A chiller is a machine that removes heat from a liquid via a a vapour-compression or absorption refrigeration cycle. This liquid can be circulated through a heat exchanger to cool air or equipment as required. Unfortunately, refrigeration creates waste heat that must be exhausted to ambient or, for great efficiency, maintenance and product life cycle environmental impact.

Both vapour-compression and absorption chillers follow the same cooling cycle. All chillers rely on three basic principles: when gas is cooled it condenses into a liquid, lowering the pressure above the liquid reduces its boiling point increasing the pressure and the heat always flows from hot to cold.

In air conditioning systems, chilled water generally transits to heat exchangers or coils, in air handling units or other kinds of terminal devices which cool the air in their space, followed by recirculating the water back to the chiller to be cooled again. These cooling coils move heat from the air to the chilled water which acts to cool and dehumidify the air.

Chillers function from a heat source. This heat typically delivers the chiller via steam, hot water or combustion. Compared to electricity powered chillers, an adsorption chiller has very low electrical power requirements. Chillers are cheap, energy-efficient and in very hot areas, solar energy has been used to operate absorption chillers.

The two main chillers are vapour compressor chiller and absorption chiller. A vapour-compression chiller consists of four primary components of the vapour-compression refrigeration cycle. They include a compressor, evaporator, condenser and a metering device. Whereas an absorption chiller uses a heat source to drive the refrigeration cycle in place of a mechanical compressor. Absorption chillers use two fluids which includes a refrigerant, typically water and an absorbent typically a lithium bromide solution or ammonia.