Classification of Air Conditioning Systems

The purpose of classifying air conditioning systems is to distinguish one type from another and to provide a background for selecting the optimum air conditioning system based on building requirements. A classification of air conditioning systems should include the classification of air and refrigeration systems in order to define a more specific system.
Air conditioning systems can be classified into three categories corresponding to their related equipment as follows:

• Individual Systems – use a self-contained , factory-made air conditioner to serve one or two rooms (e.g. room/ window air conditioner and split-type units).
• Unitary Packaged Systems – similar in nature to individual systems but serve more rooms or even more than one floor, have an air system consisting of fans, coils, filters, ductwork and outlets (e.g. in small restaurants, small shops and small cold storage rooms).
• Central (Hydronic) Systems – basically consists of three major parts:
Air system – air handling units (AHU), air distribution (air duct) system and terminals.
Water system – chilled water system, hot water system, condenser water system.
Central plant – refrigeration (chiller) plant, boiler plant.

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. “Selfcontained, 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 selfcontained, 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 Hydronic 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. Central systems are built-up systems assembled and installed on the site.

An air-handling unit (AHU) is the basic piece of equipment used in an air system. It can be either a field-assembled built-up system or a factory-made unit. Because a central system always has a chilled water system, the type of coil installed in an AHU is a water cooling coil, which is different from an air handler in a packaged system, which uses a DX (direct expansion) coil.