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air-conditioning
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What is air-conditioning?
Air-conditioning controls the temperature, humidity, purity, and motion of air in an enclosed space, irrespective of outside conditions. The process involves passing a volatile liquid refrigerant through evaporator coils, which cools the air. The vaporized refrigerant is then pressurized and forced through condenser coils, releasing heat outside.
Willis Carrier invented air-conditioning in 1902 to solve a humidity problem. By 1935, forced-air furnaces used fans to push warm air through ducts, improving heating effectiveness. An HVAC system combines mechanical cooling, heating, and ventilation.
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How does an air conditioner cool the air?
An air conditioner cools air by passing a volatile liquid refrigerant through evaporator coils, which absorb heat from the room's air as the refrigerant evaporates. This process cools and dehumidifies the air, which is then blown back into the room.
The vaporized refrigerant is then pressurized in a compressor and sent to condenser coils outside, where it reverts to liquid form, releasing the absorbed heat. This heat is expelled outside, and the liquid refrigerant re-circulates to continue the cooling process.
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What are the main parts of a basic air conditioner?
A basic air conditioner uses a volatile liquid refrigerant that passes through evaporator coils, cooling the air by evaporation and absorbing its heat. The cooled air's moisture condenses on fins over the coils and drains away.
The vaporized refrigerant then goes to a compressor, is pressurized, and moves through condenser coils that are in contact with outside air. Here, the refrigerant condenses back into liquid, giving off the heat it absorbed. A blower returns the cooled, dehumidified air into the room. In some models, the coils reverse function for winter heating; these are known as heat pumps.
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Why is air-conditioning important in hot climates?
Air conditioning is important in hot climates because it controls the temperature, humidity, and purity of air in an enclosed space, irrespective of outside conditions. In hot and humid conditions, the human body's ability to cool itself through sweating becomes impaired, potentially leading to heatstroke, a dangerous condition marked by an extremely high body temperature that can damage the central nervous system. Air conditioning helps prevent heatstroke and heat exhaustion, allowing people to maintain normal body temperature by facilitating efficient perspiration.
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How does air-conditioning affect energy use?
Air conditioning controls temperature, humidity, purity, and air motion within an enclosed space, irrespective of external conditions. A simple air conditioner uses a volatile liquid refrigerant that passes through evaporator coils, absorbing heat from the room's air. The vaporized refrigerant is then pressurized by a compressor and forced through condenser coils, releasing heat outside.
The design of air-conditioning systems varies. Self-contained units directly serve a space, while complex systems in large buildings use ducts to deliver cooled air. Temperature can be controlled by regulating the amount of cold air supplied, known as variable air volume, which is widely used in commercial and institutional buildings.
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What are some modern improvements in air-conditioning technology?
Modern air-conditioning has roots in the 19th-century textile industry, but Willis Carrier developed the first unit in the early 20th century. A vital advancement was the creation of safe, efficient refrigerant gases known as Freons in the 1930s.
Contemporary air conditioning systems design considers many factors. Complex systems in large buildings use ducts to deliver cooled air. The variable air volume method, which regulates the amount of cold air supplied, is now widely used in commercial and institutional buildings.
HEPA filters are now frequently included in air conditioning systems. These filters trap particles using randomly arranged fiberglass fibers, and air-purifying systems may also use ultraviolet light, activated carbon, and ionizers.
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air-conditioning, the control of temperature, humidity, purity, and motion of air in an enclosed space, independent of outside conditions.
An early method of cooling air as practiced in India was to hang wet grass mats over windows where they cooled incoming air by evaporation. Modern air-conditioning had its beginnings in the 19th-century textile industry, in which atomized sprays of water were used for simultaneous humidification and cooling.
In the early 20th century, Willis Carrier of Buffalo, New York, devised the “dew point control,” an air-conditioning unit based on the principle that cooled air reaches saturation and loses moisture through condensation. Carrier also devised a system (first installed in 1922 at Grauman’s Metropolitan Theatre in Los Angeles) wherein conditioned air was fed from the ceiling and exhausted at floor level. The first fully air-conditioned office building, the Milam Building in San Antonio, Texas, was constructed in the late 1920s. The development of highly efficient refrigerant gases of low toxicity known as Freons (carbon compounds containing fluorine and chlorine or bromine) in the early 1930s was an important step. By the middle of that decade American railways had installed small air-conditioning units on their trains, and by 1950 compact units had become practical for use in single rooms. Since the late 1950s air conditioning has become more common in developed regions outside the United States.
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In a simple air conditioner, the refrigerant, in a volatile liquid form, is passed through a set of evaporator coils across which air inside the room is passed. The refrigerant evaporates and, in the process, absorbs the heat contained in the air. When the cooled air reaches its saturation point, its moisture content condenses on fins placed over the coils. The water runs down the fins and drains. The cooled and dehumidified air is returned into the room by means of a blower.
In the meantime the vaporized refrigerant passes into a compressor where it is pressurized and forced through condenser coils, which are in contact with outside air. Under these conditions the refrigerant condenses back into a liquid form and gives off the heat it absorbed inside. This heated air is expelled to the outside, and the liquid recirculates to the evaporator coils to continue the cooling process. In some units the two sets of coils can reverse functions so that in winter, the inside coils condense the refrigerant and heat rather than cool the room. Such a unit is known as a heat pump.
Alternate systems of cooling include the use of chilled water. Water may be cooled by refrigerant at a central location and run through coils at other places. In some large factories a version of the earlier air-washer systems is still used to avoid the massive amount of coils needed otherwise. Water may be sprayed over glass fibres and air blown through it. Dehumidification is achieved in some systems by passing the air through silica gel which absorbs the moisture, and in others, liquid absorbents cause dehydration.
The design of air-conditioning systems takes many circumstances into consideration. A self-contained unit, described above, serves a space directly. More complex systems, as in tall buildings, use ducts to deliver cooled air. In the induction system, air is cooled once at a central plant and then conveyed to individual units, where water is used to adjust the air temperature according to such variables as sunlight exposure and shade. In the dual-duct system, warm air and cool air travel through separate ducts and are mixed to reach a desired temperature. A simpler way to control temperature is to regulate the amount of cold air supplied, cutting it off once a desired temperature is reached. This method, known as variable air volume, is widely used in both high-rise and low-rise commercial or institutional buildings.
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Distribution of air is a concern because direct exposure to the cool air may cause discomfort. In some cases, cooled air needs to be slightly reheated before it is blown back into a room. One popular method of distribution is the ceiling diffuser, from which air is blown out along the ceiling level and allowed to settle down. The linear diffuser brings air through a plenum box or duct with a rectangular opening; louvers divert the down-flowing air. Other units are circular, and their fins radiate the air. Some ceilings are perforated to allow passage of cool air, and other ceilings are simply cooled so that basic ventilation can circulate the cool air.