Do you go for a drop-down system or an accordion system? At first glance, it might not be entirely clear what that question is about, but when you consider that these are both mesh systems, the pieces of the puzzle start to fall together. Marcel Schulte, managing director of Holland Gaas, explains why this choice is currently a 'hot topic,' with the demand for insect netting picking up considerably, recently.
First of all, what is a drop-down system? "There are actually two types of drop-down systems. One system is mounted to the greenhouse deck and air window and is pulled in when the air window closes. With this system, about two-thirds of the vent window area is shade-free."
Left, drop-down system type 1: open. Right, drop-down system type 1: closed
Another system is mounted in the greenhouse cover opening in the full window opening.
Cost per year
Compared to a greenhouse without netting, both drop-down systems are still a lot better - they serve their purpose of keeping insects out. Marcel: "In terms of shading, there is a better option: the accordion system. While this is slightly more expensive to buy, it lasts much longer than a drop-down system, so in the end, the costs per year are considerably lower."
Left: Accordion system: Closed. Right: accordion system: Open
Less ventilation loss
The air throughput is significantly better with an accordion system than with flat mesh installed in the deck surface. This is due to the much larger exchange surface. This is further enhanced by the ventilation possibilities of the sides of the air window.
Nowadays, there are new developments with mesh confection in the corners. This prevents problems with cleaning the greenhouse cover, reduces the package, and increases ventilation.
Less light loss
An accordion system is also more favorable in terms of light loss. Holland Gaas also calculated this. "With a drop-down system mounted to your greenhouse deck, you have about 5% light loss. With the accordion system, it's only about 1%, compared to the transmission of the total greenhouse roof area. If you assume the principle of 1 percent light loss = 1 percent production loss, then with a drop-down system, you are actually behind after only 1 year. These calculations are done by experts but are, of course, also offered to TNO for verification."
More demand for mesh
We briefly touched on it in the introduction: the demand for insect netting is increasing considerably. Why is that? Marcel: "The use of pesticides is being increasingly reduced for various reasons. You see this in gerbera and chrysanthemum cultivation, among others, but also certainly in vegetable cultivation."
Also, Het Nieuwe Telen (The New Cultivation) plays a role in the increased demand. "Ventilation reduction used to be seen as the biggest disadvantage of insect netting."
"This is partly still the case, however, nowadays, people ventilate and screen in a different way. Air vents open less far and less often on average. Growers handle the climate very differently, largely to save energy."
"If you don't fully open air vents without mesh, you can use mesh to open the air vent further. In this way, you maintain the climate, but now without insects entering the greenhouse. So you have the best of both worlds because the disadvantage of mesh largely vanishes. Growers often initially see it as a 'necessary evil' because their crop protection products are no longer permitted. After installation, they soon see the advantages of growing with insect netting."
For more information:
Marcel Schulte 
Holland Gaas
Honderdland 30
2676 LS, Maasdijk
Tel.: +31 (0)174 - 516 180
[email protected]
www.hollandgaas.nl