How is cooling caused by evaporation?


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Cooling systems


What actually is "adiabatic cooling" -
also called "evaporative cooling"?

We already know that air has the property of absorbing water in the form of water vapor.
It always tries to evaporate water particles (to evaporate) and to store them in itself, and this until it is "saturated".

"Evaporative cooling" is a slang term for a physical phenomenon that should be better called "evaporative cooling". This means the cooling of the liquid itself and its surroundings that occurs when a liquid evaporates. This cooling is caused by the fact that the "heat of evaporation" (heat of evaporation) required for evaporation is withdrawn from the liquid and its surroundings. One calls this with the technical term "adiabatic cooling".

The evaporation process and thus the evaporation cooling is intensified if the resulting vapor is removed as quickly as possible by a dry draft, so that unsaturated air constantly reaches the point where the evaporation takes place.


Think how cold you feel when you step out of the swimming pool wet on a dry, hot but windy day and your skin dries in the air, or how cool a blown finger feels that you first dipped in a glass of water.

However, if the surrounding air is saturated with water vapor, i.e. if the relative humidity is 100%, then no more evaporation takes place and consequently no more heat dissipation.

If a fog system is used for cooling by means of evaporative cooling, it is important to know that it is not the cooling of the air in the greenhouse, but the cooling of the damp leaf or its immediate vicinity that is decisive. It is also important not to open the greenhouse ventilation completely, but to open it in a controlled manner so as not to bring in too much hot and dry air from the outside.
Most effective cooling results are achieved with an opening angle of around 30% (the open position).

A practical example:

An example from one of our reference systems in Cyprus may demonstrate how effective the cooling can be.

At a summer outside temperature of + 42 ° C (at 45% RH) we had to measure + 84 ° C inside a film tunnel!

We reached + 39 ° C by simply fogging.

After switching on a fresh air fan, which draws the hot air from the gable zone (see also "Air movements in space"), the internal temperature was only + 28 ° C with a humidity close to saturation.

Thanks to this success, cypresses can now be rooted in Cyprus in midsummer, which was previously only possible in winter with additional heating.

Apart from that, the production increased from 16,000 to 140,000 plants annually!