Agriculture Reference
In-Depth Information
The orientation of the vents which
open facing the wind (windward) favour
ventilation in relation to the vents which
open towards the side sheltered from the
wind (leeward) (Fig. 8.4), especially if they
are of the flap type (Montero and Antón,
2000a, b).
When the wind grows in intensity, the
roof vent that must be more open is the one
opposite to the wind direction (Fig. 8.5); the
suction created by the external wind forces
the air out of the greenhouse, while it is
quite risky to open the vent facing the wind
(Wacquant, 2000). If there are strong winds,
all the greenhouse vents must be closed to
avoid them breaking.
The wind effect is very small if vents on
the roof are not complemented with side-
wall openings (Montero and Antón, 2000a)
(see Fig. 8.6).
(a)
Windward ventilation
(b)
Leeward ventilation
Fig. 8.4.
Diagrams resulting from a ventilation study using flow visualization techniques, depending on
the wind direction: (a) windward (facing the wind) and (b) leeward (side sheltered from the wind). The size
of the arrows indicates the intensity of ventilation. Low-cost greenhouse, five spans, with hinged flapping-
type vents and wind velocity of 4 m s
−1
(data from 'Las Palmerillas' experimental Station, Cajamar
Foundation, Almeria, Spain).
Low pressure area
sucks out the
interior air
Wind
direction
Air rises by convection
and suction
Fig. 8.5.
The suction created by the wind on the leeward vent (protected from the wind) contributes to
the extraction of the greenhouse air, if the wind is strong. If there are sidewall vents (for air entrance) the
efficiency of ventilation is improved.
