When water evaporates into the atmosphere, it reduces the air temperature in the area where evaporation is taking place. This phenomenon is termed evaporative cooling. Based on this phenomenon, devices called evaporative coolers are available, to cool the house on a hot day. These devices are also known by names such as air coolers, desert coolers, or swamp coolers. Evaporative coolers are available in two main categories i.e. direct and indirect coolers.