In institutional, commercial, and residential buildings, air-conditioning systems are mainly for the occupants’ health and comfort.
They are often called comfort air-conditioning systems. In manufacturing buildings, air-conditioning systems are provided for product processing, or for the health and comfort of workers as well as processing, and are called processing air-conditioning systems.
Based on their size, construction, and operating characteristics, air-conditioning systems can be classified as the following.
Individual Room or Individual Systems.
An individual air-conditioning system normally employs either a single, self-contained, packaged room air conditioner (installed in a window or through a wall) or separate indoor and outdoor units to serve an individual room, “Self-contained, packaged” means factory assembled in one package and ready for use.
Unitary Packaged Systems or Packaged Systems:
These systems are installed with either a single self-contained, factory-assembled packaged unit (PU) or two split units: an indoor air handler, normally with ductwork, and an outdoor condensing unit with refrigeration compressor(s) and condenser.
In a packaged system, air is cooled mainly by direct expansion of refrigerant in coils called DX coils and heated by gas furnace, electric heating, or a heat pump effect, which is the reverse of a refrigeration cycle.
Central Hydroid or Central Systems:
A central system uses chilled water or hot water from a central plant to cool and heat the air at the coils in an air handling unit (AHU) For energy transport, the heat capacity of water is about 3400 times greater than that of air.