In the bell pepper sector, a 2016 test with double Svensson curtains led to a surprisingly positive result. Thanks to their high level of transparency and good moisture transport, the screens can both remain closed for a very long time. This benefits the quality and production. It is not surprising that various bell pepper growers, such as Kwekerij de Wieringermeer, invest in double screens because of these benefits.
A trial for bell peppers was performed at the Improvement Centere in Bleiswijk, Holland in 2016, using Svensson double energy screens. The top screen, Luxous 1547 D FR, a transparent energy screen with light-diffusing properties and the bottom screen, Svensson's newly launched Luxous 1147 FR. The novelty of the highly transparent and clear Luxous 1147 FR is the 2% more light.
"Luxous 1147 FR and 1547 D FR - the perfect combination"
The screens can remain closed for a long time thanks to their high level of transparency, allowing for increased energy savings while creating a better growing climate. Thanks to its light-diffusing properties, Luxous 1547 D FR can protect against spikes in solar light on tropical days in the summer. Louis van den Berg of Kwekerij de Wieringermeer explained how the two screens made it possible for the crop to achieve the maximum benefits possible, “Even in summer, two screens allow you to take all type of actions which benefit and protect the crop.”
Higher crop temperature
The goal of the trial was to save as much energy as possible while growing according to the principles of The New Cultivation concept. Closing the screens for multiple hours resulted in an ideal growing climate. This limits radiation heat loss at night, which results in a higher fruit temperature. Excess moisture is drained through the closed screen.
Thanks to the added transparency, the screens could remain closed longer than originally planned during the day. “There isn't a lot of light in December and January, with highly transparent screens, you remove relatively little light. After this period, we kept using the Luxous 1147 FR for extended hours. This worked out very well", says Paul Arkesteijn of Svensson. “Screen gapping was not necessary. This results in a more homogeneous greenhouse climate, allowing for a higher degree of humidity.”
The bell pepper does well with increased screen hours, making for excellent production and quality.
Both screens allow for a record number of screen hours and thus, the energy targets were easily achieved. The quality was perfect! By screening against heat radiation loss, the temperature of the fruits fluctuates less and they are less prone to shrinkage, cracks and diseases. Some fruits with interior rot were found only in the last few weeks of cultivation. The production was above average.
Usually, the use of double screens stops around mid-March in Holland. However, both screens remained 80% closed at night during the trial, which did not result in a lot of energy savings but did in fact prevent heat radiation loss.
At the end of 2016, Kwekerij de Wieringermeer underwent a 10 ha greenhouse expansion; not at their Middenmeer site, but at a new location: in Het Grootslag on the Nieuwe Dijk in Andijk. Double layer Luxous screens were chosen: a combination of the new, extra bright Luxous 1147 FR and Luxous 1347 FR.
There is a good growth climate underneath the Luxous 1147 FR, while saving as much energy possible.
“When you construct a new greenhouse, two movable screens are inevitable. For each cubic metre of gas used for cultivation, you have to wonder whether it is really necessary", says Daaf Steentjes, cultivation manager for both locations in North Holland. He can make a good comparison now, since the location in Middenmeer utilized one movable screen with a permanent foil during the first growing phase.
What really appeals to him is that the two movable screens give him all the tools he needs to create an ideal growing climate. “Two mobile screens give you more options.” This is very important for a large operation like ours. Cultivation specialists who can monitor everything are scarce, and you can no longer be everywhere in the company to control the climate from minute to minute.” In order to do this, you need tools which ensure that everything is focussed on maximum production.”
The two Luxous screens provide more screening hours compared to with a fixed foil, experiences Daaf. “The feeling of growing underneath fixed foil shouldn't be imitated. The RV is lower underneath the two screens. You sometimes need to provide a little more heat, since the crop evaporates more at a lower RV, which costs energy. But you can compensate for this by using the screens for more hours.”
Something which can only be endorsed by Louis van den Berg and something that certainly helps, is the high degree of transparency of the screen, especially Luxous 1147 FR: “You can see every spot of the greenhouse roof through the screen.”
Controlled based on tube demand
Daaf likes that the two mobile screens are controlled based on the calculated temperatures of the heating pipes.“This results in a beautiful, calm evolution of climate control without unnecessary ups-and-downs.” He still needs to see what the cultivation will bring, but he is confident. “You can greatly address peaks and valleys. Even in summer, two screens allow you to take all type of actions which benefit the crop, such as blocking excess sunlight. You can perfectly address a number of weather extremes. I still need to experience it, but I am sure that they will provide a great benefit throughout the year.”