While moving heat via machinery to provide air conditioning is a relatively modern invention, the cooling of buildings is not. The ancient Egyptians were known to circulate aqueduct water through the walls of certain houses to cool them. As this sort of water usage was expensive, generally only the wealthy could afford such a luxury.
Medieval Persia had buildings that used cisterns and wind towers to cool buildings during the hot season: cisterns (large open pools in a central courtyards, not underground tanks) collected rain water; wind towers had windows that could catch wind and internal vanes to direct the airflow down into the building, usually over the cistern and out through a downwind cooling tower. Cistern water evaporated, cooling the air in the building.
In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician Dr. John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterwards when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer Vivian M. Sherlock, he blamed the "Ice King," Frederic Tudor, for his failure, suspecting that Tudor has launched a smear campaign against his invention. Dr Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.
Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier. Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.
In 1906, Stuart W. Cramer of Charlotte, North Carolina, USA, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning," using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.
The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. "Freon" is a trade name of Dupont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134). The blend most used in direct-expansion comfort cooling is an HCFC known as R-22. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-11 and R-12 are no longer manufactured in the US, the only source for purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, known by the brand name "Puron".
Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and for improving indoor air quality.
Air conditioning applications
Air conditioning engineers broadly divide air conditioning applications into comfort and process.
Comfort applications aim to provide an indoor environment that remains relatively constant in a range preferred by humans despite changes in external weather conditions or in internal heat loads.
The highest performance for tasks performed by people seated in an office is expected to occur at 72°F (22.2 °C) Performance is expected to degrade about 1% for every 2 °F change in room temperature. The highest performance for tasks performed while standing is expected to occur at slightly lower temperatures. The highest performance for tasks performed by larger people is expected to occur at slightly lower temperatures. The highest performance for tasks performed by smaller people is expected to occur at slightly higher temperatures. Although generally accepted, some dispute that thermal comfort enhances worker productivity, as is described in the Hawthorne effect.
Comfort air conditioning makes deep plan buildings feasible. Without air conditioning, buildings must be built narrower or with light wells so that inner spaces receive sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. Comfort applications for various building types are quite different and may be categorized as
- Low-Rise Residential buildings, including single family houses, duplexes, and small apartment buildings
- High-Rise Residential buildings, such as tall dormitories and apartment blocks
- Commercial buildings, which are built for commerce, including offices, malls, shopping centers, restaurants, etc.
- Institutional buildings, which includes hospitals, governmental, academic, and so on.
- Industrial spaces where thermal comfort of workers is desired.
In addition to buildings, air conditioning can be used for comfort in a wide variety of transportation including land vehicles, trains, ships, aircraft, and spacecraft.
Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. Process applications include these:
- Hospital operating theatres, in which air is filtered to high levels to reduce infection risk and the humidity controlled to limit patient dehydration. Although temperatures are often in the comfort range, some specialist procedures such as open heart surgery require low temperatures (about 18 °C, 64 °F) and others such as neonatal relatively high temperatures (about 28 °C, 82 °F).
- Cleanrooms for the production of integrated circuits, pharmaceuticals, and the like, in which very high levels of air cleanliness and control of temperature and humidity are required for the success of the process.
- Facilities for breeding laboratory animals. Since many animals normally only reproduce in spring, holding them in rooms at which conditions mirror spring all year can cause them to reproduce year round.
- Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and cooling of equipment, aircraft air conditioning presents a special process because of the low air pressure outside the aircraft.
- Data processing centers
- Textile factories
- Physical testing facilities
- Plants and farm growing areas
- Nuclear facilities
- Chemical and biological laboratories
- Mines
- Industrial environments
- Food cooking and processing areas
In both comfort and process applications the objective may be to not only control temperature, but also humidity, air quality, air motion, and air movement from space to space.
Portable air conditioners
A portable air conditioner or portable A/C is an air conditioner on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 6,000 to 60,000 BTU/h (1800 to 18 000 watts output) and with and without electric resistance heaters. Portable air conditioners come in two forms, split and hose:
Air-cooled portable air conditioners are compressor-based refrigerant systems that use air to exchange heat, similar to a car or typical household air conditioner. These systems remove heat and water from indoor air, add heat to outside air, and discharge water to outside air, a tank, or a drain.
Split systems have separate indoor and outdoor units connected by flexible pipes, similar to permanently-installed units. (Split systems may be portable or permanently installed.)
Dual-hose portable systems discharge heat by drawing air from outside through one duct (hose), heating it, and returning it outside through another duct.
Single-hose portable systems discharge heat by drawing ambient air from the same room they are intended to cool, heating it, and blowing it outside through a duct (hose). Since this air is drawn out of the room, outside (presumably hot, humid) air is drawn into the building wherever openings exist, heating any room where outside air enters, countering the intended effect of air conditioning, and reducing efficiency.
Some units simply accumulate water in a tank, and the tank must be emptied or the air conditioning will simply stop when the tank is full. Some of this type of system can use a drain instead of a tank, provided a drain lower than the air conditioner is available. Other units pump this water, in liquid form, through small tube that can be put through a window or into a drain, and some evaporate some water into the heated discharge air. Some of the evaporating units also have tanks and will accumulate water in humid conditions.
As a rule of thumb, 400 square feet (40 m²) can be cooled per 12,000 BTU/h (3.5 kW). However, one must account for other factors which will affect the total heat and humidity loads. Note that a single-hose portable systems are rated for their technical cooling capacity, and these ratings are not adjusted for the heat and humidity they draw into buildings they are intended to "cool". Thus a single-hose system will not only cost more to operate than an otherwise-equivalent dual-hose system, it will not cool the room in which it is installed as well as a dual-hose system, and it can make other rooms hotter and more humid than they would have been with no air conditioner at all.
Mini-split air conditioners
Ductless mini-split air conditioners combine some traits of central air conditioning systems with some traits of window or through-the-wall units. They were invented as an alternative to window air conditioners for buildings where the cool-air distribution ducts of a central air conditioning system could not be installed or would be prohibitively expensive to install. An outside unit including the compressor is mounted on an exterior wall of the building, and an inside unit including the evaporator is mounted high on an interior wall, or on or in the ceiling, of the room to be cooled. They are connected refrigerant tubing, condensate drain, and control wires through a hole drilled in the room's exterior wall. An outdoor unit can be connected to one, two or multiple indoor units depending on design.
Like window air conditioners, a ductless mini-split system requires no air ducts throughout the building and allows separate "zones" in the building to have independent temperature controls. However, like a central air conditioning system, it does not block a window or require another window-sized hole in the wall, and it puts the main source of noise (the compressor) outside the building. Equipment to cool a given amount of inside space is more expensive than with window units but less expensive than with central systems. Customers buy them mostly for their quietness compared to window units, and their lower cost and ease of installation as compared to central systems. In a very large building, the need for ventilation and the need to cool air space that is far from the building's outer walls make ductless mini-split systems and window units impractical.
Central Air Conditioners
Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers.
Air conditioners help to dehumidify the incoming air, but in extremely humid climates or in cases where the air conditioner is oversized, it may not achieve a low humidity. Running a dehumidifier in your air conditioned home will increase your energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool your house. A preferable alternative is a dehumidifying heat pipe, which can be added as a retrofit to most existing systems.
Types of Central Air Conditioners
A central air conditioner is either a split-system unit or a packaged unit.
In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install.
In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.
Choosing or Upgrading Your Central Air Conditioner
Central air conditioners are more efficient than room air conditioners. In addition, they are out of the way, quiet, and convenient to operate. To save energy and money, you should try to buy an energy-efficient air conditioner and reduce your central air conditioner's energy use. In an average air-conditioned home, air conditioning consumes more than 2000 kilowatt-hours of electricity per year, causing power plants to emit about 3500 pounds of carbon dioxide and 31 pounds of sulfur dioxide.
If you are considering adding central air conditioning to your home, the deciding factor may be the need for ductwork. See the section on limitations when replacing existing systems for more information.
If you have an older central air conditioner, you might choose to replace the outdoor compressor with a modern, high-efficiency unit. If you do so, consult a local heating and cooling contractor to assure that the new compressor is properly matched to the indoor unit. However, considering recent changes in refrigerants and air conditioning designs, it might be wiser to replace the entire system.
Today's best air conditioners use 30%–50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20%–40% of your cooling energy costs by replacing it with a newer, more efficient model.
Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small a unit will not be able to attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency.
When buying an air conditioner, look for a model with a high efficiency. Central air conditioners are rated according to their seasonal energy efficiency ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output. Many older systems have SEER ratings of 6 or less. The minimum SEER allowed today is 13. Look for the ENERGY STAR label for central air conditioners with SEER ratings of 13 or greater, but consider using air conditioning equipment with higher SEER ratings for greater savings.
New residential central air conditioner standards went into effect on January 23, 2006. Air conditioners manufactured after January 26, 2006 must achieve a Seasonal Energy Efficiency Ratio (SEER) of 13 or higher. SEER 13 is 30% more efficient than the previous minimum SEER of 10. The standard applies only to appliances manufactured after January 23, 2006. Equipment with a rating less than SEER 13 manufactured before this date may still be sold and installed.
The average homeowner will remain unaffected by this standard change for some time to come. The standards do not require you to change your existing central air conditioning units, and replacement parts and services should still be available for your home's systems. The "lifespan" of a central air conditioner is about 15 to 20 years. Manufacturers typically continue to support existing equipment by making replacement parts available and honoring maintenance contracts after the new standard goes into effect.
Other Features to Look For When Buying an Air Conditioner:
A thermal expansion valve and a high-temperature rating (EER) greater than 11.6, for high-efficiency operation when the weather is at its hottest
A variable speed air handler for new ventilation systems
A unit that operates quietly
A fan-only switch, so you can use the unit for nighttime ventilation to substantially reduce air-conditioning costs
A filter check light to remind you to check the filter after a predetermined number of operating hours
An automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off.
Installation and Location of Air Conditioners
If your air conditioner is installed correctly, or if major installation problems are found and fixed, it will perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perfor
m almost as poorly as older inefficient models.
Be sure that your contractor performs the following procedures when installing a new central air conditioning system:
Allows adequate indoor space for the installation,
maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil
Uses a duct-sizing methodology such as the Air Conditioning Contractors of America
(ACCA) Manual D
Ensures there are enough supply registers to deliver cool air and enough return air
registers to carry warm house air back to the air conditioner
Installs duct work within the conditioned space, not in the attic, wherever possible
Seals all ducts with duct mastic and heavily insulates attic ducts
Locates the condensing unit where its noise will not keep you or your neighbors awake at
night, if possible
Locates the condensing unit where no nearby objects will block the flow of air to it
Places the condensing unit in a shady spot, if possible, which can reduce your air
conditioning costs by 1%–2%
Verifies that the newly installed air conditioner has the exact refrigerant charge and air flow rate specified by the manufacturer
Locates the thermostat away from heat sources, such as windows or supply registers.
If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.)
Home air conditioning systems
Residential air conditioning is ubiquitous in Japan, South Korea, Taiwan, Singapore and Hong Kong, especially in the latter two due to most of the population living in small high-rise flats in warm climates. In this area, with soaring summer temperatures and a high standard of living, air conditioning is considered a necessity and not a luxury. Air conditioners are usually window or split types, the latter being more modern and expensive. It is also increasing in popularity with the change of lifestyle in other tropical Asian nations such as India, Indonesia, Malaysia, and the Philippines.
In North America, home air conditioning is more prevalent in the South, Midwest, East Coast, the Great Lakes States and South-Eastern Canada, (Southern Ontario, and Southern Quebec), in most parts of which it has reached the ubiquity it enjoys in East Asia. Central air systems are most common in the United States, and are virtually standard in all new dwellings in most states. Older houses and buildings not retro-fitted with central air often still use window or through-wall units.
In most parts of Australia, central evaporative coolers were a popular choice, as Australia's dry climate makes this form of air conditioning very effective and economical. However, in recent times low cost reverse cycle units have led to an increase in their use, creating extreme load factor issues for the national electricity market in NEM wide heat wave conditions.
In Europe, home air conditioning is less common in part due to a more clement northern climate. Although in the southern European countries with a high standard of living, like Spain and Italy, air conditioning is becoming a necessity. Still, the lack of air conditioning in homes, in residential care homes, and in medical facilities was identified as a contributing factor to the estimated 35,000 deaths left in the wake of the 2003 heat wave. There were almost 15,000 deaths in France, and 2,000 in the UK; in contrast, only 141 died in Spain despite the higher temperatures, in part due to the extensive use of air conditioning. Due to the 2003 and the 2006 heatwaves, portable air conditioners have become more popular in France.
In many countries in the Persian Gulf, air conditioning is ubiquitous. This is due to the very harsh climate and the relatively high living standards.
Car air conditioning system
To add to the complications, we now have tough environmental regulations that govern the very simplest of tasks, such as recharging the system with refrigerant R12 commonly referred to as Freon® (Freon is the trade name for the refrigerant R-12, that was manufactured by DuPont). Extensive scientific studies have proven the damaging effects of this refrigerant to our ozone layer, and its manufacture has been banned by the U.S. and many other countries that have joined together to sign the Montreal Protocol, a landmark agreement that was introduced in the 1980's to limit the production and use of chemicals known to deplete the ozone layer.
Now more than ever, your auto mechanic is at the mercy of this new environmental legislation. Not only is he required to be certified to purchase refrigerant and repair your air conditioner, his shop must also incur the cost of purchasing expensive dedicated equipment that insures the capture of these ozone depleting chemicals, should the system be opened up for repair. Simply put, if your mechanic has to spend more to repair your vehicle - he will have to charge you more. Basic knowledge of your air conditioning system is important, as this will allow you to make a more informed decision on your repair options.
Should a major problem arise from your air conditioner, you may encounter new terminology. Words like "retrofit" and "alternative refrigerant" are now in your mechanics glossary. You may be given an option of "retrofitting", as opposed to merely repairing and recharging with Freon. Retrofitting involves making the necessary changes to your system, which will allow it to use the new industry accepted, "environmentally friendly" refrigerant, R-134a. This new refrigerant has a higher operating pressure, therefore, your system, dependant on age, may require larger or more robust parts to counter its inherent high pressure characteristics. This, in some cases, will add significantly to the final cost of the repair. And if not performed properly, may reduce cooling efficiency which equates to higher operating costs and reduced comfort.
Vehicles are found to have primarily three different types of air conditioning systems. While each of the three types differ, the concept and design are very similar to one another. The most common components which make up these automotive systems are the following:
COMPRESSOR, CONDENSER, EVAPORATOR, ORIFICE TUBE, THERMAL EXPANSION VALVE , RECEIVER-DRIER, ACCUMULATOR. Note: if your car has an Orifice tube, it will not have a Thermal Expansion Valve as these two devices serve the same purpose. Also, you will either have a Receiver-Dryer or an Accumulator, but not both.
COMPRESSOR.Commonly referred to as the heart of the system, the compressor is a belt driven pump that is fastened to the engine. It is responsible for compressing and transferring refrigerant gas.
The A/C system is split into two sides, a high pressure side and a low pressure side; defined as discharge and suction. Since the compressor is basically a pump, it must have an intake side and a discharge side. The intake, or suction side, draws in refrigerant gas from the outlet of the evaporator. In some cases it does this via the accumulator. Once the refrigerant is drawn into the suction side, it is compressed and sent to the condenser,where it can then transfer the heat that is absorbed from the inside of the vehicle.
CONDENSER. This is the area in which heat dissipation occurs. The condenser, in many cases, will have much the same appearance as the radiator in you car as the two have very similar functions. The condenser is designed to radiate heat. Its location is usually in front of the radiator, but in some cases, due to aerodynamic improvements to the body of a vehicle, its location may differ. Condensers must have good air flow anytime the system is in operation. On rear wheel drive vehicles, this is usually accomplished by taking advantage of your existing engine's cooling fan. On front wheel drive vehicles, condenser air flow is supplemented with one or more electric cooling fan(s).
As hot compressed gasses are introduced into the top of the condenser, they are cooled off. As the gas cools, it condenses and exits the bottom of the condenser as a high pressure liquid.
EVAPORATOR. Located inside the vehicle, the evaporator serves as the heat absorption component. The evaporator provides several functions. Its primary duty is to remove heat from the inside of your vehicle. A secondary benefit is dehumidification. As warmer air travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. Dust and pollen passing through stick to its wet surfaces and drain off to the outside. On humid days you may have seen this as water dripping from the bottom of your vehicle. Rest assured this is perfectly normal.
The ideal temperature of the evaporator is 32° Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the evaporator as a low pressure liquid. The warm air passing through the evaporator fins causes the refrigerant to boil (refrigerants have very low boiling points). As the refrigerant begins to boil, it can absorb large amounts of heat. This heat is then carried off with the refrigerant to the outside of the vehicle. Several other components work in conjunction with the evaporator. As mentioned above, the ideal temperature for an evaporator coil is 32° F. Temperature and pressure regulating devices must be used to control its temperature. While there are many variations of devices used, their main functions are the same; keeping pressure in the evaporator low and keeping the evaporator from freezing; A frozen evaporator coil will not absorb as much heat.
PRESSURE REGULATING DEVICES. Controlling the evaporator temperature can be accomplished by controlling refrigerant pressure and flow into the evaporator. Many variations of pressure regulators have been introduced since the 1940's. Listed below, are the most commonly found.
ORIFICE TUBE. The orifice tube, probably the most commonly used, can be found in most GM and Ford models. It is located in the inlet tube of the evaporator, or in the liquid line, somewhere between the outlet of the condenser and the inlet of the evaporator. This point can be found in a properly functioning system by locating the area between the outlet of the condenser and the inlet of the evaporator that suddenly makes the change from hot to cold. You should then see small dimples placed in the line that keep the orifice tube from moving. Most of the orifice tubes in use today measure approximately three inches in length and consist of a small brass tube, surrounded by plastic, and covered with a filter screen at each end. It is not uncommon for these tubes to become clogged with small debris. While inexpensive, usually between three to five dollars, the labor to replace one involves recovering the refrigerant, opening the system up, replacing the orifice tube, evacuating and then recharging. With this in mind, it might make sense to install a larger pre filter in front of the orifice tube to minimize the risk of of this problem reoccurring. Some Ford models have a permanently affixed orifice tube in the liquid line. These can be cut out and replaced with a combination filter/orifice assembly.
THERMAL EXPANSION VALVE. Another common refrigerant regulator is the thermal expansion valve, or TXV. Commonly used on import and aftermarket systems. This type of valve can sense both temperature and pressure, and is very efficient at regulating refrigerant flow to the evaporator. Several variations of this valve are commonly found. Another example of a thermal expansion valve is Chrysler's "H block" type. This type of valve is usually located at the firewall, between the evaporator inlet and outlet tubes and the liquid and suction lines. These types of valves, although efficient, have some disadvantages over orifice tube systems. Like orifice tubes these valves can become clogged with debris, but also have small moving parts that may stick and malfunction due to corrosion.
RECEIVER-DRIER. The receiver-drier is used on the high side of systems that use a thermal expansion valve. This type of metering valve requires liquid refrigerant. To ensure that the valve gets liquid refrigerant, a receiver is used. The primary function of the receiver-drier is to separate gas and liquid. The secondary purpose is to remove moisture and filter out dirt. The receiver-drier usually has a sight glass in the top. This sight glass is often used to charge the system. Under normal operating conditions, vapor bubbles should not be visible in the sight glass. The use of the sight glass to charge the system is not recommended in R-134a systems as cloudiness and oil that has separated from the refrigerant can be mistaken for bubbles. This type of mistake can lead to a dangerous overcharged condition. There are variations of receiver-driers and several different desiccant materials are in use. Some of the moisture removing desiccants found within are not compatible with R-134a. The desiccant type is usually identified on a sticker that is affixed to the receiver-drier. Newer receiver-driers use desiccant type XH-7 and are compatible with both R-12 and R-134a refrigerants.
ACCUMULATOR. Accumulators are used on systems that accommodate an orifice tube to meter refrigerants into the evaporator. It is connected directly to the evaporator outlet and stores excess liquid refrigerant. Introduction of liquid refrigerant into a compressor can do serious damage. Compressors are designed to compress gas not liquid. The chief role of the accumulator is to isolate the compressor from any damaging liquid refrigerant. Accumulators, like receiver-driers, also remove debris and moisture from a system. It is a good idea to replace the accumulator each time the system is opened up for major repair and anytime moisture and/or debris is of concern. Moisture is enemy number one for your A/C system. Moisture in a system mixes with refrigerant and forms a corrosive acid. When in doubt, it may be to your advantage to change the Accumulator or receiver in your system. While this may be a temporary discomfort for your wallet, it is of long term benefit to your air conditioning system.
Refrigerants
"Freon" is a trade name for a family of haloalkane refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties: they were not flammable nor obviously toxic. as were the fluids they replaced. Unfortunately, evidence has accumulated that these chlorine-bearing refrigerants reach the upper atmosphere when they escape. The chemistry is poorly understood, but the general consensus seems to be that CFCs break up in the stratosphere due to UV-radiation, releasing their chlorine atoms. These chlorine atoms act as catalysts in the breakdown of ozone, which does severe damage to the ozone layer that shields the Earth's surface from the Sun's strong UV radiation. The chlorine will remain active as a catalyst until and unless it binds with another particle, forming a stable molecule. CFC refrigerants in common but receding usage include R-11 and R-12. Newer and more environmentally-safe refrigerants include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs in turn are being phased out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs), such as R-410A, which lack chlorine.
Newer refrigerants are currently the subject of research, such as supercritical carbon dioxide, known as R-744. These have similar efficiencies compared to existing CFC and HFC based compounds.
Compression refrigeration cycle
Air filters
Health Implications
A poorly maintained air-conditioning system can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes. Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma. In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home. Poorly operating air conditioning systems can generate sound levels that contribute to hearing loss, if exposures are endured over a long term. These levels are similar to the exposure of living near a busy highway or airport for a considerable length of time. Properly functioning air conditioners are much quieter.
Energy use
It should be noted that in a thermodynamically closed system, any energy input into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the energy removal rate from the air conditioner increase . This increase has the effect that for each unit of energy input into the system (say to power a lightbulb in the closed system) requires the air conditioner to remove that energy. In order to do that the air conditioner must increase its consumption by the inverse of its efficiency times the input unit of energy. As an example presume that inside the closed system a 100 watt light bulb is activated, and the air conditioner has an efficiency of 200%. The air conditioner's energy consumption will increase by 50 watts to compensate for this, thus making the 100 W light bulb utilise a total of 150 W of energy. Note that it is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%, see Coefficient of performance.
The performance of vapor compression refrigeration cycles is limited by thermodynamics. These AC and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe their performance. The appropriate measure is the coefficient of performance (COP). However this dimensionless measure does not enjoy wide use in the United States, where the dimensional Energy Efficiency Ratio (EER) is used. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER is used, and is the Seasonal Energy Efficiency Ratio (SEER). The SEER article describes it further, and presents some economic comparisons using this useful performance measure.
Humidity control
etter classified as dehumidifiers. They work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about ⅓ of the electricity. They are also preferred by those who find the draft created by air coolers discomforting.
ASHRAE
American Society of Heating, Refrigerating, and Air-Conditioning Engineers
ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) is an organization devoted to the advancement of indoor-environment-control technology in the heating, ventilation, and air conditioning (HVAC) industry. ASHRAE was founded in 1894 to serve as a source of technical standards and guidelines. Since that time, it has grown into an international society that offers educational information, courses, seminars, career guidance, and publications. The organization also promotes a code of ethics for HVAC professionals and provides for liaison with the general public.
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