空调系统英文文献及中文翻译(2)
How air conditioners work
There are three main kinds of air-conditioning systems. Summer air conditioning cleans, cools, and removes moisture from air. Winter air conditioning cleans, heats, and adds moisture to air. Year-round air conditioning cleans and controls the temperature and moisture content of air throughout the year. All air-conditioning systems have some way of blowing, or circulating, the conditioned air through rooms.
Cleaning the air can be done in several ways. Some air conditioners force the air through filters. The filters usually consist of closely packed fiberglass wool or metal fibers that have been coated with a sticky oil or some other type of adhesive (see FIBERGLASS). As the air passes through, the dirt, dust, and soot in the air stick to the fibers. Air can also be cleaned by blowing it through sprays of water called air washers. A central air conditioner that uses this method has a row of nozzles that squirt a fine mist of water into the air. The water rinses out the dirt. Central air conditioners may also be equipped with electrostatic filters, or electrostatic precipitators. These devices put a positive electric charge on the particles of dirt in the air. Negatively charged collector plates attract the positive particles out of the air (see AIR CLEANER). Some central air conditioners force the air through porous pieces of carbon, which absorb odors.
Drug firms and hospitals require extremely pure air. They usually have air conditioners equipped with special filters. These filters remove all dirt particles down to a size of 1/85,000 inch (0.0003 millimeter). Air conditioners may also have special lamps that kill germs in the air with ultraviolet rays (see ULTRAVIOLET RAYS).
heat it in winter. Most people feel comfortable when the temperature of the air is between 68℉ (20 ℃) and 75 ℉ (24 ℃) in the winter and between 73 ℉ (23℃) and 79 ℉(26 ℃) in the summer.
To cool the air, some air conditioners blow it through sprays of cold water. The same sprays that clean the air may also cool it. Most air conditioners blow the air over coils (large groups of tubes) that are filled with cold water or a chemical refrigerant. Refrigeration machines may be used to chill the water or refrigerant that flows through these coils (see REFRIGERATION [Mechanical refrigeration]). Other air conditioners may use cold water that comes from a well, a river, or a city's water system.
Most air conditioners used in large buildings heat air by blowing it over coils filled with hot water or steam. A boiler heated by a gas or oil burner produces the hot water or steam. In some air conditioners, electric heaters warm the air. These heaters have a screen of wires heated by electricity. The air is warmed as it passes through the screen.
Controlling the moisture. The evaporation of moisture from our skin helps cool our bodies. But in summer, air often becomes humid (moist). Humid air cannot pick up as much extra moisture as dry air can. We find it difficult to cool off in humid weather, because the air does not absorb the perspiration from our bodies. The amount of moisture that people lose as perspiration depends on their activities and emotions. For example, a crowd at a basketball game perspires more than an audience in a motion-picture theater. An air conditioner must remove warm, moist air from a room and supply cool, dry air. Otherwise, the air becomes sticky and we feel uncomfortable.
The amount of moisture in air compared with the amount it can hold is called the relative humidity (see HUMIDITY). People usually feel most comfortable when the relative humidity is kept between 30 and 60 per cent.
Air conditioners can dehumidify (remove moisture from) air in several ways. Cold air cannot hold as much moisture as warm air can. When air conditioners cool air by passing it over cooling coils, the water or refrigerant in the coils can be made cold enough to cause the moisture in the air to condense (turn into a liquid). The same process occurs when the outside of a drinking glass becomes moist as it is filled with ice water.
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