Facts about "Evaporation Cooling"
From previous sections you have
already seen that air can take up water in the form of water vapour.
If water is present
the laws of physics always try to reach an equilibrium and evaporate water to be carried
by the surrounding air up to the point when the air is "saturated" with water vapour.
The term "Evaporation Cooling" describes
an effect which occurs during the evaporation of liquids in general. Whenever a liquid evaporates
the process needs some additional energy to mobilize the molecules of the liquid and thereby
the surrounding matter is deprived of this energy which results in a cooling effect. The
scientific term for this effect is "adiabatic Cooling".
The process of evaporation and therefore the
cooling effect will be enhanced greatly if the emerging water vapour is transported off by
a stream of dry air, so that at any moment in time enough unsaturated air is available to
Remember how cold you can feel if you have
been swimming on a hot and dry day and get out of the water into a windy environment
and the water clinging to your skin dries off.
Or just dip a finger in glass of water,
blow air about your finger and feel how cool this feels.
In case no air movement is present, the surrounding
air is quickly saturated, no more evaporation and no more cooling will occur.
If you want to utilize a fogging system to
cool by means of evaporation cooling the best effect is not reached by cooling of the
air in the cooled area but on the surface of the goods which are to be cooled (plants
in a conservatory, vegetable storage, ...)
It is important to notice, that the influx
of dry air is moderate, otherwise the cooling effects may be too small.
How effective evaporation cooling can work
may be described by one of our reference-systems, installed for a commercial tree propagation
nursery on Cyprus in the Mediterranean Sea.
Summer temperatures on Cyprus are usually
in the range of +42°C (at 45% rel humidity); in the inside of a tunnel-growing house
without cooling the temperature reached +84°C (!).
Simple fogging to saturation lowered the
temperature to +39°C.
Additional installation of a fan which sucked
off hot air from the upper layers of the tunnel (also see "Air Movement")
the inside temperature was lowered to +28°C with a humidity near saturation.
This cooling made it possible for this nursery
to propagate tree-cuttings also during high summer temperatures; formerly this process
was possible only during the winter season with additional heating.
Besides the evident economic profit production
was increased from former 16.000 to 140.000 plants per year !
last modified MAR 2013
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