Air Conditioning (A/C) is a system for controlling the temperature, humidity, ventilation, and purity (cleanliness) in a building or vehicle, typically to maintain a cool atmosphere in uncomfortably warm conditions. A/C can also be described as a technique for regulating the condition of ambient air for a more comfortable environment for humans or industrial products.
These four physical properties of air are controlled in air conditioning:
- Air temperature: The control of air temperature in air conditioning includes both heating and cooling processes.
- Relative humidity: A/C systems lower the humidity of the air consumed by the equipment. They do this by using a cold evaporator coil to condense water vapor from already processed air (similar to how a cold drink will condense water on the outside of a glass). This removed water is then drained, thereby reducing the relative humidity.
- Air motion or circulation: Basic A/C units have two different types of refrigeration cycle. The first type uses a heat pump to drive out hot air from the room and replaces it by blowing in cooled air though a compressor. The second type simply pumps in a refrigerant, which then evaporates and extracts the hot air, thereby leaving cooled air in its place.
- Air cleanliness: Whenever the cleanliness of the air is of an unacceptable level the A/C system needs to incorporate air purifiers or air cleaners to reduce the amount of dirt/dust particles in the air to an acceptable level.
Control of these four properties is necessary in air conditioning for the improvement of human comfort. Even more precise control over these properties is required in the operation of some industrial air conditioning units. Other properties, such as odor and air pressure, are further controlled as necessary in other sensitive environments.