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1、Air ConditioningAir conditioning controls the temperature, moisture, cleanliness, and movement of indoor air. It cools the air when the weather is hot. It warms the air when the weather is cold. Comfort depends partly on humidity, and air conditioning removes moisture from the air or adds it as need
2、ed. Removing dirt and dust from air makes the air more healthful. By controlling air movement, air conditioning brings fresh air into a room and pushes out stale air. In all these ways, air conditioning provides air that makes people comfortable at work, at play, and while sleeping. How we use air c
3、onditioning For comfort. When the weather is hot, most people enjoy eating in cool, air-conditioned restaurants. They sleep better in air-conditioned bedrooms. Airplanes, trains, ships, buses, and automobiles that are air conditioned make traveling more pleasant. Air conditioning helps keep homes cl
4、ean by taking dirt from the air. It often relieves the discomfort of hay-fever victims, because it removes pollen from the air. Air-conditioned hospitals protect the health and improve the comfort of patients and hospital staffs. During cold weather, air conditioning performs much the same services.
5、 It supplies clean, moist air that is warmed to the most comfortable temperatures for working and sleeping. In business and industry, air conditioning improves the efficiency of workers. Employees stay more alert and become less tired in air-conditioned offices and factories. They make fewer mistake
6、s and have fewer accidents. Air conditioning also protects workers against high temperatures and harmful dust, smoke, and fumes. In stores and shops, air conditioning keeps merchandise clean. It also increases sales, because people like to shop in comfort. Several industries, such as the electronics
7、 industry, work with delicate parts and therefore require air-conditioned clean rooms, which are free of dust or germs. Companies in these industries make or assemble equipment in such rooms because the tiniest speck of dust could prevent the equipment from working properly. Large computers become w
8、arm when in use and are sensitive to dust. A computer may break down unless air conditioning removes this heat and keeps the surrounding air clean. Metals and other materials expand as the temperature rises, and contract as the temperature drops. For this reason, air conditioning is used to control
9、the temperature in factories that manufacture tools or parts for instruments, watches, cameras, and other precision products. Changes in temperature would change the size of such products. Many nonmetallic materials, including textiles, paper, and tobacco, absorb moisture from the air. Too much mois
10、ture may make these materials stretch out of shape. Too little moisture in the air makes these materials dry and brittle. Almost all textile mills use air conditioning to control moisture so they can produce strong, uniform threads and fabrics. Some fibers, such as nylon and rayon, could not be made
11、 and woven into cloth without air conditioning. Even the sewing machines that mass-produce nylon stockings require proper temperature control. The needles of these machines are so small, and operate in such tiny spaces, that sudden temperature changes could cause them to jam and break. Paper stretch
12、es in wet weather, and becomes brittle in dry weather. Air conditioning helps control moisture in printing plants so the paper will remain flexible and stay the same size. This makes possible high-speed printing of newspapers, magazines, and books throughout the year. In bakeries, air conditioning c
13、ontrols the rising of bread dough. It also keeps flour from molding. Bread that is cooled in air-conditioned rooms has crack-free crusts. In drug and chemical plants, air conditioning not only provides clean air but also removes germs from air. Air conditioning keeps moisture at the proper level so
14、that powders, salts, and other chemical substances stay dry. Air-conditioning systems in commercial buildings are being used increasingly for smoke control during fires. By controlling the airflow, the systems provide smoke-free areas for evacuation and fire-fighter access. How air conditioners work
15、 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 y
16、ear. 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 bl
