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climate screen

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The new diffuse screen from Svensson provides even better light distribution than the previous version. But growers are also still very keen on the first generation of these climate screens. “I would choose this screen again straight away in any new build,” says chrysanthemum grower Wilco Hofman from Bleiswijk in the Netherlands.

The Harmony climate screen slides out slowly below the glass. The young plants underneath are enveloped in light shade. There is a marked difference in the places in the greenhouse that are not screened. The chrysanthemums are still in full sunlight there. “We often use this open structured climate screen, particularly in the bays housing the young plants,” says chrysanthemum grower Wilco Hofman of De Landscheiding in Bleiswijk. “Young plants are delicate. Diffuse light is therefore just what we want in those bays.”

Positive effect

And yet it wasn’t so much for light distribution that he bought the screen back in 2009, but rather to improve the climate in the greenhouse. “It’s an interplay between various factors. Our Santinis almost never get enough light. You don’t actually need to use a screen for plant growth; I mainly do it for cooling and to keep the humidity in the greenhouse stable. If it gets too hot, the plant’s stomata close and the plant doesn’t cool itself. Closing the screen allows the plant to cool down.”
This also has a positive impact on the young rooted chrysanthemum cuttings. The climate screen prevents the roots from drying out unevenly. “I also have an older greenhouse in ‘s-Gravenzande. We use whitewash there. The direct radiation from the open windows dries out the pots more quickly in some places than in others. That means we have to water flexibly there, which makes the crop less reliable.”

By chance

Hofman came across the Harmony screen quite by chance. He used to use a blackout screen in his greenhouse and whitewash on the glass. When he was building his new greenhouse in 2009, he temporarily transferred production to a rented greenhouse. This was equipped with a blackout screen with silver-coloured shading above it, which could be closed separately. “It struck me how pleasant it was to work under. The plants are not in full sun, but nor are you yourself. I took the idea back with me to my own greenhouse, and after taking advice we decided to have a new climate screen installed while we were building the new greenhouse.”
He has had a 45% screen ever since. The grower decided to install this open structure screen and the blackout screen together on the same wire frame. “This does mean that we can’t close the screens at the same time, but we never need to do that anyway. Installing them in this way keeps the costs down.”

Less delayed growth

Hofman was the first chrysanthemum grower to have this climate screen installed. “It is certainly not common in chrysanthemum growing,” says Ton Habraken of Svensson, the screen manufacturer. “Santini and disbud chrysanthemum growers were the first to use it. Now it’s gradually catching on among spray chrysanthemum growers as well. More and more growers are attracted by the diffuse light it provides.”
“I think its effectiveness is underestimated,” Hofman adds. “We grow chrysanthemums in lots of colours and I get the feeling that the intense colour is preserved better under this screen. But most chrysanthemum growers only grow white and yellow. Those colours are less sensitive to solar radiation.”
Whether the screen makes for faster growth, a more uniform crop or a heavier chrysanthemum, the two find it hard to say. Habraken: “Compared to the Solaro aluminium summer screen, the white Harmony screen does a better job. The research shows that Solaro absorbs some of the light, which makes the screen hot. The new screen absorbs virtually nothing at all, and that keeps the greenhouse one or two degrees cooler.”

Saving energy

“In our nursery the effect is difficult to measure because we don’t have anything to compare against,” the grower says. “But we do have less delayed growth in summer. We used to notice delayed growth in plants on extremely hot days, but since we have been closing the screen on those days, it has been happening less. That’s money in the bank.”
The screen also yields results in winter. “If it’s snowing or if it’s a dark day, I close the screen to keep the temperature in the greenhouse up. So I can reduce my pipe temperature by as much as ten percent. That saves energy.” Habraken agrees: “Our research has definitely shown that the screen can deliver energy savings of between 15 and 20 percent.”

Pleasant working environment

The only thing the chrysanthemum grower did not take into account in his choice is soiling. “The screen has not been as white as it used to be for a while now. Soil preparation work and fork lift trucks generate a lot of dust which settles on the screen and reduces diffuse light radiation. Next time I would opt for a slightly lighter screen to compensate for this.”
But they will definitely be using this kind of screen again next time they build. “Apart from all the benefits for the plant, one of the most important aspects is that it makes the working environment more pleasant. When we are working in the greenhouse, we can now close part of the screen and stand in the shade without impacting too much on the quality of the crop. It’s wonderful working in the summer with the screen closed and a light breeze blowing below it.”

Summary

A new diffuse climate screen gives 32% more light to parts of the crop shaded by the greenhouse structure compared with the classic variant. What’s more, the light is more evenly distributed so there are fewer variations in the light level. Although it’s difficult to attribute all the positive effects on the plant to the screen without a comparison, growers are seeing improvements in aspects such as colour intensity and growth. But most importantly, perhaps, it makes the greenhouse more pleasant to work in.

Text and images: Marjolein van Woerkom.

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Gerbera grower Batist, of Maasdijk, the Netherlands, fitted a new, moveable climate screen with improved light diffusing properties into one of its greenhouses this spring. Due to less direct radiation, the crop is less quickly exposed to stress and ultimately on sunny days more light can be allowed to enter the greenhouse. The combination of better light distribution and less shadow results in a more generative crop that yields more.

Thanks to the new screen installed by Ruud Batist this spring, he no longer needs to whitewash the greenhouse. He was quite pleased with the diffuse coating that he applied each spring but the permanent layer of chalk also blocked out light and heat when it was not necessary. In addition the radiation entering through open windows was sometimes too high in places, causing sensitive varieties to visibly suffer.

Perform better

“I knew it could be better,” says the mini gerbera grower. “Therefore last year at another location we installed a Harmony screen with a shading percentage of 35 per cent, which also has light diffusing properties. This meant I could be more responsive to the circumstances. This spring we installed a variant on the further developed New Harmony line in an entire greenhouse. I am convinced that this will perform even better.”

More generative

Although Batist can’t make an objective comparison between the new screen, the classical type and the diffuse coating that he previously used, he says he is very satisfied with its performance. “The new fabric lets more light through and we have a more generative crop. Several colleagues within our growers’ organisation, Colours of Nature, work with the classic screens and we regularly meet in the greenhouse. They agree with us."
The difference in generative growth is so large that the gerbera grower is at odds with the usual day length regimes. “Normally, under cooler, fertile growing conditions, such as those we experienced up to mid July, you need to maintain shorter days to keep the crop in a sufficiently generative state,” he says. “However, this screen lets through so much light without passing the critical value of 1,000 μmol, that the plants receive a generative boost.”
Batist can reduce the hours of darkness and the resulting higher light sum is, as a rule, converted into extra growth. “Many of my colleagues start to darken the greenhouse around 1 July but we can maintain a longer day. It can only translate into higher productivity.”

Further developed

Paul Arkesteijn, of Svensson, nods affirmingly. “The first generation of Harmony screens was introduced eight years ago and developments have been ongoing," he says. “At the time it was the first moveable climate screen with diffuse properties. The big difference with previous fabrics was that the usual aluminium strips in the open, knitted cloth were replaced with white plastic strips."
According to Arkesteijn these screens allow more light through which is subsequently distributed wider. By varying the number of white strips in the cloth, gerbera growers can chose a screen that shades out 25, 35 or 45% of the light.
“Three years ago we picked up the thread again,” says Arkesteijn. “In the meantime, a lot of new, independent research had been carried out into the effects of diffuse light in crops. Based on that we wanted to research which aspects of our screens could be further improved. Growers are always raising the bar higher, both for themselves and for their suppliers. Our R&D department tested several new materials and the result of that exercise is the new series.”
According to the screen specialist the diffuse property of the fabric has above all improved in the screens with a lower shading level. “That makes these versions very interesting for gerbera and rose growers for example,” he adds. “The 25 and 35 per cent versions of Classic Harmony are already used a lot in these crops. We know that when the radiation is more than 1,000 μmol PAR a gerbera crop can experience stress. Measurements show that in Batist’s greenhouse, the light level remains well below this figure under the new screen. It has a shading percentage of 23 per cent.”

Less stress, more light

Better diffusion offers several advantages. Firstly you can allow more light to enter the greenhouse before the crop suffers stress from the high direct radiation. Secondly, better light distribution reduces the amount of shadow from greenhouse parts such as gutters, columns, air mechanisms and (trellis) rafters.
Arkesteijn: “The results of a trial under practical circumstances show that under the new climate screen, the crop in the shadow receives 32 per cent more light than under the first generation screens. The sunlight is more evenly spread over all plants and all parts of the plant. The result is a more uniform and faster growing crop.”

Another step further

Batist notes that the new climate screen offers him even more opportunities to optimise the growth factor, light. “The plant balance and bud formation are influenced by many factors,” he says. “You have to use screens during the lighter months to protect the crop from excessive radiation. Whitewash offers protection but also prevents light entering when it’s not necessary. In this respect the classic screen was a clear improvement. This new screen goes a step further and enables even more light to be converted into growth and production.”

Cautious

The grower says that he hasn’t been using the diffuse climate screen for long enough to confirm his high expectations with hard figures but he expects to have them within a few months. “When comparing nurseries or different locations with varying systems and varieties even within one company you need to be careful,” he says “However, I’d be surprised if over the long term this greenhouse doesn’t stick out above the rest.”
Paul Arkesteijn also believes this new screen will be an asset to gerbera growers, among others, even though it wasn’t tested on gerberas during the development phase. “We can’t attach any crop related figures. However, we know the transmission properties inside-out and they are excellent. They are the result of three years intensive research."

Summary

A new type of climate screen with improved diffuse properties makes it possible to admit higher light levels during gerbera cultivation. This produces a generative crop response. The reduced shadow from light intercepting greenhouse parts and equipment also results in more uniform growth. On balance, this should lead to higher production.

Text and images: Jan van Staalduinen

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With the introduction of the new Harmony climate screens, Svensson proclaims to have taken diffused light to the next level. Recently conducted field tests show that crops grown in shade spots under this screen receive 32% more light in comparison to the first generation of Harmony screens.

Svensson developed Harmony for growers who are looking to combine shading and diffuse light for better growth. Measurements have shown that the new Harmony screens enable sunlight to be better distributed than ever before.

More homogeneous distribution of light

Two PAR light sensors measure the light in two comparable sections in a greenhouse, one of which is equipped with a traditional Harmony screen and the other with a new Harmony screen. The sensors continuously measured the light intensity, plotting the results on a graph:

Violet: New Harmony. Grey: Harmony.

The tests revealed that both climate screens provide diffused light, but that the new Harmony screens allow the light to be more homogeneously distributed. This results in a more uniform, faster-growing crop and better working conditions.

Source/photo:Svensson.