Absorption chillers are refrigerators that use heat energy as an input, rather than mechanical energy. Absorption chillers are useful, where electricity is no available or where there is an easily available source of heat (e.g. sun, hot water). The heat is used to evaporate a liquid to a gas. The gas then moves to the condenser where the heat dissipates and the gas is turned back into a liquid. Then, the cooled liquid is directed into the evaporator, where it turns into a gas and pulls heat from the air.