A chiller is a cooling system that removes heat by circulating heat-absorbing a refrigerant through a series of mechanisms through which the heat is released. The essential components of a chiller are a compressor, condenser, expansion valve, and evaporator. They work in unison to circulate a refrigerant that removes heat from a process, operation, or space.

There are several different types of chillers, each of which has a different process for removing heat. All chillers use air or water as a cooling method. For example, air cools a chiller system using fans, while a water-cooled chiller circulates water with a cooling tower.

Aside from the two cooling processes, chillers are further differentiated by the type of compressor they have. Compressors in all chillers have the same function: to compress the refrigerant and increase its temperature and pressure before it moves on to the condenser.