air-conditioning

air-conditioning
Control of temperature, humidity, purity, and motion of air in an enclosed space, independent of outside conditions.

In a self-contained air-conditioning unit, air is heated in a boiler unit or cooled by being blown across a refrigerant-filled coil and then distributed to a controlled indoor environment. Central air-conditioning in a large building generally consists of a main plant located on the roof or mechanical floor and intermittently spaced air-handling units, or fans that deliver air through ducts to zones within the building. The air then returns to the central air-conditioning machinery through spaces called plenums to be recooled (or reheated) and recirculated. Alternate systems of cooling use chilled water, with water cooled by a refrigerant at a central location and circulated by pumps to units with fans that circulate air locally.

* * *

      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 (Carrier, Willis Haviland), N.Y., U.S., 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 Graumann's Metropolitan Theater 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, U.S., was constructed in the late 1920s. The development of highly-efficient refrigerant gases of low toxicity known as Freons (Freon) (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.

      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.

      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.

* * *


Universalium. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • air conditioning — UK US noun [U] (UK INFORMAL also air con) ► the electrical system used for keeping the air in a building, room, or vehicle cool: »an air conditioning system »All hotel rooms have air conditioning …   Financial and business terms

  • air conditioning — air conditioning, adj. 1. a system or process for controlling the temperature, humidity, and sometimes the purity of the air in an interior, as of an office, theater, laboratory, or house, esp. one capable of cooling. 2. an air conditioning… …   Universalium

  • Air-Conditioning — Air|con|di|tio|ning, Air Con|di|tio|ning […kɔndɪʃ(ə)nɪŋ], das; s, s [engl. air conditioning]: Klimaanlage …   Universal-Lexikon

  • Air-Conditioning — Air Con|di|tio|ning, auch Air|con|di|tio|ning [...d iʃniŋ] das; s, s <aus gleichbed. engl. air conditioning> Temperaturregelung u. Frischluftzufuhr mithilfe einer Klimaanlage …   Das große Fremdwörterbuch

  • air conditioning — ► NOUN ▪ a system for controlling the humidity, ventilation, and temperature in a building or vehicle. DERIVATIVES air conditioned adjective air conditioner noun …   English terms dictionary

  • air conditioning — ☆ air conditioning n. a method of filtering air while keeping its humidity and temperature at desired levels in buildings, cars, etc …   English World dictionary

  • Air conditioning — The term air conditioning refers to the cooling and dehumidification of indoor air for thermal comfort. In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air.… …   Wikipedia

  • air conditioning — noun a system that keeps air cool and dry • Syn: ↑air conditioner • Derivationally related forms: ↑air condition, ↑air condition (for: ↑air conditioner) • Hypernyms: ↑ …   Useful english dictionary

  • air conditioning — кондиционирование wet seed conditioning кондиционирование семян по влажности water conditioning кондиционирование производственной воды heating steam conditioning кондиционирование греющего пара warm air conditioning кондиционирование теплым… …   English-Russian travelling dictionary

  • air conditioning — N UNCOUNT: oft N n Air conditioning is a method of providing buildings and vehicles with cool dry air. (in BRIT, also use air conditioning) …   English dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”