In most process cooling applications, a pumping system circulates cool water or a water/glycol solution from the chiller to the process. This cool fluid removes heat from the process and the warm fluid returns to the chiller. The process water is the means by which heat transfers from the process to the chiller.
Process chillers contain a chemical compound, called a refrigerant. There are many types of refrigerant and applications depending on the temperatures required but they all work on the basic principle of compression and phase-change of the refrigerant from a liquid to a gas and back to a liquid. This process of heating and cooling the refrigerant and changing it from a gas to a liquid and back again is the refrigeration cycle.
The refrigeration cycle starts with a low-pressure liquid/gas mix entering the evaporator. In the evaporator, heat from the process water or water/glycol solution boils the refrigerant, which changes it from a low-pressure liquid to a low-pressure gas. The low-pressure gas enters the compressor where it is compressed to high-pressure gas. The high-pressure gas enters the condenser where ambient air or condenser water removes heat to cool it to a high-pressure liquid. The high-pressure liquid travels to the expansion valve, which controls how much liquid refrigerant enters the evaporator, thereby beginning the refrigeration cycle again.
There are two types of condensers used in chillers; air-cooled and water-cooled. An air-cooled condenser uses ambient air to cool and condense the hot refrigerant gas back down to a liquid. It can be located inside the chiller or can be remotely located outside, but ultimately it rejects the heat from the chiller to the air. In a water-cooled condenser, water from a cooling tower cools and condenses the refrigerant.