Gas use without the screen had its peak at nearly
180 m³/ha hour. With the Svensson screen this was reduced to
110.
Total gas consumption for this day was calculated
to be – 1665 m³/ha without the screen and 918 m³/ha with the
Svensson screen.
Tomato plants are able to absorb and use high levels
of radiation. However, above 800 to 900 W/m² the crop starts
suffering, mainly because the crop temperature (fruits and leaves) and
transpiration levels are too high (stress).
A screen can be used quite successfully to prevent
all this.
In Mexico we recommend a shade value of around
40% for tomatoes; more shading will reduce the plants productivity.
Screens should be used only during peak hours, between 10.00 and 15.00,
and only when both temperature and radiation reach high levels.
TURKEY
Things are changing in Turkey: the vegetables
are being grown differently.
Five years ago, tomatoes, capsicums and cucumbers
were grown either in the open field or in poorly equipped small greenhouses.
But in the last five years, large-scale greenhouse projects have started
up, and vegetable production is taking place in a modern, sophisticated
way. The aim of these projects is to supply first class greenhouse
vegetables to European markets during the winter months, and we can find
these big projects both in the Izmir and Antalya regions.
An optimum climate inside the greenhouse is essential
for the successful cultivation of vegetables and flowers. Moveable
Svensson® screens are indispensable for achieving this.
Four important goals can be reached using them:
• Shading and cooling during warm and sunny days
• Optimising the air humidity
• Increasing the inside temperature during the
night when no heating is available
• Saving on fuel cost when there is a heating
system
In order to achieve the best use of a Svensson®
screen it should always be installed so it is moveable, so you can decide
whether or not to use it. This is very important, because the weather
is constantly changing. When the sun is not intense or when the sky
is overcast the screen should be withdrawn to allow all the available light
to reach the crop. Opening and closing should take place with an
automatic system, preferably connected to a climate computer. Svensson®
screens are designed so that they can be easily moved; they are very flexible
and lightweight. The small bundle when the curtains are open ensures
that the maximum amount of valuable growing light reaches the plants.
Pay back time for an investment in a moveable Svensson®
screen varies from 2 to 3 years while the lifetime under Turkish conditions
is up to 10 years.
AGROBAY, DIKKILE
Right now 8 ha is dedicated for tomato and 4 ha
for capsicum production using XLS 15F.
Early Planting
Closing the screen causes a considerable reduction,
at least 5ºC, in the day temperature inside the green house.
So the growing conditions during the spring and summer are greatly improves.
At Agrobay the screens are used for this purpose at the beginning of the
season to protect the young plants. This is needed until the end
of October. In fact the cooling effect is so good it is possible
to start planting one month earlier. However, white wash means permanent
light loss, which slows down the growth speed and development of the crop.
The screen is used again for shading and cooling
from April until the end of the crop, and this ensures that the plants
continue growing and developing fruits, and the quality of the fruit stays
at a high level.
Screens help to prevent heating problems.
Due to the availability of hot geothermal water
the need for energy saving does not exist at Agrobay. This was in
fact one of the reasons an open type of screen was chosen, to have the
optimum screen for the summer season. At Agrobay they do use the
screen during the night, but only when there is a technical problem with
the heating system. Under such circumstances the screen helps to
keep the desired temperature inside the greenhouse.
How about the results?
So far so good! Tomato production reaches a level
of more than 45 kg per m² and paprika production is up to 18 kg per
m²!
AGROSER, SERIK
Right now they have a total of 40,000 m²
of Venlo glasshouses, with another 30,000 m² under construction.
The main crop is tomatoes. For climate improvement and energy saving,
they have installed an XLS thermal screen in both greenhouses.
Climate Optimisation
Öndal explained that for him the main reason
to use the screen was to improve the inside climate. He particularly
appreciates the shading and cooling effect of the screens during hot days
with the bright sunshine of August/September and May/June. The temperature
drop with the screen is between 3 and 5ºC, which is crucial in maintaining
optimum growing conditions for the crop. In June he combines the
screen with a light whitewash of around 30% to make sure that the inside
temperature stays at the same level as the outside temperature and the
last fruits can be harvested unaffected.
Reduction in LPG Use
Another reason for using the screen is to reduce
the consumption of LPG. LPG is very expensive, so it is crucial to
use as little as possible. The screen has proven to be very effective
for this. With outside night temperatures not lower lower than 11ºC,
Öndal is able to keep the inside temperature at the desired level
of 18ºC by just closing the screens at sunset, without any additional
heating. For lower outside temperatures, heating starts, but the
LPG consumption is drastically reduced thanks to the screen. In the
closed position the screen saves no less than 57% on the energy expenses!
All together Öndal estimates that the total energy consumption has
reduced nearly 50% with the screen during the last season – this is 3 to
4 kg of LPG per m².
What about the air humidity under the screen during
the night?
Isn’t the screen increasing it too much?
Öndal has not experienced this up to now.
Thanks to its porous structure the screen transmits enough water vapour
to prevent this. Sometimes there is simply too much humidity in the
air, for instance after a rainy day, so then he opens a gap of 5% in the
screen in order to remove the superfluous water vapour. This measure
helps to maintain an optimum level of air humidity inside the greenhouse.
June 2004
