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Air conditioners also can remove moisture from air by passing it through sprays of cold water. These sprays cool the air enough to condense some of the moisture.
Moisture control is important in winter, too. Cold outside air contains little moisture. When this air is heated, it becomes extremely dry. Such air dries the skin and may irritate the nose, throat, and lungs. To prevent these discomforts, air conditioners add moisture to the air in cold weather. They do this by passing air through sprays of water or over pans of heated water. The water evaporates into the air.
Circulating the air is important because most people feel uncomfortable in motionless air. The air in a room often becomes filled with moisture and odors. This air must be removed as conditioned air is blown in.
Fans blow conditioned air through the room. The air may be blown in directly or through ducts (pipes) that lead to various parts of a building. In large commercial buildings, other fans suck out used air. To eliminate smoke and odors, the fans exhaust some of the used air by blowing it out of the building. The remaining used air is returned to the air conditioner, where it is mixed with ventilation air drawn in from outside. This mixture of inside and outside air is then conditioned and returned to the cooled room. Eventually, an air conditioner replaces all the air in a room or building with ventilation air drawn in from outside. An air conditioner can circulate air through a room at a rate of about 15 to 40 cubic feet (0.4 to 1.1 cubic meters) per minute. The amount of air circulated through a room depends on the size and speed of the fan used in the air conditioner.
Kinds of air conditioners
Room air conditioners operate on electricity or gas, and are located partly in the room to be cooled. They are enclosed in a single cabinet. They blow the conditioned air directly into the room and do not have air ducts leading to and from them. The three chief types are (1) window air conditioners, (2) consoles, and (3) self-contained air conditioners.
Window air conditioners fit into the lower part of a window and can be moved from window to window. In the air-conditioning industry, these units are called room air conditioners.
Consoles are larger than window air conditioners and stand on the floor in the room. They must be near a window or a wall opening in order to obtain outside air.
Self-contained air conditioners are the largest room air conditioners. They may stand 7 feet (2 meters) tall, and can cool an entire large room, such as a restaurant.
Central air conditioners use electricity or gas. They can supply conditioned air to a number of rooms or to an entire building from one central source. Fans blow the conditioned air through air ducts from the air conditioner to the rooms.
Central conditioners have a number of advantages over other kinds. For example, all the equipment for air conditioning a large area is located in one place. This reduces the cost of cleaning and repairing. Central conditioners can also be zoned. That is, they can supply air of different temperatures to different parts of a building. A doctor with a crowded waiting room might want cooler air than a lawyer in a smaller office. Zoning makes it possible to serve both their needs.
Combination room and central air conditioners are used in large buildings. They combine the advantages of both types. One kind of combination system has a central conditioner to condition outside air. It circulates the conditioned air to a unit in each room. The room unit controls the temperature and moisture-content of the air.
Another type of combination system furnishes cold water or a refrigerant from a central refrigeration machine to a conditioner in every room. Each room conditioner has a fan, filter, and cooling coils to condition and circulate the air.
A third variety of combination system conditions a mixture of outside and inside air. This system supplies each room with cool, conditioned air through one duct, and warmed, conditioned air through another duct. A mixing-box unit in each room mixes the two air streams to provide the right temperature. Combination systems have the advantage of supplying conditioned air or a cooling fluid from a central source. This cuts the cost of maintaining them. At the same time, the inpidual room units allow the people in each room to adjust the temperature to suit their wishes.