<P> The cooling potential for evaporative cooling is dependent on the wet - bulb depression, the difference between dry - bulb temperature and wet - bulb temperature . In arid climates, evaporative cooling can reduce energy consumption and total equipment for conditioning as an alternative to compressor - based cooling . In climates not considered arid, indirect evaporative cooling can still take advantage of the evaporative cooling process without increasing humidity . Passive evaporative cooling strategies can offer the same benefits of mechanical evaporative cooling systems without the complexity of equipment and ductwork . </P> <P> An earlier form of evaporative cooling, the windcatcher, was first used in ancient Egypt and Persia thousands of years ago in the form of wind shafts on the roof . They caught the wind, passed it over subterranean water in a qanat and discharged the cooled air into the building . Modern Iranians have widely adopted powered evaporative coolers (coolere âbi). </P> <P> The evaporative cooler was the subject of numerous US patents in the 20th century; many of these, starting in 1906, suggested or assumed the use of excelsior (wood wool) pads as the elements to bring a large volume of water in contact with moving air to allow evaporation to occur . A typical design, as shown in a 1945 patent, includes a water reservoir (usually with level controlled by a float valve), a pump to circulate water over the excelsior pads and a centrifugal fan to draw air through the pads and into the house . This design and this material remain dominant in evaporative coolers in the American Southwest, where they are also used to increase humidity . In the United States, the use of the term swamp cooler may be due to the odor of algae produced by early units . </P> <P> Externally mounted evaporative cooling devices (car coolers) were used in some automobiles to cool interior air--often as aftermarket accessories--until modern vapor - compression air conditioning became widely available . </P>

Where did the term swamp cooler come from