It takes a lot of energy to evaporate water. If the evaporation takes place in an air stream,this energy can only be taken from the air. This will therefore cool. This is what we call adiabatic cooling or evaporative cooling, a natural cooling process whose capacity depends to a large extent on the relative humidity (RH) of the air. The lower the RH, the more the air is humidified and can be cooled. Fortunately, the combination of extremely hot and extremely humid weather is not very common in our climate. Usually the humidity is pretty low on hot days. This means that the supply air can usually be cooled by 6 to 8 degrees without the humidity becoming too high. It is important that this system is properly controlled to avoid excessive humidity. Most climate computers have a cooling program and can determine the limits by means of temperature and humidity settings.
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