Evaporative coolers are cooling devices that use the evaporation of water into the air to cool the air temperature. They are sometimes called air coolers, desert coolers or swamp coolers. Evaporative coolers use a quarter of the electricity of air conditioners and are relatively inexpensive. In addition, they do not use ozone-harming chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Evaporative coolers are best suited for hot climates with low humidity. In such climates, these devices can be used in many locations, including homes, spot cooling locations, industrial plants, commercial kitchen, greenhouses, confinement farming, etc. In areas with high humidity, evaporative coolers do little to cool the air, but can be used for increased ventilation.
Evaporative coolers are available in two basic types: direct and indirect. Direct evaporative coolers contain a blower that forces air through a water-soaked pad. The pad acts like an air filter as it is cooled and humidified. One disadvantage of direct evaporative coolers is that they may increase the humidity. To prevent this problem, indirect or two-stage coolers have an additional heat-exchanging stage that uses a secondary heat exchanger to pre-cool the air. This second stage is the same as a direct cooler. With indirect evaporative coolers, the pre-cooled air passes through a permeable, wet pad and picks up humidity. Because the air was pre-cooled and cannot hold as much moisture as warm air, less humidity is added to the air-stream.
Evaporative coolers differ in terms of materials and construction and mounting style. Most evaporative coolers have an outer casing of metal or plastic with vented sides. The sides contain a centrifugal fan, an electric motor, and a water pump. Cooling pads often consist of a wool and wood mixture, or plastics and melamin paper inside a containment net. When water enters the pad, some of it is absorbed by the wood, allowing it to cool the air passing through. When choosing pads for evaporative coolers pad thickness is an important consideration. Thicker pads can be more effective than thinner pads because there is more material to absorb water. In terms of mounting styles, evaporative coolers can be located on rooftops, exterior walls, or windows. Since the air originates outside of the house or building, there must be large vents to allow air to move from inside to the outside.