Agriculture Reference
In-Depth Information
Fig. 10.9
A banana
screenhouse with a hail trap,
located at the Western Galilee
region of northern Israel.
(Source: Tanny 2007, private
collection)
2 and 4 m, in a crop of ornamental ruscus (
Ruscus hypophyllum
) 0.5 m in height,
grown under similar conditions (i.e., irrigation, nutrition, harvesting). Although net
radiation was almost identical in the two houses, air temperature near the plants, as
well as leaf temperature was higher in the lower screenhouse than in the higher one.
The average daily air temperature difference between the two houses was 1.5 °C,
and the maximum difference in leaf temperature was 2 °C at midday. The vertical
temperature gradient within the low screenhouse was ~ 3 times larger than that with-
in the high screenhouse, due to better air mixing and more significant movement of
warm air to higher levels in the higher than in the lower house. In addition, it was
shown that VPD near the plants was higher in the lower screenhouse than in the
higher one due to the higher temperature in the lower screenhouse. Most of the time,
the absolute humidity in the higher house was closer to the outside than to that in
the lower house, presumable due to the better ventilation in the higher screenhouse.
Energy Saving Considerations in Greenhouse Climate Control
About 90 % of the total energy consumption in greenhouses among the Northern Eu-
ropean countries is for heating (NN
2012b
). The climograph of one Mediterranean
and one North Europe region is shown in Fig.
10.10
. This shows that at lower lati-
tudes, e.g. Almeria-Spain, the daytime temperatures are too high for ventilation to
provide sufficient cooling during the summer. The attainment of suitable tempera-
tures then requires positive cooling. On the contrary, in temperate climates e.g. in
the Netherlands, heating is indispensable and together with ventilation enables the
temperature to be controlled over the whole year (Kittas et al.
2013
).
A study conducted in Germany stated that sometimes, small glasshouse com-
panies, where oil is the most frequently used energy source, lack state-of-the-art
technical equipment and have higher energy costs compared to large greenhouses.
In addition, many greenhouses are not optimally equipped in terms of energy con-
