FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC INSTALLATIONS

 heat is energy that spontaneously passes between a system and its surroundings in some way other than through work or the transfer of matter. When a suitable physical pathway exists, heat flows spontaneously from a hotter to a colder body. The transfer can be by contact between the source and the destination body, as in conduction; or by radiation between remote bodies; or by conduction and radiation through a thick solid wall; or by way of an intermediate fluid body, as in convective circulation; or by a combination of these.

Because heat refers to a quantity of energy transferred between two bodies, it is not a state function of either of the bodies, in contrast to temperature and internal energy. Instead, according to the first law of thermodynamics heat exchanged during some process contributes to the change in the internal energy, and the amount of heat can be quantified by the equivalent amount of work that would bring about the same change.

While heat flows spontaneously from hot to cold, it is possible to construct a heat pump or refrigeration system that does work to increase the difference in temperature between two systems. Conversely, a heat engine reduces an existing temperature difference to do work on another system.

Historically, many energy units for measurement of heat have been used. The standards-based unit in the International System of Units  is the joule . Heat is measured by its effect on the states of interacting bodies, for example, by the amount of ice melted or a change in temperature. The quantification of heat via the temperature change of a body is called calorimetry, and is widely used in practice. In calorimetry, sensible heat is defined with respect to a specific chosen state variable of the system, such as pressure or volume. Sensible heat causes a change of the temperature of the system while leaving the chosen state variable unchanged. Heat transfer that occurs at a constant system temperature but changes the state variable is called latent heat with respect to the variable. For infinitesimal changes, the total incremental heat transfer is then the sum of the latent and sensible heat.

  

When you move the lever on the thermostat to turn up the heat, this rotates the thermometer coil and mercury switch, tipping them to the left.

As soon as the switch tips to the left, current flows through the mercury in the mercury switch. This current energizes a relay that starts the heater and circulation fan in your home. As the room gradually heats up, the thermometer coil gradually unwinds until it tips the mercury switch back to the right, breaking the circuit and turning off the heat.

When the mercury switch tips to the right, a relay starts the air conditioner. As the room cools, the thermometer coil winds up until the mercury switch tips back to the left.

Thermostats have another cool device called a heat anticipator. The heat anticipator shuts off the heater before the air inside the thermostat actually reaches the set temperature. Sometimes, parts of a house will reach the set temperature before the part of the house containing the thermostat does. In this case, the anticipator shuts the heater off a little early to give the heat time to reach the thermostat.

The loop of wire above is a kind of resistor. When the heater is running, the current that controls the heater travels from the mercury switch, through the yellow wire to the resistive loop. It travels around the loop until it gets to the wiper, and from there it travels through the hub of the anticipator ring and down to the circuit board on the bottom layer of the thermostat. The farther the wiper is positioned (moving clockwise) from the yellow wire, the more of the resistive wire the current has to pass through. Like any resistor, this one generates heat when current passes through it. The farther around the loop the wiper is placed, the more heat is generated by the resistor. This heat warms the thermometer coil, causing it to unwind and tip the mercury switch to the right so that the heater shuts off.

 

 Heating elements

 

 

 The good carriers of electricity are called conductors, while the poor carriers are known as insulators. Conductors and insulators are often better described by talking about how much resistance they put up when an electric current flows through them. So conductors have a low resistance (electricity flows through them easily) while insulators have a much higher resistance (it's a real struggle for the electricity to get through). In an electric or electronic circuit, we can use devices called resistors to control how much current flows; using a dial to increase the resistance and lower the current in a loudspeaker circuit is a way of turning down the volume,

Resistors work by converting electrical energy to heat energy; in other words, they get hot when electricity flows through them. But it's not just resistors that do this. Even a thin piece of wire will get hot if you force enough electricity through it. That's the basic idea behind incandescent lamps (old-fashioned, bulb-shaped lights). Inside the glass bulb, there's a very thin coil of wire called a filament. When enough electricity flows through it, it glows white hot, very brightly—so it's really making light by making heat. Around 95 percent of the energy a lamp like this uses is turned into heat and completely wasted (using an energy-saving fluorescent lamp is far more efficient, because most of the electricity the lamp consumes is converted into light with hardly any wasted heat).

 

Now forget the light—what if the heat were the thing we were really interested in? Suddenly, we find our wasteful incandescent lamp is actually very efficient, because it converts 95 percent of the energy we feed into it to heat. Fantastic! Only there's a problem. If you've ever got close to an incandescent lamp, you'll know it gets hot enough to burn you if you touch it (don't be tempted to try). But if you stand even a meter or so away, the heat from something like a 100-watt lamp is far too feeble to reach you.

 

So what if we wanted to build an electric heater broadly along the same lines as an electric lamp? We'd need something like a scaled-up lamp filament—maybe 20–30 times more powerful so we could really feel the heat. We'd need a fairly robust material (one that didn't melt and lasted a long time through repeated heating and cooling) and we'd need it to give off lots of heat at a reasonable temperature (maybe when it glowed red hot instead of white hot, so it didn't blind us). What we're talking about here is the essence of a heating element: a sturdy electrical component designed to throw out heat when a big electric current flows through it.

 

What is a heating element

 

 

A typical heating element is usually a coil, ribbon (straight or corrugated), of strip of wire that gives off heat much like a lamp filament. When an electric current flows through it, it glows red hot and converts the electrical energy passing through it into heat, which it radiates out in all directions.

 

Heating elements are typically either nickel-based or iron-based. The nickel-based ones are usually nichrome, an alloy (a mixture of metals and sometimes other chemical elements) that consists of about 80 percent nickel and 20 percent chromium (other compositions of nichrome are available, but the 80–20 mix is the most common). There are various good reasons why nichrome is the most popular material for heating elements: it has a high melting point (about 1400°C or 2550°F), doesn't oxidize (even at high temperatures), doesn't expand too much when it heats up, and has a reasonable (not too low, not too high, and reasonably constant) resistance (it increases only by about 10 percent between room temperature and its maximum operating temperature).

 

There are lots of different kinds of heating elements. Sometimes the nichrome is used bare, as it is; other times it's embedded in a ceramic material to make it more robust and durable (ceramics are great at coping with high temperatures and don't mind lots of heating and cooling). The size and shape of a heating element is largely governed by the dimensions of the appliance it has to fit inside and the area over which it needs to produce heat. Hair curling tongs have short, coiled elements because they need to produce heat over a thin tube around which hair can be wrapped. Electric radiators have long bar elements because they need to throw heat out across the wide area of a room. Electric stoves have coiled heating elements just the right size to heat cooking pots and pans (often stove elements are covered by metal, glass, or ceramic plates so they're easier to clean).

In some appliances, the heating elements are very visible: in an electric toaster, it's easy to spot the ribbons of nichrome built into the toaster walls because they glow red hot. Electric radiators (like the one in our top photo) make heat with glowing red bars (essentially just coiled, wire heating elements that throw out heat by radiation), while electric convector heaters generally have concentric, circular heating elements positioned in front of electric fans (so they transport heat more quickly by convection). Some appliances have visible elements that work at lower temperatures and don't glow; electric kettles, which never need to operate above the boiling point of water (100°C or 212°F), are a good example. Other appliances have their heating elements completely concealed, usually for safety reasons. Electric showers and hair curling tongs have concealed elements so there's (hopefully) no risk of electrocution.

 

 

All this makes heating elements sound very simple and straightforward, but there are, in fact, many different factors that electrical engineers have to consider when they design them. In his excellent book on the subject (see references below), Thor Hegbom lists roughly 20–30 different factors that affect the performance of a typical heating element, including obvious things like the voltage and current, the length and diameter of the element, the type of material, and the operating temperature. There are also specific factors you need to consider for each different type of element. For example, with a coiled element made of round wire, the diameter of the wire and the form of the coils (diameter, length, pitch, stretch, and so on) are among the things that critically affect the performance. With a ribbon element, the ribbon thickness and width, surface area, and weight all have to be factored in.

 

You might think a heating element would need to have a really high resistance—after all, it's the resistance that allows the material to generate heat. But that's not actually the case. What generates heat is the current flowing through the element, not the amount of resistance it feels. Getting the maximum current flowing through a heating element is much more important than forcing that current through a large resistance. This might seem confusing and counter-intuitive, but it's quite easy to see why it is (and must be) true, both intuitively and mathematically.

 

Intuitively...

 

 

Suppose you made the resistance of your heating element as big as you possibly could—infinitely big, in fact. Then Ohm's law (voltage = current × resistance or V = IR) tells us the current flowing through your element would have to be infinitely small (if I = V/R, I approaches zero as R approaches infinity). You'd have a whopping great resistance, no current, and therefore no heat produced. Right, so what if we went to the opposite extreme and made the resistance infinitely tiny. Then we'd have a different problem. Although the current I might be huge, R would be virtually zero, so the current would zip through the element like an express train without even stopping, producing no heat at all.

 

What we need in a heating element is therefore a balance between the two extremes: enough resistance to produce heat, but not so it reduces the current too much. Nichrome is a great choice. The resistance of a nichrome wire is (roughly) 100 times higher than that of a wire the same size made from copper (an excellent conductor), but only a quarter as much as a similar-sized graphite rod (a fairly good conductor) and maybe only a million trillionth that of a really good insulator such as glass. The numbers speak for themselves: nichrome is an average conductor with only moderate resistance, and not remotely an insulator!

 

Mathematically

 

 

We can reach exactly the same conclusion with math. The power produced or consumed by a flow of electricity is equal to the voltage times the current (watts = volts × amps or P = VI). We also know from Ohm's law that V = IR. Eliminate V from these equations and we find the power dissipated in our element is I2R. In other words, the heat is proportional to the resistance, but also proportional to the square of the current. So the current has much more effect on the heat produced than the resistance. Double the resistance and you double the power (great!), but double the current and you quadruple the power (fantastic!). So the current is what really matters.

 

Mathematically

We often refer to electrical heating—what heating elements do—as "Joule heating" or "resistance heating," as though resistance is the only factor that matters. But, in fact, as I explained above, there are dozens of interrelated factors to consider in the design of a heating element that works effectively in a particular appliance. The resistance isn't always something you control and determine: it's often determined for you by your choice of material, the dimensions of the heating element, and so on.

 

 

 heat coil

 

 

Heater elements come in many shapes and sizes. A heating coil is a special heating device that is shaped in a spiral design. The coil is typically made from ceramic or metal and heated through electrical current. This type of design is often found in hair dryers, space heaters, and electric ovens.

 

There are many forms of heating elements available today for portable heaters. This includes gas-, solar-, and electric-powered units. Many portable space heaters use a heater coil design. This coil produces heat that is transferred into the surrounding area with a fan.

 

A heating coil is normally powered by electricity. When the coil is charged with electric power, it becomes red hot. This heat is transferred into the open area by using an exhaust fan. As the fan blows air over the coil, the coil is continually heated, which warms the air.

 

Portable heaters have an emergency override mechanism to prevent overheating. This is a safety feature that turns the heater off if the fan element stops. Without this safety feature, the heater could overheat the external container, causing the device to melt and catch on fire.

A blow dryer is a portable heating device that is used to dry hair. Most blow dryers contain an internal heating coil. This type of heating device produces extreme heat, but is an expensive form of energy. A hair dryer uses large amounts of electricity to generate the hot air. Most hair dryer elements consume the same amount of electricity as running ten 100-watt light bulbs.

 

A baseboard heating system design is similar to a heating coil design. These heaters generate heat based on electrical input. The baseboard heaters are typically placed on the floor of a room with a built-in thermostat. The baseboard heating system is made from metal that is heated with an electric charge.

 

One of the benefits of a coil design is fast, efficient heat. A larger heating coil can generate extreme heat temperatures very quickly. Most electric stoves use this coil design to produce heat for the oven. An electric oven can be quickly heated to a desired temperature.

 

Many water heaters use a heater coil design. These heaters warm the water supply that runs throughout a home or building. Water heaters keep water at a set temperature. When the temperature drops below the preselected setting, the coil is heated through an electrical charge.

 

furnace Heat exchangers

 

 

Modern air conditioners and furnaces can be complex pieces of machinery.  It is not uncommon for HVAC contractors (what does HVAC stand for?) to throw around technical terms and parts, either because they are just too used to doing it at work or, in unfortunate circumstances, because they are trying to take advantage of a customer.  As your educator, All Systems Mechanical will spend today’s post answering the question, ‘what is a heat exchanger in a furnace?‘  There are many parts to a modern furnace, but the furnace’s heat exchanger is one of the most important.  Simply put, the furnace heat exchanger is the part that heats your air, but in this post we will dig a little deeper and help ensure that you are ready to talk to your furnace repairman using the same technical terms and understanding that he does.  We will do this by first explaining what a furnace heat exchanger is, how it works, what type of fuels can be used and finally how a damaged heat exchanger can be dangerous.

 

What is a Furnace Heat Exchanger

 

A furnace’s heat exchanger is a set of tubes or coils that are looped repeatedly through the air flow inside your furnace for the purpose of heating air.  Simply put, the furnace heat exchanger is the part of your furnace that actually heats the air.  What shape these coils take is dependent on what model of furnace you have, as well as what type of fuel that your furnace uses for combustion.  For information on different furnace brands, try: Lennox vs Carrier Furnace Review.

 

How does a Furnace’s Heat Exchanger Work

 

 

Your furnace’s heat exchanger works using a very simple principle that, believe it or not, you are already familiar with.  Imagine that it’s cold outside, and you just ordered a hot cup of soup at your favorite restaurant.  Ouch!  It’s a bit too hot, so what do you do?  You blow on the soup, right?  This is exactly how your furnace heat exchanger works.  In this example, the heat exchanger is your soup, and the hot air that you are blowing off of the soup is the hot air that circulates through your house.  A furnace’s heat exchanger uses some type of fuel to combust inside of it, creating heat and getting very hot.  Your blower motor (aka your ‘fan’) then blows air over this heat exchanger (like blowing over hot soup) and into your ductwork, where it is distributed throughout your house.  That’s it – it really is that simple.

 

What Types of Fuel Can Be Used By A Furnace’s Heat Exchanger

 

A furnace’s heat exchanger can use all sorts of fuel, and the type of fuel your furnace uses depends on preference, local climate and what type of fuel is readily available in your area.  For instance, propane might be readily available in Bozeman, Montana but it is unlikely that you’d find propane as a means of furnace fuel in an off-gridder’s house in Alaska.  This is because they don’t have roads to their house and can’t have it delivered!  Your furnace heat exchanger can use many types of fuel, including: Propane (LP) Gas, Fuel Oil, Natural Gas and Electric.  Some fuels are more efficient than others:

 

Cracked Heat Exchanger Dangerous

 

 

 a cracked or damaged furnace heat exchanger is a major danger to you and your family.  Remember that your furnace is burning some type of material in order to generate heat, but this process should be taking place inside your furnace’s heat exchanger itself.  If your heat exchanger is cracked or damaged, all sorts of dangerous gasses can be leaked into your home, including carbon monoxide – aka “the silent killer.”  For more information on carbon monoxide and how it can be dangerous, take a look at the Wiki page: Carbon Monoxide.

 

How Can I Keep My Family Safe from Carbon Monoxide

 

There are a couple of ways to keep your family safe from a cracked furnace heat exchanger:

 

Make sure your house or business is filled with the proper amount of carbon monoxide detectors.  Fire detectors aren’t enough, these detectors will detect carbon monoxide in the air before it can incapacitate you.

If you have a furnace, make sure that you have it inspected annually, or every other year at a minimum.  If you don’t want to spend the money for your local HVAC contractor to come out, this inspection is something easy that you can do yourself.

No one can inspect your furnace as good as a contractor can, who has endoscopic cameras and other tools, but in order to learn how to inspect your own heat exchanger, take a look at the following do-it-yourself video; it is short and informative: Furnace Heat Exchanger Inspection.

 

Final Thoughts on a Furnace’s Heat Exchanger

 

Your furnace’s heat exchanger is one of the most critical parts of your furnace.  It is not only responsible for heating the air inside of your home, but it can be dangerous if not cared for properly.  Don’t get worried, modern heat exchangers have an abundance of safety features, so if you make sure that you do your part by having your furnace’s heat exchanger inspected regularly and ensuring that you have carbon monoxide detectors in your home, you’ll be safe and sound.  For more information troubleshooting problems with your furnace, take a look at: Furnace Not Blowing Air? and Why is my Heater Blowing Cold Air?,

 

heat exchangers

 

 

Suppose you have a gas central heating furnace (boiler) that heats hot-water radiators in various rooms in your home. It works by burning natural gas, making a line or grid of hot gas jets that fire upward over water flowing through a network of pipes. As the water pumps through the pipes, it absorbs the heat energy and heats up. This arrangement is what we mean by a heat exchanger: the gas jets cool down and the water heats up.

 

A heat exchanger is a device that allows heat from a fluid (a liquid or a gas) to pass to a second fluid (another liquid or gas) without the two fluids having to mix together or come into direct contact. If that's not completely clear, consider this. In theory, we could get the heat from the gas jets just by throwing cold water onto them, but then the flames would go out! The essential principle of a heat exchanger is that it transfers the heat without transferring the fluid that carries the heat.

 

You can see heat exchangers in all kinds of places, usually working to heat or cool buildings or helping engines and machines to work more efficiently. Refrigerators and air-conditioners, for example, use heat exchangers in the opposite way from central heating systems: they remove heat from a compartment or room where it's not wanted and pump it away in a fluid to some other place where it can be dumped out of the way.

 

 

In power plants or engines, exhaust gases often contain heat that's heading uselessly away into the open air. That's a waste of energy and something a heat exchanger can certainly reduce (though not eliminate entirely—some heat is always going to be lost). The way to solve this problem is with heat exchangers positioned inside the exhaust tail pipes or smokestacks. As the hot exhaust gases drift upward, they brush past copper fins with water flowing through them. The water carries the heat away, back into the plant. There, it might be recycled directly, maybe warming the cold gases that feed into the engine or furnace, saving the energy that would otherwise be needed to heat them up. Or it could be put to some other good use, for example, heating an office near the smokestack.

 

In buses, fluid used to cool down the diesel engine is often passed through a heat exchanger and the heat it reclaims is used to warm cold air from outside that is pumped up from the floor of the passenger compartment. That saves the need for having additional, wasteful electric heaters inside the bus. A car radiator is another kind of heat exchanger. Water that cools the engine flows through the radiator, which has lots of parallel, aluminum fins open to the air. As the car drives along, cold air blowing past the radiator removes some of the heat, cooling the water and heating the air and keeping the engine working efficiently. The radiator's waste heat is used to heat the passenger compartment, just like on a bus.

 

If you have an energy-efficient shower, it might have a heat exchanger installed in the wastewater outlet. As the water drips past your body and down the plug, it runs through the copper coils of a heat exchanger. Meanwhile, cold water that's feeding into the shower to be heated pumps up past the same coils, not mixing with the dirty water but picking up some of its waste heat and warming slightly—so the shower doesn't need to heat it so much.

 

Types of heat exchangers

 

 

All heat exchangers do the same job—passing heat from one fluid to another—but they work in many different ways. The two most common kinds of heat exchanger are the shell-and-tube and plate/fin. In shell and tube heat exchangers, one fluid flows through a set of metal tubes while the second fluid passes through a sealed shell that surrounds them. That's the design shown in our diagram up above. The two fluids can flow in the same direction (known as parallel flow), in opposite directions (counterflow or counter-current), or at right angles (cross flow). Boilers in steam locomotives work this way. Plate/fin heat exchangers have lots of thin metal plates or fins with a large surface area (because that exchanges more heat more quickly); heat exchangers in gas furnaces (gas boilers) work this way. Wikipedia's article on heat exchangers includes a comprehensive list, comparing these and various other heat-exchanger designs.

 

 

Basics of heat loss, heat gain

Understanding the fundamentals of heat loss and heat gain is critical to sizing a new or replacement heating-cooling system.

This article offers an overview of the basics of these two important hvac concepts in residential system design. It’s an excellent description for newcomers to the hvac trade.

 

No matter what you do, when it is 68°F inside a house and 0° outside, the cold will suck the heat out of the house. It will pull at a certain rate through the exposed walls and ceilings, through the windows and floors. This is known as heat transfer.

The cold air is also trying to sneak into the building through every little crack in every nook and cranny. This is known as infiltration.

 

The home’s heat, on the other hand, is trying to escape through every nook and cranny. This is known as exhalation. It’s as if the house was breathing — breathing both air and temperature in and out.

 

The total of all this leaking and losing at a specific low temperature for your region, is known as the heat loss. This total will be calculated in Btu per hour (Btuh), and the heating system will need to produce and distribute this same amount of Btuh to maintain a 68° room temperature.

 

As most rooms differ from one another, each room’s heat loss must be determined. The total loss of all rooms added together will determine the size and design of the heating system.

 

In simple structures, the mere replacement of this lost heat is sufficient; but in complex houses with open floor plans and multiple levels, the flow of heat within the building becomes a factor. Heat rising from the first floor to the second increases the demand on the first floor while decreasing the demand on the second.

 

The formula used at the website warmair.com, is a combination of three ingredients developed to reflect the internal conditions of a modern structure. It combines industry-accepted standards of heat transfer with the old-fashioned tin knocker “cfm method” of computation, blended together by 25 years experience designing and installing heating and cooling systems.

 

 

The result is an estimate of comfort.

 

In the heat loss calculation, all windows are created equal, no matter which direction they face. Disallowing for wind factors, similar types of glazings lose heat at the same rate.

On the other hand, when calculating heat gain, windows facing east and west gain more heat than those facing north and south. This results in larger quantities of air being distributed to rooms with east- and west-facing windows. This air is necessary for cooling but not for heating.

In the more northern climates, where heating is a priority, treat all window areas as east and west shaded, regardless of which direction they face. This will restore the emphasis on a balanced distribution system rather than one weighted toward solar radiation.

 

 

Cold is another word for empty. It isn’t really anything — it is, as a vacuum is, the lack of something. Cold is the lack of heat.

The earth we live on is almost empty. We live on the edge of a delicate temperature balance only some 500° above empty. The coldest it can ever get is about -460°, but “hot-wise,” temperatures can reach into the billions.

We live at the bottom of a thermometer that stretches to the moon. Our planet is a cool puddle in a desert of heat, but water works only at these narrow temperature ranges, and our life depends on this water.

It is the function of a cooling system to remove unwanted heat from a structure and relocate it to the out-of-doors. This heat exchange is accomplished by the use of the refrigeration cycle as performed by the air conditioning system.

The refrigeration cycle takes advantage of the relationships between pressure, temperature, and volume, in such a way that heat is collected inside and released outside. It uses a condenser, a compressor, and an evaporator to accomplish this task.

The condenser and compressor are located outside of the house, while the evaporator is located inside the air distribution system. The quantity of heat that needs to be removed to maintain indoor comfort, on a specific warm day for your region, is known as the heat gain for your structure.

A building gains heat from actual outdoor temperature and humidity levels. It gains heat from the people inside of it, from the lights, computers, copiers, dishwashers, ovens, etc. (Many contractors distribute an extra 1,500 Btu of cooling to the kitchen to offset the heat given off by the appliances, and an extra 400 Btu to various rooms for occupants.)

But mostly it gains heat from its exposure to sunlight, from solar radiation. The hot sun beats down on the walls and the roof, the sunlight pours through the windows and warming the floors it lands on.

 

 heating seasonal performance factor

 Air-Source Heat Pump (ASHP):

 

 

 

A central air conditioner is a product, which is powered by single phase electric current, air cooled, rated below 65,000 Btu per hour, not contained within the same cabinet as a furnace, the rated capacity of which is above 225,000 Btu per hour, and is a heat pump or a cooling unit only.

 

Single Package:

A single package unit is an air source heat pump or central air conditioner that has all major assemblies enclosed in a single cabinet.

 

A split system is an air source heat pump or central air conditioner that has one or more of the major assemblies separated from the others,

 

Heating Seasonal Performance Factor (HSPF):

HSPF is the total space heating required in region IV during the space heating season, expressed in Btu, divided by the total electrical energy consumed by the heat pump system during the same season, expressed in watt-hours.

 

Seasonal Energy Efficiency Ratio (SEER):

SEER is the total heat removed from the conditioned space during the annual cooling season, expressed in Btu, divided by the total electrical energy consumed by the air conditioner or heat pump during the same season, expressed in watt-hours,

 

Energy Efficiency Ratio (EER):

EER is the ratio of the average rate of space cooling delivered to the average rate of electrical energy consumed by the air conditioner or heat pump. This ratio is expressed in Btu per watt.h (Btu/W.h).

 

Initially those are two separate effects. Think of when you slowly compress a gas with a piston in a thermally insulated cylinder. It gets hot because you've put in energy by doing work on it. The energy can come back out as work if the piston is allowed to move back out. If you heat the gas up the same amount by say rubbing two plates together in it, you can't get as much work out because the piston wasn't compressed. So heating by compression doesn't reduce free-energy (the ability to do work) but heating by friction does. Another way to say that is that compressive heating (at least if it's slow enough) doesn't increase entropy, but frictional heating does.

 

If you look at what happens when the space shuttle passes through the atmosphere, the atmosphere is not compressed overall, just heated. So overall the energy loss is through friction. On the way, however, a bit of energy is stored in compressed air before getting lost via friction in the air as it re-expands.

 

The enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a solid to a liquid at constant pressure. This energy includes the contribution required to make room for any associated change in volume by displacing its environment against ambient pressure. The temperature at which the phase transition occurs is the melting point. By convention, the pressure is assumed to be 1 atm (101.325 kPa) unless otherwise specified.

 

 

The 'enthalpy' of fusion is a latent heat, because during melting the introduction of heat cannot be observed as a temperature change, as the temperature remains constant during the process. The latent heat of fusion is the enthalpy change of any amount of substance when it melts. When the heat of fusion is referenced to a unit of mass, it is usually called the specific heat of fusion, while the molar heat of fusion refers to the enthalpy change per amount of substance in moles.

The liquid phase has a higher internal energy than the solid phase. This means energy must be supplied to a solid in order to melt it and energy is released from a liquid when it freezes, because the molecules in the liquid experience weaker intermolecular forces and so have a higher potential energy (a kind of bond-dissociation energy for intermolecular forces).

When liquid water is cooled, its temperature falls steadily until it drops just below the line of freezing point at 0 °C. The temperature then remains constant at the freezing point while the water crystallizes. Once the water is completely frozen, its temperature continues to fall.

The enthalpy of fusion is almost always a positive quantity; helium is the only known exception. Helium-3 has a negative enthalpy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative enthalpy of fusion below 0.77 K (−272.380 °C). This means that, at appropriate constant pressures, these substances freeze with the addition of heat. In the case of 4He, this pressure range is between 24.992 and 25.00 atm (2,533 kPa)

 

Carbon dioxide is a waste product of respiration and is formed from carbon and oxygen which were originally part of the food molecules. Heat energy may be released from cells during respiration. Metabolism is a word for all the chemical reactions in a living organism.

 

The typical central air conditioning system is a split system, with an outdoor air conditioning, or "compressor-bearing unit" and an indoor coil, which is usually installed on top of the furnace in the home.

Using electricity as its power source, the compressor pumps refrigerant through the system to gather heat and moisture from indoors and remove it from the home.

Heat and moisture are removed from the home when warm air from inside the home is blown over the cooled indoor coil. The heat in the air transfers to the coil, thereby "cooling" the air.

The heat that has transferred to the coil is then "pumped" to the exterior of the home, while the cooled air is pumped back inside, helping to maintain a comfortable indoor temperature.

Central air conditioning can also be provided through a package unit or a heat pump.

Indoor comfort during warm weather – Central air conditioning helps keep your home cool and reduces humidity levels.

Cleaner air – As your central air conditioning system draws air out of various rooms in the house through return air ducts, the air is pulled through an air filter, which removes airborne particles such as dust and lint. Sophisticated filters may remove microscopic pollutants, as well. The filtered air is then routed to air supply duct-work that carries it back to rooms.

Quieter operation – Because the compressor-bearing unit is located outside the home, the indoor noise level from its operation is much lower than that of a free-standing air conditioning unit.

It really does happen, though, so to understand heat pump operation, let's start with the basics. I discussed heat flow, thermal energy, and temperature. heat flows when you have a temperature difference (ΔT). So if you're trying to get heat out of 40°F air, what do you have to do? Put it in contact with something that's at a temperature lower than 40°F! That's the job of the refrigerant in a heat pump.

There are four basic processes in the refrigeration cycle. All are important, but in my opinion, the expansion valve is where the magic happens. Whether you're using it for a refrigerator, air conditioner, or heat pump, achieving a low temperature is the key, and that's what the expansion valve does for you.

A CO2 cartridge gets very cold because it does the same thing an expansion valve in a heat pump does.Here's an example for you that you may have experience with, especially if you're a serious bicyclist. CO2 cartridges contain carbon dioxide under high pressure. (Does this count as carbon sequestration?) When you use them to inflate a bicycle tube, for example, the cartridge gets very cold. Try it! It also works with aerosol cans like hairspray. This is a thermodynamic property of gases. When they're allowed to expand freely, their temperature drops.

Same thing happens in a fridge, AC, or heat pump. The refrigerant is pushed through the expansion valve, and the temperature of the refrigerant drops -- a lot. So, that cold outdoor air is actually the warmer object then, when it comes in contact with the outdoor coil of your heat pump. And, as we know, heat likes to move from warmer objects to cooler objects. Once we get that heat from the air into the refrigerant, it's just a matter of bringing it into the house and then transferring it into your home's air.

 

Heat Reclaim Systems

 

 

A recreational ice facility is highly dependent on a refrigeration system to provide the necessary cooling to produce and maintain an ice surface. The electrically driven refrigeration equipment is the highest ongoing non-labor cost of operation for your facility.

 

The entire refrigeration process is devoted to removing heat from the ice and disposing of it outdoors at the condenser. Since a great deal of heat is being conveyed by the refrigeration system anyway, it makes economic sense to harness this valuable source of free energy. With a properly integrated building design, the real dollar value of recovered heat can easily exceed the cost of electricity several times over.

 

Benefits include:

 

Drastically reduced facility operating expense

Increase in refrigeration system operating efficiencies

Reduction in dependence on fossil fuels

Some good uses of heat reclaim are:

 

Heating of public areas

Heating of bleachers

Under-floor heating

Ice resurfacing machine water heating

Dehumidifier reactivation

Walkway and driveway snow melting

Domestic hot-water heating

Swimming pool heating

Fresh air makeup pre-heat

Snow melt pit

 

It is possible to provide the entire facility's heating requirement with free waste heat. With the addition of an opportunistic thermal gathering system, you can provide all of the facility heat at a minimal operating cost. In many cases, this valuable resource has been the tipping point of turning unprofitable facilities into profitable facilities. There is generally a very quick payback on first costs, and some rebates apply. By leasing equipment, your costs can be much less than your savings, providing you with an immediate positive cash flow.

 

 

How It Works: Heat Recovery Ventilator

 

 

While necessity may be the mother of invention, it's increasing costs that spawn efficiency. Before the '70s, we happily cranked up the thermostat when the house felt chilly. Once heating costs went through the roof, though, we all put on sweaters and started looking for ways to save. And, with up to 40 percent of our heating dollar going to air infiltration—otherwise known as drafts—sealing the place up began to seem like the best defense against high heating bills.

 

Over a period of time, older homes began to sport new, tight windows and doors, insulation and vapor-barrier improvements, modern siding, and caulk for every crack through which air might pass. New homes left the drawing board designed to be tight, and builders became familiar with the new materials and skills needed to meet market demand and updated regulations. Homes were finally becoming thermally efficient. What some began to wonder, though, was whether they were habitable.

 

It turns out that those heat-robbing drafts had a role in the ecosystem of the home—they provided fresh air to breathe. Without realizing it, builders before the energy crisis had been installing an effective, albeit haphazard, ventilation system. If you could afford the heating bills, it worked.

 

Why Ventilate

 

 

Life inside today's tight home generates both moisture and pollutants. The moisture comes from cooking, washing, showers and breathing. At excessive levels, moisture condenses on windows and can cause structural deterioration. Areas of excessive moisture are also breeding grounds for mold, mildew, fungi, dust mites and bacteria. You know you have a problem if you find moisture collecting on your windows, or if you notice black spots on walls. These unsightly spots indicate mildew growth. Mold spores and dust easily become airborne and circulate freely throughout the house, possibly causing a range of symptoms and allergic reactions.

 

In addition to excessive moisture and biological contaminants, appliances that utilize combustion have the potential for allowing gases, including carbon monoxide, and other pollutants to escape into the air. Some common sources may include gas ranges and water heaters, unvented space heaters, leaky chimneys and wood-burning appliances. Even breathing can add to the problem when carbon dioxide reaches excessive levels, creating stale air.

 

And that's not all that gets into the air. If your home is new, the very products it's made of can give off gases that are less than agreeable to your comfort and good health, and in many areas of the country there's a concern about radon seeping from the ground.

 

Open A Window

 

 

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) sets the standard for residential ventilation at a minimum of .35 air changes per hour, and not less than 15 cubic feet per minute (cfm) per person. An old home may very well exceed these values—especially on a windy day. However, on a calm winter day, even a drafty house may fall below the recommended minimum ventilation standard.

 

There are partial solutions to the indoor air-quality problem. For example, an electrostatic filter installed in a forced-air heating system will reduce airborne contaminants, but it won't help with moisture, stale air or gaseous pollutants. And, local exhaust fans can remove excess moisture in the kitchen, bath and laundry area, but create negative pressure inside the house. As they pump air out, the resultant vacuum slowly draws air into and through the house structure, bringing with it odors, dust and contaminants. In areas where radon is a problem, the negative pressure may increase radon levels.

 

A better whole-house solution is to create balanced ventilation. This way, one fan blows the stale, polluted air out of the house while another replaces it with fresh. Of course, if the fresh air is cold, you need to warm it up, and that costs money.

 

Holding The Heat

 

 

A heat-recovery ventilator (HRV) is similar to a balanced ventilation system, except it uses the heat in the outgoing stale air to warm up the fresh air. A typical unit features two fans—one to take out household air and the other to bring in fresh air. What makes an HRV unique is the heat-exchange core. The core transfers heat from the outgoing stream to the incoming stream in the same way that the radiator in your car transfers heat from the engine's coolant to the outside air. It's composed of a series of narrow alternating passages through which incoming and outgoing airstreams flow. As the streams move through, heat is transferred from the warm side of each passage to the cold, while the airstreams never mix.

 

Depending on the model, HRVs can recover up to 85 percent of the heat in the outgoing airstream, making these ventilators a lot easier on your budget than opening a few windows. And, an HRV contains filters that keep particulates such as pollen or dust from entering the house. You will, though, find your energy bill going up slightly to pay for replacing the heat that isn't recovered. An average HRV installation can run from $2000 to $2500, but costs will vary widely depending on the specific situation.

 

Although an HRV can be effective in the summer months, when it will take heat from incoming fresh air and transfer it to stale air-conditioned exhaust air, it's most popular in colder climates during the winter. If the temperature falls below about 20° F, however, frost can build up inside the exchange core. To handle this, a damper closes off the cold airstream and routes warm air through the core. After several minutes, a timer opens the fresh-air port and ventilation continues.

 

A typical HRV for residential use might move as much as 200 cfm of air, but the fan speed can be set to suit the air quality in the home. For example, a slow to medium fan speed may be adequate for normal living, while a house full of guests might require the highest setting. Controls are available for intermittent and remote operation.

 

HRVs are ideal for tight, moisture-prone homes because they replace the humid air with dry, fresh air. In climates with excessive outdoor humidity, an energy-recovery ventilator is more suitable. This device is similar to an HRV, but dehumidifies the incoming fresh airstream.

 

 

How heat recovery works.

Heat Recovery Ventilators (HRV) reclaim energy from exhausted stale indoor air to temper incoming fresh air - heat is retained during cooler seasons, and removed during warmer seasons. These systems capture about 70 percent of the energy already expended to temper incoming air. BROAN HRV systems are designed to be ducted, whole-house solutions. They will meet ventilation needs based on square footage of the structure and maintain recommended air changes per hour.

 

 

 

How energy recovery works.

Energy Recovery Ventilators (ERV) from BROAN are typically recommended for use in warmer climates where it is desired to remove humidity from incoming fresh air. While not a dehumidifier, ERV systems transfer moisture from incoming, humid air to the stale indoor air that is being vented to the outside. BROAN ERV systems are designed to be ducted, whole-house solutions. They will meet ventilation needs based on square footage of the structure, and maintain recommended air changes per hour.

 

 heat sink

 

A heat sink (also commonly spelled heatsink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature at optimal levels. In computers, heat sinks are used to cool central processing units or graphics processors. Heat sinks are used with high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light emitting diodes (LEDs), where the heat dissipation ability of the component itself is insufficient to moderate its temperature.

A heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, such as the air. Air velocity, choice of material, protrusion design and surface treatment are factors that affect the performance of a heat sink. Heat sink attachment methods and thermal interface materials also affect the die temperature of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's performance by filling air gaps between the heat sink and the heat spreader on the device. A heat sink is usually made out of copper and/or aluminium. Copper is used because it has many desirable properties for thermally efficient and durable heat exchangers. First and foremost, copper is an excellent conductor of heat. This means that copper's high thermal conductivity allows heat to pass through it quickly. Aluminum is used in applications where weight is a big concern.

 

 

A heatsink is a device that is attached to a microprocessor chip to keep it from overheating by absorbing its heat and dissipating it into the air. Generally, a microprocessor's temperature should not run in excess of 50-55 degrees Celsius while under a full load. In Intel computers, the heatsink is positioned either on top of the microprocessor (in computers with a ZIF socket) or on the side of it (in later Pentiums in which the microprocessor fits into a Slot 1 interface). The heatsink may be held in place on the microprocessor by a clip. To ensure that the heatsink can absorb as much heat as possible, thermal grease is used to create a seal between the two devices.

When you buy a computer or a separate microprocessor, the heatsink comes with it. Most heatsinks are aluminum and have "fins" that extend from the base. An active heatsink is one that comes with a fan, sometimes called a heatsink/fan combo (HSF). A passive heatsink is one that comes without a fan.

 

 heat tape

 

We talk to folks all the time who ask us for "heat tape" when what they're really looking for is heat trace cable – which is also known as heating cable, heat tracing cable, or heater cable. The confusion is understandable: lots of hardware stores sell roof de-icing kits that include heating cable, but call it "heat tape." (If that's what you're looking for, you've come to the right place; you can find those roof heating cable kits here.) But despite the similarity in names, there is a difference! There are a few industrial and scientific applications where you could use either one, but most applications clearly call for one or the other. This page will discuss the differences between heat tape and heating cable, as well as some of the applications where one or the other should be used, and you'll find links to the pages where you can purchase our heat tapes and heat trace cables. We also have some information on a similar, lesser-known but very useful, product, heating cords.

 

Heating cable

 

 

Heating cable looks more like standard two-conductor house wiring cable (Type NM or Romex™) and is not nearly as flexible as heat tape – most varieties are about as flexible as a garden hose. The stiffness is related to one of the main differences between them and heat tapes: heating cables are enclosed in a housing that protects the heating elements and means you can use the heater in a broader range of environments. Heating cable can also be cut to length and terminated with electrical connections, and in fact we sell it by the foot. There are two main types of heating cable:

 

Self-regulating or self-limiting heating cable is made so that it will not rise above a certain temperature. (This doesn't mean that it will stay at the right temperature without a temperature control, only that it won't overheat and burn out. The name misleads many people—so we've written an article about what "self-regulating" really means. We recommend at least a basic thermostat.) They are on the low end of the temperature range, with styles suitable for applications up to 250°F. They are available in 120 V and 240 V versions; the latter can also run at 208, 220, or 277 V. Self-regulating cables come in two varieties:

 

Standard-temperature self-regulating cable ranges up to 150°F. It's available with nominal heat outputs of 3 W/ft, 5 W/ft, 8 W/ft, and 10 W/ft.

Mid-temperature self-regulating cable ranges up to 250°F. It's available with nominal heat outputs of 5 W/ft, 10 W/ft, and 15 W/ft.Constant-wattage heating cable, by contrast, doesn't control its own temperature, so it requires a controller. It is available for higher temperatures, with styles ranging up to 500°F. It can be run on a wider range of voltages: 120, 208, 240, 277, and 480 V. It comes in several varieties, each of which has different advantages.

 

Heat tape

 

 

Heat tape is the product to use for applications where small, cylindrical sections need high power densities (which usually indicates high temperatures as well). Most heat tape is available on 120 V and 240 V versions, with power ranging from 52 W to 3,135 W. The power density, which we measure in W/in², ranges from 4.3 W/in² up to 13.1 W/in² for the high-temperature versions. Heat tape is a constant-wattage product, as opposed to self-regulating products that have built-in protection against overheating, and for this reason you must use a temperature controller of some type with it.

 

As far as dimensions go, one of the biggest differences between heat tape and heating cable is that heat tape is sold in fixed lengths – ours range from 2 to 20 feet in length, depending on the style. With the exception of cut-to-length heat tape (which is not available for online sale, though you can contact us to find out more), you cannot trim heat tape to length.

 

We carry several different varieties of heat tape for a wide range of applications:

 

Silicone rubber heat tapes are a good heat tape for applications up to 450°F, and are chemical- and moisture-resistant. (Note that does not mean that they are chemical- and moisture-proof; they cannot be immersed!) They're also available

with a built-in adjustable thermostat and

in a grounded version for applications in ordinary locations up to 305°F.

Fiberglass-insulated heat tapes come without controls – no built-in thermostat. They are available in several different configurations:

A grounded version that is suitable for applications to 482°F.

A version suitable for use on electrically non-conductive surfaces, and

one for use on conductive surfaces – both of which can be used for application temperatures up to 900°F.

Heat tapes made of Samox™, a high-temperature woven fabric, are available for applications to 1400°F, and come in two varieties:

A version for use on electrically non-conductive surfaces and

A version for use on conductive surfaces.

 

Heating cords

 

 

Heating cords are much like heating tapes, but are rounded in cross-section. This decreases the exposure surface and makes heat conduction somewhat less efficient, but the advantage is a heater that is much more forgiving of being wrapped imprecisely. Heating tapes must be wrapped very carefully to ensure that the full flat width of the tape is in constant contact with the surface being heated. If heating tape is switched on while a section of it is exposed to air on both sides – whether because it's bridging a corner or because it's been kinked during wrapping – that section won't be able to transfer its heat to the other object, and all that heat will build up in the tape and overheat it. Heating cord, being circular, can't get kinked and doesn't have flat sides. (However, you do still need to make sure that no sections of the cable are exposed in the air without contact to the heated object, or it will still be likely to overheat.)

 

We can create built-to-order heating cords (just contact us for a quote), and we have stock heating cords, which are available in two styles:

 

Standard-temperature heating cords, for temperatures up to 900°F, with a 120 V supply from 64 to 260 W.

High-temperature heating cords, for temperatures up to 1400°F, with a 120 or 240 V supply from 266 to 1500 W.

 

 heat transfer

 

 

All matter is made up of molecules and atoms. These atoms are always in different types of motion (translation, rotational, vibrational). The motion of atoms and molecules creates heat or thermal energy. All matter has this thermal energy. The more motion the atoms or molecules have the more heat or thermal energy they will have,

What is temperature?

 

From the video above that shows movement of atoms and molecules it can be seen that some move faster than others. Temperature is an average value of energy for all the atoms and molecules in a given system. Temperature is independent of how much matter there is in the system. It is simply an average of the energy in the system.

 

How is heat transferred?

 

 

Heat can travel from one place to another in three ways: Conduction, Convection and Radiation. Both conduction and convection require matter to transfer heat.

 

If there is a temperature difference between two systems heat will always find a way to transfer from the higher to lower system.

 

CONDUCTION--

 

Conduction is the transfer of heat between substances that are in direct contact with each other. The better the conductor, the more rapidly heat will be transferred. Metal is a good conduction of heat. Conduction occurs when a substance is heated, particles will gain more energy, and vibrate more. These molecules then bump into nearby particles and transfer some of their energy to them. This then continues and passes the energy from the hot end down to the colder end of the substance.

 

CONVECTION--

 

Thermal energy is transferred from hot places to cold places by convection. Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. Cooler liquid or gas then takes the place of the warmer areas which have risen higher. This results in a continous circulation pattern. Water boiling in a pan is a good example of these convection currents. Another good example of convection is in the atmosphere. The earth's surface is warmed by the sun, the warm air rises and cool air moves in.

 

RADIATION--

 

 

Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object as is the case with conduction and convection. Heat can be transmitted though empty space by thermal radiation often called infrared radiation. This is a type electromagnetic radiation . No mass is exchanged and no medium is required in the process of radiation. Examples of radiation is the heat from the sun, or heat released from the filament of a light bulb.

 

Heat transfer is the exchange of thermal energy between physical systems. The rate of heat transfer is dependent on the temperatures of the systems and the properties of the intervening medium through which the heat is transferred. The three fundamental modes of heat transfer are conduction, convection and radiation.

 

Hepa filter

 

 

HEPA stands for high-efficiency particulate air. A HEPA filter is a type of mechanical air filter; it works by forcing air through a fine mesh that traps harmful particles such as pollen, pet dander, dust mites, and tobacco smoke.

 

Selecting and Using an Air Filter

You can find HEPA filters in most air purifiers. These are small, portable units that may work for a single room. If you are considering buying a HEPA filter, find out how much air that the filter can clean. Be sure you buy one that is big enough for the room where you plan to use it.

The best room for a unit is the one where you spend most of your time -- usually your bedroom. You can find HEPA filters in most home improvement stores or online marketplaces.

Some vacuum cleaners have HEPA filters that trap more dust from their exhaust. HEPA-equipped vacuums throw less dirt and fewer microscopic dust mites back into the room as you vacuum. Some people say allergy symptoms improve after using these vacuums.

 

How Much Can HEPA Filters Help?

 

Using a HEPA filter in your home can remove most airborne particles that might make allergies worse. But the particles suspended in air are not the only ones in your home. There are far more in your rugs, bedding, and drapes, and resting on countertops and tabletops. So it's important to keep these areas clean. It's also important, when possible, to get rid of the source of allergens and irritants. For example, the only effective way to keep tobacco smoke out of your home is to not smoke.

These filters can be part of a plan to remove irritating particles from your home. Other parts of that strategy should be to:

 

Vacuum frequently.

Replace carpets with wood, tile, or vinyl flooring.

Keep pets outdoors if you are allergic to pet dander or at least away from your sleeping area.

Change bedding frequently and wash sheets in hot water.

Replace draperies and curtains with roll up shades.

Use plastic covers over mattresses and pillows.

Use high-efficiency furnace filters.

 

 

Hermetic compressor:

 

 

A hermetic or sealed compressor is one in which both compressor and motor are confined in a single outer welded steel shell. The motor and compressor are directly coupled on the same shaft, with the motor inside the refrigeration circuit. Thus the need for a shaft seal with the consequent refrigerant leakage problem was eliminated. All the refrigerant pipeline connections to the outer steel shell are by welding or brazing. The electrical conductors to the motor are taken out of the steel shell by sealed terminals made of fused glass. The figure below shows the cut-away view of a hermetic compressor. One can see the cooper windings inside the outer shell and also the refrigerant conections (copper pipes). Hermetic compressors are ideal for small refrigeration systems, where continuous maintenance (replenishing refrigerant and oil charge etc) cannot be ensured. Hence they are widely used in domestic refrigerators, room air conditioners etc. Since, the motor is in the refrigerant circuit, the efficiency of hermetic compressor based systems is lower as the heat dissipated by the motor and compressor becomes a part of the system load. Also material compatibility between the electrical windings, refrigerant and oil must be ensured. Since the complete system is kept in a welded steel shell, the hermetic compressors are not meant for servicing. A variation of hermetic compressor is a semi-hermetic compressor, in which the bolted construction offers limited serviceability.

 

The hermetically sealed reciprocating compressor is widely used for the refrigeration and air conditioning applications. You can find it in all the household refrigerators, deep freezers, window air conditioners, split air conditioners, most of the packaged air conditioners.

Hermetically Sealed Refrigeration Compressors

The hermetically sealed reciprocating compressor is widely used for the refrigeration and air conditioning applications. In all the household refrigerators, deep freezers, window air conditioners, split air conditioners, most of the packaged air conditioners, the hermetically sealed reciprocating compressor is used. The hermetically sealed reciprocating compressor is very easy to handle, and requires low maintenance. They are used with motor power requirements from 1/20 to 71/2 hp.

 

 

Construction of the Hermetically Sealed Reciprocating Compressor

In hermetically sealed compressor, in one side of the enclosed casing the various parts of the compressor like cylinder, piston, connecting rod and the crankshaft are located. If it is a multi-cylinder compressor, there are more than two cylinders inside the casing. On the other side of the casing is the electric winding inside which the shaft of the motor rotates. This motor can be single speed or multi-speed motor. In hermetically sealed compressors the crankshaft of the reciprocating compressor and the rotating shaft of the motor are common. The rotating shaft of the motor extends beyond the motor and forms the crankshaft of the hermetically sealed reciprocating compressor.

 

All these parts of the hermetically sealed compressor are assembled and enclosed in a strong and rigid casing made up of welded steel shell. The steel shell comprises of two half rounded steel bodies that are welded together to form the casing for the hermetically sealed compressor. In some cases the two halves of the shell can be bolted together instead of welding, which permits easy opening of the casing in case of compressor burnout.

 

The hermetically sealed compressors have inbuilt lubrication system for the lubrication of the piston and cylinder and crankshaft. The lubricant also acts the coolant for the piston and cylinder. Additionally, the cool suction refrigerant also offers cooling effect.

 

Externally, the casing has refrigerant suction and discharge connections that are connected to the evaporator and condenser respectively. There is also socket for the electrical connection.

The typical condenser unit with the hermetically sealed compressor ,Such condenser units are called as hermetic condenser units.

 

One of the most popular types of the hermetically sealed compressors are the reciprocating compressors. They were the first to be used as the hermetically sealed compressors are still being used widely. These days the vane type of rotary compressor has become more popular. It is considered that the rotary type of hermetically sealed compressor consumes less electricity, makes lesser noise, requires lesser maintenance, and is cheaper than the reciprocating type of hermetically sealed compressor. This is because the rotary compressors has less frictional parts and have only a rotor. The centrifugal types of hermetically sealed compressor are used for the large units.

 

In hermetically sealed compressor, in one side of the enclosed casing the various parts of the compressor like cylinder, piston, connecting rod and the crankshaft are located. If it is a multi-cylinder compressor, there are more than two cylinders inside the casing. On the other side of the casing is the electric winding inside which the shaft of the motor rotates. This motor can be single speed or multi-speed motor. In hermetically sealed compressors the crankshaft of the reciprocating compressor and the rotating shaft of the motor are common. The rotating shaft of the motor extends beyond the motor and forms the crankshaft of the hermetically sealed reciprocating compressor.

 

The hermetically sealed compressors are used widely in the refrigeration and air conditioning applications because of several advantages, here are some of them:

 

1) The hermetically compressors can be moved easily from one place to the other place, they are highly portable. One does not have to disassemble the compressor from the motor and no coupling, belt and pulley arrangement is involved.

 

2) The whole condenser unit of the refrigeration or the air conditioning unit comprising of the condenser and the compressor can be moved easily from one place to the other. Its location can be changed easily.

 

3) Since no coupling, belt or pulley is involved, the maintenance is lesser.

 

4) The lubrication system of the hermetically sealed compressor is inherent and no external lubrication is required, unless the fresh gas charging is done.

 

5) The installation of the hermetically sealed compressor is very easy. The suction and discharge connections and the electrical connections are available externally.

 

6) Hermetically sealed compressors have very long life, the companies offer warranty period of up to seven years for these compressors.

 

Apart from the many advantages the hermetically sealed compressor has some disadvantages, as mentioned below:

 

1) When the motor winding of the hermetically sealed compressor burns, the whole compressor has to be replaced. In such cases though the company gives some compensation for the old damaged compressor, still it’s a costly affair to replace the whole compressor of your household refrigerator or air conditioner. Not only you will have to replace the compressor, but fresh gas charging has to be done. In open type of compressor, if the motor winding burns, merely the winding has to be changed.

 

2) If any parts of the compressor like the cylinder, piston etc, gets damaged, again the whole hermetically sealed compressor has to be replaced and then one has to do fresh gas charging. In open type of compressor one can easily replace various parts of the compressor.

 

The various advantages offered by the hermetically sealed compressor outdo a few disadvantages that they offer. It is due to this reason that they are used so extensively in household refrigerators and wide variety of air conditioners. In fact the open type of compressors just can't replace the hermetically sealed compressors. The companies have made mechanism offering long warranty periods for hermetically sealed compressor and their easier replacement in case of damages.

 

hermetic systems

 

 

The Difference Between a Hermetically Sealed, Open, or Semi-Hermetic Gas Compressor

Basically, a hermetic seal is one that is airtight. It is a common designator for systems that deal with gas compression and transmission. In such systems, hermeticity is a level specified for a particular test method under specific conditions of usage. In compressors for refrigeration systems, the type of hermeticity is also described by the logistics of the system, in other words, the relationship of the compressor and motor drive in relation to the vapor or gas that is being compressed.

 

Industry Designations

 

Industry designates the various compression schemes as hermetically sealed or as semi-hermetic. In all cases of hermetic and most cases of semi-hermetic, the motor and compressor comprise an integrated unit, and operate within the pressurized gas environment of the system. In this way, the compressor unit and the gas form a symbiotic relationship. The unit compresses the gas and the gas cools the unit.

 

Semi Versus Full Hermetic Seals

 

 

The difference between semi-hermetic and hermetic compressors is that the latter is manufactured in a one-piece welded steel casing that is never intended to be opened. That means that any parts that fail within the compressor require that the entire compressor be replaced. In contrast, semi-hermetic compressors can be opened for repair. The main advantage of both types of compressors is that neither offers a leakage path for gas to escape to the outside world.

 

Open Compressors

 

The main advantage of open compressors is that they can be driven by sources other than electricity, such as a turbine or an internal combustion engine. However, they are susceptible to leakage over time, particularly as the seals begin to age and degrade. Seals are often a thermoplastic material, which must be kept lubricated in order to maintain the seal’s effectiveness. At regular intervals, these seals must be replaced. For this reason, an important part of compressor maintenance is a schedule that alerts technicians to replace the compressor seals. In this case, it behooves the technicians to have a ready source of 100% OEM compatible seals ready for installation,

 

 

Hidden heat

Converting states of matter from one form into another requires the involvement of heat energy. For example, converting water at 100°C into steam at 100°C requires the input of 2260 kJ per kg of water, whereas to convert 1 kg of ice at 0°C into water at 0°C involves the input of 334 kJ.

 

This ‘hidden heat’ (so called because, as the change occurs, there is no change in temperature) is referred to as ‘latent heat’.

 

Note that the change liquid → gas requires far more energy than the change solid → liquid, because the liquid particles have to be given sufficient energy to completely break free from one another to get into the gaseous state. In the change solid → liquid, the particles are freed from fixed positions into a more mobile arrangement, allowing for movement in between and over one another.

 

Latent heat of vaporisation

 

 

The heat energy needed to convert a liquid at its boiling point to a gas at the same temperature is referred to as latent heat of vaporisation.

The reverse process – latent heat of condensation – results in an expulsion of heat energy from the system.

The amount of latent heat of vaporisation for any given liquid is dependent on two main factors:

The molecular/atomic structure of the liquid.

The mass of the liquid undergoing the change

Water has a very high value. This is because attractive forces between the water molecules in the liquid state, known as hydrogen bonds, need to be overcome to release the molecules into the gaseous state.

 

Making use of latent heat

 

The liquid to gas/gas to liquid cycle has been extensively studied from the scientific energy in/energy out perspective. The technological outcome of this has been the development of highly efficient heating and cooling systems both in the industrial and household settings.

 

Fridge and freezer design has the evaporator component on the inside of the cabinet with the condenser component on the outside. This arrangement allows the inside cabinet area to be cooled, with heat from the condenser escaping to the surrounding air on the outside.

 

Heat pumps operate in the same way but the design is such that the unit can either heat or cool room air depending on the setting.

 

The working fluid used for most household fridges, freezers and heat pumps nowadays is tetrafluoroethane. It has replaced chlorofluorocarbons (CFCs) because of the harm these chemicals were doing to the ozone layer in the upper atmosphere.

Tetrafluoroethane has a relatively low latent heat of vaporisation and low boiling point, but its chemical inertness and low toxicity make it an ideal working fluid. In the industrial setting, ammonia and propane are often used as the working fluids.

 

high pressure control

 

 

A high pressure switch (HPS) and a low pressure switch (LPS) are protective devices for the compressor and refrigeration circuit. The high pressure switch monitors the system for an inoperative outdoor motor, and/or a dirty/restricted condenser (outdoor) coil. The low pressure switch monitors the refrigeration system for a loss of refrigerant charge, and may also be helpful in stopping the evaporator (indoor) coil from freezing up due to a dirty filter or low airflow over the coil. I say "may" because the low pressure switch cut-out setting could be set too low (15-20 lbs.) to be of any help. An evaporator coil could start to form ice at 30 lbs. low pressure charge.

 

If either one of these switches trip, the HVAC unit will shut down. The control needs to be reset to resume operation. Some switches are reset only from inside the HVAC unit. Others may be reset from the thermostat by turning the thermostat subbase "system" switch off, and back on again, or by doing the same to the HVAC unit's main panel circuit breaker.

 

A low ambient control (LAC) is useful when high internal heat loads dictate operation in the cooling mode during colder outdoor temperatures. Examples of this would be in an electrical equipment room, telecommunications building, a restaurant, or in loaded computer room applications. Extended operation of the compressor in the cooling mode when the outdoor temperature is less than 65?F can cause the indoor coil to freeze up. The low ambient control cycles the outdoor fan motor in response to refrigerant pressure and conditions. This keeps the system pressures from reaching the condition where icing would occur. Because the outdoor fan "cycles," it may appear to the end user that the condenser motor is defective. Although, this is not the case, an uninformed end user observing a low ambient control in operation could initiate a service call not covered by a first year labor warranty.

 

A time delay relay (TDR) protects the system against short cycling of the compressor from power interruption, and thermostat problems (due to vibrations, door slamming, or quick "putzing" adjustments by the user). The time delay relay is usually set for a 5 minute delay after the last time the compressor was energized. This device is useful in temporary mobile offices with mercury bulb thermo-stats. It protects the compressor contactor from chattering.

 

A dirty-filter switch is used to determine when the HVAC unit filter needs changing. It is a simple device that senses a pressure differential across the filter. From a dry set of contacts, it can turn on a light, or even cut the 24 volt power to the stat, shutting the unit off. The dirty-filter switch is manually reset from inside the HVAC unit when the filter is changed.

 

Start kits or start assist devices are used to help start a single phase compressor with tight bearings, or with a lower than (normal) 230 volt power supply to the compressor. A start kit includes a start capacitor and a potential relay specific to the single phase compressor in the application. A start assist device is all-in-one and is more popular with the service contractors. Some contractors feel a start assist does not provide the same boost as a start kit, but a start assist device usually gets the job done. A start kit is not meant to substitute for providing the proper voltage to the compressor.

 

If low main power voltage is your problem, first try to boost or improve the power supply to the building. If it can not be improved, a buck/boost transformer should be added to boost the power to the proper level required by the HVAC unit. Adding a buck/boost transformer requires monitoring of the buildings movement from one site to another. The first location may have low voltage, and the next location may not. The transformer boost of the next location may be above the operating range of the HVAC unit, and the buck/boost transformer will need to be removed from the electrical circuit.

 

Some units have compressor control circuit boards with a time delay relay for short cycling protection. They provide for one retry after the high or low pressure switch trips. This is to insure a condition was not a fluke before shutting the HVAC unit down. Most compressor control circuit boards can be reset inside the building by cycling either the thermostat's system switch or the HVAC unit's main panel circuit breaker to off, and then back on.

 

Phase monitors are used on three phase HVAC units to protect "scroll" compressors from running back-wards, and eventually seizing up. Running a scroll compressor backwards for more than an hour will pump the oil out of the bottom bearing. An hour is not a very long amount of time, especially when the set up crew does not know to turn off the HVAC unit prior to applying initial power.

 

 

Last is the brown out control. It prevents the HVAC unit from starting if the high voltage is not within the operating range of the system (usually 197-253 volts for 230 volt power supply). This control is very useful on mobile offices that continually change locations, because the available local voltage may vary from site to site. When the voltage is not within +10% of the selected voltage, the end user may only know their HVAC unit is not working, not that the voltage to the HVAC unit is too low or too high. While a brown out control would not prevent an HVAC service call, it does protect your asset from abuse. Payment for the HVAC service call then becomes the responsibility of the end user. Include such provision in your lease contracts.

 

 

Every optional control has a purpose, and therefore no one control can be recommended over the rest. From time to time, I am asked just which optional controls would be the best, and at the same time be somewhat cost effective. The "cost effective" part is fairly relative and philosophical. If a control can save the compressor from a burn out, a dirty filter from icing the coil, or a low voltage service call, how much is it worth? In other words, if a $ 50-0 control saves a $ 500-900 service call, can your company afford to put that control on every HVAC unit?

 

Mechanically speaking you should include all of the above items to protect the unit and yourself from problems. That wasn't the question, however. Financially, I would suggest a high and low pressure switch, a compressor control circuit board, and a two inch pleated filter. Then add the other devices as needed for the specific resolution desired. If your site continually has low voltage, add a brown out control. If your three phase HVAC units have scroll compressors, add a phase monitor. If most of your customers are telecommunication shelter users, add a low ambient control, etc.

 

high side

 

 

The basic manifold gauge set

The basic manifold gauge set usually has three hoses. Two hose will be attached to the service ports on the vehicle during service. Each hose has its own identifying color. In most cases, the hose intended for the low pressure service port is blue, and the hose intended for the high pressure service port is red. The middle hose should be yellow. That yellow hose will be attached to the refrigerant cylinder while charging or the vacuum pump when the system is being evacuated of air and moisture. Your manifold gauge set should have a corresponding gauge and control knob for each of the two service hoses. Like the color of the hose, the gauges and control knobs will usually be colored to indicate high or low pressure.

 

What are all the numbers on the high and low side gauge,

 

 

The low side pressure gauge is called a compound gauge. That means it can be used to measure pressure or vacuum. The numbers around the outside of this gauge indicate pressure in pounds per square inch (PSIG), and the numbers near the bottom indicate vacuum in inches of mercury. The smaller scales near the middle of the gauge list the temperature relationship of different refrigerants. The gauges pictured here lists the temperature of R12, R22, and R502. Regardless of which refrigerant is being used, the scale designated as PSI is the one used to read system pressures when charging and diagnosing an a/c system. The working pressure of this gauge is from 0 to 120 PSI.

 The red, high side gauge is used to measure the high pressure side of the a/c system. This gauge has no markings that indicate vacuum. It reads positive pressure only. The working pressure of this gauge is also much higher than the low side gauge.  Notice the scale on this high side gauge reads from 0 to 500 PSI

 

I hooked up the service hoses with the car turned off. Both gauges show pressure. What does this mean?

The pressure readings you see when the a/c system is not operating is called static pressure. When the system is off, and temperature is stable, the pressure you see on both the high and low side gauges should be the same, or very close.  Both the high and low side of the system have equalized.

 

What static pressure should I expect to see when I hook up my gauge set.

Each refrigerant has it's own static pressure at every corresponding degree in temperature. The important thing to keep in mind is static pressure changes based on temperature. Any change of temperature brings with it a change of pressure. The greater the temperature, the greater the pressure. You can use a refrigerant pressure chart to find static pressures at various temperatures. Static pressure will not be used to determine if a system is fully charged. Using the chart below, if the R-134a system has a static pressure of 88 psi at 80 degrees F., we can then assume the system has some amount of liquid refrigerant. The system may be full -or - may not be. At the same temperature, if the system showed only 75 psi, we could say with confidence, the system is low. This is because static pressures shown on a temperature chart would show inadequate pressure for the presence of any liquid refrigerant.

 

Can I tell if the system is full with a static pressure reading?

No. We might determine if there is liquid refrigerant in the system, but we won't be able to tell how much liquid it contains. For example, a thirty pound can of refrigerant will show the same pressure whether it has thirty pounds in it or if it only has 1 ounce. With static pressure, you will only know if the system has some amount of liquid refrigerant present.

 

What good is a static pressure reading then?

With our initial pressure reading, we can tell if the system has enough pressure to satisfy the low pressure switch and enable the compressor to operate. Static pressure is used to determine if a jug of refrigerant is contaminated with air. Static pressure can also be used to determine if a system has enough pressure to begin leak testing. Your static pressure should be no lower than 50 psi when leak testing.

 What's the minimum static pressure I need for the compressor to operate?

Most systems will have a low pressure cut off switch that turns the system off at approximately 20 psi. The compressor will not function again until the pressure reaches approximately 45 psi. So, In most cases, you will need a static pressure of at least 45 psi before you begin to see the compressor operate.

You can begin testing with only 45 psi. You won't get any cold air, but you should should start to see some compressor engagement. As soon as the compressor engages, it will cycle off rather quickly when the suction side of the compressor draws the pressure on the low side below 20 psi.. You will see the low side gauge at 45 psi, drop quickly to 20 psi, at which point the compressor will cycle off. Then the low side gauge will climb back up to 45 psi as the high and low side equalize. At this point, he compressor will kick back on and the cycle will repeat itself. This is called short cycling. This rapid cycling of the compressor is a good indication that the system is low of refrigerant.

 

When charging, what should my low and high side pressure be?

Ah, this is the most asked question there is. There is no magic answer for this question though. There are too many variables. Compressor (engine) RPM and airflow across the condenser are always changing, thus engine speed is always affecting pressure. System design, blower speed, mode setting, refrigerant type, all cause variance in high and low side pressure. For this reason we simply can't say 30 on the low side and 200 on the high side. Though I might add, that's about where you'll usually end up. The reason 30 psi on the low side is just about right is because that translates into an evaporator temperature somewhere around the freezing point of water. Look at your low side R12 gauge and you'll see a temperature scale right next to your pressure scale. That low side pressure translates into evaporator temperature. Since moisture collects on the evaporator, we would like to keep the evaporator temperature slightly above the freezing point. R134a low side pressure will be be slightly lower (27 PSI) at this temperature. Again, refrigerant type is one of those variables we have to consider.

 

What should the high side pressure be?

 

 

With R12 systems, high side pressure is usually 1.8 to 2.1 times ambient temperature. That means on an 80 degree day, with moderate humidity, we would expect to see between 144 to 168 PSI on the high side. On hot humid days (with R12), you could say ambient temperature plus 100 PSI., and be pretty close.

With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On that same 80 degree day we would see between 176 and 200 PSI on the high side of an R134a system. The system operates in a specific range based on outside ambient temperature. High side pressure has a broad range relative to temperature because of heat load on the evaporator, humudity, airflow across the condenser, and engine speed.

 

Can I test the system with only 45 psi?

 

 

You can begin testing with only 45 psi. You won't get any cold air, but you should should start to see some compressor engagement. As soon as the compressor engages, it will cycle off rather quickly when the suction side of the compressor draws the pressure on the low side below 20 psi.. You will see the low side gauge at 45 psi, drop quickly to 20 psi, at which point the compressor will cycle off. Then the low side gauge will climb back up to 45 psi as the high and low side equalize. At this point, he compressor will kick back on and the cycle will repeat itself. This is called short cycling. This rapid cycling of the compressor is a good indication that the system is low of refrigerant.

 

When charging, what should my low and high side pressure be?

 

Ah, this is the most asked question there is. There is no magic answer for this question though. There are too many variables. Compressor (engine) RPM and airflow across the condenser are always changing, thus engine speed is always affecting pressure. System design, blower speed, mode setting, refrigerant type, all cause variance in high and low side pressure. For this reason we simply can't say 30 on the low side and 200 on the high side. Though I might add, that's about where you'll usually end up. The reason 30 psi on the low side is just about right is because that translates into an evaporator temperature somewhere around the freezing point of water. Look at your low side R12 gauge and you'll see a temperature scale right next to your pressure scale. That low side pressure translates into evaporator temperature. Since moisture collects on the evaporator, we would like to keep the evaporator temperature slightly above the freezing point. R134a low side pressure will be be slightly lower (27 PSI) at this temperature. Again, refrigerant type is one of those variables we have to consider.

 

 

 

 

 

With R12 systems, high side pressure is usually 1.8 to 2.1 times ambient temperature. That means on an 80 degree day, with moderate humidity, we would expect to see between 144 to 168 PSI on the high side. On hot humid days (with R12), you could say ambient temperature plus 100 PSI., and be pretty close.

With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On that same 80 degree day we would see between 176 and 200 PSI on the high side of an R134a system. The system operates in a specific range based on outside ambient temperature. High side pressure has a broad range relative to temperature because of heat load on the evaporator, humudity, airflow across the condenser, and engine speed.

 

Should I test with doors open or closed, high idle, blower on high or low?

 

We like to test with the system in MAX position on high blower with doors closed. Windows can be open. MAX (recirculate) mode is preferred since we'll need to have the hood up while charging and testing. In fresh air mode, hot engine heat can be drawn into the fresh air cowl under the wiper blades. Same reason we would like to test with doors closed. We would like to keep engine and exhaust heat from causing abnormal heat load on the evaporator. We're not bothered by having the windows down, since this helps create a typical and stable heat load. And it's easy to reach in and feel how cold the vent temps are getting.

Testing should be done with blower speed on high. Low blower speed will reduce heat load on the evaporator to the point where compressor cycling can occur. We want nice stable conditions when testing. When needed, low blower speed can be used to force low side pressure down during testing and adjustment of compressor cut-out pressure.

 

If 30 PSI is a good low side pressure, then why isn't the system cooling?

 

 

Well, there are a couple reasons, but let's look at the most common.  Let's take the fixed orifice tube system for example.  You can have a system evaporator pressure of 30 psi, and still be low on refrigerant. Let's assume that only half the evaporator is full of boiling, heat removing, liquid refrigerant. Only half the air traveling through the coil is being cooled. Pressure readings indicate core temperature is near thirty degrees, but half the core isn't removing any heat. The system is close to being full, but that  discharge air is only slightly cool.  On the fixed orifice tube system, most people will charge until the inlet of the evaporator, and the outlet of the evaporator are within a degree or two of each other.  That indicates the quantity of refrigerant is enough that the entire coil is being used.  At this point, the boiling liquid will spill into the accumulator, thus the outlet tube will be very cold.  If the system has a TXV or H block, you will not be able to charge by feeling the evaporator outlet tube like we can on a FOT system.  The TXV is very efficient and is designed to tightly control liquid refrigerant from spilling out of the evaporator.  The area we would measure is in the evaporator box, and not accessible for this purpose. 

Secondly, who says the system isn't working.  You need to consider the chance of a blend door problem. Just because cold air isn't coming from the vent doesn't mean the system isn't working. I've seen cars with sweat rolling off the accumulator and low pressure line to the compressor, and the technician is under the hood scratching his head because no cold air is coming from the vents. If the low side lines are obviously cold, and pressures are within range, we should think about looking inside the vehicle for the problem.

 

How can I tell if the compressor is bad?

 

 

Usually the compressor will show the inability to generate enough suction and pressure at or near idle speeds.

If engine speed needs to be substantially increased to bring pressures in range, that's a sign that the compressor is getting weak.  Often the complaint is... only cools when the engine is reved - or - only cools when driving down the road.

Sometimes it's very simple.  If we hook the gauges up and see 80 psi on the low side, and 80 psi on the high side, and the compressor hub is spinning, it's likely that compressor is done.  It's not producing suction, and it's not producing pressure.  We could add or remove refrigerant and still nothing would happen. The compressor must be able to pull a vacuum, and create pressure.  Compressors that use a variable stroke are often misdiagnosed as being defective, when only the internal pressure control device is at fault.

 

How can I tell if the orifice tube is clogged?

 

 

A restricted orifice will usually show as very low suction side pressure and lower than normal high side pressure.  When the compressor kicks in, the suction against the restricted orifice will cause the compressor to quickly cycle out.  After compressor disengagement, the rise in suction side pressure will usually be very slow.   Rapid compressor disengagement and slow engagement may indicate a clogged orifice.   A clogged orifice tube will starve a compressor of oil.

 

How can I tell if the expansion valve is bad?

 

 

This has to be our least favorite item to diagnose.  We've had expansion valves quit working while on the road and show no signs of problem back in the shop.  What's worse, an expansion valve can stick closed, stick open, or hang somehwere in between.

Of all the bad expansion valves seen over the years, I think those that stick closed are most common.  Those are the easy ones.  Gauges will show very low suction side pressure along with lower than normal high side pressure.  The low side may even draw into a vacuum. That's a big clue.  Those that appear to be stuck closed may have inlet screens clogged with ground up desiccant particles.  This will look like beach sand packed into the inlet.

It's common for a defective expansion valve to stick closed, however, the expansion valve can also stick open.  This is indicated by higher than normal low side pressure, and slightly higher than normal high side pressure.  To some, this might appear as a weak compressor or slightly overcharged system.

 

high temperature refrigeration

What Causes High Compressor Discharge Temperature

 

 

The compressor's discharge temperature is often an overlooked temperature when troubleshooting a refrigeration or air conditioning system. However, it is very important because it's an indication of the amount of heat absorbed in the evaporator and suction line, and any heat of compression generated by the compression process.

Because the compressor's discharge temperature is superheated, a pressure-temperature relationship does not exist and it must be read directly on the discharge line by some sort of temperature-measuring device.

 

The compressor's discharge temperature should be measured about 1 to 2 inches away from the compressor on the discharge line. This discharge temperature should never exceed 225°F. Carbonization and oil breakdown can occur if compressor discharge temperatures exceed 225°.

 

 

The three causes for high discharge temperatures are:

 

High condensing temperature.

Low evaporator pressures and temperatures.

High compression ratios.

 

HIGH CONDENSING TEMPERATURE

 

 

There are many potential causes of high compressor discharge temperatures. A high condensing temperature is one of them.

When the condensing temperature is high, the compressor must compress the refrigerant from the low-side (evaporating) pressure to an elevated high-side (condensing) pressure. This added work done by the compressor would raise the heat of compression. Thus, the compressor's discharge temperature will be higher.

 

Remember, condensing temperature is the temperature the refrigerant is as it changes from a vapor to a liquid in the condenser. There is a pressure-temperature relationship with the condensing temperature because of the phase change. A gauge reading on the high side of the system is all that is needed to find the condensing temperature. Convert this pressure to a temperature using a pressure-temperature chart. This is the condensing temperature.

 

However, there are many causes for high condensing temperatures, which will also cause high discharge temperatures; high condensing temperatures cause high compressor discharge temperatures. Listed below are causes for high condensing temperatures:

 

 

Dirty condenser.

High ambient temperature.

Noncondensable (air) in the system.

Condenser fan out.

Restricted airflow over condenser.

Refrigerant overcharge.

Wrong refrigerant.

High heat load on evaporator.

 

LOW EVAPORATOR PRESSURES AND TEMPS

Low evaporator pressures also may cause a high compressor discharge temperature. When evaporator pressures are low, the compressor must compress refrigerant from this lower evaporator pressure to the condensing temperature. This added work of compression would make the heat of compression higher. Thus, the compressor's discharge temperature will be higher.

Remember, evaporator temperatures are the temperature of the refrigerant as it changes from a liquid to a vapor in the evaporator. There is a pressure-temperature relationship with the evaporating temperature because of the phase change.

 

A gauge reading on the low side of the refrigeration system is all that is needed to find the evaporating temperature. Convert this pressure to a temperature using a pressure-temperature chart. This will be the evaporating temperature.

 

However, there are many causes for low evaporating pressures and temperatures, which will also cause high compressor discharge temperatures, since low evaporating pressures cause high compressor discharge temperatures. Listed below are causes of low evaporator pressures:

 

1 Dirty evaporator coil.

2 Iced up evaporator coil.

3 Evaporator fan motor out.

4 Shortage of airflow over the evaporator.

5 Frosted evaporator coil from high humidity.

6 Frosted evaporator coil from a bad defrost heater or other defrost component malfunction.

7 Low heat load on the evaporator coil.

8 Defrost intervals set too far apart on the time clock.

9 Undercharge of refrigerant.

10 End of the running cycle.

11 Partially plugged filter-drier.

12 Compressor inlet screen partially plugged.

13 Restricted liquid line.

14 Wrong refrigerant.

15 Metering device starving.

 

High compression ratios are a result of high condensing pressures or low evaporator pressures, or both. So, any time there are high condensing pressures or low evaporator pressures, or both, there will be high compression ratios. And, anytime there is a high compression ratio either from high condensing or low evaporator pressures, or both, there will be more work added to the compression stroke of the compressor. This will cause the heat of compression to increase and the compressor will have a higher discharge temperature.

Compression ratio is defined as the absolute discharge pressure divided by the absolute suction pressure. Discharge pressure and condensing pressure are one in the same and will be used interchangeably throughout this article. The same holds true for suction pressure and evaporating pressure.

 

Compression ratio = Absolute discharge pressure ÷ Absolute suction pressure

 

A compression ratio of 8 to 1 (expressed as 8:1) simply means that the discharge pressure is 8 times the magnitude of the suction pressure.

 

Again, a compression ratio of 12.3:1 simply indicates to the technician that the "absolute" or true discharge pressure is 12.3 times as great as the absolute suction pressure.

 

The volumetric efficiency is expressed as a percentage from 0 percent to 100 percent. Volumetric efficiency is defined as the ratio of the actual volume of the refrigerant gas pumped by the compressor to the volume displaced by the compressor pistons. A high volumetric efficiency means that more of the piston's cylinder volume is being filled with new refrigerant from the suction line and not re-expanded clearance volume gases. The higher the volumetric efficiency, the greater the amount of new refrigerant that will be introduced into the cylinder with each down stroke of the piston, and thus more refrigerant will be circulated with each revolution of the crankshaft.

 

The system will now have better capacity and a higher efficiency. So, the lower the discharge pressure, the less re-expansion of discharge gases to suction pressure. Also, the higher the suction pressure, the less re-expansion of discharge gases, because of the discharge gases experiencing less re-expansion to the higher suction pressure and the suction valve will open sooner.

The compressor's volumetric efficiency depends mainly on system pressures. In fact, the farther apart the discharge pressure's magnitude is from the suction pressure's magnitude, the lower the volumetric efficiency is because of more re-expansion of discharge gases to the suction pressure before the suction valve opens. Compression ratio is the ratio that measures how many times greater the discharge pressure is than the suction pressure; in other words, their relative magnitudes. Remember, a compression ratio of 10:1 indicates that the discharge pressure is 10 times as great as the suction pressure, and a certain amount of re-expansion of vapors will occur in the cylinder before new suction gases will enter.

 

This is why lower compression ratios will cause higher volumetric efficiencies and lower discharge temperatures. So, keep those compression ratios as low as possible by keeping condensing pressures low and evaporator pressures high.

 

high vacuum pump

 

 

High vacuum pumps provide evacuation of chambers or systems into the high vacuum (10-3 to 10-8 torr) or ultra-high vacuum (<10-8 torr) range of pressure. Mechanical pumps and venturi generators operate in the medium to rough vacuum ranges.

 

As far as air-coolers are concerned, defrost is the “inevitable . The frost needs to be melted, or it will severely impact the performance of an aircooler, and eventually could totally block the air flow. There are several negative implications associated with hot gas defrost. Additional compressor energy is required to melt the frost/ice layers formed around the evaporator’s fins and tubes. At least, a part of this energy is transferred back to the refrigerated space or heats up the evaporator. It eventually needs to be removed during the cooling process. Finally, the time used for defrost is not used for cooling. This could be a very important factor in food processing plants, where defrost could significantly limit productivity levels. In addition, other important but less obvious consequences may undermine integrity such as the mechanical stress undergone by key components. A lot of failures found on valves and controls used around evaporators may be attributed to wrong valve configuration and or settings.

 

The main source of mechanical stress is the combination of high pressure coming from the condenser side, high discharge temperature and high pressure differential. When combined, those factors could be quite dangerous and even destructive. Today we also see that there is an increased number of companies using CO2 for low temperature plants, and quite often in combination with hot gas defrost. At the same time, the situation with CO2 in this case is even more complex than with ammonia, as the pressure level and pressure differentials are much higher. The complications of hot gas defrost with CO2 may have caused some customers to avoid this kind of defrost method and look for other alternatives, such as electrical or brine defrost.

 

Hot gas defrost is one of the most efficient ways to melt the frost formed on an evaporator (Pearson, 2006). As there is an increased focus on the reduction of energy consumption, performing a quick and efficient defrost is key to achieving overall energy consumption goals of the refrigeration system. In most cases, it would be also the most cost effective way when compared to e.g. brine defrost. This article focuses on valves and controls configurations that could be applied for such systems as well as the ways to optimize the process.

 

hot gas defrost

 

 

 Defrost Efficiency Considerations

There are a few studies targeting the understanding and improvement of hot gas efficiency of refrigeration systems. A number of the critical points could be summarized as follows:

 

1. Hot gas defrost pressure. A popular misconception is that the higher the defrost temperature, the better. In reality a number of studies indicate (Stoecker, 1983) that a source of lower pressure and temperature gas could obtain good results as well. There is most likely an optimal pressure / temperature (Hoffenbecker, 2005) that would achieve the highest efficiency.

 

2. Hot gas defrost time. In the industrial refrigeration, it is very typical to set up defrost based on a fixed time adjusted during the start-up of the installation. The problem with this approach is that in many cases this time would be on a “safe side” to ensure having a fully clean evaporator.

What happens in reality when the defrost is finished earlier, is that the efficiency of defrost significantly drops.

 

3. Another significant inefficiency during the hot gas defrost could be contributed to the vapour passing through the defrost pressure regulator. This vapour needs to be recompressed, and it also increases the requirement for the hot gas feed to the evaporator. The amount of vapour passing is depending of the type of defrost control in the condensate line. Pressure controlled or liquid level controlled.

 

4. The amount of energy used for melting the ice during the defrost is more than double (Stoeker, 1983, Hoffenbecker, 2005) of what is actually needed to melt the ice. The rest of the energy goes for heating the space, evaporator, tubing and the drip pan.

 

5. Finally, it should be mentioned that the ice is first melted on the coil, then the ice crashes in to a drain pan and then finally melts completely.

What is important here is that the process is sequential; with initially higher demand for defrost in the coil, and only later in the drain pan.

 

6. When the hot gas defrost is started, the initial refrigerant inrush might create a liquid hammer, especially if the evaporator still has some liquid refrigerant that has not been drained. This also occurs if the hot gas supply lines contains pockets of condensed liquid being propelled by the supplied hot gas pressure, and gas pockets to implode.

 

Let’s consider those issues in relation to the valves and controls used to control a hot gas defrost process.

 

presents a typical industrial refrigeration evaporator with hot gas defrost. Control valves for the evaporator could be divided in the 4 main groups:

 

1. Pumped liquid feed to the evaporator. This valve train typically includes stop valves, filter, a solenoid valve, a regulating valve, a check valve and a final stop valve.

 

2. Hot gas feed line. Traditionally it has a stop valve, a filter, another solenoid valve and a stop valve

 

3. Condensate line. Here we either see a pressure controlled valve or a float principle to drain the liquid. Both significantly different defrost principles

as we see later.

 

4. Wet return line. This line needs to have an automatic shut off valve and a stop valve.

 

The defrost process could be divided into 4 main sections. First, the liquid supply to the evaporator is shut off. Evaporator fans should still run for sometime, suction valve remains open in order to make sure that remaining liquid refrigerant will boil out. Second, the suction valve will be closed, evaporator fans will be stopped, the hot gas solenoid valve will be opened and the feed of the evaporator with the hot gas starts. Thirdly, when the defrost is finished, the hot gas solenoid valve will be closed, the suction valve will be opened. Finally, the liquid feed is opened again, water droplets on the evaporator fins are allowed to freeze , and only then the evaporator fans will be started again.

 

Critical considerations in the hot gas defrost process are avoiding pressure/temperature stresses and system inefficiency by managing a slow pressure built up in the cooler at the start of defrost and at the same time a slow pressure release from the cooler after the process. Both hot gas solenoid and main suction valve selection are critical when aiming for a safe and efficient defrost process.

 

 

Furnace hot surface ignitors are found on most modern furnaces to light the gas flames upon unit start-up. Electricity passes through the Silicon Carbide or the newer Silicon Nitride ignitor and makes it glow red hot. Operating under normal conditions a hot surface ignitor will last for 3 to 5 years (Silicone Nitride lasts about twice as long). During that time ignitors will eventually crack and need to be replaced. Like a light bulb, they are a regular replacement item. Most ignitors are interchangeable as long as they fit in the furnace space provided.

 

1.  Verify that all wire connections are secure from the furnace to the hot surface ignitor.

 

2.  Does the hot surface ignitor have any visible abnormal spots on it.? A burned hot surface ignitor will typically have a white or burned spot when it has failed. The below hot surface ignitor failed due to a "bad spot."

3. Does the hot surface ignitor glow when the furnace cycles?

 

4.  You will need a multimeter to check the power of the hot surface ignitor. Disconnect the plug going to the ignitor. Use your Multimeter to see if you have 115 volts. Make sure you do this on startup of Heating unit. After a minute or so it will be times out. Then you will have to shut the heating system off and then turn it back on again.

OR

A. You will need a multimeter to check the resistance of the hot surface ignitor.  A hot surface ignitor uses resistance just like a light bulb to glow hot in order to light the gas.  It typically has a life span of 2 to 3 years depending on the usage and the conditions of the furnace.  Set the multimeter so it can properly measure a resistance of 10 to 200 ohms.  Disconnect the hot surface ignitor from the control board and measure the resistance.  A good hot surface ignitor will have a resistance of 40 to 90 ohms.  Greater than 90 ohms indicates a failing or failed hot surface ignitor.

 

5.  If your hot surface ignitor is good, then you need to verify power from the control board or ignition controller.  Disconnect the hot surface ignitor and measure the voltage coming from the controller.  A good reading is 115 to 120 VAC.  If there is no voltage and the furnace is cycling for a call for heat, then the furnace control board or ignition controller needs to be replaced,

 

Standard Electric Water Heater

 

 

This section provides an overview of standard electric water heaters. The first part of this section has illustrations, photographs, and a brief description of each part. The second part of this section describes the operation of standard electric water heaters. When this section is completed, the reader should have a basic understanding of how a standard electric water heater transfers heat into water.

Element - The element consists of an inner wire surrounded by filler material enclosed in a sheath of copper or stainless steel. The thermostat allows electrical current to flow through the inner wire, and from the wire's resistance, creates heat, which is transferred through the filler material to the outer sheath and is then absorbed by the water. Elements may be available in different wattages, and materials, to meet specific heating requirements.

When installing a new electric water heater, or following draining the tank for maintenance purposes, the tank should be completely re-filled before applying power to the elements. Energizing a heating element that is not fully submerged in water is referred to as "dry firing," and will cause the element to immediately burn out.

Control Circuit - The standard single-phase control circuit consists of a high limit control switch with a reset button, upper thermostat, lower thermostat, two heating elements, and wires. The upper thermostat first sends electrical energy to the upper element until the water temperature in the upper third of the tank reaches the thermostat setting. Power is then transferred to the lower element until the remaining water reaches the lower thermostat setting. If the water temperature exceeds 170°F, the high limit control switch will trip, shutting off power to the elements. Single element water heaters have one element mounted at the bottom of the tank, controlled by a single thermostat and high limit switch.

 

Standard Electric Water Heater Operation

 

 

Electric water heaters operate by use of either one or two direct immersion heating elements, controlled by either thermostats or a microprocessor control module, which heat the water in the tank to the desired temperature. Many options exist, including the wattage/voltage of the elements, the type of material of which the elements are constructed, the amount of insulating foam surrounding the tank, in addition to the storage capacity of the tank.

The standard residential electric water heater control circuit consists of a manual reset high limit switch, an upper thermostat, lower thermostat, two heating elements, and wires.

When power is initially turned on to the unit, the upper element is energized and heats the water in the upper third of the tank,

When the upper third of the tank is heated to the temperature set on the upper thermostat, power is switched to the lower heating element. The lower element continues to heat until the water temperature in the lower portion of the tank is heated to the lower thermostat setting,As hot water is drawn from the top of the tank, the dip tube delivers cold water to the bottom of the tank ,

Eventually the cold water mixes with the hot, lowering the temperature to below the lower thermostat setting and the bottom element is energized. If enough water is drawn to cool the upper third of the tank, the upper thermostat will send power to the upper element first. When the upper third of the tank is heated, power will again be switched to the lower element ,

If the upper element burns out, the water heater will cease to function because the upper thermostat will never be satisfied and power will never be switched to the lower element.

If the water temperature in the tank reaches 170°F, the manual reset high limit switch will be tripped. This switch can be reset by firmly pushing the red button above the upper thermostat.

Single element water heaters have one element mounted at the bottom of the tank controlled by a single thermostat and high limit switch.

 

Humidifers

 

 

One of the less enthralling aspects of cold weather is dry indoor air. Interiors tend to be overheated, and humidity may drop as low as 10 percent. Adequate humidity is 25 percent to 50 percent, the range where people feel comfortable. Many people combat winter dryness with a humidifier. Here’s what a humidifier can do—not all of it good.

Adequate humidity can help prevent or alleviate dry skin, eyes and nasal passages. And since you feel warmer in warm humid air than in dry, you can keep your thermostat lower, which also helps prevent dry skin.

A humidifier can ease symptoms of a cold, sore throat or cough. Cold dry air dries mucus, making it harder to clear from your nasal passages. Moist air helps loosen it.

Whether proper humidity can prevent colds is hard to say. Some experts think that dry air irritates nasal passages, making you more susceptible to colds. People with asthma often find it more difficult to breathe dry cold air. However, very high humidity (over 60 percent) can provide a good environment for viruses and bacteria. And it promotes the growth of mold, which can cause allergies in sensitive people.

Most humidifiers are not regulated by the Food and Drug Administration (FDA), since they claim only to increase room comfort levels. However, devices that deliver medication via the vapor must be cleared by the FDA.

In spite of some recent design improvements, humidifiers are generally hard to keep clean. If not kept very clean, humidifiers can be a source of indoor air pollution, microbes and allergens. They may also emit minerals and other substances in the water. If your water contains contaminants, the humidifier will spray them into the air.

Other drawbacks: Using tap water in a humidifier is usually not a good idea, because the minerals in it may be dispersed in the air as white dust. Minerals may also appear as a crusty deposit inside the humidifier, which is a surface on which bacteria and mold can grow. One option is to use demineralized water. Some models come with demineralizing filters, but these have to be frequently changed and are expensive.

The cost of running them—anywhere from $30 to $85 a year—often exceeds their price.

They can be noisy.

 

Humidifier types and models

 

 

You can spend $20 on an inexpensive table model or up to $500 on a floor model (console). Here are the four general types of portable humidifiers:

Evaporative humidifiers: These are the most common kind. Water is absorbed by a wick filter and sent into the air by a fan. Some have a moving belt in a tank of water.

Steam humidifiers or vaporizers: Often the cheapest, they turn water into steam, thus killing microorganisms. They pose a risk of fire and scalding and thus are not recommended if you have small children or pets. The minerals from the water can clog the machines.

Cool-mist humidifiers or impellers: Water is pumped upward from a tank and “impelled” against fan blades, which disperse it in the air.

Ultrasonic humidifiers: These use high-frequency vibrations to turn water into mist.

 

Keeping your humidifier clean

Before you use your unit for the first time, clean it. Afterward, never put it away without cleaning it. Follow the manufacturer’s instructions. Here are some guidelines:

For humidifiers under 5 gallon capacity: Clean every day—that is, empty the tank, wipe dry, and refill. Sanitize every seven days, as follows: empty and refill with a solution of bleach (1 teaspoon of bleach to 1 gallon of water). Soak for 20 minutes and rinse. Brush away mineral deposits and rinse again with a 50 percent solution of vinegar.

For humidifiers over 5 gallon capacity:Empty every day and refill with clean water. Every third day, clean surfaces with hydrogen peroxide or vinegar (to kill molds). Every two weeks, sanitize with bleach, following the instructions above.

Though some newer models claim to have antibacterial features, microbes can still grow, and you still need to clean the humidifier regularly.

And keep in mind

Your humidifier will do a better job if your house is well insulated and has a vapor shield (that’s an impermeable layer on the inner side of the insulation).

If somebody in your home is allergic to mold or dust mites or has asthma, talk to your doctor before using a humidifier.

When you’re not using the humidifier, leave it clean and empty.

To make sure that the machine is doing a good job and not making the air too humid, buy a hygrometer, which measures moisture in the air. A digital wireless model costs about $20. Many humidifiers now come with a built-in hygrometer, called a humidistat, that automatically switches the machine on and off. But these are not always accurate or reliable.

If you have forced-air heat in your home, you can add a humidifying unit to the system to humidify the whole house. These do not pollute the air and are almost maintenance-free— you may have to change the filter occasionally. Central units may cost $300 or more, plus installation, but are inexpensive to run.

 

An electronic device analogous to a thermostat but which responds to relative humidity, not temperature. Humidistats are used in a number of devices including dehumidifiers, humidifiers, and microwave ovens. In humidifiers and dehumidifiers the humidistat is used where constant relative humidity conditions need to be maintained such as a refrigerator, greenhouse, or climate controlled warehouse. When adjusting the controls in these applications the humidistat would be what is being set. In microwaves they are used in conjunction with "smart cooking" 1-button features such as those for microwave popcorn. Humidistats employ hygrometers but are not the same. A humidistat has the functionality of a switch and is not just a measuring instrument like a hygrometer is.

For Heating Ventilating and Air Conditioning (HVAC) of buildings, humidistats or humidity sensors are used to sense the air relative humidity in the controlled space and turn on and off the HVAC equipment,

 

 humidity

 

 

Humidity is the amount of water vapor in the air. Water vapor is the gaseous state of water and is invisible.Humidity indicates the likelihood of precipitation, dew, or fog. Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table or humidex. The amount of water vapor that is needed to achieve saturation increases as the temperature increases. As the temperature of a parcel of air becomes lower it will eventually reach the point of saturation without adding or losing water mass. The differences in the amount of water vapor in a parcel of air can be quite large, for example; A parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30 °C, but only 8 grams of water per cubic meter of air at 8 °C

 

There are three main measurements of humidity: absolute, relative and specific. Absolute humidity is the water content of air at a given temperature expressed in gram per cubic meter.Relative humidity, expressed as a percent, measures the current absolute humidity relative to the maximum (highest point) for that temperature. Specific humidity is a ratio of the water vapor content of the mixture to the total air content on a mass basis.

 

 

                                                            new content chapter 10

ignition

 

 

An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark ignition internal combustion engines is in petrol road vehicles: cars (autos), four-by fours (SUVs), pickups, vans, trucks, buses.

 

Compression ignition Diesel engines ignite the fuel-air mixture by the heat of compression and do not need a spark. They usually have glowplugs that preheat the combustion chamber to allow starting in cold weather. Other engines may use a flame, or a heated tube, for ignition. While this was common for very early engines it is now rare.

 

Burning Velocity

 

Burning velocity is a measure of the rate at which reactants are moving into the flame from a reference point located on the moving frame. The Flame speed is a measure of how quickly the flame is traveling from a fixed reference point. Burning velocity of a Bunsen Burner flame can be measured using a number of methods.

 

ignition transformer

 

 

The Ignition transformer takes line voltage and steps it up to the approximately 10,000 volts to create the spark that jumps the gap between the ignition electrodes. The voltage and amperage supplied to the cleaning system are not appropriate for creating the needed ignition spark.

 

 

The pump motor requires 115, 230 or 460 volts for operation. The ignition electrodes for the oil burner, however, will require a much higher voltage (usually 8,000 to 10,000 volts) for the ignition spark to arc across the gap between the electrodes.

 

What The Ignition Transformer Does

A transformer is used to increase the voltage from the voltage supplied by the electric utility to the voltage required by the ignition electrodes. The power supplied to a transformer always equals the power provided by the transformer. This basic expression of a transformer always equals the power provided by the transformer. This basic expression of a fundamental physical principle is expressed as "power in = power out."

 

A transformer increases or decreases amperage exactly inversely to any increase or decrease in voltage. In other words, if a transformer doubles the voltage of a 20 amp, 115-volt current, and the result would be a 230-volt, 10 amp current. Transformers come in two basic types: step-up, which increase voltage and step-down, which reduce voltage. A step-up transformer is used in the ignition transformer role.

 

In most modern gun-type burners the ignition transformer is mounted on a hinge on the burner assembly. When ignition transformer swings shut like a door, the bus bars on the transformer make contact with the electrodes. When power is provided to the transformer, a spark is created at the gap between the electrodes. The transformer can be swung back for testing or inspection of the bus bars to see if they are properly aligned. Look for signs of arcing within the burner housing. If the transformer is bad, it should be replaced. Replace with a transformer of the same rated output.

 

Caution: Do not use a large insulated screwdriver to check for arcing between the bus bars. Use proper transformer testing equipment or turn the job over to a qualified electrician.

 

Note: 12-volt ignition systems and new, solid-state ignition systems have slightly different components but operate on the same principles. Full-featured systems with multiple-pass coils will generally have the ignition transformer mounted with other electrical components. Check the equipment manual to identify the proper transformer.

 

impeller

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Boiler Circulation Problems | Troubleshooting Hydronic Water Loops

 

Kate, there can be several things wrong that keeps the water from circulating through the water loop. The first place to start is the circulator pump which should be located near the boiler in the near boiler piping. I would check the aquastat to make sure it is engaging the circulator pump as the aquastat has relay that turns the circulator on when there is a call for heat and temperature inside the jacket is the right set point temperature according to what the aquastat is set for in temperature ranges.

The best way to do this is with a multi-meter to make sure the out put to the pump is 120 volts as most pumps for residential systems work off of 120 volts. If you have 120 volts on the terminal connections where the wires go to the pump then the aquastat is good and the relay is working as it should. Now you should check the pump. You want to know if there is flow going through the pipe from one side of the pump to the other.

 

Boiler Circulation Problems | Troubleshooting Hydronic Water Loops - Direct Drive Versus Non-Direct Drive

 

 

Some pumps have a linkage or coupling device that goes from the motor to the bearing assembly where the impeller is located. The impeller pushes the water through the pipe and some pumps do not have coupling devices but are direct drive. In other words, the pump motor is directly attached to the impeller with certain pumps. Pumps with coupling devices need to have the coupling device inspected to make sure it is not broken. If the coupling device is broken it needs to be replaced and that was your circulation problem.

If it is a direct-drive circulator pump then you need to inspect the impeller to make sure it is good. Impellers do go bad from time to time and need to be replaced.  If this is the case you should really call a boiler technician to fix the problem as many will have the parts on their truck and can have you up and running in an hour or so. They will also know the correct procedure for replacing the impeller without causing additional problems which if you really do not know what you are doing you can cause additional problems. Other problems with the circulator can be a bad motor or a leaking bearing assembly. Some circulator pumps require maintenance while other pumps are maintenance free.

 

Boiler Circulation Problems - Air Problems and Troubleshooting

Automatic Air Vent Water - Air Bleeders for Hydronic loops

The next thing that can cause the water not to circulate in the water loop including to the radiators is hydronic air lock. This is when you get air into the loop. Air will build up usually on a riser or in a radiator. It is necessary to remove the air from the system. Many radiators and even baseboards have manual air bleeders on them. The air bleeders require a key to open them and hopefully you have an air bleeder key. If you have an air bleeder key then you can go around to all your radiators and open these air bleeders with the key. Take a rag with you and open the air bleeder until you get water. In some cases, you will get water only and in other cases, you will get lots of air. Let all the air bleed from the system. As much as possible. Your system should also have automatic air bleeders or automatic air vents located somewhere in the loop. Typically these are located on the risers of the piping and they automatically vent any air that gets into the loop. The are usually very reliable and need little maintenance but time to time they can stop working and need to be replaced. Again if these need to be replaced an HVAC technician should replace these.

 

Conclusion - Boiler Circulation Problems & Troubleshooting Hydronic Water Loops

One last thing you can check if you have circulation problems is the shut off valves in the piping. If someone haphazardly played around with one of these valves and turned it off then you will definitely not have flow going through the water loop. Check to make sure these valves are open. Hopefully, it is as simple as opening a valve but probably not the case. Good Luck to you and I hope your problem gets solved soon.

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indoor quality air

Is poor indoor air quality making you sick?

Protect yourself against six hidden hazards in your home,

 

Indoor air quality isn’t on most people’s radar. Only 9 percent of Americans consider it a threat to their health, and 70 percent aren’t concerned about it at all, according to a recent survey by the Consumer Reports National Research Center. But many of the things people do—or don’t do—can add to the stew of airborne contaminants in their homes and worsen asthma, allergies, and other health conditions.

 

Almost half of Americans use air fresheners at least once a week, and 34 percent use candles or incense that frequently, our nationally representative survey found. Roughly 40 percent rarely or never clean their humidifier or kitchen range hood, though they use it daily. One quarter have never cleaned or replaced their furnace filter. And almost 20 percent still smoke at home or let others smoke there. All of those things can worsen indoor air quality.Many problems are easy to fix—or avoid. Here’s our advice on how to protect your family and home.

Invisible killers: Carbon monoxide and radon

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Carbon monoxide and radon are colorless, odorless, and deadly. CO kills quickly. Faulty gas ranges, cooktops, and furnaces can emit CO, as can wood, kerosene, and propane heaters. Gas generators also emit CO, so don’t run them in a garage or outside near open windows.

 

Radon is the top cause of lung cancer among nonsmokers, though it can take years of exposure. It seeps from rocks, soil, or water beneath your house. Radon levels can vary greatly, even from home to home on the same block. The only way to know whether your house has a radon problem is to test for it.

 

What you can do

Have your heating system and any other fuel-burning appliance inspected annually.

 Install a CO alarm on each level, including the basement.

Change the batteries on your CO alarm according to your owner’s manual, or at least every year. Only 53 percent of those we surveyed said they did that.

Replace your CO alarm every five years.

Run a long-term (90-day or longer) radon test. They cost $20 to $40 and are sold online. If your home has 2 to 4 picocuries per liter (pCi/L) of radon or higher, consider treatment ($800 to $2,500).

 

Even vented gas ranges, cooktops, furnaces, and fireplaces can release harmful gases, soot, and particles into the air if they’re not properly installed and maintained. The same is true with vented wood-burning stoves and fireplaces. Unvented fuel-burning appliances always release small amounts of those substances.

 

When someone in your household smokes, the nicotine released by the cigarettes or cigars adheres to walls, carpeting, drapes, and other indoor surfaces and can react with nitrous acid (chiefly from unvented gas appliances) to form carcinogens, according to a recent Department of Energy study.

 

What you can do

 

 

Always run the exhaust hood when using your gas range or cleaning your oven, or open a window.

Periodically inspect burner ports on your gas stove and clean clogged ones with a needle.

Clean a frequently used chimney annually.

Ban smoking from your house.

 

Household cleaners

 

 

A 2009 study by the Environmental Working Group identified 457 air contaminants—24 linked to serious health concerns, including cancer—in 21 household cleaners. Products labeled “green” were better overall, though the group found 93 contaminants in Simple Green Concentrated Cleaner.

 

That’s partly because many claims on cleaning products aren’t based on any standards. Products with the Design for the Environment (DfE) label from the Environmental Protection Agency have been screened by a third party and contain relatively safe ingredients.

 

Fragrances in cleaners are seldom disclosed. Many manufacturers list product ingredients on their websites, but they don’t have to list fragrance ingredients. And one fragrance can contain 50 to 200 compounds, including dozens of volatile organic compounds. Terpenes, for example, give products a pine or lemon scent, but they’re linked to respiratory problems. They also can react with ambient ozone to form formaldehyde, a known carcinogen, and other irritants. But William Troy, Ph.D., a former chairman of the International Fragrance Association North America, says people need to consider exposure levels. “Fragrance exposure via cleaners is low,” he says, “and does not present a hazard to the consumer.”

 

What you can do

 

 

Though it sounds obvious, always read product labels and follow directions for use. And open a window or run a fan when cleaning.

 If you have asthma or allergies, use products without fragrances or those with the DfE label.For a homemade glass cleaner, mix 1 tablespoon of vinegar or lemon juice with 1 quart of water. To clean toilets, use baking soda or vinegar and a toilet brush. To help get rid of odors, sprinkle baking soda on rugs or carpets, wait 15 minutes, then vacuum.

 

 Air fresheners, candles, and incense

 

Behind the soothing fragrances of air fresheners, candles, and incense are volatile organic compounds. Air fresheners can also contain phthalates, which are linked to cancer and reproductive problems.

“A few manufacturers changed their products after our 2007 report found phthalates in 12 of 14 air fresheners we tested,” says Gina Solomon, M.D., a senior scientist at the Natural Resources Defense Council. “That’s good, because companies are reformulating to make their products safer, but it’s also bad because it’s hard to know what’s currently in any given product.”

Scented candles and incense also release soot and particles into the air, which can trigger asthma attacks and allergic reactions.

“Most patients who stop using scented products have noticed an improvement in their symptoms,” says Stanley Fineman, M.D., president of the American College of Allergy, Asthma and Immunology.

 

What you can do

 

If you or someone in your household has serious allergies or asthma, avoid air fresheners, candles, and incense.

If pollen or related allergies keep you from opening windows, run your air conditioner or forced-air cooling system with a clean filter. Or consider a filter-based air purifier.

 

Interior mold

 

 

The ideal indoor relative humidity is between 30 to 50 percent. Less than that and nasal passages can become dry. At higher levels mold can grow. Humidifiers and dehumidifiers can help or create more problems.

Humidifiers should be emptied daily and disinfected regularly because mold can grow within 24 to 48 hours on wet surfaces. Mold and bacteria in the tank can be released into the air. Dehumidifier filters and tanks also need maintenance, though not as much. Check the manufacturer’s directions.

Bathroom exhaust fans also reduce humidity but need cleaning to avoid dust buildup, a medium for germs.

Not all cleaning is smart. Air ducts need cleaning only in limited circumstances—when there’s visible mold, pests, or dust clogging them. Still, 49 percent of survey respondents clean their ducts at least once a year.

 

What you can do

 

 

Every season, check gutters, leaders, and downspouts for proper pitch, clogs, and broken fasteners or connections.

Make sure that gutter pipes extend at least 5 feet from the house and that the soil around the foundation slopes away from the house.

Avoid mold test kits; we’ve found them to be unreliable.

Treat small areas of mold with a mixture of 1 part chlorine bleach and 16 parts water. Wear goggles, an N-95 respirator, and heavy-duty gloves. Make sure to ventilate the room when you’re working,

 

Old lead-based paint

 

Planning to paint? Old lead-based paint is the most significant source of lead poisoning in the U.S. Roughly 35 million homes, or about half of those built before lead-based paint was banned in 1978, have lead paint, according to a recent federal study. Yet only 17 percent of those we surveyed said they had their homes checked for it.

You can put yourself in danger by scraping, sanding, or burning lead-based paint. Lead can also be released when painted surfaces rub against each other, as when a window is opened. Children are particularly at risk.

 

What you can do

If you have young children and an older home, have it tested for lead by an EPA- or state-certified pro using an XRF machine, or have paint-chip analysis by an EPA-certified lab.

Mop floors and wipe windows and surfaces that children might chew on, such as crib rails.

Leave lead-based paint undisturbed if it’s in good condition, except where painted surfaces rub against each other. For damaged areas, follow the EPA’s guidelines for removing lead paint or hire a painter who is EPA-certified.

 

Natural draft: When air or flue gases flow due to the difference in density of the hot flue gases and cooler ambient gases. The difference in density creates a pressure differential that moves the hotter flue gases into the cooler surroundings.  

Forced draft: When air or flue gases are maintained above atmospheric pressure. Normally it is done with the help of a forced draft fan,

Induced draft: When air or flue gases flow under the effect of a gradually decreasing pressure below atmospheric pressure. In this case, the system is said to operate under induced draft. The stacks (or chimneys) provide sufficient natural draft to meet the low draft loss needs. In order to meet higher pressure differentials, the stacks must simultaneously operate with draft fans.

Balanced draft: When the static pressure is equal to the atmospheric pressure, the system is referred to as balanced draft. Draft is said to be zero in this system,

 

Induced-draft Furnace Heat Exchanger Inspection Procedure

 

 

Gas Furnace Safety Gas furnaces are known for their safety, performance and longevity. This is largely due to their certification to nationally recognized safety standards and the building standards and codes that require equipment be installed according to the manufacturers’ installation instructions.

 

Despite the excellent safety record of gas furnaces, there have been infrequent reports of gas furnace heat exchanger problems. To address these situations, an industry-accepted procedure known as the “Three-Step Method for Detecting Unacceptable Flue Gas Leakage from Furnace Heat Exchangers” has been used since the early 1980's to conduct field inspections of gas-fired furnace heat exchangers.

 

Though this procedure has been effective fortesting heat exchangers in natural draft furnaces, its effectiveness for testing heat exchangers on induced-draft furnaces that maintain a significant negative pressure within the heat exchanger has been questioned. Though it is unlikely for an induced-draft furnace to leak flue products from the heat exchanger to the circulated airstream, a new test procedure has been developed that enhances the existing three-step methodology to make it more applicable, reliable and repeatable for the inspection of induced-draft furnace heat exchangers. 
 

 

Step 1: Look for Flame Disturbances

 

 

Start the furnace and observe any changes in the flame pattern as the circulating air  blower starts operating. Look for floating flames, flame roll out or flame distortion. These conditions indicate a possible split seam, open crack, severe deterioration of the heat exchanger or gasketing material, or physical separation of the connected parts. Flame disturbance that occurs after the blower comes on is a good indication that a heat exchanger problem may exist.

 

Other air leaks in the vicinity of the burners may also cause flame disturbances and should be corrected. If these disturbances are significant and cannot be corrected by eliminating the air leaks near the burners, skip to Step 5 for physical inspection of the heat exchanger.

 If no flame disturbances are observed, proceed to Step 2 below.

 

 Measure CO Levels in the AirstreaM

NOTE: To ensure accuracy of the measurements, take more than one reading and average the results to obtain the CO level.

 

 

With the furnace still running, measure the CO level in the return airstream near the

furnace and record the value. Then measure the CO level in the supply airstream at a location in the system where the air is well mixed. Generally, a location downstream of one or more bends in the ductwork is a good place to take the sample for this measurement. Record this value.

 

If there is no measurable difference in the CO in the return and supply airstreams, it islikely the furnace is not leaking CO into the air stream. If the measured value is below 9 ppm, the OHSA acceptable maximum,

 

If there is no difference in the CO concentration between the return and supply air, but there is CO detected in the air stream, there may be another source of CO in the home such as other gas-fired appliances, an automobile operating in a garage, or a fireplace in operation. Discuss sources with the home owner.

 

 If the CO in the supply air is less than the CO in the return air, it is possible that there is an error in the measurement. Repeat Step 2 with a different gas analyzer if possible.

 

 If the CO in the supply air is greater than the CO in the return air, it is possible that the furnace is generating the CO that is leaking into the airstream.

 

NOTE: If the inspection described in Step 5 does not show holes, cracks or separated seams, further investigation is necessary to determine the source of the CO contamination. 

Measure CO Levels in Flue Pipe

 Allow the furnace to run for at least five minutes.  Then measure the CO in the flue pipe, using a properly calibrated combustion analyzer. If the CO reading is less than 200 ppm, no further action is necessary. If the CO reading is 200 ppm or higher,

Verifying Proper Installation

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Verify that the furnace installation complies with the manufacturer’s requirements and any applicable codes. Refer to the manufacturer’s installation instructions if

available.  Verify the gas orifice size, gas input rate and manifold pressure, proper conversion for fuel type and altitude (if applicable), vent lengths, duct static pressure and the provision for adequate combustion air to the furnace.

 

 Check the furnace for any damaged or disconnected wires or hoses.

 Check for misaligned burners.

Inspect the vent system and combustion air pipe (if applicable) to check for holes or blockage.

 

Make corrections as necessary and then recheck CO in a flue gas sample. If the CO is still at 200 ppm or higher in the flue gas,

 

Visually Inspect Heat Exchanger

 

 

Disassemble the furnace until you can visually inspect all heat exchanger exterior surfaces.

Any crack or hole that is big enough to affect combustion will be easily visible to the naked eye. DO NOT use water or smoking agents to check for leaks.

Furnace heat exchangers joints are not hermetically sealed, so a small amount of leakage is normal. If there are any abnormal splits, cracks or holes, the heat exchanger must be replaced.

 

induction motor

 

 

One of the most common electrical motor used in most applications which is known as induction motor. This motor is also called as asynchronous motor because it runs at a speed less than its synchronous speed. Here we need to define what is synchronous speed. Synchronous speed is the speed of rotation of the magnetic field in a rotary machine and it depends upon the frequency and number poles of the machine. An induction motor always runs at a speed less than synchronous speed because the rotating magnetic field which is produced in the stator will generate flux in the rotor which will make the rotor to rotate, but due to the lagging of flux current in the rotor with flux current in the stator, the rotor will never reach to its rotating magnetic field speed i.e. the synchronous speed. There are basically two types of induction motor that depend upon the input supply - single phase induction motor and three phase induction motor. Single phase induction motor is not a self starting motor which we will discuss later and three phase induction motoris a self-starting motor.

 

We need to give double excitation to make a machine to rotate. For example if we consider a DC motor, we will give one supply to the stator and another to the rotor through brush arrangement. But in induction motor we give only one supply, so it is really interesting to know that how it works. It is very simple, from the name itself we can understand that induction process is involved. Actually when we are giving the supply to the stator winding, flux will generate in the coil due to flow of  current in the coil. Now the rotor winding is arranged in such a way that it becomes short circuited in the rotor itself. The flux from the stator will cut the coil in the rotor and since the rotor coils are short circuited, according to Faraday's law of electromagnetic induction, current will start flowing in the coil of the rotor. When the current will flow, another flux will get generated in the rotor. Now there will be two flux, one is stator flux and another is rotor flux and the rotor flux will be lagging w.r.t to the stator flux. Due to this, the rotor will feel a torque which will make the rotor to rotate in the direction of rotating magnetic flux. So the speed of the rotor will be depending upon the ac supply and the speed can be controlled by varying the input supply. This is the working principle of an induction motor of either type – single and three phase.

 

Types Induction Motor

Single Phase Induction Motor

 

 

1 Split phase induction motor

2 Capacitor start induction motor

3 Capacitor start capacitor run induction motor

4 Shaded pole induction motor

 

Three Phase Induction Motor

 

 

1 Squirrel cage induction motor

2 Slip ring induction motor

 

We had mentioned above that single phase induction motor is not a self starting and three phase induction motor is self starting. So what is self starting? When the machine starts running automatically without any external force to the machine, then it is called as self starting. For example we see that when we put on the switch the fan starts to rotate automatically, so it is self starting. Point to be noted that fan used in home appliances is single phase induction motor which is inherently not self starting. How? Question arises How it works? We will discuss it now.

Why is Three Phase Induction Motor Self Starting?

 

 

In three phase system, there are three single phase line with 120° phase difference. So the rotating magnetic field is having the same phase difference which will make the rotor to move. If we consider three phases a, b and c, when phase a is magnetized, the rotor will move towards the phase a winding a, in the next moment phase b will get magnetized and it will attract the rotor and then phase c. So the rotor will continue to rotate.

 

Why Single Phase Induction Motor is not Self Starting?

 

 

It will be having only one phase still it makes the rotor to rotate, so it is quite interesting. Before that we need to know why single phase induction motor is not a self starting motor and how the problem is overcome. We know that the ac supply is a sinusoidal wave and it produces pulsating magnetic field in uniformly distributed stator winding. Since pulsating magnetic field can be assumed as two oppositely rotating magnetic fields, there will be no resultant torque produced at the starting and due to this the motor does not run. After giving the supply, if the rotor is made to rotate in either direction by external force, then the motor will start to run. This problem has been solved by making the stator winding into two winding, one is main winding and another is auxiliary winding and a capacitor is fixed in series with the auxiliary winding. This will make a phase difference when current will flow through the both coils. When there will be phase difference, the rotor will generate a starting torque and it will start to rotate. Practically we can see that the fan does not rotate when the capacitor is disconnected from the motor but if we rotate with hand it will start to rotate. So this is the reason of using capacitor in the single phase induction motor. There are several advantages of induction motor which makes this motor to have wider application. It is having good efficiency up to 97%. But the speed of the motor varies with the load given to the motor which is an disadvantage of this motor. The direction of rotation of induction motor can easily be changed by changing the sequence of three phase supply, i.e. if RYB is in forward direction, the RBY will make the motor to rotate in reverse direction. This is in the case of three phase motor but in single phase motor, the direction can be reversed by reversing the capacitor terminals in the winding.

 

replacing inefficient equipment 

Every day, our customers are faced with numerous challenges related to the operations of their buildings. They need to keep employees and tenants happy, while at the same time trying to deal with reduced capital and/or maintenance budgets. Often, reduced budgets result in older HVAC equipment not being replaced and once vigorous maintenance programs being scaled back. Not only is this harmful to the long-term condition of the mechanical equipment in a building, it has a tremendous negative impact to the energy consumption of the equipment. This results in higher utility bills and wasted energy.

 

Building owners, property managers, and facilities staff need to understand the correlation between old, inefficient equipment and wasted energy (money).

 

One way for them to save money and energy is to consider upgrading their old, inefficient HVAC equipment with new, energy efficient versions.

 

The following are six important reasons upgrading to newer, energy efficient HVAC equipment makes sense:

 

 

1 Costs less to operate, making it a great investment.

2 Requires less maintenance, which means less money spent on repair and a consistent and comfortable temperature in your building.

3 Rebates and incentives are available to reduce costs.

AAA Heating and Cooling handles all of the paperwork for a hassle free process

4 Does not produce Freon and other CFC refrigerants. This reduces the cost of repairing leaks.

*For older units, the standard refrigerant R22 was $10/lb. two years ago and is now $25/lb. and rising.

5 Reduces energy consumption. Reducing energy use during peak summer periods in Portland can significantly reduce utility costs by at least 15%.

6 Reduces energy waste. Portland has mandated that energy use in buildings be reduced. Energy efficient equipment helps meet the goals outlined in ETO’s Buildings Plan.

 

 

Always be sure to view these upgrades as investments. You can do this by looking at the life cycle cost benefits of installing the most efficient unit possible. These include factoring in rebates, tax incentives, and annual operating costs from the “base” unit to the most efficient. If this is done properly, you will find the lowest first-cost unit is almost always the most expensive unit to own.

 

To sum it up, replacing old, inefficient HVAC equipment is environmentally responsible, resulting in lower utility costs, a reduced carbon footprint, improved air quality, and a greener work environment.

 

An inert gas is a gas which does not undergo chemical reactions under a set of given conditions. The noble gases often do not react with many substances.[1] Inert gases are used generally to avoid unwanted chemical reactions degrading a sample. These undesirable chemical reactions are often oxidation and hydrolysis reactions with the oxygen and moisture in air. The term inert gas is context-dependent because several of the noble gases can be made to react under certain conditions.

 

Purified argon and nitrogen gases are most commonly used as inert gases due to their high natural abundance (78% N2, 1% Ar in air) and low relative cost.

 

Unlike noble gases, an inert gas is not necessarily elemental and is often a compound gas. Like the noble gases the tendency for non-reactivity is due to the valence, the outermost electron shell, being complete in all the inert gases.[2] This is a tendency, not a rule, as noble gases and other "inert" gases can react to form compounds.

 

infrared humidifier

 

 

The Importance of Humidity Control With ever-increasing requirements for reliability and availability, environmental control is critical to protecting today’s sensitive computer systems. A clean, filtered environment with precise control over temperature and humidity is mandatory. This requirement is not limited to large data centers. With space at a premium, small offices, storage rooms and even closets are being utilized for servers, routers and other electronic equipment. Proper consideration for temperature and humidity control is just as important for these locations.

 

During facility design or remodeling, humidity control is often given less priority than temperature control, air movement and other more obvious variables. Temperature changes, dust, drafts, radiant heat and odors are sometimes more noticeable than slight changes in humidity. However, ignoring the impact of humidity can result in serious long-term problems, including damage to equipment and to the facility’s infrastructure.

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In most cases, the optimal relative humidity range for a data center environment is 45-50 percent. An above-normal level of moisture in the air can corrode switching circuitry, which can result in malfunctions and equipment failures. In data processing equipment, hygroscopic (moisture absorbing) circuit boards expand and contract with fluctuating humidity levels. Expansion and contraction of these boards can break

 

microelectronic circuits and edge connectors. On the opposite end of the spectrum, low humidity can cause static electricity that will interfere with normal equipment operation and potentially destroy electronic components should a static discharge occur.

 

Humidity must be considered within the context of the total data center environment. The 2001 ASHRAE Fundamentals Handbook states, “A well-planned control system must coordinate the performance of the temperature and humidity equipment.” This suggests that humidity control, and more specifically, the type of humidifier, be considered as an important factor in an overall environmental control plan specific to the needs of a particular facility.

 

A Word About Vapor Seals

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Any effort to maintain acceptable relative data center humidity levels is virtually impossible without use of a vapor seal to isolate the room’s atmosphere from conditions external to the room. Vapor barriers may be created using plastic film, vaporretardant paint, vinyl wall coverings and vinyl floor systems, in combination with careful sealing of all openings, such as doors and windows, into the room. The vapor seal may be one of the least expensive, but most important and often overlooked, factors to controlling relative humidity levels in a data center.

 

Evaporative: The evaporative approach to humidification uses an evaporative pad with air blowing across it. Typically, hot water is run over the pad and evaporated as the air travels through it. The warmer the water, the more effective the process is, using the energy in the water to aid the process. This approach is commonly seen in residential applications and is an inexpensive method of humidification. However, it generally does not provide the precision, cleanliness or speed-ofresponse required by data center operations.

Immersion: Immersion humidifiers incorporate electric heating elements in a reservoir of water to provide humidification. Immersed heating elements raise the temperature in a tank, boiling the water and generating steam that is sent to a dispersal unit for absorption into the air. This type of humidifier is slow to react to humidity changes if it has been off for a while, and typically does not control the amount of minerals from the water that get introduced into the air. This method is generally not recommended for data center applications.

 

Infrared humidifiers use high intensity quartz infrared lamps over a stainless steel humidifier pan. The infrared radiation from the lamps breaks the surface tension of the water, allowing the air flowing across it to evaporate and carry the moisture away as a particlefree vapor. This provides very precise and fast humidification.

 

Steam canister humidifiers use electrodes inserted into the water reservoir to pass current through the water, causing it to boil and to discharge pure steam at 212°F at atmospheric pressure through a steam distributor. This approach provides greater application flexibility than the infrared since the canister does not need to be mounted in the conditioned air stream, but it cannot react to changes in humidity as quickly if it has been off for a while.

 

This approach is limited to use in steam-heated buildings or where steam can be otherwise injected into the system. Consequently, it is not an option for most data center facilities.

 

The ultrasonic approach uses a Piezoelectric transducer that converts a high frequency electronic signal into high frequency mechanical oscillation, which ultimately converts water into vapor at low temperature and pressure. Ultrasonic humidifiers get high marks for energy efficiency, but they require mineral-free water for trouble-free operation. The cost and maintenance of the water treatment system plus the cost of the humidifier itself can often negate potential energy savings. Additionally, humidifier placement is very critical to proper operation.

 

insulation electrical

An electrical insulator is a material whose internal electric charges do not flow freely, and therefore make it nearly impossible to conduct an electric current under the influence of an electric field. This contrasts with other materials, semiconductors and conductors, which conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors.

 

A perfect insulator does not exist, because even insulators contain small numbers of mobile charges (charge carriers) which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as the breakdown voltage of an insulator. Some materials such as glass, paper and Teflon, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics.

 

 

Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers. They support the weight of the suspended wires without allowing the current to flow through the tower to ground.

 

Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation.

 

intermittent ignition and standing

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  There are two types of pilot functions: Standing pilots and intermittent pilots. Standing pilots are always on; they’re just standing there. Older gas furnaces in houses had them. Old water heaters had them. Most gas kilns have them. They involve pushing a reset button on a safety valve. Pushing the button down causes gas to flow to the pilot where it is ignited. Once ignited it usually energizes a thermocouple that sends a signal back to the safety valve telling it that there is a flame present. Take your finger off the button and gas can now go to the main burner. As long as the pilot is lit (standing), the thermocouple stays energized and the valve stays open. It’s pretty simple stuff. It’s pretty effective. There are other ways to monitor a standing pilot such as UV scanners, and flame rectification, but the main idea is that the pilot light is always on. Using these more technical (and expensive forms) of monitoring a pilot are rare with a standing pilot. The reason that UV and flame rods (rectification) are not often used with standing pilots is their speed of response. UV and flame rods usually have a response time of about 1 second while thermocouples have a response time of 30-45 seconds. The controls that are connected to these faster monitoring devices can read and react faster. There is not a need for the manual aspect (holding a button down) that is usually required with a standing pilot.

 

 

So, intermittent pilots are faster. And, because of this, they use electronics to activate them. Intermittent pilots always involve two components: a spark ignition component and a sensor. A signal says to the burner system, “we need heat”. An electric solenoid valve opens and sends gas to the pilot and at the same time a spark starts trying to light the gas coming out of the pilot. The instant the pilot ignites, the sensor tell the intermittent pilot control, “Houston, we have ignition”. Instantly another electric solenoid valve opens to the main burner and we’re off to the races. Like modern gas heating systems in houses, if a temperature is reached, everything is turned off (including the pilot) until heat is again needed. Then, the cycle starts again; open pilot valve, start spark, see pilot flame, open main gas valve, main burner ignites from the pilot. If the intermittent pilot control can’t instantly detect the pilot flame, everything comes to a screeching halt. Now, in the kiln world, you may have an intermittent pilot and think it is a standing pilot because it is always on. Sounds sorta’ confusing huh? It’s not really. Most pottery kilns just demand heat constantly so the pilot and main burner stay on until you turn them off or a controller says that you’ve reached your destination and shuts things down. Most commercial kilns that have some sort of “start” button are using an intermittent pilot. If it lights itself, it’s intermittent whether it stays on all the time or cycles. One of the other main differences is the use of electricity. A standing pilot system does not necessarily require electricity. An intermittent system always has an electrical component. It has to have one. The spark, sensor, and pilot control all need some juice. A thermocouple-standing pilot system doesn’t need but a whisper of electricity. The heat on the thermocouple generates all the electric current needed (a very, very small one).

 

    The two differentiations that I’ve talked about apply to the monitoring of pilot flames, not the actual pilots themselves. Almost any kind of pilot can be set up as a standing pilot or an intermittent pilot. What do I mean as any kind of pilot? I mean the physical structure of the pilot. There are little target pilots that hit a small shell-shaped piece of metal and throw the flame onto the thermocouple. There are pilots that have fins that provide extra grounding area. There are Venturi burners with air shutters that act as pilots. Any of these pilots can be set up as either standing or intermittent systems. It’s all about how they are controlled. It’s all about how they are watched over.

 

 internal heat defrost

 

 

 

Ball valve Valve that uses a round ball in the flow chamber in the valve. The round ball is bored to the approximate inside diameter of the pipe and also offers very little resistance or pressure drop to the flow of water or fluid flow. The handle only has to be turned 90 degrees to fully open or close the valve.FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Lake View, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  technicians, service repair and installation Armstrong, azrikam the price is right heating and air conditioning ac hvac  company

 

Crankcase pressure regulator A valve installed in the suction line, usually close to the compressor. It is used to keep a low-temperature compressor from overloading on a hot pulldown by limiting the pressure to the compressor.FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Wood Dale, Illinois ac hvac rooftop units residentail and commercail  heating and air conditioning  repairman service repair and installation Goodman, azrikam the price is right heating and air conditioning ac hvac  company

Current sensing relay An inductive relay coil usually located around a wire used to sense current flowing through the wire. Its action usually opens or closes a set of contacts.FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Bensenville, Illinois ac hvac rooftop units residentail and commercail  heating and air conditioning   specailists, service repair and installation Frigidaire ,azrikam the price is right heating and air conditioning ac hvac  company,

Defrost termination and fan delay control A temperature-activated switch that stops the defrost cycle and returns the equipment to the refrigeration cycle.FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Itasca, Illinois ac hvac rooftop units residentail and commercail  heating and air conditioning  maintenance, service repair and installation Gibson, azrikam the price is right heating and air conditioning ac hvac  company

Discharge service valve The valve at the top of a compressor cylinder that shuts on the downstroke to prevent high pressure gas from reentering the compressor cylinder, allowing low-pressure gas to enter. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Edison Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  furnace service repair and installation carrier, azrikam the price is right heating and air conditioning ac hvac  company

 

 

Electronic evaporator pressure regulator Located at the evaporator outlet. They control the discharge air temperature. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Jefferson Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning   heating service repair and installation Bryant, azrikam the price is right heating and air conditioning ac hvac  company

 

External heat defrost A defrost system for a refrigeration system where the heat comes from some external source. It might be an electric strip heater in an air coil, or water in the case of an ice maker.  FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Galewood, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  air conditioning service repair and installation Armstrong, azrikam the price is right heating and air conditioning ac hvac  company

 

Fan cycling head-pressure control Simple and reliable method when a unit has one small fan because only one fan is cycled. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Belmont Heights, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  installations, service repair and installation Arcoaire, azrikam the price is right heating and air conditioning ac hvac  company

 

Fan speed control These devices can be used with multiple fans, where the first fans are cycled off by temperature and the last fan is controlled by head pressure or condensing temperature. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Dunning, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  replacements service repair and installation Ameristar, azrikam the price is right heating and air conditioning ac hvac  company

 

Filter-drier A type of refrigerant filter that includes a desiccant material that has an attraction for moisture. The filter drier will remove particles and moisture from refrigerant and oil. 

 

 

Heat exchanger A device that transfers heat from one substance to another, 

 

 

High-pressure control A control that stops a boiler heating device or a compressor when the pressure becomes too high. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Belmont Central, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  fixing, service repair and installation AirEase, azrikam the price is right heating and air conditioning ac hvac  company

 

Internal heat defrost Heat provided for defrost from inside the system, for example, hot gas defrost.  FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONSOld Irving Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  repairing,  service repair and installation York, azrikam the price is right heating and air conditioning ac hvac  company

 

King valve A service valve at the liquid receiver's outlet in a refrigeration system. 

 

 

Liquid floodback Liquid refrigerant returning to the compressor's crankcase during the running cycle. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Hollywood Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  servicing, service repair and installation Weather King, azrikam the price is right heating and air conditioning ac hvac  company

 

Liquid refrigerant distributor The device is used between the expansion valve and the evaporator on multiple circuit evaporators to evenly distribute the refrigerant to all circuits.

 

 

Low-ambient control Various types of controls that are used to control head pressure in air-cooled air-conditioning and refrigeration systems that must operate year round or in cold weather. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS West Ridge, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  technicians, service repair and installation Tempstar, azrikam the price is right heating and air conditioning ac hvac  company

 

Low pressure control A pressure switch that can provide low charge protection by shutting down the system on low pressure. It can also be sued to control space temperature.

 

 

Migration When the refrigerant moves to some place in the system where it is not supposed to be, such as when oil migrates to a compressor crankcase.

 

 

Multiple evaporators When more than two evaporators are used with one compressor.

 

 

Net oil pressure Difference in the crankcase pressure and the compressor oil pump outlet pressure FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS River West, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  professionals, service repair and installation NuTone, azrikam the price is right heating and air conditioning ac hvac  company

 

Oil separator Apparatus that removes oil from a gaseous refrigerant,

 

 

One-time relief valve A device (made of low melting temperature metal) used in pressure vessels that is sensitive to high temperatures and relives the vessel contents in an overheating situation. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Ravenswood, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  cooling service repair and installation luxaire, azrikam the price is right heating and air conditioning ac hvac  company

 

Planned defrost Shutting trhe compressor off with a timer so that the space temperature can provide the defrost. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Wicker Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning   furnace service repair and installation Lennox, azrikam the price is right heating and air conditioning ac hvac  company

 

Pressure access ports Places in a system where pressure can be taken or registered. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Near North Side, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning   heating service repair and installation Heil, azrikam the price is right heating and air conditioning ac hvac  company

 

Random or Off cycle defrost Defrost provided by the space temperature during the normal off cycle. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS West Town, Chicago, IL ac hvac heating rooftop units residentail and commercail  and air conditioning  air conditioning service repair and installation Goodman, azrikam the price is right heating and air conditioning ac hvac  company

 

Receiver Is located in the liquid line and is used to store the liquid refrigerant after it leaves the condenser. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Humboldt Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  installations, service repair and installation Gibson, azrikam the price is right heating and air conditioning ac hvac  company

 

Refrigerant sight glass Is located anywhere liquid flow exist and anywhere it can serve a purpose. Used to observe the refrigerant as it moves along the line

.

 

 

Shutters and dampers A component in an air-distribution system that restricts airflow for the purpose of air balance. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Irving Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  checking, service repair and installation Fraser Johnston, azrikam the price is right heating and air conditioning ac hvac  company

 

Solenoid valve Is the component most frequently used to control fluid flow.

 

 

Spring-loaded relief valve Normally brass with a neoprene seat. Mainly used in applications because of the increased cost of refrigerants and ozone depletion scares.

 

 

Suction-line accumulator A reservoir in a refrigeration system suction line that protects the compressor from liquid floodback, FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Bucktown, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning repairing, service repair and installation Concord, azrikam the price is right heating and air conditioning ac hvac  company

 

Suction line filter drier Removes foreign matter from the refrigerant.

 

 

Suction service valve A manually operated valve with front and back seats located at the compressor, FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Gold Coast, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  servicing, service repair and installation carrier, azrikam the price is right heating and air conditioning ac hvac  company

 

Two temperature valve A valve used in systems with multiple evaporators to control the evaporator pressures and maintain different temperatures in each evaporator. Sometimes called a holdback valve. FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS Lincoln Park, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  serviceman, service repair and installation Bryant, azrikam the price is right heating and air conditioning ac hvac  company

 

inverter

 FREE ESTIMATES FOR NEW FURNACE AND AC AIR CONDITIONING HVAC  INSTALLATIONS O'Hare, Chicago, IL ac hvac rooftop units residentail and commercail  heating and air conditioning  heating and air conditioning free estimates  experts, service repair and installation Concord, azrikam the price is right heating and air conditioning ac hvac  company

An inverter is an electric apparatus that changes direct current (DC) to alternating current (AC). It is not the same thing as an alternator, which converts mechanical energy (e.g. movement) into alternating current.

Direct current is created by devices such as batteries and solar panels. When connected, an inverter allows these devices to provide electric power for small household devices. The inverter does this through a complex process of electrical adjustment. From this process, AC electric power is produced. This form of electricity can be used to power an electric light, a microwave oven, or some other electric machine.

An inverter usually also increases the voltage. In order to increase the voltage, the current must be decreased, so an inverter will use a lot of current on the DC side when only a small amount is being used on the AC side.

Inverters are made in many different sizes. They can be as small as 150 watts, or as large as 1 megawatt (1 million watts).

 

 Isolation relays

 

 

This is a simple way to add a relay to your micro controller or CNC controller. It runs off 5V and most controllers can easily drive it. The circuit is optically isolated from the relay, so your controller is protected from voltage spikes and surges. It does this by shining light across a gap to a sensor. No electrically conductive items cross this gap. This is a great way to add things like spindle power control to your CNC project or have an Arduino control high power devices.

 

Relay Coil Voltage: 5V

Logic Voltage: 5V (logic low activates relay)

Relay Current: 10amp

Relay Voltage: 250VAC or 30VDC

There are two ways to use these relays. See the images for connecting the circuits.

 

Isolated

 

In isolated mode the relay is completely electrically isolated from the control side. Large voltage spikes, shorts, etc. will not affect your controller. Therefore you need two separate voltage sources. One is for the relay side. This is put in the terminals closest to the edge. Use the two center terminal labeled Positive Relay Coil Power and Negative Relay Coil Power. The next column of terminals is for the controller side of the isolation. You need to supply your 5V, GND and signal from your controller on these.

 

Non-isolated

 

Sometimes you don’t have a second power supply handy and want to use the 5V and GND from the controller for both sides of the isolation barrier. You can do this by using jumpers to connect Positive Opto Input Power to Positive Relay Input Power and connect Negative Opto Input Power to Negative Relay Input Power on the column of terminals closest to the edge.

 

Controlling Relay

See the “Typical Application” in the images section above. You need to provide power and ground the the opto and a control signal. The opto inverts the logic so a low signal (GND) energizes the relay.

 

 

Intermittent Ignition Device (IID) more HVAC definitions. IIDs are linked to a furnace or boiler's thermostat and light the pilot by means of a spark or other heat source when needed. IIDs are more fuel-efficient than the traditional approach of maintaining a continuously burning pilot flame.

 

 

A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solid-state relays. Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits as amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another circuit. Relays were used extensively in telephone exchanges and early computers to perform logical operations.

 

A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

 

 

Magnetic latching relays require one pulse of coil power to move their contacts in one direction, and another, redirected pulse to move them back. Repeated pulses from the same input have no effect. Magnetic latching relays are useful in applications where interrupted power should not be able to transition the contacts.

 

Magnetic latching relays can have either single or dual coils. On a single coil device, the relay will operate in one direction when power is applied with one polarity, and will reset when the polarity is reversed. On a dual coil device, when polarized voltage is applied to the reset coil the contacts will transition. AC controlled magnetic latch relays have single coils that employ steering diodes to differentiate between operate and reset commands.