Agriculture Reference
In-Depth Information
To avoid high humidity levels and be
able to remove water vapour, up to 0.25% of
the surface of PE films can be perforated
(Bakker
et al
., 1995). The modern woven
materials allow for the absorption of a cer-
tain amount of condensed water droplets,
avoiding them dripping over the crop.
If energy-saving screens are to be used
during daylight hours, it will be necessary
that they have good PAR transmission.
The climate control screens are prefer-
ably of woven or joined materials, based on
PE or polyester, depending on their intended
use. They can be used with aluminium sheets
to achieve different degrees of shading and
energy saving, with white translucent sheets
to decrease the direct radiation and increase
the diffuse component of radiation, or col-
oured sheets to alter the light spectrum in the
greenhouse (Bakker
et al
., 1995).
ease of maintenance; (iv) the energy econ-
omy, if heating must be used; and (v) the
price.
Limiting ourselves to the most common
types, the choice is between the artisan and
the industrial greenhouses. Artisan green-
houses use flexible plastic films and are of
low cost. Of the industrial greenhouses, the
most common are the Venlo greenhouses, of
Dutch origin, which use glass as cladding,
and the multi-span greenhouses, with a
curved-roof shape which are very popular
in regions with a mild climate and which
normally use a flexible film as cladding,
although they may use rigid panels in the
cover (Figs 4.12-4.16).
The artisan greenhouse covered with
flexible film and little equipment consti-
tutes the low cost and lower agronomic per-
formance option, whereas the sophisticated
glasshouse is at the other extreme. Between
these two extremes there are a number of
intermediate options. Chapter 14 summa-
rizes the information on costs of greenhouse
construction.
The choice of a greenhouse of the
appropriate technological level must be the
result of a compromise between the techni-
cal and economic requirements, in order to
achieve sustainable production.
Greenhouse: Options
When choosing a greenhouse the main
aspects to consider must be: (i) the trans-
mission to PAR radiation which determines
the productivity potential; (ii) the solidity
and durability; (iii) the functionality and
B
B
A
A
Fig. 4.12.
Curved-roof tunnel greenhouse, common in the Mediterranean area. A, Opening separating
the plastic film; B, vent.
