Based on actual function, a chiller may be air-cooled or water-cooled. Depending on the process by which it cools temperature, it can be classified as either a vapor compression or vapor absorption system. Based on the primary compression within the chiller system, they can be reciprocating, centrifugal or screw. Contingent on actual processing package, chillers are either portable or packaged. Based on central system, they can be on central chilling or a central cooling tower principle. Evaporative coolers adopt a simpler scheme of classification based on the process by which they evaporate water: direct or indirect cooling. Modern evaporative coolers can come in two-speed models, with or without bleed-off valve units, or in small portable or window packages.
Chiller refrigeration systems work by lowering fluid temperatures (water cooled) or eliminating water from the air (air cooled). In contrast, evaporative coolers or swamp coolers lower ambient temperature by water evaporation. These two systems have other notable differences and the choice on which to use depends on a variety of factors.
Chillers, whether air or water-cooled, mechanically function using four basic parts: a compressor, a condenser, an evaporator and an expansion valve. Consequentially, the assembly of the basic elements requires a holding tank and a control panel. Evaporative coolers have a basin, cooling pads, centrifugal fan, heat exchanger (indirect types have a second one), and a pump.
When the evaporator in chillers receives heat, the heat combines with the refrigerant to transform into vapor or gas. The compressor pressurizes the gas, enabling atmospheric water or air to eliminate heat. The condenser, utilizing the water in the cooling tower or the surrounding air, eliminates the heat and recycles the transformed gas back to fluid form for further use by the evaporator. The dispersed coolant within the holding tank is distributed by the pump to the evaporator and finally to the equipment within which the chiller is installed or to the system that requires the cooling. The whole process is monitored and managed by the system control panel. With evaporative coolers, the centrifugal fan first takes warm ambient air through the cooling pads, after which cooled air then gets blown out and distributed throughout the area. The pads need to be replaced seasonally. Distribution outlets keep the pads wet and moisture distills through the pads to a basin. The pump conveys the accumulated water back to the cooling pads. In some systems, a bleed valve constantly replaces evaporated water to keep it at operational level.
Common industries and applications using chillers include the beverage industry, HVAC (Heating, Ventilating and Air Conditioning) systems, laser, medical, plastics, printing and rubber industries. Evaporative coolers find use in the cooling of residences, as alternatives to or in tandem with other cooling systems, such as heat pumps or air conditioners.