The functioning of evaporative coolers is based on the thermodynamic process called adiabatic saturation. It involves spraying a mist or fog of water into the air-stream entering a gas turbine; thereby saturating the air with water vapor before it enters the compressor. The evaporation of these water droplets takes energy out of the air thus reducing the inlet temperature to approximately the ambient wet bulb temperature. Gas turbines generally loose power when the inlet air temperature increases. Because of the temperature reduction caused by the saturation process, the use of evaporative coolers can increase power output of gas turbine power plants. The proper application of these devices requires the correct understanding of a) the basis of the site capacity requirement, b) the functioning of evaporative coolers, c) the use of statistical weather data, and d) site weather variations on both a daily and long term basis. It is frequently thought that evaporative coolers are not useful unless the site has near desert weather conditions. This is far from the truth. Depending on the contractual requirements to provide capacity, evaporative coolers can be justified for relatively humid sites as well as for the drier locations. Average or high temperatures in combination with an average or high relative humidity are frequently used in evaluating the application of evaporative coolers, even though they may lead to a very misleading combination of weather parameters. The value of evaporative coolers is discussed as well as a method for correctly evaluating the use of evaporative coolers with examples at four locations around the world.

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