By Norm Christopherson @copyrighted material
Those of us in the heating and cooling industry know that our business allows us to consider many aspects of the liquids, gases and solids around us. This is especially true when we heat, cool and cause them to change physical states.
The ice machine uses the changes in state of a refrigerant to cause water to change state and produce ice. So, an ice machine is a device that uses the change of state of one substance to cause another substance to change its state. Water is the raw material and ice is the product. So, here are some interesting facts about water and ice.
Water is a most remarkable substance even though we often perceive it as ordinary. We wash in it, swim in it, drink it, make ice from it, skate on it and cook in it, although not all at the same time. Almost 75% of the Earth is covered with water and about 70% of the human body consists of water. Most of our food is water; mushrooms are 98% water, tomatoes are 95% water, milk is 90% water, potatoes are 80% water and beef is 61% water. More than half of the world’s animal and plant life live in the water. There is water in the Earth’s atmosphere, on the Earth’s surface and under the ground. Approximately 75% of all the Earth’s fresh water is contained in glaciers which are 100% fresh water and the ice thickness at the poles is as much as 10,000 feet thick. As common as water is it actually acts in some very uncommon ways.
Water is unique in that it is the only natural substance that exists in all three states, solid, liquid and gas at the temperatures normally found on Earth. And, under certain conditions water can exist in all three states (Called the “triple point”) at the same time. The unit of heat quantity, the BTU is based upon how much heat it takes to change the temperature of one pound of water by one degree F. The specific heat of water is the basis of comparison for the specific heats of all other substances. We even rate the cooling capacity of air conditioning and refrigeration equipment on the cooling rate capacity of a ton of melting ice.
Water has one of the highest heat capacities of all substances. In fact, a 1-inch diameter pipe carrying heated or cooled water is capable of transporting heat at the same rate as a 10 by 18 inch duct in a forced air system.
When water is cooled the speed of its’ molecules slow down and it becomes more dense just as with all other substances. As the temperature drops molecules gather closer together increasing the density. Water reaches its greatest density at 4 degrees C or 39 degrees F. However, when water freezes something quite strange happens. As the water freezes its density reverses and the water expands. The density of ice is less than that of liquid water and this is why ice floats on water. This accounts for the fact that ice freezes and remains at the top of bodies of water and why lakes do not freeze from the bottom up. The power of freezing ice expanding is incredible. No container can be constructed that can withstand the power of expansion when water inside the container expands upon freezing.
Water has one of the highest latent heat values of all liquids making it an ideal substance for use in evaporative coolers and cooling towers. And, it is non-toxic, relatively inexpensive and recyclable.
The surface tension of water is amazing. A metal needle can float on water due to the surface tension or skin water builds up at its surface. This also allows some insects to actually “walk on water”. This same surface tension is called capillary action that allows water to climb up a drinking straw to a level above the surface of the water in the container the straw is placed. The smaller the diameter the hollow straw, the higher the water climbs. Any crack, crevice or small space will attract and hold water due to this capillary action or surface tension. This is exactly how molecular sieve driers attract and hold moisture in a refrigeration system. The desiccant is a material containing many small tubes, crevices and tiny pockets that attract and hold water molecules. The capillary action or surface tension of water also causes water in a mechanical refrigeration system to become attracted to the cracks, crevices and tiny spaces in a compressor or around joints in tubing. This attraction is so great that it requires an evacuation as low as 500 microns to break the moisture’s surface tension in order to vaporize the moisture during an evacuation. Even then not all the moisture may be removed which is why we install a filter-drier containing a desiccant.
Pure water is also an insulator to electrical current, that is, it has a high dielectric strength. It only becomes an electrical conductor when minerals or salts are dissolved in the water. And, speaking of that, water is the universal solvent. Almost every other substance has been found dissolved in water. Water has a neutral Ph and is neither an acid nor a base.
If you ask most people, which is heavier, dry air or water vapor, they will answer, water vapor. This is obviously incorrect when you consider the fact that clouds (A collection of water vapor) are high in the sky. If water vapor were denser than dry air we would all be constantly in the fog, which would account for some of our foggy thinking. Actually, a solid understanding of water vapor is important to an understanding of the study of psychrometrics.
Water and ice have many other physical, chemical and thermal qualities that make it unique from all other substances. So the next time you are drinking a glass of water, measuring relative humidity, repairing an ice machine, evacuating a system or installing a filter-drier, think about the qualities and value of water, a most amazing substance.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications. He can be contacted at norman.christopherson@jci.com
Wednesday, May 5, 2010
Economizers Simplified
The Concept Of The Economizer
In a nutshell
By Norm Christopherson @copyrighted material
The function of the economizer is as its name implies, to “economize” or save on cooling costs. Obviously, it costs money to operate the compressor. If the compressor can be shut down and the system still provide adequate cooling, energy savings can be realized.
Heat internal to the building such as people, lights, computers, copy machines, motors and other machines causes the temperature inside a structure to increase. Heat soaked up by the building structure may also continue to heat the building long after the temperature outside the building has dropped. There are times when the temperature outside a building is lower than the temperature inside.
Whenever the cooling system is calling for cooling and the temperature outside is cool enough it is economical to shut off the compressor and bring in cool outside air to satisfy the cooling needs of the building. Such is the function of an air economizer system.
There is one drawback to this type of control system. Even though the thermostat acknowledges that the outside air temperature is low enough to cool the building, the outside air may be too humid to provide adequate comfort for the building occupants. The occupants will feel cool but clammy. The solution is an economizer that adds a second control which works in harmony with the outdoor thermostat and measures the outdoor air humidity. Such a control is called an “enthalpy” control. The term “enthalpy” means, total heat. The enthalpy control measures both sensible and latent heat in the air and only allows outside air to be used for cooling if the air is both cool and dry enough to satisfy the space conditions.
If the indoor thermostat calls for cooling and the outside air enthalpy (total heat) is low enough then the economizer brings in this cooler and less humid air and uses it for cooling instead of operating the compressor. Using the outside air for cooling is less expensive than operating the compressor to provide cooling.So an enthalpy control is a control which checks to see if both the temperature (sensible heat) and the humidity (latent heat) are low enough to be used for cooling. This combination provides for the greatest comfort at the least cost.
Not all economizers use enthalpy controls. Some just check the outside air temperature and do not check the outside air humidity. Those controls do not provide the same levels of comfort as enthalpy controlled economizers.
Economizers can save a great deal of energy. They can also waste energy if they are not operating properly or are improperly adjusted. For example, if the outside air dampers are not closing properly when the outside air temperature is high, then hot air is unnecessarily entering the building and causing the air conditioning compressor to operate longer and under higher loads thus consuming a great deal more energy than necessary.
If the dampers are open too far during the heating season the heating system must heat the extra outside air entering the structure. Such extra heating and cooling costs can be quite high. The cost of a service call to repair such a problem is often less than the cost of one or two months of energy wasted.
Many economizers are not functioning at all or are out of service because they are not well understood by some service technicians. Many service technicians simply disable them. It is essential that economizers are working properly and saving energy rather than increasing costs.
Since air economizers control and vary the amount of outside (fresh) air brought into a structure, they play an integral role in maintaining the quality of indoor air. A properly operating economizer can greatly improve indoor air quality (IAQ) and reduce air quality related illnesses. Therefore, it is important for the service technician have at least some knowledge of indoor air quality and its relationship to the heating and cooling system operation.
Air economizers are available for residential and commercial systems and can be retrofitted to most systems as energy conserving devices. Most packaged light commercial systems (rooftop systems) have an economizer add-on package as an option which can be installed when the system is new or may added to the system later.
Economizer Maintenance
The following items should be checked at least annually to ensure the air economizer is operating properly:
Setting & operation of the outdoor thermostat or enthalpy control.
Condition of the outdoor thermostat or enthalpy control.
Proper setting and operation of the economizer mixed air thermostat.
Proper damper operation and lubrication.
Minimum damper position adjustment.
Correct operation of the system when a call for cooling comes from the thermostat.
Function and condition of the economizer damper motor.
Condition of the wiring and electrical terminations.
Since the enthalpy control is located in the outdoor air air-stream and is a relatively sensitive control, it is not uncommon to have to replace it every few years depending upon the location of the equipment and the weather extremes in the area. The cost of a replacement control is usually recovered quickly through the energy saved. Economizer service should be a part of the scheduled maintenance performed at least on a yearly basis.
Just as our automobiles need regular service so do residential and commercial heating & cooling systems. Like automobiles, the frequency of service depends upon how it is operated, how often & long it operates and the environment where it operates. Like automobiles, well maintained systems operate more efficiently, last longer and fail less often.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications.
He can be contacted at norman.christopherson@jci.com
In a nutshell
By Norm Christopherson @copyrighted material
The function of the economizer is as its name implies, to “economize” or save on cooling costs. Obviously, it costs money to operate the compressor. If the compressor can be shut down and the system still provide adequate cooling, energy savings can be realized.
Heat internal to the building such as people, lights, computers, copy machines, motors and other machines causes the temperature inside a structure to increase. Heat soaked up by the building structure may also continue to heat the building long after the temperature outside the building has dropped. There are times when the temperature outside a building is lower than the temperature inside.
Whenever the cooling system is calling for cooling and the temperature outside is cool enough it is economical to shut off the compressor and bring in cool outside air to satisfy the cooling needs of the building. Such is the function of an air economizer system.
There is one drawback to this type of control system. Even though the thermostat acknowledges that the outside air temperature is low enough to cool the building, the outside air may be too humid to provide adequate comfort for the building occupants. The occupants will feel cool but clammy. The solution is an economizer that adds a second control which works in harmony with the outdoor thermostat and measures the outdoor air humidity. Such a control is called an “enthalpy” control. The term “enthalpy” means, total heat. The enthalpy control measures both sensible and latent heat in the air and only allows outside air to be used for cooling if the air is both cool and dry enough to satisfy the space conditions.
If the indoor thermostat calls for cooling and the outside air enthalpy (total heat) is low enough then the economizer brings in this cooler and less humid air and uses it for cooling instead of operating the compressor. Using the outside air for cooling is less expensive than operating the compressor to provide cooling.So an enthalpy control is a control which checks to see if both the temperature (sensible heat) and the humidity (latent heat) are low enough to be used for cooling. This combination provides for the greatest comfort at the least cost.
Not all economizers use enthalpy controls. Some just check the outside air temperature and do not check the outside air humidity. Those controls do not provide the same levels of comfort as enthalpy controlled economizers.
Economizers can save a great deal of energy. They can also waste energy if they are not operating properly or are improperly adjusted. For example, if the outside air dampers are not closing properly when the outside air temperature is high, then hot air is unnecessarily entering the building and causing the air conditioning compressor to operate longer and under higher loads thus consuming a great deal more energy than necessary.
If the dampers are open too far during the heating season the heating system must heat the extra outside air entering the structure. Such extra heating and cooling costs can be quite high. The cost of a service call to repair such a problem is often less than the cost of one or two months of energy wasted.
Many economizers are not functioning at all or are out of service because they are not well understood by some service technicians. Many service technicians simply disable them. It is essential that economizers are working properly and saving energy rather than increasing costs.
Since air economizers control and vary the amount of outside (fresh) air brought into a structure, they play an integral role in maintaining the quality of indoor air. A properly operating economizer can greatly improve indoor air quality (IAQ) and reduce air quality related illnesses. Therefore, it is important for the service technician have at least some knowledge of indoor air quality and its relationship to the heating and cooling system operation.
Air economizers are available for residential and commercial systems and can be retrofitted to most systems as energy conserving devices. Most packaged light commercial systems (rooftop systems) have an economizer add-on package as an option which can be installed when the system is new or may added to the system later.
Economizer Maintenance
The following items should be checked at least annually to ensure the air economizer is operating properly:
Setting & operation of the outdoor thermostat or enthalpy control.
Condition of the outdoor thermostat or enthalpy control.
Proper setting and operation of the economizer mixed air thermostat.
Proper damper operation and lubrication.
Minimum damper position adjustment.
Correct operation of the system when a call for cooling comes from the thermostat.
Function and condition of the economizer damper motor.
Condition of the wiring and electrical terminations.
Since the enthalpy control is located in the outdoor air air-stream and is a relatively sensitive control, it is not uncommon to have to replace it every few years depending upon the location of the equipment and the weather extremes in the area. The cost of a replacement control is usually recovered quickly through the energy saved. Economizer service should be a part of the scheduled maintenance performed at least on a yearly basis.
Just as our automobiles need regular service so do residential and commercial heating & cooling systems. Like automobiles, the frequency of service depends upon how it is operated, how often & long it operates and the environment where it operates. Like automobiles, well maintained systems operate more efficiently, last longer and fail less often.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications.
He can be contacted at norman.christopherson@jci.com
Troubleshooting the Refrigerant Cycle with Superheat & Subcooling
by Norm Christopherson @copyrighted material
(For those who need a refresher on what superheat & subcooling are, read the article,
Superheat & Subcooling Made Easy)
· Troubleshooting is a matter of temperature differences.
o Superheat is a temperature differential
o Subcooling is a temperature differential
o Evaporator entering air versus leaving air temperature is a
differential.
o Condenser entering air versus leaving air temperature is a
differential.
o These four temperature differentials are the critical
measurements used to determine all refrigerant related
problems. Often a manifold gauge set is not even necessary.
· Critical Temperature Differentials
o Air temperature drop over the evaporator should not exceed 20
degrees F.
o Air temperature rise over the condenser should not exceed 30
degrees F.
o The low side superheat should be between 20 and 30 degrees.
o The condenser subcooling should not exceed 15 degrees.
· An air temperature drop over the evaporator greater than 20 degrees
indicates low evaporator airflow.
· An air temperature rise over the condenser greater than 30 degrees
indicates low condenser airflow.
· A low side superheat less than 20 degrees indicates too much liquid
refrigerant is in the low side.
· A low side superheat greater than 30 degrees indicates too little
refrigerant is in the low side.
· A condenser subcooling exceeding 15 degrees indicates too much
liquid refrigerant is in the high side.
· Comparing these readings will lead to an understanding of what is
wrong with the system. For example, assuming adequate airflow over
both the evaporator and condenser the following is true.
o High superheat with high condenser subcooling indicates a
restriction. Too much liquid is in the high side and too little in
the low side.
o Low superheat with high subcooling indicates an overcharge.
Too much liquid on both sides.
o High superheat with low condenser subcooling indicates an
undercharge. Not enough liquid on either side.
Low side superheat and condenser subcooling simply tell us where the refrigerant is
located. Too much refrigerant on the high side and too little on the low side indicates a
restriction. Too much on both sides indicates an overcharge and not enough on either
side indicates an undercharge.
Norm Christopherson is an HVAC seminar speaker, author and consultant. He can be
reached at norman.christopherson@jci.com
(For those who need a refresher on what superheat & subcooling are, read the article,
Superheat & Subcooling Made Easy)
· Troubleshooting is a matter of temperature differences.
o Superheat is a temperature differential
o Subcooling is a temperature differential
o Evaporator entering air versus leaving air temperature is a
differential.
o Condenser entering air versus leaving air temperature is a
differential.
o These four temperature differentials are the critical
measurements used to determine all refrigerant related
problems. Often a manifold gauge set is not even necessary.
· Critical Temperature Differentials
o Air temperature drop over the evaporator should not exceed 20
degrees F.
o Air temperature rise over the condenser should not exceed 30
degrees F.
o The low side superheat should be between 20 and 30 degrees.
o The condenser subcooling should not exceed 15 degrees.
· An air temperature drop over the evaporator greater than 20 degrees
indicates low evaporator airflow.
· An air temperature rise over the condenser greater than 30 degrees
indicates low condenser airflow.
· A low side superheat less than 20 degrees indicates too much liquid
refrigerant is in the low side.
· A low side superheat greater than 30 degrees indicates too little
refrigerant is in the low side.
· A condenser subcooling exceeding 15 degrees indicates too much
liquid refrigerant is in the high side.
· Comparing these readings will lead to an understanding of what is
wrong with the system. For example, assuming adequate airflow over
both the evaporator and condenser the following is true.
o High superheat with high condenser subcooling indicates a
restriction. Too much liquid is in the high side and too little in
the low side.
o Low superheat with high subcooling indicates an overcharge.
Too much liquid on both sides.
o High superheat with low condenser subcooling indicates an
undercharge. Not enough liquid on either side.
Low side superheat and condenser subcooling simply tell us where the refrigerant is
located. Too much refrigerant on the high side and too little on the low side indicates a
restriction. Too much on both sides indicates an overcharge and not enough on either
side indicates an undercharge.
Norm Christopherson is an HVAC seminar speaker, author and consultant. He can be
reached at norman.christopherson@jci.com
Superheat & Subcooling / Sensible & Latent Heats Made Simple
By Norm Christopherson
The purpose of this article is to provide a simple explanation of these terms for those who desire a concise understanding as well as a review for those who understand the terms but want to review them. An understanding of these terms and the concepts related to them is essential to understanding the air conditioning and refrigeration mechanical – refrigerant cycle as well as being necessary to troubleshooting cycle problems.
Superheat:
Most materials can exist in three forms, solids, liquids and gases. Water is a common example. Water can exist as a solid (ice), a liquid, or a gas or vapor (steam). Only a gas or vapor (these are interchangeable terms), can be superheated. Let’s use water as an example as we explain these terms.
Water at sea level boils at 212 degrees F. When heated to 212 degrees F the molecules which make up water are moving at a high enough speed that they overcome the air pressure above the water. As additional heat is added to liquid water at 212 degrees, the water begins to boil. As the water boils it is changing state from a liquid to a gas. In addition, during the boiling process the temperature remains the same (212 degrees F). There is no change in temperature during a change of state. This phenomenon is true for all substances as they change state no matter how much heat is added. As long as the water is still boiling and not all the water has completely changed to a gas (steam) the temperature remains at 212 degrees F. This means that a thermometer placed in boiling water will remain at 212 degrees throughout the boiling process even though heat is added to cause the water to boil. This heat of boiling is called latent heat. The word “latent” is a Latin word for “hidden”. The heat added to the water is hidden from the thermometer since the temperature remains unchanged during the boiling process.
After all the water has changed to a gas or vapor (steam), then the addition of still more heat to the vaporized water or steam will cause the temperature of the steam to increase above its boiling temperature of 212 degrees. Any increase in temperature of the steam above its boiling point (212 degrees) is called “superheat”. Steam at 213 degrees F is superheated by one degree F.
Superheat is then any temperature of a gas above the boiling point for that liquid. When a refrigerant liquid boils at a low temperature of 40 degrees in a cooling coil and then the refrigerant gas increases in temperature superheat has been added. If this refrigerant changed from a liquid to a gas or vapor at 40 degrees and then the refrigerant vapor increased in temperature to 50 degrees F, then it has been superheated by 10 degrees.
We commonly think of boiling as always being accomplished by a liquid when it is hot. This is because we are familiar with boiling water. However, air conditioning and refrigeration systems use liquids (refrigerants) with much lower boiling points. If a liquid refrigerant boils at -10 degrees and is then warmed up to zero degrees, it is then a superheated gas containing 10 degrees of superheat. Heating that same refrigerant gas to +10 degrees means that it now has been superheated by 20 degrees.
Lowering the pressure over a liquid lowers the boiling point. There is less pressure above the liquid to overcome. That is why water at the top of a mountain may boil at 190 degrees (depending upon the altitude) rather than at 212 degrees F. By controlling the pressure over a liquid, we can control the boiling temperature. That is why a service technician monitors the pressures in an air conditioning system. The technician is actually monitoring the pressures and temperatures where the refrigerant is changing state.
Saturation:
Saturation is simply the term used to describe the point where a change of state in a substance is taking place. For water at sea level, the boiling temperature is 212 degrees F. Therefore, we say the saturation (boiling temperature) is 212 degrees. As soon as the temperature of the steam is heated above it’s “saturation” temperature, it has been superheated. Refrigerant that has boiled (turned into a vapor) at 40 degrees has a saturation temperature of 40 degrees. If the refrigerant vapor is heated to 41 degrees it is no longer saturated, it is then superheated by 1 degree. Remember, only a gas or vapor can be superheated. Superheat is any temperature of a gas or vapor above its saturation temperature.
Subcooling:
Subcooling is now easy to understand. Only liquids and solids can be subcooled. Subcooling is any temperature of a liquid or solid below its saturation temperature. Let’s use water as an example again. Liquid water at sea level has a saturation (boiling) temperature of 212 degrees F. If we were to add heat to the saturated water it would first boil away with no change in temperature (remember latent heat?) and then become superheated if still more heat were added to the vapor (steam) after it had all turned to a vapor.
Instead of boiling our 212 degree water by adding heat, we shall remove heat from the 212 degree water. As heat is removed from the liquid water it’s temperature will drop below its boiling (saturation) temperature. Water at 211 degrees has been subcooled by one degree F. If the temperature of the water is decreased to 180 degrees the water has been subcooled from 212 degrees to 180 degrees. That is, it has been subcooled by 32 degrees. When you drink 180 degree coffee, you are drinking a subcooled liquid!
Sensible Heat & Latent Heat:
Sensible heat is heat that can be measured by a thermometer. Anytime heat is added or removed from a substance and a temperature change occurs, a sensible heat change has taken place. Since both superheat and Subcooling are changes in temperature, they are both sensible heat processes.
When an air conditioning system cools air sensible heat has been removed. In fact, since the air is a gas or vapor and is heated far above its boiling (saturation) point, it is superheated air. Yes, you are breathing superheated air as the air is hundreds of degrees above the temperature at which the gases which make up air would condense back into liquid form.
Superheated does not necessarily mean hot. And, subcooled does not necessarily mean cold. Superheat and Subcooling are determined by the boiling temperature of the substance and unlike water many substances have low boiling temperatures.
Recalling that latent heat is the heat which is added to a liquid to cause it to change from a liquid to a gas (boiling) without a change in temperature, let’s go to the next step. When a gas or vapor is above its boiling point it is said to be superheated. Cooling the gas removes it’s superheat. When all the superheat is removed from a gas, the gas will condense back into a liquid. The heat removed from a saturated gas to allow it to condense back into a liquid is once again latent or hidden heat and is not a sensible heat process. That is, during the process of changing from a gas to a liquid it occurs at a constant temperature therefore a thermometer will not detect any temperature change. That is latent heat.
Air contains water vapor or moisture. Humid air is not comfortable. Too much humidity (moisture) in air is uncomfortable. As air containing too much moisture passes over a properly designed, installed and operating air conditioning system, the air is cooled by the air conditioning coil (evaporator) located at the indoor blower section. If the air containing the moisture is cooled to the condensing temperature (dew point) of the moisture in the air, some of the moisture will condense and deposit on the coil and fins of the cooling coil. Since the water vapor is changing from a gas or vapor to a liquid, this is a latent heat process. The condensed water should run off the coil and be drained away.
A properly operating air conditioning system both cools (a sensible heat process) and dehumidifies (a latent heat process) the air. For example, given a 3-ton residential air conditioning system, a percentage of the total capacity of the system is utilized to cool the air while the remaining percentage of the total capacity is used to dehumidify the air. Properly controlling both the temperature (sensible heat) and the humidity (latent heat) will provide the optimum comfort for the occupants.
Measuring Heat:
Latent heat cannot be directly measured as we can sensible heat. In order to properly adjust, troubleshoot and repair air conditioning equipment it is necessary that we understand heat and how to measure heat.
Superheat and Subcooling are both sensible heats and therefore can be measured with a thermometer. Superheat and Subcooling are also temperature differentials. That is, each is a number of degrees a gas or liquid are above or below their saturation temperatures. It is essential that a service technician be able to accurately measure these differentials and diagnose system operation from them.
A high quality, accurate electronic thermometer capable of measuring temperature differentials is almost an essential tool for the technician and highly useful to the interested homeowner. An example of such an instrument is Bacharach’s “Dual Channel. Model TH3000, digital thermometer” with data hold and max hold functions.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications. He is currently a senior training specialist with Johnson Controls.
He can be contacted at norman.christopherson@jci.com
The purpose of this article is to provide a simple explanation of these terms for those who desire a concise understanding as well as a review for those who understand the terms but want to review them. An understanding of these terms and the concepts related to them is essential to understanding the air conditioning and refrigeration mechanical – refrigerant cycle as well as being necessary to troubleshooting cycle problems.
Superheat:
Most materials can exist in three forms, solids, liquids and gases. Water is a common example. Water can exist as a solid (ice), a liquid, or a gas or vapor (steam). Only a gas or vapor (these are interchangeable terms), can be superheated. Let’s use water as an example as we explain these terms.
Water at sea level boils at 212 degrees F. When heated to 212 degrees F the molecules which make up water are moving at a high enough speed that they overcome the air pressure above the water. As additional heat is added to liquid water at 212 degrees, the water begins to boil. As the water boils it is changing state from a liquid to a gas. In addition, during the boiling process the temperature remains the same (212 degrees F). There is no change in temperature during a change of state. This phenomenon is true for all substances as they change state no matter how much heat is added. As long as the water is still boiling and not all the water has completely changed to a gas (steam) the temperature remains at 212 degrees F. This means that a thermometer placed in boiling water will remain at 212 degrees throughout the boiling process even though heat is added to cause the water to boil. This heat of boiling is called latent heat. The word “latent” is a Latin word for “hidden”. The heat added to the water is hidden from the thermometer since the temperature remains unchanged during the boiling process.
After all the water has changed to a gas or vapor (steam), then the addition of still more heat to the vaporized water or steam will cause the temperature of the steam to increase above its boiling temperature of 212 degrees. Any increase in temperature of the steam above its boiling point (212 degrees) is called “superheat”. Steam at 213 degrees F is superheated by one degree F.
Superheat is then any temperature of a gas above the boiling point for that liquid. When a refrigerant liquid boils at a low temperature of 40 degrees in a cooling coil and then the refrigerant gas increases in temperature superheat has been added. If this refrigerant changed from a liquid to a gas or vapor at 40 degrees and then the refrigerant vapor increased in temperature to 50 degrees F, then it has been superheated by 10 degrees.
We commonly think of boiling as always being accomplished by a liquid when it is hot. This is because we are familiar with boiling water. However, air conditioning and refrigeration systems use liquids (refrigerants) with much lower boiling points. If a liquid refrigerant boils at -10 degrees and is then warmed up to zero degrees, it is then a superheated gas containing 10 degrees of superheat. Heating that same refrigerant gas to +10 degrees means that it now has been superheated by 20 degrees.
Lowering the pressure over a liquid lowers the boiling point. There is less pressure above the liquid to overcome. That is why water at the top of a mountain may boil at 190 degrees (depending upon the altitude) rather than at 212 degrees F. By controlling the pressure over a liquid, we can control the boiling temperature. That is why a service technician monitors the pressures in an air conditioning system. The technician is actually monitoring the pressures and temperatures where the refrigerant is changing state.
Saturation:
Saturation is simply the term used to describe the point where a change of state in a substance is taking place. For water at sea level, the boiling temperature is 212 degrees F. Therefore, we say the saturation (boiling temperature) is 212 degrees. As soon as the temperature of the steam is heated above it’s “saturation” temperature, it has been superheated. Refrigerant that has boiled (turned into a vapor) at 40 degrees has a saturation temperature of 40 degrees. If the refrigerant vapor is heated to 41 degrees it is no longer saturated, it is then superheated by 1 degree. Remember, only a gas or vapor can be superheated. Superheat is any temperature of a gas or vapor above its saturation temperature.
Subcooling:
Subcooling is now easy to understand. Only liquids and solids can be subcooled. Subcooling is any temperature of a liquid or solid below its saturation temperature. Let’s use water as an example again. Liquid water at sea level has a saturation (boiling) temperature of 212 degrees F. If we were to add heat to the saturated water it would first boil away with no change in temperature (remember latent heat?) and then become superheated if still more heat were added to the vapor (steam) after it had all turned to a vapor.
Instead of boiling our 212 degree water by adding heat, we shall remove heat from the 212 degree water. As heat is removed from the liquid water it’s temperature will drop below its boiling (saturation) temperature. Water at 211 degrees has been subcooled by one degree F. If the temperature of the water is decreased to 180 degrees the water has been subcooled from 212 degrees to 180 degrees. That is, it has been subcooled by 32 degrees. When you drink 180 degree coffee, you are drinking a subcooled liquid!
Sensible Heat & Latent Heat:
Sensible heat is heat that can be measured by a thermometer. Anytime heat is added or removed from a substance and a temperature change occurs, a sensible heat change has taken place. Since both superheat and Subcooling are changes in temperature, they are both sensible heat processes.
When an air conditioning system cools air sensible heat has been removed. In fact, since the air is a gas or vapor and is heated far above its boiling (saturation) point, it is superheated air. Yes, you are breathing superheated air as the air is hundreds of degrees above the temperature at which the gases which make up air would condense back into liquid form.
Superheated does not necessarily mean hot. And, subcooled does not necessarily mean cold. Superheat and Subcooling are determined by the boiling temperature of the substance and unlike water many substances have low boiling temperatures.
Recalling that latent heat is the heat which is added to a liquid to cause it to change from a liquid to a gas (boiling) without a change in temperature, let’s go to the next step. When a gas or vapor is above its boiling point it is said to be superheated. Cooling the gas removes it’s superheat. When all the superheat is removed from a gas, the gas will condense back into a liquid. The heat removed from a saturated gas to allow it to condense back into a liquid is once again latent or hidden heat and is not a sensible heat process. That is, during the process of changing from a gas to a liquid it occurs at a constant temperature therefore a thermometer will not detect any temperature change. That is latent heat.
Air contains water vapor or moisture. Humid air is not comfortable. Too much humidity (moisture) in air is uncomfortable. As air containing too much moisture passes over a properly designed, installed and operating air conditioning system, the air is cooled by the air conditioning coil (evaporator) located at the indoor blower section. If the air containing the moisture is cooled to the condensing temperature (dew point) of the moisture in the air, some of the moisture will condense and deposit on the coil and fins of the cooling coil. Since the water vapor is changing from a gas or vapor to a liquid, this is a latent heat process. The condensed water should run off the coil and be drained away.
A properly operating air conditioning system both cools (a sensible heat process) and dehumidifies (a latent heat process) the air. For example, given a 3-ton residential air conditioning system, a percentage of the total capacity of the system is utilized to cool the air while the remaining percentage of the total capacity is used to dehumidify the air. Properly controlling both the temperature (sensible heat) and the humidity (latent heat) will provide the optimum comfort for the occupants.
Measuring Heat:
Latent heat cannot be directly measured as we can sensible heat. In order to properly adjust, troubleshoot and repair air conditioning equipment it is necessary that we understand heat and how to measure heat.
Superheat and Subcooling are both sensible heats and therefore can be measured with a thermometer. Superheat and Subcooling are also temperature differentials. That is, each is a number of degrees a gas or liquid are above or below their saturation temperatures. It is essential that a service technician be able to accurately measure these differentials and diagnose system operation from them.
A high quality, accurate electronic thermometer capable of measuring temperature differentials is almost an essential tool for the technician and highly useful to the interested homeowner. An example of such an instrument is Bacharach’s “Dual Channel. Model TH3000, digital thermometer” with data hold and max hold functions.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications. He is currently a senior training specialist with Johnson Controls.
He can be contacted at norman.christopherson@jci.com
The Essentials Of Working With R-410A Refrigerant
The Essentials Of Working With R-410A
By Norm Christopherson
Several major manufacturers are producing comfort air conditioning equipment using refrigerant 410A. The trend towards the use of 410A continues to grow and there is a demand for technicians who are comfortable working with this higher-pressure replacement for refrigerant 22. Due to the differences between refrigerant 22 and the newer 410A, there is a concern within the industry regarding what those differences are as well as the additional training required to safely work on 410A systems.
In an effort to properly educate installation and service technicians on the safe use, proper installation and servicing of 410A systems, several industry organizations, backed by numerous manufacturers created the “AC & R Safety Coalition”. This coalition produced a safety & training booklet and with the aid of ESCO Institute created a voluntary R-410a technician certification test. Although the 410A safety & training certification is not mandated by any government agency there is a movement to certify as many installers and technicians as possible in an effort to improve the understanding and safe handling of this higher pressure refrigerant.
Some manufacturers, contractors and industry organizations seem to be “almost” requiring those who do business with them or work for them to become certified in the safe and proper use of R-410A. Although this particular certification is voluntary, failure to certify may cost contractors and technicians some lost business.
The purpose of this article is to provide a brief overview of the essentials of working with R-410a. Those who have the time and opportunity to attend a R-410a certification seminar are encouraged to do so. Most of the seminars and published materials on this topic not only cover the specific differences necessary to the safe and proper handling of 410a, but they also review information that technicians should already know anyway.
In this article only the essential differences between R-22 usage and R-410A usage will be discussed. However, if a technician is going to take the voluntary 410A safety exam he or she will be required to answer a number of general questions common to the function, operation and servicing of all mechanical compression cooling systems. Every technician is expected to have a good solid knowledge of the complete mechanical cycle, superheat, subcooling, latent heats and the major components of a system. A review of the basic system, accessories and even global warming and ozone depletion is essential.
Why 410A?
Refrigerant 410A was developed to replace refrigerant 22 because R-22 is being phased out due to its ozone depletion potential. R-410A has no ozone depletion potential but does have a higher global warming potential. However, according to experts, the overall global warming potential with R-410A should decrease because of its higher efficiency reducing power plant emissions.
The Essentials Of R-410A
System Pressures
Technicians with R-22 experience will need to become familiar with working with high and low side pressures that are much higher when using R-410A. A typical R-22 system operating normally with a head pressure of 260 psig at a 120-degree condensing temperature and a low side pressure of 76 psig at a 45-degree evaporator saturation temperature will find the equivalent pressures in a R-410A system to be much higher.
A normally operating R-410A system with the same condensing temperature of 120 degrees and a 45 degree evaporator saturation temperature will have a high side pressure of 418 psig and a low side pressure of 130 psig.
Although refrigerant 410A is a near-azeotrope and has a slight temperature glide, there is no need to correct for refrigerant dew point and bubble point differences. Superheat and subcooling calculations can be calculated the same way we have always done with R-22 refrigerant. The only difference will be the higher pressure-temperature relationship when reading the temperature-pressure chart. The temperature glide for R-410A is only .3 degrees Fahrenheit and can be ignored and fractionation is not a concern.
Compression Ratio & System Efficiency
At first glance, one might ask the question, with 410A operating at higher pressures are the compression ratio higher and the efficiency less? The answer is no, the compression ratio is about the same or slightly lower than that of R-22 and the efficiency is higher. Compression ratio is the absolute high side pressure divided by the absolute low side pressure. The compression ratio is affected by the pressure differential between the high and low sides of the system not how high both pressures are. Using the previous examples comparing the operating pressures of an R-22 system to an R-410A system, the R-22 system would have a compression ratio of 3.02:1, while the R-410A system would have a compression ratio of 2.98:1. The actual efficiency gains from R-410A are due to its superior thermodynamic values over R-22. Under identical operating conditions the discharge temperature on a 410A system may actually be lower than on an R-22 system.
With all else being equal, it is possible to manufacture an R-410A air conditioning system that is physically smaller using less refrigerant and a smaller compressor than an R-22 system of the same capacity and SEER rating.
Compressors
Compressors used on 410A systems use thicker metals to withstand the higher operating pressures. Therefore, only a compressor designed for 410A should be used with 410A. The ideal compressor type for use with 410A is a scroll built to withstand the higher pressures. The scroll compressor has the advantage over the reciprocating compressor when comparing volumetric efficiencies and internal heat transfer losses between the suction and discharge ports. Scroll compressors compress the refrigerant in stages through the use of up to six individual pockets in its scroll assembly while reciprocating compressors raise the pressure from the suction pressure to the high side pressure in a single stroke. In addition, the scroll compressor’s suction and discharge openings are farther apart than those in a reciprocating compressor thus decreasing heat transfer losses between the suction and discharge ports.
The internal pressure relief valves inside the compressor opens at a pressure between 550 & 625 psig on compressors designed for R-410A service. Compressors designed for R-22 service have internal pressure relief valve settings that open between 375 & 450 psig. So only compressors rated to work with R-22 should be used with R-22 and those rated for use with R-410A used with R-410A.
Metering Devices
The metering device used in a 410A system must be about 15% smaller in capacity as opposed to a metering device used in a R-22 system of the same capacity. It is imperative that only a metering device designed and properly sized for R-410A be used on a R-410A system. In fact, no parts designed for R-22 use should be used on a 410A system.
Refrigerant Lines
Refrigerant lines used for R-410A must be properly sized for R-410A systems. It is possible to use existing refrigerant lines from an R-22 system in a R-410A system installation if they are of the correct size however, they must be cleaned of all debris and oil. The best practice is to replace the lines with new copper liquid and suction lines to ensure they are clean and do not have any weak areas that could be a problem at the higher operating pressures of 410A.
Driers & System Accessories
The desiccants used in R-410A systems are the same as those used for most other refrigerants. Zeolites, molecular sieve type desiccants work on the principle of a material with small pockets or areas that adsorb moisture by the process of capillary action. This type of desiccant seems to work well with all modern refrigerants including R-410A. The metal shell containing the filter-drier however, must be thicker to withstand the higher pressures of 410A. Therefore, only use filter-driers rated for use on R-410A. R-410A filter-driers are those rated for pressures no less than 600 psig.
When removing a filter-drier from a system it should be cut out with a tubing cutter not a torch flame. The desiccant in a filter drier adsorbs and holds moisture better when it is cool or cold. Therefore, if the desiccant is heated moisture may be driven out of the desiccant and into the system creating a moisture problem. This is of greater concern on R-410A systems because the oil used (POE) is highly hygroscopic. Once moisture is absorbed in a POE oil it is difficult to remove. Usually an oil change is necessary.
The practice of replacing the filter-drier every time the system is opened is particularly important on R-410A systems because of the hygroscopic nature of the oil used.
Pressure Control Settings
Because of the higher operating pressures, the high & low-pressure control settings must be higher than those encountered on R-22 systems. The recommended high-pressure control settings are a cut-out pressure of 610 psig and a cut-in pressure of approximately 500 psig. The recommended low-pressure control setting is a cut-out pressure of 50 psig. Make sure the pressure control you are using on a 410A system has the correct pressure range allowing it to be adjusted for the correct pressures.
Oil
R-410A systems use a synthetic Poly Ester (POE) oil. This oil has superior lubricating ability over the mineral oils commonly used in R-22 systems. Only POE oil should be used in a 410A system. However, not all POE oils are the same. There is a variety of POE oil types and grades therefore, it is important to know which POE oil is in the system being serviced. Mixing some POE oils may create a compatibility problem and lead to a system failure.
All POE oils are highly hygroscopic. That is, they absorb moisture quickly and hold the moisture they absorb. Once absorbed, the moisture cannot be removed through system evacuation even at vacuum pressures of 500 microns. Therefore, it is important to prevent moisture from getting in the oil in the first place. The general recommendations for handling POE oil is to keep it in a metal container, transfer it with an oil pump and keep the container sealed except when absolutely necessary. POE oils are also irritating to the skin and a real medical concern if it comes in contact with your eyes. Gloves and safety glasses are essential items when working with this oil.
Brazed Connections
The higher operating pressures encountered with R-410A systems requires the use of brazing materials rated to withstand these pressures. Some technicians have used lower temperature solders when making tubing connections on R-22 systems. Such should not be the practice on R-410A systems. It is the author’s opinion that only high temperature brazing materials such as Silphos type brazing rod or one of the silver solders should be used on any R-22 system. It is even more important to use suitable brazing materials on R-410A systems.
Moisture & Evacuation
The hygroscopic nature of the oils used in R-410A systems cannot be over-emphasized. Moisture can be a significant problem to the proper operation and life expectancy of any system operating on the mechanical refrigerant cycle. Therefore, it is more important than in the past to take precautions to keep moisture out of a system during installation and service, to evacuate to 500 microns and replace filter-driers when a system has been opened. Questionable workmanship that may have gotten us by when working on R-22 systems will not be tolerated by R-410A systems.
System Conversions
System conversions are simply out of the question. After reading this far, it should be obvious that the differences in construction of R-410A systems exceed the practical and economic limits of converting an R-22 system to R-410A.
Tools
Gauge manifold sets, hoses, recovery cylinders and the recovery machine must be rated for the higher pressures encountered with R-410A. An attempt to use standard refrigerant service tools on 410A systems is very dangerous and simply foolish. This is a safety issue of great concern to the industry and is one of the reasons the AC&R Safety Coalition was formed and R-410A safety & handling certification was established.
Recovery cylinders must be rated for R-410A use. These cylinders meet the Department Of Transportation, DOT 4BA 400 or DOT 4BW 400 standards for recovery cylinders. Be very careful here, it would be very easy and convenient to use whatever recovery cylinder was handy rather than the correct cylinder. Such a mistake could be the last one a technician makes.
Leak Detection
R-410A is an HFC refrigerant. Therefore, any leak detection device or method that works for other HFC refrigerants will work for R-410A.
Recovery of 410A
Standard recovery procedures for R-410A remain unchanged. The only difference is the necessity to use a recovery machine and cylinders approved for the higher pressures of R-410A.
Charging
Since R-410A has a slight (.3 degree) fractionation it like all other 400 series refrigerants must be charged in the liquid state. Otherwise, follow the manufacturers recommended charging procedure. The dewpoint and bubble point temperatures may be ignored (They are not even listed on temperature-pressure charts for R-410A) when calculating system superheat and subcooling.
Personal Safety
Personal safety is always of utmost importance when working on any job or piece of equipment. Safety glasses and gloves should be worn no matter what refrigerant is being used. However, because of the higher pressures of R-410A safety is of even greater significance. If it is necessary to heat a cylinder of R-410A to raise its pressure in cooler weather, heat the cylinder with water no hotter than 90 degrees and never heat the cylinder with a flame. Don’t allow the cylinder to reach temperature more than 125 degrees Fahrenheit during transport or storage. A cylinder of R-410A at 125 degrees exerts a cylinder pressure of 450 psig.
Attend a 410A safe use and handling seminar and take the voluntary 410A certification exam developed by the AC & R Safety Coalition. Set yourself and your contractor apart as certified, qualified and safe providers of the new 410A systems. This refrigerant and its systems are here to stay.
@Copyrighted material, Norm Christopherson is a senior training specialist with Johnson Controls. He can be reached at norman.christopherson@jci.com
By Norm Christopherson
Several major manufacturers are producing comfort air conditioning equipment using refrigerant 410A. The trend towards the use of 410A continues to grow and there is a demand for technicians who are comfortable working with this higher-pressure replacement for refrigerant 22. Due to the differences between refrigerant 22 and the newer 410A, there is a concern within the industry regarding what those differences are as well as the additional training required to safely work on 410A systems.
In an effort to properly educate installation and service technicians on the safe use, proper installation and servicing of 410A systems, several industry organizations, backed by numerous manufacturers created the “AC & R Safety Coalition”. This coalition produced a safety & training booklet and with the aid of ESCO Institute created a voluntary R-410a technician certification test. Although the 410A safety & training certification is not mandated by any government agency there is a movement to certify as many installers and technicians as possible in an effort to improve the understanding and safe handling of this higher pressure refrigerant.
Some manufacturers, contractors and industry organizations seem to be “almost” requiring those who do business with them or work for them to become certified in the safe and proper use of R-410A. Although this particular certification is voluntary, failure to certify may cost contractors and technicians some lost business.
The purpose of this article is to provide a brief overview of the essentials of working with R-410a. Those who have the time and opportunity to attend a R-410a certification seminar are encouraged to do so. Most of the seminars and published materials on this topic not only cover the specific differences necessary to the safe and proper handling of 410a, but they also review information that technicians should already know anyway.
In this article only the essential differences between R-22 usage and R-410A usage will be discussed. However, if a technician is going to take the voluntary 410A safety exam he or she will be required to answer a number of general questions common to the function, operation and servicing of all mechanical compression cooling systems. Every technician is expected to have a good solid knowledge of the complete mechanical cycle, superheat, subcooling, latent heats and the major components of a system. A review of the basic system, accessories and even global warming and ozone depletion is essential.
Why 410A?
Refrigerant 410A was developed to replace refrigerant 22 because R-22 is being phased out due to its ozone depletion potential. R-410A has no ozone depletion potential but does have a higher global warming potential. However, according to experts, the overall global warming potential with R-410A should decrease because of its higher efficiency reducing power plant emissions.
The Essentials Of R-410A
System Pressures
Technicians with R-22 experience will need to become familiar with working with high and low side pressures that are much higher when using R-410A. A typical R-22 system operating normally with a head pressure of 260 psig at a 120-degree condensing temperature and a low side pressure of 76 psig at a 45-degree evaporator saturation temperature will find the equivalent pressures in a R-410A system to be much higher.
A normally operating R-410A system with the same condensing temperature of 120 degrees and a 45 degree evaporator saturation temperature will have a high side pressure of 418 psig and a low side pressure of 130 psig.
Although refrigerant 410A is a near-azeotrope and has a slight temperature glide, there is no need to correct for refrigerant dew point and bubble point differences. Superheat and subcooling calculations can be calculated the same way we have always done with R-22 refrigerant. The only difference will be the higher pressure-temperature relationship when reading the temperature-pressure chart. The temperature glide for R-410A is only .3 degrees Fahrenheit and can be ignored and fractionation is not a concern.
Compression Ratio & System Efficiency
At first glance, one might ask the question, with 410A operating at higher pressures are the compression ratio higher and the efficiency less? The answer is no, the compression ratio is about the same or slightly lower than that of R-22 and the efficiency is higher. Compression ratio is the absolute high side pressure divided by the absolute low side pressure. The compression ratio is affected by the pressure differential between the high and low sides of the system not how high both pressures are. Using the previous examples comparing the operating pressures of an R-22 system to an R-410A system, the R-22 system would have a compression ratio of 3.02:1, while the R-410A system would have a compression ratio of 2.98:1. The actual efficiency gains from R-410A are due to its superior thermodynamic values over R-22. Under identical operating conditions the discharge temperature on a 410A system may actually be lower than on an R-22 system.
With all else being equal, it is possible to manufacture an R-410A air conditioning system that is physically smaller using less refrigerant and a smaller compressor than an R-22 system of the same capacity and SEER rating.
Compressors
Compressors used on 410A systems use thicker metals to withstand the higher operating pressures. Therefore, only a compressor designed for 410A should be used with 410A. The ideal compressor type for use with 410A is a scroll built to withstand the higher pressures. The scroll compressor has the advantage over the reciprocating compressor when comparing volumetric efficiencies and internal heat transfer losses between the suction and discharge ports. Scroll compressors compress the refrigerant in stages through the use of up to six individual pockets in its scroll assembly while reciprocating compressors raise the pressure from the suction pressure to the high side pressure in a single stroke. In addition, the scroll compressor’s suction and discharge openings are farther apart than those in a reciprocating compressor thus decreasing heat transfer losses between the suction and discharge ports.
The internal pressure relief valves inside the compressor opens at a pressure between 550 & 625 psig on compressors designed for R-410A service. Compressors designed for R-22 service have internal pressure relief valve settings that open between 375 & 450 psig. So only compressors rated to work with R-22 should be used with R-22 and those rated for use with R-410A used with R-410A.
Metering Devices
The metering device used in a 410A system must be about 15% smaller in capacity as opposed to a metering device used in a R-22 system of the same capacity. It is imperative that only a metering device designed and properly sized for R-410A be used on a R-410A system. In fact, no parts designed for R-22 use should be used on a 410A system.
Refrigerant Lines
Refrigerant lines used for R-410A must be properly sized for R-410A systems. It is possible to use existing refrigerant lines from an R-22 system in a R-410A system installation if they are of the correct size however, they must be cleaned of all debris and oil. The best practice is to replace the lines with new copper liquid and suction lines to ensure they are clean and do not have any weak areas that could be a problem at the higher operating pressures of 410A.
Driers & System Accessories
The desiccants used in R-410A systems are the same as those used for most other refrigerants. Zeolites, molecular sieve type desiccants work on the principle of a material with small pockets or areas that adsorb moisture by the process of capillary action. This type of desiccant seems to work well with all modern refrigerants including R-410A. The metal shell containing the filter-drier however, must be thicker to withstand the higher pressures of 410A. Therefore, only use filter-driers rated for use on R-410A. R-410A filter-driers are those rated for pressures no less than 600 psig.
When removing a filter-drier from a system it should be cut out with a tubing cutter not a torch flame. The desiccant in a filter drier adsorbs and holds moisture better when it is cool or cold. Therefore, if the desiccant is heated moisture may be driven out of the desiccant and into the system creating a moisture problem. This is of greater concern on R-410A systems because the oil used (POE) is highly hygroscopic. Once moisture is absorbed in a POE oil it is difficult to remove. Usually an oil change is necessary.
The practice of replacing the filter-drier every time the system is opened is particularly important on R-410A systems because of the hygroscopic nature of the oil used.
Pressure Control Settings
Because of the higher operating pressures, the high & low-pressure control settings must be higher than those encountered on R-22 systems. The recommended high-pressure control settings are a cut-out pressure of 610 psig and a cut-in pressure of approximately 500 psig. The recommended low-pressure control setting is a cut-out pressure of 50 psig. Make sure the pressure control you are using on a 410A system has the correct pressure range allowing it to be adjusted for the correct pressures.
Oil
R-410A systems use a synthetic Poly Ester (POE) oil. This oil has superior lubricating ability over the mineral oils commonly used in R-22 systems. Only POE oil should be used in a 410A system. However, not all POE oils are the same. There is a variety of POE oil types and grades therefore, it is important to know which POE oil is in the system being serviced. Mixing some POE oils may create a compatibility problem and lead to a system failure.
All POE oils are highly hygroscopic. That is, they absorb moisture quickly and hold the moisture they absorb. Once absorbed, the moisture cannot be removed through system evacuation even at vacuum pressures of 500 microns. Therefore, it is important to prevent moisture from getting in the oil in the first place. The general recommendations for handling POE oil is to keep it in a metal container, transfer it with an oil pump and keep the container sealed except when absolutely necessary. POE oils are also irritating to the skin and a real medical concern if it comes in contact with your eyes. Gloves and safety glasses are essential items when working with this oil.
Brazed Connections
The higher operating pressures encountered with R-410A systems requires the use of brazing materials rated to withstand these pressures. Some technicians have used lower temperature solders when making tubing connections on R-22 systems. Such should not be the practice on R-410A systems. It is the author’s opinion that only high temperature brazing materials such as Silphos type brazing rod or one of the silver solders should be used on any R-22 system. It is even more important to use suitable brazing materials on R-410A systems.
Moisture & Evacuation
The hygroscopic nature of the oils used in R-410A systems cannot be over-emphasized. Moisture can be a significant problem to the proper operation and life expectancy of any system operating on the mechanical refrigerant cycle. Therefore, it is more important than in the past to take precautions to keep moisture out of a system during installation and service, to evacuate to 500 microns and replace filter-driers when a system has been opened. Questionable workmanship that may have gotten us by when working on R-22 systems will not be tolerated by R-410A systems.
System Conversions
System conversions are simply out of the question. After reading this far, it should be obvious that the differences in construction of R-410A systems exceed the practical and economic limits of converting an R-22 system to R-410A.
Tools
Gauge manifold sets, hoses, recovery cylinders and the recovery machine must be rated for the higher pressures encountered with R-410A. An attempt to use standard refrigerant service tools on 410A systems is very dangerous and simply foolish. This is a safety issue of great concern to the industry and is one of the reasons the AC&R Safety Coalition was formed and R-410A safety & handling certification was established.
Recovery cylinders must be rated for R-410A use. These cylinders meet the Department Of Transportation, DOT 4BA 400 or DOT 4BW 400 standards for recovery cylinders. Be very careful here, it would be very easy and convenient to use whatever recovery cylinder was handy rather than the correct cylinder. Such a mistake could be the last one a technician makes.
Leak Detection
R-410A is an HFC refrigerant. Therefore, any leak detection device or method that works for other HFC refrigerants will work for R-410A.
Recovery of 410A
Standard recovery procedures for R-410A remain unchanged. The only difference is the necessity to use a recovery machine and cylinders approved for the higher pressures of R-410A.
Charging
Since R-410A has a slight (.3 degree) fractionation it like all other 400 series refrigerants must be charged in the liquid state. Otherwise, follow the manufacturers recommended charging procedure. The dewpoint and bubble point temperatures may be ignored (They are not even listed on temperature-pressure charts for R-410A) when calculating system superheat and subcooling.
Personal Safety
Personal safety is always of utmost importance when working on any job or piece of equipment. Safety glasses and gloves should be worn no matter what refrigerant is being used. However, because of the higher pressures of R-410A safety is of even greater significance. If it is necessary to heat a cylinder of R-410A to raise its pressure in cooler weather, heat the cylinder with water no hotter than 90 degrees and never heat the cylinder with a flame. Don’t allow the cylinder to reach temperature more than 125 degrees Fahrenheit during transport or storage. A cylinder of R-410A at 125 degrees exerts a cylinder pressure of 450 psig.
Attend a 410A safe use and handling seminar and take the voluntary 410A certification exam developed by the AC & R Safety Coalition. Set yourself and your contractor apart as certified, qualified and safe providers of the new 410A systems. This refrigerant and its systems are here to stay.
@Copyrighted material, Norm Christopherson is a senior training specialist with Johnson Controls. He can be reached at norman.christopherson@jci.com
Dessicants and Filter-Driers
By Norm Christopherson
Filter-driers play a pivotal role in the operation of hvac systems. At the heart of the drier is the desiccant held in the drier’s cylindrical metal container. As important as the filter-drier is few actually understand how they work. Here are some details.
The word “desiccate” means to dry out completely and a desiccant is a material or substance that accomplishes the moisture removal. Moisture in the mechanical refrigeration cycle is detrimental to the operation and life of the system. The filter-drier is an accessory that performs the functions of filtering out particles and removing and holding moisture to prevent it from circulating through the system.
Moisture In A System
Consider a chemist working with chemical elements to create new substances. The chemist combines atoms of selected elements to cause them to bond or link together to form new combinations of molecular structures. These new molecular structures are called compounds. Chemists perform such creations in the process of developing new synthetic oils, refrigerants, glues, rubbers, metal allows and a host of other products that are useful in many ways.
Some combinations of atomic elements create molecular structures that can be either useful or harmful. Acids are formed when the right combination of elements are linked together chemically. If we have a use for the acid and use it for its intended purpose, all is well. However, in some cases unwanted chemical combinations occur where we least want them and where they cause serious harm. Under certain circumstances hydrochloric and hydrofluoric acids chemically form in the mechanical refrigerant system. This, of course is what we want to prevent.
Again, let us consider how the chemist facilitates the chemical bonding process. The chemist wants certain chemical reactions to take place in an effort to create new substances that hopefully have special properties that are useful. Perhaps the chemist is attempting to create a new refrigerant to replace another that is being phased-out. The chemist combines particular elements to form bonds or links that when complete meet all the qualities of a great refrigerant. A catalyst is anything that hastens, encourages or helps bring about a result. Heat is one of chemistry’s most active catalysts. A chemist may purposely add heat to a beaker of chemicals to cause them to combine to form a new substance.
The HVAC System As A Chemistry Set
That’s right, the mechanical refrigeration system consisting of a compressor, condenser, metering device, evaporator, copper lines, oil and refrigerant are a complete chemistry set including several powerful catalysts!
The system contains components which consist of a number of metals such as the iron casting of the compressor, copper lines, steel condenser, aluminum evaporator, brass valves and fittings and perhaps still other metals in smaller quantities. The components are assembled using still other metals and chemicals during the brazing process. Flux is applied to facilitate the chemical process of brazing and heat is applied with a torch as the catalyst.
Still other materials (chemicals) are contained in the system. Compressor motor winding insulation and varnishes, epoxy glues and perhaps rubber and gasket materials are applied. Of course, two of the major chemical materials that constantly circulate through the system are the refrigerant and oil.
The system contains a vast number of chemicals. (Everything physical is chemical and consists of atoms capable of bonding with atoms of other elements under the right circumstances) Now, if yet additional elements are introduced to the existing combination of elements making up the system the chemical bonding possibilities become still greater. During the installation or servicing of the system air consisting of hydrogen, nitrogen and oxygen may be introduced. Moisture may be introduced and flux or even powder from the inside of Armaflex insulation may get into the system. The moisture and oxygen are very active components that act as catalysts themselves.
Additional catalysts in the form of heat of compression as well as latent heat in the condenser and pressure are present. Imagine the possibilities! The chemicals present are compressed, heated and liquefied. Then they are evaporated and cooled as the pressure is released. Then, the process is continually repeated for hours, days and months until a chemical reaction takes place. On hot days the high temperature and pressure on the high side of the system reaches still higher levels. The catalysts of heat and pressure could almost make a chemist jealous.
When a chemical reaction occurs the typical chemical bonding creates hydrochloric and hydrofluoric acids. These acids then go to work breaking down the metals and other materials of construction adding soluble metal to the chemical reaction. A number of other chemical reactions may take place and the circulating refrigerant and oil carry the entire mix throughout the system where it can continue the process.
One authority on acids informs us that for every 18 degrees Fahrenheit an acid is heated, its activity level doubles.
Eventually, the motor winding insulation may be destroyed and the motor windings begin to pass electrical current between each other. As the motor begins to burnout smoldering products from the burning motor are pumped throughout the system. Remember, the motor will be cooking and burning while the compressor is pumping these products through the system. Liquid refrigerant and oil are fairly good cleaning agents so the piping where liquid refrigerant is located may remain fairly clean of the resulting debris. However, in the evaporator a distillation process is taking place, the refrigerant is changing from a liquid to a gas so the debris becomes separated from the refrigerant and begins getting deposited in the evaporator and suction line. This is why the low side of a system that has experienced a compressor burnout is where the majority of the debris is located.
Keep It Clean!
The case has been made as to how important it is to prevent chemical reactions from taking place in a system. It almost seems from what we have described up to this point that it could be difficult to prevent chemical breakdown from occurring. Fortunately, the installation crew and service technician can prevent system failure due to a chemical reaction.
It is imperative that installation and service technicians prevent foreign materials, air, moisture, brazing flux, carbon created during brazing and Armaflex insulation powder from entering or remaining in a system. Good piping practice includes bleeding a small amount of dry nitrogen through the system while brazing. Pipe ends need to be sealed prior to sliding pipe insulation over the piping. A good 500 micron evacuation should be reached to remove air and moisture before charging with refrigerant. And, the addition of a properly sized filter-drier is important on both new systems as well as anytime a system is opened for service. The filter-drier is designed to both remove any particulates that may circulate as well as collect and hold any moisture that may remain in the system. The use of a filter-drier containing a good desiccant has become even more important with the advent of R-410A systems, which utilize the highly hygroscopic synthetic Poly Ester oils.
How A Desiccant Works
Modern filter-driers contain desiccants that function on the principle of adsorption. Adsorption is not the same as absorption. The term absorption is commonly misused in the technical sense of the term. When we say that a sponge or paper towel absorbs a liquid spill we are using the term in its non-technical sense. Actually, absorption is the attraction and holding power through chemical action. Modern desiccants do not function on the basis of a chemical attraction. The desiccants commonly used in filter-driers utilize the process of adsorption. Adsorption is a physical process and is simpler and easier to understand then the more complex chemical process of absorption.
The modern desiccant of choice is a material called zeolite. Zeolite has gained in popularity over the older desiccants activated alumina, silica gel, calcium chloride and calcium oxide. Zeolite is a mineral that occurs in nature or can be manufactured. Zeolite is an inorganic tan or gray porous solid consisting of a structure of pores and tiny chamber capable of collecting and holding moisture through capillary action. Adsorption is the physical trait of capillary action whereby moisture is drawn into small pores much like a sponge or paper towel collects liquid spills. There are hundreds of different zeolites each with its own micro sized shape, lattice structure and size. Zeolites can be selected to collect and hold many different substances according to the molecular size and structure of the specific molecule one wishes to collect. The zeolite selected for use in a filter-drier is selected to adsorb moisture while allowing refrigerant to pass through. One example of a zeolite is a very light and porous volcanic rock. Zeolite filters are used as desiccants and filters for refrigerant, acids, specific chemicals and to remove ammonia in fish tanks.
Zeolite desiccants are formed into a porous solid core, which is placed in the filter-drier container. Older loose fill desiccants like silica gel occasionally broke down into particles or dust that sometimes left the filter-drier and circulated through the system often creating a restriction especially on capillary tube systems. This was avoided by positioning the filter-drier vertically so pressure pulsations in the system did not shift the loose fill back and forth physically breaking down the loose fill. Solid core zeolite desiccant filter-driers may be installed in any position. Most solid core desiccants are molded into a cylindrical block with a tapered axial hole down the center to allow for the uniform flow of the refrigerant through the entire bed of desiccant. This is why filter-driers are directional with the direction of flow indicated on the container. Installing the filter-drier in the wrong direction causes non-uniform refrigerant to desiccant contact and increases pressure drop. Bi-flow filter-driers are available for heat pump applications.
Capacity
Capacity refers to the amount of moisture the desiccant in the filter-drier can hold. Capacity is measured in “parts per million”. One part per million (ppm) is one part of water per million parts of refrigerant. In practical terms this would be approximately equal to one drop of water in a 125-pound drum of refrigerant. Desiccant capacities are rated at 75 & 125 degrees F. The older desiccant, activated alumina had a moisture holding capacity of 4 grams of moisture per each 100 grams of desiccant. Silica gel had a moisture holding capacity of 3 grams of moisture per each 100 grams of desiccant. Modern zeolite, molecular sieve desiccants have a capacity of approximately 16 grams of moisture per 100 grams of desiccant.
The capacity of a desiccant is temperature dependent. The colder the desiccant the more moisture it can hold. Therefore, locating a filter-drier in a cooler location is an advantage. Removing a brazed filter-drier with a torch flame causes moisture to be driven out of the desiccant and into the system. Generally, it is better to cut the filter-drier out with a tubing cutter.
Location
The desiccant works better at removing and holding moisture when it is placed in a refrigerant line where the refrigerant is in the liquid state. The filter-drier is often called a “liquid line filter-drier” for this reason.
Suction Line Filter-Driers
The desiccant is still able to adsorb moisture when applied to the suction line but not quite as effectively. Special suction line filter-driers are made for cleaning up a system after a compressor burnout. A larger shell is used to minimize pressure drop on suction line driers. Suction line filter-driers marked as “HH” driers contain carbon filter material in addition to the zeolite desiccant. The carbon and zeolite are capable of capturing and holding acids as well as moisture. Suction line filter-driers used to clean up a system after a burn out should be replaced until the system is known to be clean and no longer tests positive for acids in the system. A suction line filter-drier with an excessive pressure drop across it should not be left in a system. An excessive pressure drop in the suction line reduces the volumetric efficiency of the compressor thus reducing system-operating capacity. Many suction line filter driers have a pressure tap on the inlet end so the pressure on the inlet of the drier can be compared to the pressure at the suction service valve at the compressor. Still other suction line filter-driers have pressure taps on both the inlet and outlet.
Alcohol Additives
Some technicians add alcohol-based additives to a moisture-ridden system to prevent moisture from freezing and restricting the metering device. Modern zeolite molecular sieve desiccants have the ability to adsorb these additives to an even greater degree than moisture. It is possible for a desiccant that has already captured moisture to release some of that moisture and replace it with the alcohol additive thus reducing the moisture capacity of the desiccant.
Reactivating Filter-Driers
In the past, some have attempted to reactivate and reuse a filter-drier by heating and evacuating the desiccant. Heating and evacuating does actually remove much of the moisture and allow the drier to be used again. However, oils, carbon and other particles are not removed during this reactivation attempt. In fact, the oil may be cooked into the desiccant creating new contamination possibilities. The cost of a new filter-drier is not worth the effort and is not recommended.
Don’t allow a system to become an out of control chemistry set. Good piping practice, a nitrogen purge during brazing, a deep evacuation and the proper installation and use of filter-driers containing modern and effective molecular sieve desiccants will prevent many system failures. Many compressor failures are blamed on the compressor when the actual problem was caused by a system problem. That system problem may have been a chemical problem due to moisture.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications. He currently is a senior training specialist for Johnson Controls.
Filter-driers play a pivotal role in the operation of hvac systems. At the heart of the drier is the desiccant held in the drier’s cylindrical metal container. As important as the filter-drier is few actually understand how they work. Here are some details.
The word “desiccate” means to dry out completely and a desiccant is a material or substance that accomplishes the moisture removal. Moisture in the mechanical refrigeration cycle is detrimental to the operation and life of the system. The filter-drier is an accessory that performs the functions of filtering out particles and removing and holding moisture to prevent it from circulating through the system.
Moisture In A System
Consider a chemist working with chemical elements to create new substances. The chemist combines atoms of selected elements to cause them to bond or link together to form new combinations of molecular structures. These new molecular structures are called compounds. Chemists perform such creations in the process of developing new synthetic oils, refrigerants, glues, rubbers, metal allows and a host of other products that are useful in many ways.
Some combinations of atomic elements create molecular structures that can be either useful or harmful. Acids are formed when the right combination of elements are linked together chemically. If we have a use for the acid and use it for its intended purpose, all is well. However, in some cases unwanted chemical combinations occur where we least want them and where they cause serious harm. Under certain circumstances hydrochloric and hydrofluoric acids chemically form in the mechanical refrigerant system. This, of course is what we want to prevent.
Again, let us consider how the chemist facilitates the chemical bonding process. The chemist wants certain chemical reactions to take place in an effort to create new substances that hopefully have special properties that are useful. Perhaps the chemist is attempting to create a new refrigerant to replace another that is being phased-out. The chemist combines particular elements to form bonds or links that when complete meet all the qualities of a great refrigerant. A catalyst is anything that hastens, encourages or helps bring about a result. Heat is one of chemistry’s most active catalysts. A chemist may purposely add heat to a beaker of chemicals to cause them to combine to form a new substance.
The HVAC System As A Chemistry Set
That’s right, the mechanical refrigeration system consisting of a compressor, condenser, metering device, evaporator, copper lines, oil and refrigerant are a complete chemistry set including several powerful catalysts!
The system contains components which consist of a number of metals such as the iron casting of the compressor, copper lines, steel condenser, aluminum evaporator, brass valves and fittings and perhaps still other metals in smaller quantities. The components are assembled using still other metals and chemicals during the brazing process. Flux is applied to facilitate the chemical process of brazing and heat is applied with a torch as the catalyst.
Still other materials (chemicals) are contained in the system. Compressor motor winding insulation and varnishes, epoxy glues and perhaps rubber and gasket materials are applied. Of course, two of the major chemical materials that constantly circulate through the system are the refrigerant and oil.
The system contains a vast number of chemicals. (Everything physical is chemical and consists of atoms capable of bonding with atoms of other elements under the right circumstances) Now, if yet additional elements are introduced to the existing combination of elements making up the system the chemical bonding possibilities become still greater. During the installation or servicing of the system air consisting of hydrogen, nitrogen and oxygen may be introduced. Moisture may be introduced and flux or even powder from the inside of Armaflex insulation may get into the system. The moisture and oxygen are very active components that act as catalysts themselves.
Additional catalysts in the form of heat of compression as well as latent heat in the condenser and pressure are present. Imagine the possibilities! The chemicals present are compressed, heated and liquefied. Then they are evaporated and cooled as the pressure is released. Then, the process is continually repeated for hours, days and months until a chemical reaction takes place. On hot days the high temperature and pressure on the high side of the system reaches still higher levels. The catalysts of heat and pressure could almost make a chemist jealous.
When a chemical reaction occurs the typical chemical bonding creates hydrochloric and hydrofluoric acids. These acids then go to work breaking down the metals and other materials of construction adding soluble metal to the chemical reaction. A number of other chemical reactions may take place and the circulating refrigerant and oil carry the entire mix throughout the system where it can continue the process.
One authority on acids informs us that for every 18 degrees Fahrenheit an acid is heated, its activity level doubles.
Eventually, the motor winding insulation may be destroyed and the motor windings begin to pass electrical current between each other. As the motor begins to burnout smoldering products from the burning motor are pumped throughout the system. Remember, the motor will be cooking and burning while the compressor is pumping these products through the system. Liquid refrigerant and oil are fairly good cleaning agents so the piping where liquid refrigerant is located may remain fairly clean of the resulting debris. However, in the evaporator a distillation process is taking place, the refrigerant is changing from a liquid to a gas so the debris becomes separated from the refrigerant and begins getting deposited in the evaporator and suction line. This is why the low side of a system that has experienced a compressor burnout is where the majority of the debris is located.
Keep It Clean!
The case has been made as to how important it is to prevent chemical reactions from taking place in a system. It almost seems from what we have described up to this point that it could be difficult to prevent chemical breakdown from occurring. Fortunately, the installation crew and service technician can prevent system failure due to a chemical reaction.
It is imperative that installation and service technicians prevent foreign materials, air, moisture, brazing flux, carbon created during brazing and Armaflex insulation powder from entering or remaining in a system. Good piping practice includes bleeding a small amount of dry nitrogen through the system while brazing. Pipe ends need to be sealed prior to sliding pipe insulation over the piping. A good 500 micron evacuation should be reached to remove air and moisture before charging with refrigerant. And, the addition of a properly sized filter-drier is important on both new systems as well as anytime a system is opened for service. The filter-drier is designed to both remove any particulates that may circulate as well as collect and hold any moisture that may remain in the system. The use of a filter-drier containing a good desiccant has become even more important with the advent of R-410A systems, which utilize the highly hygroscopic synthetic Poly Ester oils.
How A Desiccant Works
Modern filter-driers contain desiccants that function on the principle of adsorption. Adsorption is not the same as absorption. The term absorption is commonly misused in the technical sense of the term. When we say that a sponge or paper towel absorbs a liquid spill we are using the term in its non-technical sense. Actually, absorption is the attraction and holding power through chemical action. Modern desiccants do not function on the basis of a chemical attraction. The desiccants commonly used in filter-driers utilize the process of adsorption. Adsorption is a physical process and is simpler and easier to understand then the more complex chemical process of absorption.
The modern desiccant of choice is a material called zeolite. Zeolite has gained in popularity over the older desiccants activated alumina, silica gel, calcium chloride and calcium oxide. Zeolite is a mineral that occurs in nature or can be manufactured. Zeolite is an inorganic tan or gray porous solid consisting of a structure of pores and tiny chamber capable of collecting and holding moisture through capillary action. Adsorption is the physical trait of capillary action whereby moisture is drawn into small pores much like a sponge or paper towel collects liquid spills. There are hundreds of different zeolites each with its own micro sized shape, lattice structure and size. Zeolites can be selected to collect and hold many different substances according to the molecular size and structure of the specific molecule one wishes to collect. The zeolite selected for use in a filter-drier is selected to adsorb moisture while allowing refrigerant to pass through. One example of a zeolite is a very light and porous volcanic rock. Zeolite filters are used as desiccants and filters for refrigerant, acids, specific chemicals and to remove ammonia in fish tanks.
Zeolite desiccants are formed into a porous solid core, which is placed in the filter-drier container. Older loose fill desiccants like silica gel occasionally broke down into particles or dust that sometimes left the filter-drier and circulated through the system often creating a restriction especially on capillary tube systems. This was avoided by positioning the filter-drier vertically so pressure pulsations in the system did not shift the loose fill back and forth physically breaking down the loose fill. Solid core zeolite desiccant filter-driers may be installed in any position. Most solid core desiccants are molded into a cylindrical block with a tapered axial hole down the center to allow for the uniform flow of the refrigerant through the entire bed of desiccant. This is why filter-driers are directional with the direction of flow indicated on the container. Installing the filter-drier in the wrong direction causes non-uniform refrigerant to desiccant contact and increases pressure drop. Bi-flow filter-driers are available for heat pump applications.
Capacity
Capacity refers to the amount of moisture the desiccant in the filter-drier can hold. Capacity is measured in “parts per million”. One part per million (ppm) is one part of water per million parts of refrigerant. In practical terms this would be approximately equal to one drop of water in a 125-pound drum of refrigerant. Desiccant capacities are rated at 75 & 125 degrees F. The older desiccant, activated alumina had a moisture holding capacity of 4 grams of moisture per each 100 grams of desiccant. Silica gel had a moisture holding capacity of 3 grams of moisture per each 100 grams of desiccant. Modern zeolite, molecular sieve desiccants have a capacity of approximately 16 grams of moisture per 100 grams of desiccant.
The capacity of a desiccant is temperature dependent. The colder the desiccant the more moisture it can hold. Therefore, locating a filter-drier in a cooler location is an advantage. Removing a brazed filter-drier with a torch flame causes moisture to be driven out of the desiccant and into the system. Generally, it is better to cut the filter-drier out with a tubing cutter.
Location
The desiccant works better at removing and holding moisture when it is placed in a refrigerant line where the refrigerant is in the liquid state. The filter-drier is often called a “liquid line filter-drier” for this reason.
Suction Line Filter-Driers
The desiccant is still able to adsorb moisture when applied to the suction line but not quite as effectively. Special suction line filter-driers are made for cleaning up a system after a compressor burnout. A larger shell is used to minimize pressure drop on suction line driers. Suction line filter-driers marked as “HH” driers contain carbon filter material in addition to the zeolite desiccant. The carbon and zeolite are capable of capturing and holding acids as well as moisture. Suction line filter-driers used to clean up a system after a burn out should be replaced until the system is known to be clean and no longer tests positive for acids in the system. A suction line filter-drier with an excessive pressure drop across it should not be left in a system. An excessive pressure drop in the suction line reduces the volumetric efficiency of the compressor thus reducing system-operating capacity. Many suction line filter driers have a pressure tap on the inlet end so the pressure on the inlet of the drier can be compared to the pressure at the suction service valve at the compressor. Still other suction line filter-driers have pressure taps on both the inlet and outlet.
Alcohol Additives
Some technicians add alcohol-based additives to a moisture-ridden system to prevent moisture from freezing and restricting the metering device. Modern zeolite molecular sieve desiccants have the ability to adsorb these additives to an even greater degree than moisture. It is possible for a desiccant that has already captured moisture to release some of that moisture and replace it with the alcohol additive thus reducing the moisture capacity of the desiccant.
Reactivating Filter-Driers
In the past, some have attempted to reactivate and reuse a filter-drier by heating and evacuating the desiccant. Heating and evacuating does actually remove much of the moisture and allow the drier to be used again. However, oils, carbon and other particles are not removed during this reactivation attempt. In fact, the oil may be cooked into the desiccant creating new contamination possibilities. The cost of a new filter-drier is not worth the effort and is not recommended.
Don’t allow a system to become an out of control chemistry set. Good piping practice, a nitrogen purge during brazing, a deep evacuation and the proper installation and use of filter-driers containing modern and effective molecular sieve desiccants will prevent many system failures. Many compressor failures are blamed on the compressor when the actual problem was caused by a system problem. That system problem may have been a chemical problem due to moisture.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications. He currently is a senior training specialist for Johnson Controls.
Tuesday, May 4, 2010
COMPRESSOR RELIABILITY
By Norm Christopherson
The heart of both an electric refrigerator and an air conditioner is the compressor; it’s most costly component. No other electro-mechanical device comes close to the reliability of the Semihermetic or fully-hermetic compressor. Consider the following comparison.
On the average it operates in a refrigerator at full speed almost half the time. That is about 4000 hours out of 8760 hours in a year.
In 15 years that would be 60,000 hours.
If your automobile operated 60,000 hours at only 50 miles per hour that would be 3 million miles!
That is 120 trips around the world at the equator, or 6 round trips to the moon.
It does this without a valve job, new points, new plugs or even an oil change.
Unless the compressor has a problem, neither lubricating oil nor refrigerant are added over the 15, 20 or even 30 years that many compressors operate.
Search your mind. Can you think of any other electro-mechanical device with a comparable record of reliability and operating life?
The next time someone states that they don’t make things to last as long as they use to, consider the compressor.
The majority of compressor failures are not due to the compressor but rather to a system problem causing the compressor to fail. It is important to determine the cause of a compressor failure when replacing a defective compressor or the replacement compressor is bound to fail as well. Don’t be too quick to blame a failed compressor on the compressor.
Learn the causes of compressor failures and make it a habit of checking the system for the potential causes of compressor failures.
Norm is a technical writer, seminar speaker and test proctor for EPA, 410A and ESCO & NATE certifications as well as a senior training specialist with Johnson Controls
He can be contacted at norman.christopherson@jci.com
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