Agriculture Reference
In-Depth Information
Photo 8.4.
The injection ventilation fans must avoid the introduction of insects, by covering the air inlets,
where external air is drawn inside, with proper screens.
Sprinkler
Fan
External dry air
Internal air,
humid and cool
Porous pad
Vent flaps
in open
position
Water recovery
Fig. 8.10.
Scheme of a mechanical ventilation system with water evaporation in pads (pad and fan).
8.6.2
Fogging and misting
The droplets must also be produced at a
certain height above the canopy, so that as
they fall very slowly they will evaporate before
reaching the plants, absorbing energy and
decreasing the air temperature. This system
may allow for a decrease of up to 6°C under
Mediterranean conditions (Urban, 1997a),
while under very dry conditions the tempera-
ture reduction can reach up to 7-10°C
(Conellan, 2002). Under high radiation condi-
tions, both fog systems and shading can be
complemented (Plate 19).
In the misting systems the droplets are
higher and they fall rapidly and wet the
The aim of fog-mist systems is to generate a
fog or mist to cool the interior of the green-
house (Photo 8.5).
Water droplets must be small enough so
they do not wet the plants, to avoid the
development of diseases and the deposit of
salts contained in the water, when the water
evaporates from the surface of the leaves
between two fogging episodes. In fogging
systems, the optimum range of water drop-
let sizes is between 0.5 and 50 mm, for maxi-
mum efficiency (ASAE, 2002).
