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How An Evaporative Cooler Works

The principle of evaporative cooling is relatively simple. Air moving past water will cause the water to evaporate. The heat necessary to cause evaporation is drawn out of the passing airstream and hence the air is cooled. The human body uses this principle to control body temperature by varying the amount of moisture on the skin surface (perspiration). The evaporation of this moisture cools the skin and helps to lower the body temperature.

The modern evaporative cooler uses a fan to draw outside air through wet filter pads. This filters the air of impurities and lowers the air temperature due to the evaporation of water within the pads. The cooled air is then distributed or directed into the building. The filter pads are wet by a pump which pumps water up to the top of the pads, from where it trickles down. The moisture content of the supplied air is increased, however this does not matter provided the air is cooled sufficiently.


By controlling the airflow (fan speed), the temperature in the building may be controlled. Since the supply air is not re-circulated, provision must be made to allow the air to escape from the building once the air has finished cooling. This may be done by simply opening doors or windows, or by the provision of relief ducts or fans.

Because an evaporative cooler is continuously evaporating water, it naturally requires a water supply. In addition, the salts in the supply water don't evaporate, and gradually increase the salt concentration in the tank. The salts then precipitate out on the pads, causing water to drip onto the roof. To overcome this you need either a continuous bleed or a salinity meter and a pump-out valve

Although evaporative cooling works best in dry climates, it is still possible to give reasonable comfort in higher humidity areas, eg. Brisbane, AUSTRALIA, by simply increasing the airflow, provided the air temperature is not too high. Evaporative cooling works everywhere except in areas that have both a high temperature and a high moisture content simultaneously (eg. Darwin, AUSTRALIA, during the "wet"). See also climate.htm

There are three main types of evaporative coolers. These are ducted evaporative coolers, wall/window coolers, and portable evaporative coolers. Click on the links to see if any of these would be suitable for you.

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