An air-conditioning system can precisely control temperature, humidity and air quality although more commonly the phrase is used to describe a system that cools.

Generally air-conditioning comes in three standard variations:

Centralised air systems

Heating and cooling is performed in a central location and distributed via ductwork.

Partially centralised air/water systems

Centrally cooled or heated air is further heated or cooled on entry to rooms.

Local systems

All operations are performed locally.

Within these three generic examples more specific air-conditioning systems can be specified, to provide precise function for specialist uses.