Agriculture Reference
In-Depth Information
characteristics of the plastic film used. Its
implementation requires the use of special
fixing systems and the ventilation system
must be consequently adapted (Photo 7.1).
To maintain the inflating pressure, low
power turbines are used (250 W for 1000
m
2
) to maintain a pressure in excess of
40-60 Pa. Care must be taken to avoid inter-
nal condensation in the insulating air cham-
ber, which may limit the light transmission
even more, so it is advisable to take the air
for inflation from the outside.
It must be clarified that the reduced
light transmittance of the double-inflated
plastic greenhouse might not be necessarily
a disadvantage. For example, it might very
well be impossible to grow a crop in the
winter time with the low amount of avail-
able ambient light even if all the light was
transmitted by the greenhouse cover. In this
case, a potentially additional 5-10% light
available inside a glass-covered green-
house, as compared with the double-
inflated plastic house, would be of little
practical benefit. However, the reduced
light availability and the more diffuse
nature of the transmitted light in a
double-inflated plastic house, in the sum-
mer months, has resulted in a cooler
and more gentle greenhouse environment
for crops (especially suitable for sensitive
crops such as cucumber) with significant
benefits to producers who are interested in
long-season cropping.
7.3.2
Mobile thermal screens
The function of mobile thermal screens is
threefold: (i) they limit the volume to be
Double wall
Screen
Double cover
Fig. 7.3.
Greenhouse insulation devices: double external walls, thermal screen and double roof cover.
Photo 7.1.
Greenhouses made of inflated double plastic film improve the insulation conditions but
require special fixing systems.
