A water chiller is a complex system, no matter for scroll water chiller or screw water chiller, air cooled chiller or water cooled chiller, but the basic components are compressor, condenser, thermostatic expansion valve (TXV), and evaporator. Starting at the compressor, the refrigerant coming from the evaporator is compressed from a saturated gas to a high-pressure, high-temperature gas. The now hot gas is passed through the condenser, where it is cooled and condensed into a saturated liquid by rejecting the heat to the cooler ambient air (air-cooled condenser) or to facility water (water-cooled condenser). The refrigerant then passes through the TXV, across which its pressure and temperature drop considerably. The refrigerant temperature is now lower than that of the process liquid and, as a result, heat is transferred from the process fluid to the refrigerant causing it to evaporator into a low-pressure gas. The cycle is once again repeated as the gas flows back to the compressor.
The condenser and evaporator of industrial water chillers are heat exchangers that transfer heat from one medium to another. In the case of an air-cooled condenser, an aluminum-finned cooper tube air heat exchanger is used for rejecting heat from the hot refrigerant gas to the ambient air. A water-cooled condenser, uses a liquid-to-liquid heat exchanger to transfer heat from the hot refrigerant gas to the facility water. In the case of evaporator, a liquid-to-liquid heat exchanger is typically used to transfer heat from the process fluid to the refrigerant. The performance of a heat exchanger depends on many factors, including the process fluid used, incoming fluid temperautre, flow rates, materials of construction, and design of the heat exchanger. With all other factors being equal, the driving force behind the transfers of heat from one fluid to another is the difference in incoming fluid temperature.