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Evaporative cooling is a cooling technique which uses the evaporation of water to lower the temperature. Humans actually use evaporative cooling naturally when they sweat as they heat up, and the sweat evaporates, lowering body temperature. The same principle can be used to bring the air temperature down in warm climates. This type of cooling is generally only suitable for hot, dry climates. In a humid climate, evaporative cooling cannot work as well, and it can cause the humidity to reach an uncomfortable level.
The basic design of an evaporative cooler consists of a fan which pulls hot air through a series of water soaked pads. As the air moves through the pads, it cools down, and the cool air can be vented directly into a room or into a duct system. The humidity will also increase slightly, thanks to the water in the air, which can actually be beneficial in very dry climates where the dry air leads to issues like cracked lips and dry skin.
One advantage to evaporative cooling is that the air feels fresher. Air conditioning works on a closed system, while evaporative cooling actually requires windows to be open for ventilation so that warm air from the house can escape and the evaporative cooling device can push in cooled air. Since recycled air can sometimes be stifling, some people enjoy the sensation of a steady fresh breeze created with evaporative cooling. People can direct the breeze by opening and closing various windows.
Using evaporative cooling is also much less expensive than air conditioning. It requires a fraction of the energy, although it does require water, and thus can cut cooling costs significantly. In addition, it is more environmentally friendly, which can be a benefit in the eyes of some consumers. With a precooled evaporative cooler which cools air through heat exchange before passing it through the cooler, the system can be even more efficient. Two stage evaporative cooling, as this is known, is sometimes expensive to implement, but it saves in the long term.
People sometimes refer to evaporative coolers as desert coolers, wet air coolers, or swamp coolers. They are suitable for warm, dry climates all over the world, and many evaporative cooling systems have a vent only option which can be used to move air around without cooling it when the weather is more temperate and people just want ventilation. These systems tend to be available from home supply stores located in climates where they are suitable for use.