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Air conditioners for vehicles. In automobiles, the refrigeration unit is located under the hood near the engine. The engine drives the unit by means of a belt connected to the engine. Air ducts feed the conditioned air into the car.
Buses often have a separate motor to drive the refrigerating equipment. This equipment may be located either in the rear of the bus or under one side near the luggage compartment. The air conditioner is in the roof of the bus. It supplies cool, conditioned air to the seats through ducts running along the roof.
In a railroad passenger car, an electric motor or a gasoline engine drives a refrigeration unit located under the car. The air conditioner is mounted over the entrance at one end of the car. Fans in the conditioner blow the air through ducts to outlets that are located in the car.
Airplanes require special air-conditioning units. Much of the equipment is made of aluminum to save weight. The refrigeration and air-conditioning units for large airplanes are usually located in the wings. In smaller aircraft, these units may be in the body of the airplane. Air turbines drive the refrigeration equipment. Air ducts feed the conditioned air to different parts of the airplane.
On ships, the refrigeration equipment is installed in the engine room or in a mechanical equipment room. The air-conditioning units are located throughout the ship. Air-conditioning equipment for ships must be extra strong to withstand the rolling and pitching motion of the water. Special metals are used to resist corrosion by seawater.
Choosing a window air conditioner
Two facts should be kept in mind when selecting a window air conditioner. (1) The capacity (cooling power) of the air conditioner should be suitable for the room. (2) The electric power requirements for the air conditioner must match the electric system available for it.
Capacity of air conditioners. The size of a room and the number of people using it help determine the capacity of the air conditioner needed. So do the number, size, and direction of the windows in a room, the wattage of appliances and lights, and the amount of wall insulation.
An air conditioner that has a lower capacity than needed will not keep a room cool. An oversized unit will control the temperature, but it may not reduce excess humidity. Such a unit will run only a short time before the temperature falls. It may not even run long enough to remove much moisture from the air.
Manufacturers rate the capacity of air conditioners in four ways: (1) British thermal units, (2) watts and kilowatts, (3) tons of refrigeration, and (4) horsepower.
British thermal units. One British thermal unit (Btu) equals the amount of heat needed to raise the temperature of 1 pound (0.45 kilogram) of water from 59 BTU to 60 BTU. The Btu per hour rating is the basic measurement for air conditioning, and should always be used to specify the capacity of an air conditioner. An air conditioner with a capacity of 12,000 Btu's per hour can remove enough heat from the air it is conditioning to raise 12,000 pounds (5,440 kilograms) of water one degree Fahrenheit each hour. The cooling capacities of room air conditioners range from 4,000 to 36,000 Btu's per hour.
Watts and kilowatts are the units used to measure air-conditioner capacity in the metric system. One watt equals 3.4 Btu's per hour.
Tons of refrigeration. One ton of refrigeration removes the amount of heat needed to melt 1 short ton (0.9 metric ton) of ice at 32 ℉ (0 ℃) in 24 hours. A one-ton air-conditioning unit can remove 288,000 Btu's of heat in 24 hours, or 12,000 Btu's per hour (3,510 watts). A two-ton air-conditioning unit can remove twice this amount, and so on.
Horsepower measures the power needed to run the refrigeration equipment that cools the air. One horsepower equals 745.7 watts.
Electric power requirements. Local electrical codes govern the kind of motor that can be connected to different kinds of electrical systems. Most air conditioners that have a capacity rating of up to 14,000 Btu's per hour operate on 110-volt, single-phase current. Larger air conditioners need either 220-volt or 220-440-volt, three-phase current. See ELECTRIC GENERATOR (Kinds of AC generators).