Fahrenheit developed the first modern thermometer — the mercury thermometer, with more refined measurements than previous temperature gauges. Fahrenheit’s thermometer was a take on an alcohol-based thermometer invented by Olaus Roemer, a Danish scientist. Roemer marked two points on his thermometer — 0 as the lowest point, 60 as the temperature of boiling water, 7.5 as the point where ice melted and 22.5 as body temperature.

 

Because the mercury thermometer was more accurate, Fahrenheit decided to expand the Roemer scale by multiplying its values by four. He made adjustments to those metrics based on further research, even putting the thermometer under his wife’s armpit to gain a body temperature.

In his initial scale, the zero point was determined by placing the thermometer in an equal mix of ice, water, and salt (ammonium chloride). This stable temperature was set as 0. The second point, at 32, was an equal mix of ice and water. The third point, 96, was approximately the human body temperature, referred to as "blood-heat."

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While Fahrenheit documented in an article that he used the boiling and freezing points of water to build his scale, there were some conspiracy theorists who thought he had other motives for using those numbers. Some believe that Fahrenheit was a Freemason, and because there are 32 degrees of enlightenment, he chose to use 32 as the melting temperature of water. However, there is no record that the scientist was a Freemason.

 

In yet another story, it is said that Fahrenheit believed that a person would freeze to death at 0 degrees and would succumb to a heat stroke at 100.

 

The scale was recalibrated after his death, marking 32 and 212 as the exact melting and boiling points of plain water, minus the salt. It also makes the normal body temperature 98.6, which is what has become the standard.

 

That change made Celsius-to-Fahrenheit conversions easier. The size of the Fahrenheit "degree" is five-ninths the size of the same unit on Celsius and Kelvin temperature scales. This makes it easier to provide more exact measurements without using fractions in the Fahrenheit scale. 

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The Fahrenheit and Celsius scales converge at minus 40 F, so that minus 40 F and minus 40 C represent the same temperature.

 

Who uses Fahrenheit?

 

Fahrenheit has widely been replaced by Celsius in most countries and for most applications. In the late 1960s and 1970s, the Celsius scale was phased in by governments around the world as part of the move to standardize on metric measurements.

 

Today, the scale is primarily used in the United States, and is also used in the Cayman Islands, Palau, Bahamas and Belize. While other branches of science use the Celsius scale, U.S. meteorologists continue to use the Fahrenheit scale for weather forecasting and reporting. Canadian meteorologists sometimes use the Fahrenheit scale alongside the Celsius scale.

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Supporters of the Fahrenheit scale note that a degree on the Fahrenheit scale is the temperature change that the average person can detect.

 

fan

It feels almost intuitive that the moving air would help keep you cool. After all, that's what a breeze does and, in a pinch, waving a folder in front of your face on a hot day will provide a little relief. But since temperature is a feature of the molecular properties of a substance, the air itself isn't made any cooler by movement—it just makes us feel cooler when it blows by.

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On a hot day—or on a not so hot day if it's "wind chill" you're talking about—moving air helps your body with the cooling off process. Humans lose heat—a necessity for thermoregulation—through conduction, radiation, convection, and evaporation. The final two are what account for fans' effects. On a hot day, your body sweats to lose heat through the evaporation of that moisture. In still air, that evaporation causes the area immediately surrounding your skin to reach body temperature and 100 percent humidity—rendering it essentially ineffective to continue the process. A fan, or a breeze, helps by replacing this hot, humid air with cooler, drier air that allows for more evaporation.

 

Similarly, even without sweat, our body loses heat to the surrounding air simply by convection. If our internal temperature is higher than that of the surrounding air, energy—and thus heat—is transferred. However, once again, in motionless air, this simply creates a boundary area of hot air around you. The breeze from the fan carries that hot air away and perpetuates the process, effectively cooling you off.

 

fan assisted draft

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Over the years we have received many questions regarding venting induced-draft, AKA

fan assisted furnaces in common with water heaters. There are several items to consider, and

understand, to properly inspect gas appliances. These items are the definitions of fan assist furnace

and gravity venting directly from the National Fuel Gas Code (also known as NFPA 54 or

NFGC) and the four vent categories of gas appliances.

 Furnace, Gravity, with integral fan. These are known by many names, such as induced draft

furnace, Plus 80 (AFUE rating) and fan-assisted furnace. Fan Assist or Fan Assist Combustion System

furnaces have an integral fan, commonly called the inducer fan, which is installed solely to overcome the

internal furnace resistance, in the heat exchanger, to airflow. The exhaust after the heat exchanger relies

Once you get into “Plus 90” or so appliances (sometimes even furnaces at 85% or so) the flue gases are

too cool and B-Vent cannot be used nor can they be commonly vented with other appliances. These Plus

90 appliances might be induced, however, they will be equipped with condensate drains due to the potential

for condensation of the combustion gases inside the flue because they exit so cool.

 

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“Gravity” means these furnaces rely upon on the basic principal of the "stack effect" of a

heated chimney, in which the flue gas is less dense (hotter) than the ambient air surrounding the

appliance creating a pressure difference (negative) inside the flue. This is subject to flue size,

height, temperature and the availability of “dilution” air through the draft diverter or combustion

chamber to create flow up the chimney. Gravity appliances are Category I vent appliances. To

achieve correct draft the flue gas must be hot; usually 300-400 F or so for fan assist Plus 80 appliances,

the combustion process to allow for adequate flue stack temperature and evacuation of the heat

exchanger. All Category I gas appliances can use B-Vent (sometimes a portion of single-wall

connector) as the typical flue. B-Vent is a galvanized steel coaxial pipe with a circulation air annular

space between the inner and outer liner. It is also called “insulated” connector or chimney

in the Codes. Other venting Category appliances are either positive pressure or have a potential

for condensation and appropriate materials must be used. Type B-Vent is approved only for

Category I venting rated appliances.

 

 

 one appliances are very common; these would be our typical induced draft “Plus 80”

The left indicates a “Plus 90” high efficiency unit venting with Category IV methods only, due to the cool flue gas. There is no mention of common venting with any other appliance. The left text box from a “Plus 80” induced draft furnace instructions clearly indicates use Category 1 venting only and common venting may be allowed. In fact, many new furnaces now arrive with stickers on the front indicating they may be common vented due to the confusion regarding induced draft furnaces,

 

Since induced draft furnaces that are Category I rated can be common vented with other

Cat I appliances, we know we can use the proper GAMA tables to size the vents. These will be

listed “two or more appliances” and maximum combined BTU input amounts will appear in the FAN (Fan Assist) plus NAT (natural draft vent, like a water heater) common vent columns. The smaller appliance should enter the common flue above the larger BTU rated appliance and as high as possible whenever practical. However, if the smaller appliance must be below, the increase in vent size for the common vent must occur below the larger appliance inlet.  Many new furnaces now arrive with stickers on the front indicating they may be common vented due to the confusion regarding induced draft furnaces,

 

 

fan cycling

t’s all about pressure, and how you have to switch fans off and on to regulate the condenser head pressure.  At first glance, the whole concept of condenser head pressure reminded me of high school physics, and that reminded me of how much I really never understood thermodynamics.  But being the controlling person that I am, here goes a very cursory explanation of how fan cycling is used to control condenser head pressure.

So how does this apply to fan cycling?  One of the most common ways to regulate condenser head pressure is by turning fans off and on triggered by pre-set pressure ranges.  Johnson Controls offers a wide range fan cycling products.  The P70AA-118C offers single and dual pressure control for non-corrosive refrigerants such as R-12, R22, R-500, or R-502.  This can handle pressure ranges from 100-400 psig.  Johnson Controls also offers the P170AA-118C and SEC Ultra Cap, the P470 Electronic Pressure Control and Transducer.  Choose the System 450 for multiple motors.  When you need variable speed control, there is the P266 and VFD66.

 

fan relay coil

 

How relays work

Here are two simple animations illustrating how relays use one circuit to switch on a second circuit.When power flows through the first circuit (1), it activates the electromagnet (brown), generating a magnetic field (blue) that attracts a contact (red) and activates the second circuit (2). When the power is switched off, a spring pulls the contact back up to its original position, switching the second circuit off again.

 

This is an example of a "normally open" (NO) relay: the contacts in the second circuit are not connected by default, and switch on only when a current flows through the magnet. Other relays are "normally closed" (NC; the contacts are connected so a current flows through them by default) and switch off only when the magnet is activated, pulling or pushing the contacts apart. Normally open relays are the most common.

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The input circuit (black loop) is switched off and no current flows through it until something (either a sensor or a switch closing) turns it on. The output circuit (blue loop) is also switched off.

When a small current flows in the input circuit, it activates the electromagnet (shown here as a red coil), which produces a magnetic field all around it.

The output circuit operates a high-current appliance such as a lamp or an electric motor.Suppose you want to build an electronically operated cooling system that switches a fan on or off as your room temperature changes. You could use some kind of electronic thermometer circuit to sense the temperature, but it would produce only small electric currents—far too tiny to power the electric motor in a great big fan. Instead, you could connect the thermometer circuit to the input circuit of a relay. When a small current flows in this circuit, the relay will activate its output circuit, allowing a much bigger current to flow and turning on the fan. Wicker Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates  furnace service repair and installation Lennox, azrikam the price is right heating and air conditioning ac hvac  company

 

 

Feedback Loops 

Feedback Loops can enhance or buffer changes that occur in a system.

Positive feedback loops enhance or amplify changes; this tends to move a system away from its equilibrium state and make it more unstable.

Negative feedbacks tend to dampen or buffer changes; this tends to hold a system to some equilibrium state making it more stable.

Understanding negative and positive connections is helpful for understanding loop structure.

 

 

 A positive connection is one in which a change (increase or decrease) in some variable results in the same type of change (increase or decrease)in a second variable. The positive connection in the figure below for a cooling coffee cup implies that the hotter the coffee is the faster it cools. The variables Tc and Tr are coffee and room temperature respectively.

 

 

A negative connection is one in which a change (increase or decrease) in some variable results in the opposite change (decrease/increase) in a second variable. The negative connection in the figure below for a cooling coffee cup implies a positive cooling rate makes the coffee temperature drop. Oak Park, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates experts, service repair and installation Maytag, azrikam the price is right heating and air conditioning ac hvac  company

 

When these two connections are combined we get a negative feedback loop as shown at left in which the coffee temperature approaches the stable equilibrium of the room temperature. Going around the loop the positive connection times the negative connection gives a negative loop feedback effect. This same trick of multiplying the signs of the connections around a loop together to find out whether it is a positive or negative feedback loop works for more complicated loop structures with many more connections.

 

 filter drier

The Importance Of Filter-Driers

Filter-driers play a pivotal role in the operation of air conditioning and refrigeration systems. At the heart of the unit is the desiccant held in its cylindrical metal container. As important as the filter-drier is, many actually do not understand how it works. Here are some details. River West, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates professionals, service repair and installation NuTone, azrikam the price is right heating and air conditioning ac hvac  company

The word desiccate means to dry out completely and a desiccant is a material or substance that accomplishes the moisture removal. Moisture in the mechanical refrigeration cycle is detrimental to the operation and life of the system. The filter-drier is an accessory that performs the functions of filtering out particles and removing and holding moisture to prevent it from circulating through the system.

 

Moisture In A System

Some combinations of atomic elements create molecular structures that can be either useful or harmful. Acids are formed when the right combination of elements are linked together chemically. If we have a use for the acid and use it for its intended purpose, all is well. However, in some cases unwanted chemical combinations occur where we least want them and where they cause serious harm. Under certain circumstances, hydrochloric and hydrofluoric acids chemically form in the mechanical refrigerant system. This, of course, is what we want to prevent.

 

Again, let us consider how the chemist facilitates the chemical bonding process. The chemist wants certain chemical reactions to take place in an effort to create new substances that hopefully have special properties that are useful. Perhaps the chemist is attempting to create a new refrigerant to replace another that is being phased out. The chemist combines particular elements to form bonds or links that when complete meet all the qualities of a suitable refrigerant. A catalyst is anything that hastens, encourages, or helps bring about a result. Heat is one of chemistry’s most active catalysts. A chemist may purposely add heat to a beaker of chemicals to cause them to combine to form a new substance.

 

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An air conditioning/refrigeration system is much like a chemistry set. The system, consisting of a compressor, condenser, metering device, evaporator, copper lines, oil, and refrigerant, acts like a complete chemistry set, including several powerful catalysts.

The system contains components which consist of a number of metals such as the iron casting of the compressor, copper lines, steel condenser, aluminum evaporator, brass valves and fittings, and perhaps still other metals in smaller quantities. The components are assembled using still other metals and chemicals during the brazing process. Flux is applied to facilitate the chemical process of brazing, and heat is applied with a torch as the catalyst.

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Still other materials (chemicals) are contained in the system. Compressor motor winding insulation and varnishes, epoxy glues, and perhaps rubber and gasket materials are applied. Of course, two of the major chemical materials that constantly circulate through the system are the refrigerant and oil.

 

 

 

Additional catalysts in the form of heat or compression, as well as latent heat in the condenser and pressure are present. Imagine the possibilities. The chemicals present are compressed, heated, and liquefied. Then they are evaporated and cooled as the pressure is released. Then the process is continually repeated for hours, days, and months until a chemical reaction takes place. On hot days, the high temperature and pressure on the high side of the system reaches still higher levels. The catalysts of heat and pressure could almost make a chemist jealous.

 

When a chemical reaction occurs, the typical chemical bonding creates hydrochloric and hydrofluoric acids. These acids then go to work breaking down the metals and other materials of construction, adding soluble material to the chemical reaction. A number of other chemical reactions may take place, and the circulating refrigerant and oil carry the entire mix throughout the system where it can continue the process.

 

One authority on acids informs us that for every 18 degrees F an acid is heated, its activity level doubles.

 

Eventually, the motor winding insulation may be destroyed and the motor windings begin to pass electrical current between each other. As the motor begins to burn out, smoldering products from the burning motor are pumped throughout the system. Remember, the motor will be cooking and burning while the compressor is pumping these products through the system. Liquid refrigerant and oil are fairly good cleaning agents, so the piping where liquid refrigerant is located may remain fairly clean of the resulting debris. However, in the evaporator a distillation process is taking place, the refrigerant is changing from a liquid to a gas, so the debris becomes separated from the refrigerant and begins getting deposited in the evaporator and suction line. This is why the low side of a system that has experienced a compressor burnout is where the majority of the debris is located.

 

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The case has been made as to how important it is to prevent chemical reactions from taking place in a system. It almost seems from what we have described up to this point that it could be difficult to prevent chemical breakdown from occurring. Fortunately, the installation crew and service technician can prevent system failure due to a chemical reaction.

It is imperative that installation and service technicians prevent foreign materials, air, moisture, brazing flux, carbon created during brazing, and insulation powder from entering or remaining in a system. Good piping practice includes bleeding a small amount of dry nitrogen through the system while brazing. Pipe ends need to be sealed prior to sliding pipe insulation over the piping. A good 500-micron evacuation should be reached to remove air and moisture before charging with refrigerant. And, the addition of a properly sized filter-drier is important on both new systems as well as anytime a system is opened for service.

 

The filter-drier is designed to both remove any particulates that may circulate as well as collect and hold any moisture that may be present in the system. The use of a filter-drier containing a good desiccant has become even more important with the advent of R-410A systems, which utilize the highly hygroscopic synthetic polyolester oils.

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How Desiccants Work

The modern desiccant of choice is a material called zeolite. Zeolite has gained in popularity over the older desiccants such as activated alumina, silica gel, calcium chloride, and calcium oxide. Zeolite is a mineral that occurs in nature or can be manufactured. It is an inorganic tan or gray porous solid consisting of a structure of pores and tiny chambers capable of collecting and holding moisture through capillary action. Adsorption is the physical trait of capillary action whereby moisture is drawn into small pores much like a sponge or paper towel collects liquid spills.

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There are hundreds of different zeolites, each with its own micro-sized shape, lattice structure, and size. Zeolites can be selected to collect and hold many different substances according to the molecular size and structure of the specific molecule one wishes to collect. The zeolite selected for use in a filter-drier is selected to adsorb moisture while allowing refrigerant to pass through. One example of a zeolite is a very light and porous volcanic rock. Zeolite filters are used as desiccants and filters for refrigerant, acids, specific chemicals, and to remove ammonia in fish tanks.

 

Zeolite desiccants are formed into a porous solid core, which is placed in the filter-drier container. Older loose-fill desiccants like silica gel occasionally broke down into particles or dust that sometimes left the filter-drier and circulated through the system, often creating a restriction especially on capillary tube systems. This was avoided by positioning the filter-drier vertically so pressure pulsations in the system would not shift the loose fill back and forth and physically break it down. Solid-core zeolite desiccant filter-driers may be installed in any position. Most solid-core desiccants are molded into a cylindrical block with a tapered axial hole down the center to allow for the uniform flow of the refrigerant through the entire bed of desiccant. This is why filter-driers are directional with the direction of flow indicated on the container. Installing the filter-drier in the wrong direction causes non-uniform refrigerant to desiccant contact and increases pressure drop. Bi-flow filter-driers are available for heat pump applications.

 

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Capacity refers to the amount of moisture the desiccant in the filter-drier can hold. Capacity is measured in parts per million (ppm). One ppm is one part of water per million parts of refrigerant. In practical terms, this would be approximately equal to one drop of water in a 125-pound drum of refrigerant. Desiccant capacities are rated at 75 and 125 degrees F. The older desiccant, activated alumina, had a moisture holding capacity of 4 grams of moisture per 100 grams of desiccant. Silica gel had a moisture holding capacity of 3 grams of moisture per 100 grams of desiccant. Modern zeolite molecular sieve desiccants have a capacity of approximately 16 grams of moisture per 100 grams of desiccant.

The capacity of a desiccant is temperature dependent. The colder the desiccant, the more moisture it can hold. Therefore, locating a filter-drier in a cooler location is an advantage. Removing a brazed filter-drier with a torch flame causes moisture to be driven out of the desiccant and into the system. Generally, it is better to cut the filter-drier out with a tubing cutter.

 

Location

The desiccant works better at removing and holding moisture when it is placed in a refrigerant line where the refrigerant is in the liquid state. The filter-drier is often called a “liquid line filter-drier” for this reason.

 

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The desiccant is still able to adsorb moisture when applied to the suction line but not quite as effectively. Special suction line filter-driers are made for cleaning up a system after a compressor burnout. A larger shell is used to minimize pressure drop on suction line driers. Suction line filter-driers marked as “HH” driers contain carbon filter material in addition to the zeolite desiccant. The carbon and zeolite are capable of capturing and holding acids as well as moisture. Suction line filter-driers used to clean up a system after a burnout should be replaced until the system is known to be clean and no longer tests positive for acids in the system.

A suction line filter-drier with an excessive pressure drop across it should not be left in a system. An excessive pressure drop in the suction line reduces the volumetric efficiency of the compressor, thus reducing system operating capacity. Many suction line filter-driers have a pressure tap on the inlet end so the pressure on the inlet of the drier can be compared to the pressure at the suction service valve at the compressor. Still other suction line filter-driers have pressure taps on both the inlet and outlet.

 

Reactivating Filter-Driers 

 

In the past, some have attempted to reactivate and reuse a filter-drier by heating and evacuating the desiccant. Heating and evacuating does actually remove much of the moisture and allow the drier to be used again. However, oils, carbon, and other particles are not removed during this reactivation attempt. In fact, the oil may be cooked into the desiccant, creating new contamination possibilities. The cost of a new filter-drier is not worth the effort and is not recommended.

Don’t allow a system to become an out of control chemistry set. Good piping practice, a nitrogen purge during brazing, a deep evacuation, and the proper installation and use of filter-driers containing modern and effective molecular sieve desiccants will prevent many system failures. Many compressor failures are blamed on the compressor when the actual cause was a system problem. That system problem may have been a chemical problem due to moisture.

 

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The AC condenser coils need regular maintenance and cleaning along with the indoor AC evaporator coils because the condenser unit is other half a split central air conditioner system. The purpose of the condenser coil is to release the heat absorbed by the refrigerant at the evaporator coils inside the home so it’s ready for the next cooling cycle. If the condenser coils are clogged with dirt or the fins are bent it will block air flow through the coils and interfere with the heat exchange. This causes the system to work harder and drives up your electric bill.

 

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flame proving device

Troubleshooting a flame rectification system 

 

The method used to prove flame in most gas-fired products produced in the last seven or eight years is often misunderstood. This method is usually known as “flame rectification.”

Many servicers believe the flame sensor takes an active role in proving flame, and because of this, believe the sensors sometimes fail. Let’s look at what happens.

 

In order to verify flame, the ignition control must establish current flow using the flame as a conductor. (Did you know that carbon molecules in a flame will conduct an electrical current

 

 

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When everything is working right, the moment flame touches the sensor, the module establishes and monitors this current flow.

The voltage at the sensor is ac (alternating current), but because of the great difference in mass between the flame sensor and the furnace chassis, this voltage is “rectified” from ac to dc (direct current), usually less than 10 microamps. As long as this current flow exists, the ignition control will power the gas valve.

 

The flame sensor is not sensing anything. The flame sensor’s only “claim to fame” is that it is resistant to the effects of being immersed in flame.

 

 

A flame sensor can become coated with a silica-type material. (Silica is a component of glass and glass is a great insulator.) When this happens, all that is required is a cleaning of the sensor with a light abrasive. That’s the mechanical side. Now let’s look at what can go wrong electrically.

 

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We know that 115 vac has one hot leg and one neutral. The black (or common) leg has the potential to ground. The neutral does not.

Apply this to what we just learned about flame sensing and think about what will happen if a furnace is installed with the neutral and common reversed.

 

The module must establish current flow through the flame to ground, right? So if the black and white are switched in the junction box or the receptacle, there is no flame sense because there is no voltage potential.

 

Everything else in the unit works fine, but a few seconds after the burners light . . . the module closes the gas valve because the power for the flame-proving circuit is not there. What if the common and neutral are connected properly, but the flame still drops out for “no reason?” Check the ground to the unit. Here’s how: You have already measured between common (black) and ground and read 120 vac. Now measure between neutral (white) and ground to be sure you have no voltage (0.0 vac).

 

Remember, your flame-sense current is very small, usually less than 10 microamps dc. Think about what would happen to the flame-sense current if there were another voltage potential at the furnace chassis because of a poor ground.

 

The same problems can occur on a gas pack if the unit is not properly grounded. You might also have problems on a three-phase unit if the “stinger” leg is the line that winds up as the ignition control’s power source. The ignition control needs a clean, properly polarized voltage source to do its job.

 

 flame rectification 

 

Flame rectification is a phenomenon in which a flame can act as an electrical rectifier. The effect is commonly described as being caused by the greater mobility of electrons relative to that of positive ions within the flame, and the asymmetric nature of the electrodes used to detect the phenomenon.

 

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A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices.

 

Float switches range from small to large and may be as simple as a mercury switch inside a hinged float or as complex as a series of optical or conductance sensors producing discrete outputs as the liquid reaches many different levels within the tank. Perhaps the most common type of float switch is simply a float raising a rod that actuates a microswitch.A very common application is in sump pumps and condensate pumps where the switch detects the rising level of liquid in the sump or tank and energizes an electrical pump which then pumps liquid out until the level of the liquid has been substantially reduced, at which point the pump is switched off again. Float switches are often adjustable and can include substantial hysteresis. That is, the switch's "turn on" point may be much higher than the "shut off" point. This minimizes the on-off cycling of the associated pump.

 

Some float switches contain a two-stage switch. As liquid rises to the trigger point of the first stage, the associated pump is activated. If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered. This stage may switch off the source of the liquid being pumped, trigger an alarm, or both.

 

floating head pressure 

 

 we made the case that reducing head pressure lowers the operating expense of the compressor. However, it was also shown that reducing it too much can adversely affect the health and longevity of the system.

 

We can conclude that the determining factor in deciding what the minimum allowable head pressure should be is the minimum thermostatic expansion valve (TEV) pressure drop (delta-P) required for its capacity to meet the demands of the evaporator load. Once that has been determined, it becomes a simple matter of adjusting the head pressure controls on the system to maintain that minimum.

 

There are several different methods of maintaining head pressure, and it is important to understand the principles of how each one operates so they can be set correctly. In addition, on systems that utilize more than one method of head pressure control, setting them to operate together is imperative. Northlake,  Illinois ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates experts, service repair and installation day and night, azrikam the price is right heating and air conditioning ac hvac  company

The common methods of head pressure control are:

 

1 Fan cycling.

2 Condenser flooding.

3 Condenser splitting.

 

Fan Cycling 

 

The capacity of the condenser mentioned in the first article, rated at 150,000 Btuh (at 110 degrees F and a 10 degree temperature difference [TD]), is based on all of the fans operating. If this is an eight-fan condenser, we can reduce the condenser capacity as needed by cycling off the fans.

Typically, fan motors 1 and 2 would be controlled by a pressure control, fan motors 3 and 4 by another pressure control, etc. This would allow for four stages of fan cycling. A typical pressure control setup is shown in Table 1. Excluding a cold, windy day, where the wind is able to blow through the tube bundle on the condenser, the head pressure would never fall below 160 psig with this control strategy.

While this is a simple method of control, it does have a few disadvantages. For example, on a cool day, when the head pressure reaches 170 psig, pressure control No. 2 will open the control circuit for the contactors powering fan motors No. 3 and 4.

Once fan motors No. 3 and 4 cycle off, the head pressure will gradually start to rise, as the reduction in airflow has reduced the condenser capacity. The corresponding refrigerant saturation temperature will also rise. In the receiver, where liquid and vapor are present, the refrigerant always will be at a saturated condition. (For example, R-404A is 78 degrees at 170 psig.)

For simplicity, we will assume the pressure in the receiver is equal to the head pressure. In an operating system, there would be some pressure loss in the piping and flow controls, resulting in a receiver pressure that would be less than the head pressure.

When the switch in pressure control No. 2 closes at 190 psig, the temperature of the refrigerant in the receiver will be 85 degrees (saturation temperature at 190 psig).

With the second bank of fan motors operating, the head pressure will fall rapidly, as will the corresponding saturation temperature. The temperature reduction of saturated refrigerant in the receiver is accomplished by liquid flashing into vapor.

As a portion of the liquid flashes, it absorbs enough heat from the remaining liquid to lower its temperature to the new saturation condition. Depending on the refrigerant level in the receiver, and how quickly the pressure falls, the ability to provide vapor-free refrigerant to the liquid header may be compromised temporarily.

If there is little or no subcooling in the liquid line, flashing may occur all the way to the TEV inlet. This temporary disruption of vapor-free refrigerant to the TEV results in erratic operation and poor superheat control.

In addition, as the pressure controls cycle the fan motors, and pressure fluctuates between cut-ins and cut-outs, the available CP across the TEV port will vary. In a perfect world, the condition of the refrigerant at the TEV inlet would be constant year-around. Allowing the head pressure to fluctuate up and down every few minutes will result in TEV capacities that proportionally fluctuate.

 

 

Condenser Flooding 

 

The ability to maintain constant head pressure (liquid pressure) during varying periods of low ambient operation would be ideal. One method of achieving this is to use condenser flooding valves. In larger systems, two valves are required. (See Figure 1.)

The first, commonly referred to as the condenser holdback valve, is installed at the outlet of the condenser. Its function is to maintain a constant pressure in the condenser.

The ORIT valve is normally closed, and opens on a rise of inlet pressure. If the ORIT valve was set to maintain 180 psig, it would simply remain closed until the condenser pressure increased to that level.

While the ORIT valve is closed, the compressor continues to pump refrigerant into the condenser. As heat is removed from the superheated discharge vapor, it will start to condense into a liquid and the liquid refrigerant will start backing up from the inlet of the closed ORIT valve, flooding a portion of the condenser.

The portion of the condenser that is full of liquid refrigerant (flooded) no longer serves as a condenser. Flooding a portion of the condenser reduces its effective condensing surface, and therefore its capacity. When the appropriate amount of condenser flooding has occurred, the reduced condenser capacity will cause the pressure to increase to 180 psig. At this point, the ORIT will begin to open and allow refrigerant to flow into the receiver.

Pressure regulating valves can control either upstream pressure or downstream pressure, but not both. When the ORIT throttles, maintaining constant condensing pressure by flooding the condenser, it does so at the expense of its outlet pressure (receiver pressure).

The ORIT valve may influence receiver pressure, but it cannot maintain it at a constant level. Without an additional regulating valve, the pressure in the receiver will be erratic during periods of low ambient operation due to the ORIT valve throttling.

A second valve is necessary to maintain constant receiver pressure. It is commonly referred to as the receiver pressurizing valve.

The CROT valve is normally open, and closes on rise in outlet pressure. It is set typically to maintain a pressure approximately 20 psig less than the ORIT valve setpoint. As the ORIT valve throttles, maintaining constant condenser pressure and interrupting the flow of refrigerant to the receiver, it is the CROT valve that maintains a constant pressure in the receiver.

The benefit of condenser flooding is the ability to provide very consistent liquid pressure in the receiver during periods of low ambient operation. Consistent liquid pressure will result in very stable TEV operation during the winter months.

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There are two drawbacks to this method of head pressure control.

First, extra refrigerant is required to accomplish condenser flooding. The approximate percentage of required condenser flooding can be calculated (as with Sporlan's Bulletin 90-31).

During extremely low ambient conditions, it may be necessary to flood upwards of 85 percent of the condenser. Depending on the size of the condenser, this may require several hundred pounds of extra refrigerant. In today's marketplace, this can become quite expensive.

 

Second, receivers should be sized such that they are at 80 percent of their capacity while containing the entire system charge.

If extra charge is needed in the system for condenser flooding, a larger receiver will be required. The extra refrigerant added to flood the condenser during periods of low ambient will be in the receiver during the warmer months.

In systems where the additional refrigerant charge hasn't been considered in the receiver sizing, the technician will have to remove refrigerant every spring to prevent high discharge pressures at design ambient, only to add it back in the fall when it will be required for flooding.

 

 

Condenser Splitting Wood Dale, Illinois ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates repairman service repair and installation Goodman, azrikam the price is right heating and air conditioning ac hvac  company

Reducing the amount of extra charge for condenser flooding can be accomplished by splitting the condenser into two identical circuits: one for summer-winter operation, and the other for summer operation only. The summer condenser will be cycled off as needed during periods of low ambient. This requires the addition of a condenser splitting valve, a three-way valve that will be installed in the discharge line. (See Figure 2.)

When the valve (for example, the Sporlan 12D13B-SC) is de-energized, the main valve piston is positioned to enable refrigerant to flow from the inlet port equally to the two outlet ports, feeding both condenser halves.

When required, energizing the solenoid coil will shift the main piston, closing off the flow of refrigerant to the port on the bottom of the valve. This removes the summer half of the condenser from the circuit, and now the minimum head pressure can be maintained by flooding the summer-winter half of the condenser.

To prevent the summer condenser from logging refrigerant during low ambient periods, a check valve is installed at its outlet. This will eliminate the possibility of refrigerant backflow into the idle summer condenser.

While a check valve isn't necessary at the outlet of the summer-winter condenser for backflow prevention, it is added so that the delta-P through each condenser is equal. This is necessary to ensure equal refrigerant flow through the two condensers.

If the B version is not used, a dedicated pump-out solenoid valve is required, which vents the idle condenser to the suction header through a restriction such as a cap tube. The pump-out line also must have a check valve installed to prevent backflow.As an alternative to a three-way split condenser valve, two normally open solenoid valves can be used. (See Figure 3.) In this application there would be a normally open solenoid at the inlet of the summer condenser, which would cycle closed during low ambient conditions. An identical solenoid is installed at the inlet of the summer-winter condenser. It does not require a solenoid coil; this valve is installed to maintain equal pressure drop through the two condensers.

As in the three-way split condenser valve application, a check valve will be necessary for the outlet of each condenser. With this method, a dedicated normally closed pump-out solenoid valve will be required to vent the refrigerant from the idle summer condenser into the suction header.

 

 

Summary 

 

Allowing the head pressure in supermarket refrigeration systems to operate at reduced levels during periods of low ambient results in lower compressor motor amperage, increased compressor efficiency, and lower monthly utility bills.

Head pressure has a direct effect on available delta-P across the TEV port, which, in addition to evaporator and liquid refrigerant temperatures, will determine the TEV capacity.

The minimum delta-P required to deliver the necessary TEV capacity to meet the load demand of the evaporator is the limiting factor on how low the head pressure can be allowed to float. Once this is calculated, based on TEV capacity data, the minimum head pressure can be determined and used to establish the setpoints of the head pressure control devices.

While several methods of head pressure control are available, one that allows the head pressure (liquid pressure) to remain constant is desirable. This is best accomplished by condenser flooding valves, which maintain consistent head pressure by flooding a portion of the condenser with liquid refrigerant.

While condenser flooding valves provide the most consistent head pressure, this method requires adding extra refrigerant to the system.

Using a three-way condenser splitting valve (or two normally open solenoid valves) will offer the ability to reduce the condenser capacity by 50 percent during low ambient conditions.

After cycling off the summer condenser, the remaining summer-winter condenser can utilize the flooding method with a minimum of additional refrigerant to maintain constant head pressure.

 

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An important difference between a flooded evaporator and a direct expansion (DX) evaporator is that the flooded evaporator operates in conjunction with a low-pressure receiver. The receiver acts as a separator of gaseous and liquid refrigerant after the expansion valve and ensures a feed of 100% liquid refrigerant to the evaporator. Unlike in a direct expansion (DX) evaporator, the refrigerant is not fully evaporated and superheated at the flooded evaporator outlet. The leaving refrigerant flow is a two-phase mixture with typically 50-80% gas.

 

Flooded evaporators, which are sometimes called wet evaporators, are divided into forced-flow evaporators and thermosiphon evaporators. Forced-flow evaporators use a pump or an ejector as the driving force, while the density difference between liquid and gaseous refrigerant drives thermosiphon systems. Des Plaines, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates trouble shooting service repair and installation Maytag, azrikam the price is right heating and air conditioning ac hvac  company

 

The thermosiphon compression cycle 

In addition to the basic equipment in a direct expansion refrigeration circuit, i.e. evaporator, compressor, condenser and expansion valve, the flooded system needs a receiver  to separate the twophase mixture after the expansion valve, The refrigerant leaving the bottom of the receiver is 100% liquid. Deerfield, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates repairing,  service repair and installation NuTone, azrikam the price is right heating and air conditioning ac hvac  company

 

flow through receiver

 

 

 

flue Elk Grove , IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates fixing, service repair and installation Payne, azrikam the price is right heating and air conditioning ac hvac  company

The method for recovering contained nitrogen from flue gas obtained in combustion of hydrocarbon fuel, which method comprises the steps of cooling the hot flue gas discharged from said combustion to effect condensation of contained water, separating out the liquid condensate, compressing the remaining vapor and subjecting said vapor to deoxygenation by reaction with hydrogen to convert residual-free oxygen therein to water, and subjecting the deoxygenated vapor to pressure swing adsorption for removal therefrom of contained contaminants including CO2 and water with resulting production and recovery of substantially pure nitrogen.

The method as defined in claim 1 wherein the starting flue gas is that obtained from a furnace employed in catalytic reforming of a methane-rich hydrocarbon charge, wherein the reformate is subjected to pressure swing adsorption effecting removal of residual hydrocarbons and carbon oxide gases therefrom with the recovery of a substantially pure hydrogen product stream, a portion of said hydrogen product stream being utilized in the recited deoxygenation reaction.

The method as defined in claim 2 wherein a portion of said substantially pure hydrogen product stream is blended with the recovered substantially pure nitrogen to provide a gas mixture for production of NH3.

 The method as defined in claim 2 wherein the removal of CO2 from said flue gas and the removal of CO2 from said reformate are separately carried out in separate adsorbent beds.

The method as defined in claim 2 wherein said reformate prior to being subjected to pressure swing adsorption is freed of contained carbon monoxide by catalytic water gas shift conversion to CO2.

The method as defined in claim 5 wherein the reformate is that obtained by subjecting a major portion of said methane-rich hydrocarbon charge to a first primary reforming step in the presence of added steam and subjecting a minor portion of said methane-rich hydrocarbon charge to a second primary reforming step in the presence of added steam wherein heat for said second primary reforming step is provided by indirect heat exchange with the combined products from said first and second primary reforming steps.

The method as defined in claim 2 wherein the removal of CO2 from said flue gas and the removal of CO2 from said reformate are effected in consecutive adsorption steps in the same adsorption bed.

 

flue draft Glencoe, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates checking, service repair and installation Tappan, azrikam the price is right heating and air conditioning ac hvac  company

Method and apparatus for regulating the flue draft in heating systems including a combustion volume, a flue communicating with the combustion volume, and a vent opening between heated ambient air and the flue, the regulation being accomplished by sensing the flow of air through the vent into the flue, and modulating the setting of a downstream damper to maintain such flow at a predetermined, positive but minimal value. A particularly preferred embodiment includes a temperature sensor positioned at the flue side of the vent and connected to a control system to maintain the damper at such a position that the temperature at such location is at a predetermined value above that of the ambient air temperature, and thus indicative of flow of ambient air into the flue at minimal values approaching incipient spillage of combustion gases at the vent,

 

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 In a heating device including a combustion zone, a flue to collect combustion products from the combustion zone, and a vent to the surrounding atmosphere defined at a location between the combustion zone and the flue, the improvement comprising;

means positioned at the vent adjacent to but spaced from the flue to sense air flow through the vent; a damper positioned in the flue downstream of the vent; and

means to position the flue damper in response to the air flow sensing means to maintain a predetermined substantially fixed flow of air through the vent and into the flue during combustion in the combustion zone;

 A heating device as set forth in claim 1 in which the air flow sensing means comprises a temperature sensor positioned at the vent in a location adjacent to but spaced from the flue whereby the temperature sensor will be indirectly heated by the combustion products while in the air flow through the vent. A heating device as set forth in claim 2 in which the temperature sensor is a thermistor.

 A heating device as set forth in claim 2 in which a second temperature sensor is positioned in the air adjacent the heating device, and the means to position the damper in response to the air flow sensing means does so in response to a temperature differential between the temperature sensor positioned in the vent and the second temperature sensor.

A heating device as set forth in claim 1 in which the vent comprises a draft hood and a temperature sensor comprises the means to sense flow of air through the vent with the temperature sensor being positioned within the draft hood adjacent the inlet thereof.

 A heating device as set forth in claim 6 which further includes a second temperature sensor positioned in the air surrounding the heating device and in which the predetermined level at which the first temperature sensor is maintained is a predetermined temperature differential relative to the second temperature sensor.

 A heating device as set forth in claim 6 in which the predetermined temperature at which the temperature sensor is maintained is an absolute temperature of a predetermined level.

 A heating device as set forth in claim 6 which further includes thermostat means to initiate combustion in the combustion zone, and in which the means to position the flue damper is responsive to operation of the thermostat to terminate combustion to fully close the damper means in the flue.

A heating device as set forth in claim 9 in which the means to position the flue damper first fully opens the flue damper upon operation of the thermostat to initiate combustion, and thereafter responds to the temperature level at the temperature sensor.

the improvement comprising:

means positioned at the draft hood in a location adjacent to but spaced from the flue to sense air flow from the surrounding atmosphere through the draft hood;

valve means positioned in the flue downstream of the draft hood;

means to drive the valve means to restrict and open flow through the flue; and

control means responsive to the air flow means through the draft hood to activate the valve means drive means and position the valve means in a position to establish and maintain a predetermined substantially fixed flow of air through the draft hood to the flue as measured by the air flow sensing means.

 A heating device as set forth in claim 11 in which the flow means comprise a temperature sensor positioned adjacent the inlet of the draft hood to the flue.

 A heating device as set forth in claim 11 in which the means to drive the valve means includes means to fully open the valve means in the event of termination of power to the heating device.

 A heating device as set forth in claim 11 in which thermostat means start and stop combustion in the combustion zone and in which the control means initially opens the valve means fully upon initiation of combustion by the thermostat means, thereafter monitors the air flow into the draft hood to maintain optimum flow to the flue, and finally terminates flow through the flue by closing the valve means upon termination of the combustion by the thermostat means and upon completion of scavenging of the combustion products.

 A heating device as set forth in claim 11 in which the means to drive the valve means comprises an electric motor operably connected to the valve means by gear train means.

 A method of operating a heating device including a combustion zone, a flue to collect combustion products from the combustion zone and a vent to the air surrounding the heating device defined between the combustion zone and the end of the flue downstream of the combustion zone, the method comprising;

positioning valve means damper located in the flue downstream of the vent to restrict flow through the flue to a flow rate which provides a predetermined rate of flow of air through the vent and flue as a result of the flow rate measured; and

maintaining the flow of air through the vent into the flue at the predetermined level by repositioning the valve means in response to a change in the measured flow rate at the vent, whereby loss of heated air surrounding the heating device through the vent is minimized and combustion products are retarded in their flow from the heating device to improve efficiency of the heating device.

A method of efficiently operating a heating device comprising;

initiating combustion in a combustion zone,

substantially fully opening a flue damper positioned in a flue receiving the combustion products from the combustion zone;

moving the flue damper to a more restrictive position until the measured rate of flow of air through the draft hood is at a predetermined level;

opening the flue damper to a less restrictive position when the measured rate of flow of air through the draft hood falls below the predetermined level to restore the predetermined flow rate of air;

terminating combustion in the combustion zone; and

fully closing the flue damper after exhausting the combustion products from the combustion zone and flue.

 A method of efficiently operating a heating device as set forth in claim 21 in which the flue damper is moved by an electric motor operably connected thereto in response to the measured flow rate of surrounding air through the draft hood.

 A method of efficiently operating a heating device as set forth in claim 21 in which the combustion in the combustion zone is initiated and terminated by thermostat means.

 

What is ID fan and FD fan Harwood Heights, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates repairman service repair and installation Armstrong, azrikam the price is right heating and air conditioning ac hvac  company

In a boiler arrangement, a forced draft fan will draw in air and force it into the combustion chamber of the boiler, where it mixes with the fuel being supplied. FD fans are typically used to regulate the proper amount of air-to-fuel ratios in an effort to maximize fuel efficiency and to minimize EPA-regulated emissions, such as NOx (Nitrogen Oxides).

 

Induced Draft fans are commonly used to draw flue gases from the combustion chamber and through the rest of the system to the stack. They help most to regulate the pressure inside of the boiler system.

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In smaller boiler systems, the use of either an FD or ID fan is sufficient, but in large operations, such as the 600 MW power plant I work at, both FD and ID fans are used together to regulate all of the above-mentioned factors simultaneously.

 

In some cases, additional fans are also added to the system, such as "Primary Air" fans and "Booster" fans. PA fans are typical in coal-burning operations, as more air is needed for the complete combustion of coal than an FD fan alone can provide. PA fans also provide transport and tempering air that is used to move pulverized coal from storage to the furnace. "Booster" fans are also typical of coal operations these days, as all of the additional equipment associated with "clean coal technology" adds a greater amount of pressure resistance in the exit path of flue gases, which a booster fan helps overcome.

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Factory-assembled cooling towers can be crossflow or counterflow, induced draft or forced draft, depending on the application. While all applications are different, the factory-assembled Marley NC crossflow, induced draft tower is widely used for HVAC and light industrial applications.

 

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Refrigeration systems consist of four major components, these are the compressor, condenser, expansion device (usually a TX valve) and evaporator. The evaporator is a heat exchanger used to transfer heat from the air of a refrigerated space to the refrigerant. Evaporators are usually constructed of a fin and tube coil, fan/s, a cabinet which includes a condensate drain. In rooms operating below 0°C heaters are included to defrost the coil.

Actrol have a variety of evaporators available to suit many different commercial and light industrial refrigeration applications. Typical applications include under-bar cabinets, display fridges, walk-in coolrooms, walk-in freezers, food processing applications and beverage cooling in restaurants, shops, supermarkets, take-away stores, food manufacturers, farms, pubs and clubs.

 

Refrigeration Evaporators 

 

Refrigeration systems consist of four major components, these are the compressor, condenser, expansion device (usually a TX valve) and evaporator. The evaporator is a heat exchanger used to transfer heat from the air of a refrigerated space to the refrigerant. Evaporators are usually constructed of a fin and tube coil, fan/s, a cabinet which includes a condensate drain. In rooms operating below 0°C heaters are included to defrost the coil.

Actrol have a variety of evaporators available to suit many different commercial and light industrial refrigeration applications. Typical applications include under-bar cabinets, display fridges, walk-in coolrooms, walk-in freezers, food processing applications and beverage cooling in restaurants, shops, supermarkets, take-away stores, food manufacturers, farms, pubs and clubs.

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Medium and low temperature evaporator defrost cycles

Condensate will form on the evaporator coil as it operates below the dew point temperature of the air. In air conditioning this condensate will flow down the drain but in refrigeration the coil operates below 0°C so this water will freeze causing the evaporator to become inefficient over time.

In medium temperature applications an evaporator will defrost whenever the compressor cycles off as the refrigerated space temperature is above the freezing point of water.

Low temperature applications require preset defrost cycles. During a defrost cycle the compressor and evaporator fans are cycled off and the defrost heaters are cycled on. The defrost cycle is terminated by time or temperature and after a drain period the compressor is started followed by the evaporator fan/s. This ensures only cold refrigerated air is circulated within the refrigerated space.

 

Cabinet coolers Niles, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates fixing, cleaning service repair and installation day and night, azrikam the price is right heating and air conditioning ac hvac  company

Cabinet coolers are designed specifically for reach in cabinets, glass door display cabinets, sandwich and pizza bar cabinets and other small applications. Actrol cabinet coolers are designed to have a small footprint and overall dimensions to maximise the usable space within the refrigerated cabinet. The air flows from the fan through the heat exchanger coil, this is called forced draft. Cabinet coolers are available in medium and low temperature versions,

 

Low Profile Evaporators Norridge, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates checking, service repair and installation Fraser Johnstone, azrikam the price is right heating and air conditioning ac hvac  company

Low profile evaporators are designed for small walk-in coolrooms especially rooms with low ceiling heights and reach-in display rooms as found in liquor stores and take away food outlets. The low profile refers to the height of the evaporator unit. Most low profile evaporators are forced draft. (Air flows from the fan through the coil). Low profile evaporators are available in both medium and low temperature.

 

Walk in Coolroom and Freezer Evaporators

This is the most commonly sold evaporator and is used in coolrooms and freezers. Many models are available, as this style covers an enormous capacity range from very small walk-in rooms to large cold storage facilities with truck loading bays. The fan diameter and number of fans increases as the refrigeration capacity increases. Evaporators with less than 500mm fans are used in rooms with ceiling heights of less than 3m (metres). Evaporators with 500mm or greater diameter fans are used in rooms with ceiling heights of 3m or more, as larger diameter fans move more air. This style evaporator uses induced draft fans, so the air is sucked or induced through the heat exchanger coil. This increases the air throw to provide refrigerated air to every corner of larger refrigerated spaces. These evaporators are available in medium and low temperature versions.

 

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The first cooling systems for food involved using ice. Artificial refrigeration began in the mid-1750s, and developed in the early 1800s. In 1834, the first working vapor-compression refrigeration system was built. The first commercial ice-making machine was invented in 1854. In 1913, refrigerators for home use were invented. In 1923 Frigidaire introduced the first self-contained unit. The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s. Home freezers as separate compartments (larger than necessary just for ice cubes) were introduced in 1940. Frozen foods, previously a luxury item, became commonplace.

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Freezer units are used in households and in industry and commerce. Commercial refrigerator and freezer units were in use for almost 40 years prior to the common home models. Most households[citation needed] use the freezer-on-top-and-refrigerator-on-bottom style, which has been the basic style since the 1940s. A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. Newer refrigerators may include automatic defrosting, chilled water and ice from a dispenser in the door.

 

Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a 4 L Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about 1 m wide with a capacity of 600 L. Refrigerators and freezers may be free-standing, or built into a kitchen. The refrigerator allows the modern family to keep food fresh for longer than before. Freezers allow people to buy food in bulk and eat it at leisure, and bulk purchases save money.

 

freezers 

 

Freezer units are used in households and in industry and commerce. Food stored at or below −18 °C (0 °F) is safe indefinitely.[7] Most household freezers maintain temperatures from −23 to −18 °C (−9 to 0 °F), although some freezer-only units can achieve −34 °C (−29 °F) and lower. Refrigerators generally do not achieve lower than −23 °C (−9 °F), since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers are generally upright units resembling refrigerators or chests (upright units laid on their backs). Many modern upright freezers come with an ice dispenser built into their door. Some upscale models include thermostat displays and controls, and flatscreen televisions have even been incorporated.

 

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Freezing, or solidification, is a phase transition in which a liquid turns into a solid when its temperature is lowered below its freezing point

 

For most substances, the melting and freezing points are the same temperature; however, certain substances possess differing solid–liquid transition temperatures. For example, agar displays a hysteresis in its melting point and freezing point. It melts at 85 °C (185 °F) and solidifies from 32 °C to 40 °C (89.6 °F to 104 °F)

 

Crystallization  Rolling Meadows, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates  furnace service repair and installation Lennox,azrikam the price is right heating and air conditioning ac hvac  company 

 

Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that, as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to slow removal of heat when in contact with air, which is a poor heat conductor. Because of the latent heat of fusion, the freezing is greatly slown down and the temperature will not drop anymore once the freezing starts but will continue dropping once it finishes.[citation needed] Crystallization consists of two major events, nucleation and crystal growth. Nucleation is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure. The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size.

 

Supercooling

 

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Certain materials, such as glass and glycerol, may harden without crystallizing; these are called amorphous solids. Amorphous materials as well as some polymers do not have a freezing point, as there is no abrupt phase change at any specific temperature. Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Such materials are characterized by a glass transition that occurs at a glass transition temperature, which may be roughly defined as the "knee" point of the material's density vs. temperature graph. Because vitrification is a non-equilibrium process, it does not qualify as freezing, which requires an equilibrium between the crystalline and liquid state.

 

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Some substances, such as water and bismuth, expand when frozen,

 

Freezing of living organisms, 

Many living organisms are able to tolerate prolonged periods of time at temperatures below the freezing point of water. Most living organisms accumulate cryoprotectants such as anti-nucleating proteins, polyols, and glucose to protect themselves against frost damage by sharp ice crystals. Most plants, in particular, can safely reach temperatures of −4 °C to −12 °C. Certain bacteria, notably Pseudomonas syringae, produce specialized proteins that serve as potent ice nucleators, which they use to force ice formation on the surface of various fruits and plants at about −2 °C.The freezing causes injuries in the epithelia and makes the nutrients in the underlying plant tissues available to the bacteria.

 

 

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Freon is the cooling agent used in most air conditioning systems. Every air conditioning system needs a refrigerant (also called a coolant) that actually creates the cool air -- that's the role of Freon.

As necessary as Freon is to the optimal performance of your your air conditioner, you do not want to handle a potential Freon problem yourself. If you do believe your air conditioner's refrigerant lines might need recharging, call a professional to do it. In fact, it's probably a good idea to call a professional to inspect your air conditioning system just before the beginning of each cooling season. There are very few air conditioning repairs you can handle yourself, so it makes sense to bring in a professional to give your AC a check-up before you need it to do any serious cooling (in the hottest summer months),

Freon is a registered trademark of The Chemours Company, which uses it for a number of halocarbon products. They are stable, nonflammable, moderately toxic gases or liquids which have typically been used as refrigerants and as aerosol propellants. These include the chlorofluorocarbons (CFCs) that cause ozone depletion (such as chlorodifluoromethane), but also include newer refrigerants which typically include fluorine instead of chlorine and do not deplete the ozone layer. Not all refrigerant is labelled as "Freon" since Freon is a brand name for the refrigerants R-12, R-13B1, R-22, R-502, and R-503 manufactured by The Chemours Company. Winnetka, IL ac hvac rooftop units residentail and commercail  heating and air conditioning free estimates  specailists, service repair and installation Trane, azrikam the price is right heating and air conditioning ac hvac  company

 

history

The first CFCs were synthesized by Frédéric Swarts in the 1890s. In the late 1920s, a research team was formed by Charles Franklin Kettering in General Motors to find a replacement for the dangerous refrigerants then in use, such as ammonia. The team was headed by Thomas Midgley, Jr.[1] In 1928, they improved the synthesis of CFCs and demonstrated their usefulness for such a purpose and their stability and nontoxicity. Kettering patented a refrigerating apparatus to use the gas; this was issued to Frigidaire, a wholly owned subsidiary of General Motors.[2] In 1930, General Motors and DuPont formed Kinetic Chemicals to produce Freon. Their product was dichlorodifluoromethane and is now designated "Freon-12", "R-12", or "CFC-12". The number after the R is a refrigerant class number developed by DuPont to systematically identify single halogenated hydrocarbons, as well as other refrigerants besides halocarbons.

Most uses of CFCs are now banned or severely restricted by the Montreal Protocol, as they have been shown to be responsible for ozone depletion.[3] Brands of Freon containing hydrofluorocarbons (HFCs) instead have replaced many uses, but they, too, are under strict control under the Kyoto protocol, as they are deemed "super-greenhouse effect" gases. They are no longer used in aerosols, but to date no suitable, general use alternatives to the halocarbons have been found for refrigeration that are not flammable or toxic, problems the original Freon was devised to avoid.

 

 furnace 

 

A furnace is a device used for high-temperature heating. The name derives from Greek word fornax, which means oven.

In American English and Canadian English usage, the term furnace on its own refers to the household heating systems based on a central furnace (known either as a boiler, or a heater in British English), and sometimes as a synonym for kiln, a device used in the production of ceramics. In British English, a furnace is an industrial furnace used for many things, such as the extraction of metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns.

The term furnace can also refer to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, and is part of the standard English names for many metallurgical furnaces worldwide.

A large furnace is a major appliance that is permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boiler or residential hot water boiler. The most common fuel source for modern furnaces in the United States is natural gas; other common fuel sources include LPG (liquefied petroleum gas), fuel oil, coal or wood. In some cases electrical resistance heating is used as the source of heat, especially where the cost of electricity is low.

Modern high-efficiency furnaces can be 98% efficient and operate without a chimney. The small amount of waste gas and heat are mechanically ventilated through PVC pipes that can be vented through the side or roof of the house. Fuel efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency).

 

Natural draft 

 

The first category would be natural draft, atmospheric burner furnaces. These furnaces consisted of cast-iron or riveted-steel heat exchangers built within an outer shell of brick, masonry, or steel. The heat exchangers were vented through brick or masonry chimneys. Air circulation depended on large, upwardly pitched pipes constructed of wood or metal The pipes would channel the warm air into floor or wall vents inside the home. This method of heating worked because warm air rises. The system was simple, had few controls, a single automatic gas valve, and no blower. These furnaces could be made to work with any fuel simply by adapting the burner area. They have been operated with wood, coke, coal, trash, paper, natural gas, and fuel oil. Furnaces that used solid fuels required daily maintenance to remove ash and "clinkers" that accumulated in the bottom of the burner area. In later years, these furnaces were adapted with electric blowers to aid air distribution and speed moving heat into the home. Gas and oil-fired systems were usually controlled by a thermostat inside the home, while most wood and coal-fired furnaces were controlled by the amount of fuel in the burner and position of the fresh-air damper on the burner access door.

 

Forced-air 

 

The second category of residential furnace is the forced-air, atmospheric burner style with a cast-iron or sectional steel heat exchanger. This style furnace was used to replace the big, natural draft systems, and was sometimes installed on the existing gravity duct work. The heated air was moved by blowers which were belt driven and designed for a wide range of speeds. These furnaces were still big and bulky compared to modern furnaces, and had heavy-steel exteriors with bolt-on removable panels. Energy efficiency would range anywhere from just over 50% to upward of 65% AFUE. This style furnace still used large, masonry or brick chimneys for flues and was eventually designed to accommodate air-conditioning systems.

 

Forced draft 

 

The third category of furnace is the forced draft, mid-efficiency furnace with a steel heat exchanger and multi-speed blower. These furnaces were physically much more compact than the previous styles. They were equipped with combustion air blowers that would pull air through the heat exchanger which greatly increased fuel efficiency while allowing the heat exchangers to become smaller. These furnace may have multi-speed blowers and were designed to work with central air-conditioning systems.

 

Condensing 

 

The fourth category of furnace is the high-efficiency, or condensing furnace. High-efficiency furnaces can achieve from 89% to 98% fuel efficiency. This style of furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. Because the heat exchanger removes most of the heat from the exhaust gas, it actually condenses water vapor and other chemicals (which form a mild acid) as it operates. The vent pipes are normally installed with PVC pipe versus metal vent pipe to prevent corrosion. The draft inducer allows for the exhaust piping to be routed vertically or horizontally as it exits the structure. The most efficient arrangement for high-efficiency furnaces include PVC piping that brings fresh combustion air from the outside of the home directly to the furnace. Normally the combustion air (fresh air) PVC is routed alongside the exhaust PVC during installation and the pipes exit through a sidewall of the home in the same location. High efficiency furnaces typically deliver a 25% to 35% fuel savings over a 60% AFUE furnace.

 

Heat distribution 

 

The furnace transfers heat to the living space of the building through an intermediary distribution system. If the distribution is through hot water (or other fluid) or through steam, then the furnace is more commonly called a boiler. One advantage of a boiler is that the furnace can provide hot water for bathing and washing dishes, rather than requiring a separate water heater. One disadvantage to this type of application is when the boiler breaks down, neither heating nor domestic hot water are available.

Air convection heating systems have been in use for over a century, but the older systems relied on a passive air circulation system where the greater density of cooler air caused it to sink into the furnace, and the lesser density of the warmed air caused it to rise in the ductwork, the two forces acting together to drive air circulation in a system termed "gravity-feed" the layout of the ducts and furnace was optimized for short, large ducts. This caused the furnace to be referred to as an "octopus" furnace.

 

A photo of a modern forced-air gas furnace with associated ductwork nearby.

Forced-air gas furnace, design circa 1991.

By comparison, most modern "warm air" furnaces typically use a fan to circulate air to the rooms of house and pull cooler air back to the furnace for reheating; this is called forced-air heat. Because the fan easily overcomes the resistance of the ductwork, the arrangement of ducts can be far more flexible than the octopus of old. In American practice, separate ducts collect cool air to be returned to the furnace. At the furnace, cool air passes into the furnace, usually through an air filter, through the blower, then through the heat exchanger of the furnace, whence it is blown throughout the building. One major advantage of this type of system is that it also enables easy installation of central air conditioning, simply by adding a cooling coil at the outlet of the furnace.

 

Air is circulated through ductwork, which may be made of sheet metal or plastic "flex" duct, and is insulated or uninsulated. Unless the ducts and plenum have been sealed using mastic or foil duct tape, the ductwork is likely to have a high leakage of conditioned air, possibly into unconditioned spaces. Another cause of wasted energy is the installation of ductwork in unheated areas, such as attics and crawl spaces; or ductwork of air conditioning systems in attics in warm climates.

 

Furnace types 

 

 

Single-stage 

 

A single-stage furnace has only one stage of operation, it is either on or off. This means that it is relatively noisy, always running at the highest speed, and always pumping out the hottest air at the highest velocity.

One of the benefits to a single-stage furnace is typically the cost for installation. Single-stage furnaces are relatively inexpensive since the technology is rather simple.

 

Two-stage  

 

 

This type has two stages of operation, full speed and half (or reduced) speed. Depending on the demanded heat, they can run at a lower speed most of the time. They can be quieter, move the air at less velocity, and will better keep the desired temperature in the house.

 

Modulating 

 

This type of furnace can modulate the heat output and air velocity nearly continuously, depending on the demanded heat and outside temperature. This means that it only works as much as necessary and therefore saves energy.

 

 

                                                                  

glow coil furnace

 

Some service technicians may be surprised to learn that the silicon carbide element of a hot surface igniter (HSI) can be handled without damage. However, it is better and safer to handle the igniter by the ceramic holder. The myth that the silicon carbide tip cannot be handled because body oils cause contamination is untrue.

On a typical heating system with HSI, a call for heat (thermostat contacts closed) will send a 24-V signal to the igniter module. When energized, the module will power up the igniter. If the module is a prepurge model, it will delay 15 or 30 sec before the igniter is activated. On prepurge models, the module will energize the combustion blower or other relays at the beginning of the cycle.

 

 

Note: A 17- or 20-sec igniter can be used on a 34- or 40-sec application, but you could not use a 17- or 20-sec module with a 24- or 40-sec igniter.

 

At the end of the igniter warm-up period, the gas valve main opens. The igniter will remain on for a specific amount of time (seconds) depending on the specific ignition module being used. This “on” time or trial for ignition time can vary, depending on the specific ignition module being used. When main burner ignition occurs, the flame is sensed by the igniter (local sense) or by a remote sensor (remote sense).

 

With the main burner flame established, the igniter is turned off (12 V is shut off to the igniter).

Note: The burner flame must be detected within the timed trial for ignition. If no flame is detected, the gas main valve is de-energized, shutting off the gas flow. The system may go into lockout or, if it has a retry model, it will retry the number of times allocated.

 

Problem: Hot Surface Igniter Does Not Glow 

 

Possible causes:

No main power;

Faulty transformer;

Faulty thermostat;

Faulty limit switch;

Faulty blower interlock switch (pressure switch, combustion blower proving switch);

Faulty hot surface igniter; or

Faulty ignition control or integrated control.

 

Solution: Perform normal system checks of main power, secondary or transformer, etc. With power on and the thermostat calling, check voltage at the 24 V or TH to 24 V ground at the module or integrated control.

 

 

Procedure:

 

1.            Do a visual check of the igniter for signs of damage or cracks. The sleeving over the wire should be examined for chafing, burned portions, or cuts in the wire. The connectors should be properly seated and free from oxidation and/or corrosion. Look for hot spots on the igniter. Observe the igniter during heat up. If a bright, white line across one of the igniter legs is detected, a crack may exist that could cause premature failure.

 

Allow the igniter to cool and perform a resistance test. Addi-tional signs of a crack are an “open” igniter (shows no continuity when tested), or a buildup of white silica dust around the bright spot. Replace the igniter if you see these cracks.

 

2.            There are several possible causes for repeated igniter failures. One of the causes could be high supply voltage. A hot surface igniter can burn out at approximately 132 V. Even voltages in excess of 125 V may reduce igniter life. If high voltage is present, the power company should be requested to lower the power.

 

3.            Other causes for igniter failure include drywall dust, fiber glass insulation, sealants, or other contaminants that may accumulate on the igniter. In some cases, condensate dripping on the igniter causes it to fail.

 

4.            Furnace or boiler short cycling, delayed ignition, or an overgassed condition also contribute to shortened igniter life.

 

 

Igniter Glows But Main Burner Won’t Light 

 

Possible causes:

Improper igniter alignment;

Faulty ignition control;

Faulty gas valve;

High inlet pressure (lp gas);

Polarity reversed; or

No earth ground.

 

Solution: Make sure gas is available at the gas valve. Too high a pressure will lock up the gas valve. Make sure the igniter is in position (you cannot move the igniter from its designed position).

Check for a good earth ground from L1 to the furnace chassis, you should read 120 V; if not, check and/or repair ignition ground wire or ignition control mounting screws. A jumper from ground to the gas line should give a good ground. Check for 24 V to the gas valve; if yes and the valve does not open, replace the valve; if no, replace the ignition module.

 

Procedure:

 

 1. If the igniter is going to be used as a sensor, make sure the flame is capable of providing a good rectification signal. Make sure that about 3¼ to 1 in. of the flame sensor or igniter sensor is continuously immersed in the flame for the best flame signal. Bend the bracket or the flame sensor, and/or relocate the sensor as necessary. Do not relocate an igniter or combination igniter-sensor. 

 

2. Check for excessive (more than 1,000°F/538°C) temperature at the ceramic insulator on the flame sensor. Excessive temperature can cause a short to ground; move the sensor to a cooler location or shield the insulator. Do not relocate an igniter or combination igniter-sensor.

3. Check for a cracked ceramic insulator, which can cause a short to ground, and replace the sensor if necessary. Make sure that the electrical connections are clean and tight. Replace damaged wire with moisture-resistant No. 18 wire rated for continuous duty up to 221°F/105°C.

 

 

Checking The Flame Signal

It is important to realize that when the igniter is also being used as a sensor, there is some difficulty in being able to actually check the microamps.

According to a “Norton Igniter Products Technical Bulletin,” “Sensing through flame rectification, be it direct (through the igniter) or remote (separate flame) involves certain components and variables. The object is to use the ionized particles in the flame (burning gas) to conduct a current and complete an electrical circuit. 

 

“The control module initiates an ac signal that is sent out to the igniter. The flame acts as a diode and converts the ac signal to a rectified dc signal. The strength of the signal required to prove the flame, and therefore to keep the gas valve open, is dependent on the control module and varies from one control manufacturer’s brand to another. Signal strength can be affected by the type of burner, position of the igniter in the flame, age of the igniter, type of gas, coating on the igniter, and any impurities that could have built up over time. It is imperative that the flame remains in contact with the burner, and that the burner and control module have the same common ground.

“When using the igniter as the sense unit, it is important to remember that as an igniter ages, a thin silicon oxide (SiO2) layer is formed on the surface. This is part of the normal aging process of a silicon carbide (SiC) igniter. As this oxide layer is formed, it actually helps seal the underlying SiC grains and inhibits further rapid oxidation. The SiO2 that has formed is a glass which is an insulator, and will diminish the strength of the flame signal that is being sent out. Whether the signal will still be strong enough to keep the valve open as the igniter ages is application dependent.”

 

 

Main Burner Shuts Off Before T-stat Is Satisfied 

 

 Possible causes: 

 

 

Improper igniter alignment;

Faulty ignition control;

Contaminated igniter and/or sensor (remote sensing);

Bad burner ground.

 

Solution:

 

 Check for proper polarity. Check for proper igniter position; make sure there is proper ignition control grounding.

Check for foreign matter on the igniter or sensor. Clean or replace. Check the main burner ground by checking continuity between ground and burner. If previous checks are OK, you may need to check the microamps on the system.

The procedure for checking the flame signal with HSI when the igniter is also being used as a sensor is outlined in the two following procedures.

 

Procedure one:

 

Note: Do not attempt this measurement unless you are familiar with line voltage measurements. The HSI, line, and meter leads will be live during this measurement; touching them may result in electrical shock.

 

1.            Remove all power.

2.            Remove lower HSI wire from the electronic module. Place a single-pole, single-throw (spst) switch (rated for at least 5 A @120 vac) between the lower HSI terminal and the disconnected lead. Make sure the switch is in the closed position.

3.            Attach the red (positive, +) lead of W136 meter (or equivalent) through a 1-meg resistor to the electronic module side of the switch. Attach the black (negative, -) lead to the W136 to the igniter side of the switch.

4.            Make sure the meter is set on the µA scale.

5.            Reapply power.

6. After the burner is lit and the hot surface igniter turns off, open the switch and read the µA. Never open the switch while the hot surface igniter is energized. This may damage the W136 meter.

7.            After the reading is taken, remove all power and reconnect the system. Minimum readings for proper operation should be 0.8 µA.

 

 

Procedure two:

 

1.            With the power off, remove the lead from the module that feeds 120 vac to the igniter.

2.            The lead removed from the module should be connected to the alligator clip, and the alligator clip to the HSI terminal on the module.

3.            Plug the two banana plugs into the multimeter; observe the polarity (red into red, black into black).

4.            Turn the power on and call for heat. The igniter should glow and burner ignition should commence.

5.            At anytime after ignition, push the momentary switch (NC); it will open and you should read microamps on your meter.

 

 ground wire 

 

 Grounding is a method of giving electricity the most effect way to return to ground via the service panel. You see current flows from the panel to the outlet or device to power it up. The neutral wire is the return path for unused current. The ground wire is an additional path for electrical current to return safely to ground without danger to anyone in the event of a short circuit. In that instant, the short would cause the current to flow through the ground wire, causing a fuse to blow or a circuit breaker to trip. Ground wires used on power tools, vacuums, and other portable devices are made much safer when they incorporate the use of a third prong, thus a ground connection. Often people do an unthinkable act of cutting off the ground tab of an extension cord or power tool. This usually happens when the outlet being used has no ground, thus a polarized plug.

 

An ungrounded electrical box, appliance, power tool, or extension cord could become a danger if there is no path to ground, except through you.You see, without a ground wire, your body may complete the ground path and you may be shocked or electrocuted. In older homes with cloth wrapped wire or in homes with knob and tube wiring, this is the case. As you know, newer appliances and some tools come equipped with a three-pronged cord, incorporating a ground for protection. Remember, any contact with a metal box, appliance or electrical panel that has no ground can potentially make you the ground connection, so be extra careful!

 

 

 

And while we’re on the subject of grounding, I’m often asked if using a receptacle adapter is OK. First of all, I’m not a fan of doing something half way. I’d rather change the receptacle to a grounded receptacle and have the ground wire connected to the receptacle and the box. Although you can use an adapter and connect the center cover-plate screw to the adapter to gain a ground if the box is grounded, it just seems like a skimpy, lazy way to fix the real problem, the need for a new receptacle. Changing the receptacle may be more of a need than a want in many ways. The receptacle may be a regular style now, but may require a GFCI in it's place due to recent code changes. One change is that you need GFCI's in basements, garages and anywhere there is concrete on the floor, including wet areas and outdoors.

 

Receptacles that have only a hot and neutral slot are called polarized receptacles. By having a smaller hot wire slot and a larger neutral slot on a polarized receptacle, the electrical current flows the appropriate way through the circuit. For safe use of these receptacles, double-insulated power tools can be used in polarized receptacle circuits. These safety features can reduce the risk of electrical shock, but once again, my advice is to replace the receptacle and rewire if needed to convert the circuit into a properly grounded circuit and receptacle.

 

gas pressure switch

 

Gas Pressure Switches

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Our gas switches monitor natural or LP gas pressure and are designed to cut off the electrical control circuit when pressure rises above or drops below the desired preset limit. Accurate and reliable, models are available in numerous settings, types, and enclosures.

a gas pressure switch that accurately monitors pressure and breaks the electrical control when pressure rises above or drops below the desired set point. It is made with a durable plastic enclosure and a die-cast aluminum inlet base.

a gas pressure switch that accurately monitors pressure and breaks the electrical control circuits when pressure rises above or drops below the desired set point. Made with a durable plastic enclosure and die-cast aluminum inlet base, the switch is sturdy and dependable,

 Single is a high-low gas pressure switch that monitors pressure and cuts off the electrical control circuit when pressure rises above or drops below the desired set point. The high and low gas pressure settings are adjustable. All models are available in reset or recycle type.

 a high-low gas pressure switch that monitors pressure and cuts off the electrical control circuit when pressure rises above or drops below the desired set point. The high and low gas pressure settings are adjustable. All models are available in reset or recycle type.

 a gas pressure switch that monitors pressure and breaks the electrical control circuit when pressure drops below or rises above the desired set point. The gas pressure settings are adjustable.

a gas pressure switch that monitors pressure and breaks the electrical control circuit when pressure rises above or drops below the desired set point. Made of rugged die-cast aluminum, it offers reliability, repeatability, and accuracy.

Single is an accurate and reliable switch. It features a two-circuit control in which each set point controls two independent dry contacts to switch to two different voltages. The high and low pressure settings are adjustable. Available in reset and recycle types.

Double is an accurate and reliable switch. It features a two-circuit control in which each set point controls two independent dry contacts to switch to two different voltages. The high and low pressure settings are adjustable. Available in reset and recycle types.

 

 

gas valve

 

Most gas fittings utilize a counter-clockwise thread. This is reverse of any other fitting. The purpose of this thread design is to ensure that an unsafe gas valve cannot be installed in a gas line. For example, a shutoff valve for water or another substance could be manufactured of steel; this type of valve could spark when turned and cause an explosion if it were installed on a gas line. By using a specific gas-only fitting thread, the potential for this kind of trouble can be eliminated.

When installing any new gas valve or fitting, it is wise to use a bubble test to ensure that no leaks are present. The bubble test is performed by using a mixture of soap and water and applying it to all gas line connections. Any leaking gas will cause a bubble to form in the soapy water. If any bubbles are detected, the fitting must be tightened or redone. Typically, a quality connection will include the use of a Teflon liquid or tape sealant applied to the threads.

Many gas valves used on main supply lines will include a locking lug. The locking lug is a device fashioned into the valve that allows a padlock to be installed. This lock keeps the valve in the closed position until removed by the person who installed it. This is a safety device that is used to prevent tampering or accidental gas flow to an open line, which could result in an explosion or poisoning of people in the vicinity.

Many gas valve designs used on heaters and furnaces require the user to push the valve down and hold it down in order to ignite the unit. This is another safety feature intended to make it difficult to unintentionally ignite the gas. By creating such safety devices in the gas valve, accidental fires, explosions and deaths can be reduced.

 

 

How does a gas valve work

 

A gas valve regulates the amount of gas needed to produce a consistent flow without any gas leaking. This type of valve is generally found on appliances that require gas, and the valve is important to the operation and safety of gas appliances. 

 

A gas valve is used to control gas pressure and provide safety features. A gas burner is normally located under an appliance and the burner is used to ignite the gas. The valve controls the pressure of the gas and the amount supplied to the appliance. Controlling the pressure is required to avoid fires and explosions caused by too much pressure. If the pressure is not high enough, though, the appliance will not get the amount of ignited gas required for it to function properly.

Gas valves are also placed on appliances for safety reasons. The valve has the ability to detect whether gas is being heated. After the gas travels across the pilot light, the gas is ignited. The ignited gas has an increase in temperature that is detected by the valve. When a specific temperature is detected, the gas valve cuts off the supply. Reducing the supply helps prevent potentially lethal gas from escaping or lingering in the area.

 

gate valve

 

 On opening the gate valve, the flow path is enlarged in a highly nonlinear manner with respect to percent of opening. This means that flow rate does not change evenly with stem travel. Also, a partially open gate tends to vibrate from the fluid flow. Most of the flow change occurs near shutoff with a relatively high fluid velocity causing gate and seat wear and eventual leakage if used to regulate flow. Typical gate valves are designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss.

Bonnets provide leakproof closure for the valve body. Gate valves may have a screw-in, union, or bolted bonnet. Screw-in bonnet is the simplest, offering a durable, pressure-tight seal. Union bonnet is suitable for applications requiring frequent inspection and cleaning. It also gives the body added strength. Bolted bonnet is used for larger valves and higher pressure applications.

Another type of bonnet construction in a gate valve is pressure seal bonnet. This construction is adopted for valves for high pressure service, typically in excess of 2250 psi (15 MPa). The unique feature of the pressure seal bonnet is that the bonnet ends in a downward-facing cup which fits inside the body of the valve. As the internal pressure in the valve increases, the sides of the cup are forced outward. improving the body-bonnet seal. Other constructions where the seal is provided by external clamping pressure tend to create leaks in the body-bonnet joint.

Gate valves may have flanged ends which are drilled according to pipeline compatible flange dimensional standards. Gate valves are typically constructed from cast iron, ductile iron, cast carbon steel, gun metal, stainless steel, alloy steels, and forged steels.

All-metal gate valves are typically used in ultra-high vacuum chambers to isolate regions of the chamber,

 

 

 natural gas

 

 

Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium.

It is formed when layers of decomposing plant and animal matter are exposed to intense heat and pressure supplied by existing under the surface of the Earth over millions of years. The energy that the plants originally obtained from the sun is stored in the form of chemical bonds in the gas.

Natural gas is a fossil fuel used as a source of energy for heating, cooking, and electricity generation. It is also used as fuel for vehicles and as a chemical feedstock in the manufacture of plastics and other commercially important organic chemicals. It is a non-renewable resource.

Natural gas is found in deep underground rock formations or associated with other hydrocarbon reservoirs in coal beds and as methane clathrates. Petroleum is another resource and fossil fuel found in close proximity to and with natural gas. Most natural gas was created over time by two mechanisms: biogenic and thermogenic. Biogenic gas is created by methanogenic organisms in marshes, bogs, landfills, and shallow sediments. Deeper in the earth, at greater temperature and pressure, thermogenic gas is created from buried organic material.

When gas is associated with petroleum production it may be considered a byproduct and be burnt as flare gas. The World Bank estimates that over 150 cubic kilometers of natural gas are flared or vented annually. Before natural gas can be used as a fuel, it must be processed to remove impurities, including water, to meet the specifications of marketable natural gas. The by-products of this processing include: ethane, propane, butanes, pentanes, and higher molecular weight hydrocarbons, hydrogen sulfide (which may be converted into pure sulfur), carbon dioxide, water vapor, and sometimes helium and nitrogen.

Natural gas is often informally referred to simply as "gas", especially when compared to other energy sources such as oil or coal. However, it is not to be confused with gasoline, especially in North America, where the term gasoline is often shortened in colloquial usage to gas.

Natural gas was used by the Chinese in about 500 BCE (possibly even 1000 BCE. They discovered a way to transport gas seeping from the ground in crude pipelines of bamboo to where it was used to boil salt water to extract the salt, in the Ziliujing District of Sichuan. The world's first industrial extraction of natural gas started at Fredonia, New York, United States in 1825.By 2009, 66 000 km³ (or 8%) had been used out of the total 850 000 km³ of estimated remaining recoverable reserves of natural gas.[10] Based on an estimated 2015 world consumption rate of about 3400 km³ of gas per year, the total estimated remaining economically recoverable reserves of natural gas would last 250 years at current consumption rates. An annual increase in usage of 2–3% could result in currently recoverable reserves lasting significantly less, perhaps as few as 80 to 100 years,