Industrial chillers can be air-cooled or water-cooled. Water-cooled chillers incorporate the use of cooling towers which improve the chiller’s thermodynamic effectiveness as compared to air-cooled chillers. This is due to heat rejection at or near the air's wet-bulb temperature rather than the sometimes much higher dry-bulb temperature. There are typically four types of compressors used on chillers. These are reciprocating, centrifugal, and screw and scroll. These can be powered by electric, steam, or gas turbine power. They produce their cooling effect through a process known as vapor-compression.
Absorption chillers are also a type of industrial chiller. The absorption chiller’s thermodynamic cycle is driven by an external heat source. These heat sources can come from steam, hot water, or combustion. Absorption chillers have very low electrical power requirements compared to electrically powered chillers. However, the heat source demand can be large and for the same tonnage capacity, they require much larger cooling towers than vapor-compression chillers. Absorption chillers are considered very energy efficient where inexpensive, high grade heator waste heat is available.
Industrial chillers are usually complete, packaged, closed-loop systems. They include the evaporator, condenser, pumps, associated valves and temperature control systems. A closed loop industrial chiller circulates a coolant or water (with additives) at a constant set temperature and pressure. The coolant or water flows from the chiller to the application point of use and back. Most industrial chillers use refrigeration as the cooling process. Some rely on air or water flowing over coils containing the coolant to regulate temperature.
Water is the most commonly used coolant within process chillers, although coolant mixtures (mostly water with a coolant additive to enhance heat dissipation) are frequently employed. A newer development in industrial water chillers is the use of water cooling instead of air cooling. In this system the condenser does not cool the refrigerant with air, water is used. The water is cooled by a cooling tower. This reduces the energy requirements allows a reduction in the size of the chiller. This is due to the small surface area of the condenser and the absence of cooling fans. Theabsence of fans also reduces noise levels. When determining the specifications for an industrial chiller the following should be considered:
Power source chiller rating chiller cooling capacity evaporator capacity evaporator material evaporator type condenser material condenser capacity, ambient temperature fan type noise level limits piping and plumbing materials, number of compressors type of compressor number of circuits, coolant requirements refrigerant type fluid leaving temperature efficiency expectations
Pump sizes are also important. This will be driven by flow, pressure, pump material, motor voltage, motor electrical class, motor rating and pump rating.
Industrial chiller control features that should be considered when selecting between industrial chillers include the local control panel, remote control panel, fault indicators, temperature indicators, and pressure indicators. Additional considerations include emergency alarms, hot gas bypass, water switchover, and mobility.