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Den Berk’s excellent practical experiences with Diffulite+ glass

In 2011, Den Berk BVBA of Merksplas (Belgium) expanded their existing greenhouse of 11 ha by another 9 ha. In this, the entrepreneurs Koen Lauwerysen and Luc Beirinckx made a well-considered choice of the roof glass Diffulite+. An autumn crop and one year-round cultivation later they are still highly satisfied with this choice.
The Den Berk BVBA operation was built in two phases. Between the building of the first phase in 2008 and the second one in 2011, as a result of research and practical experience, more and more attention was paid to the possibilities of diffuse and anti-reflective glass. The entrepreneurs Koen and Luc realised this too. For as entrepreneurs they consider a sustainable future perspective to be paramount.

Den_Berk.jpgAerial photo during the construction of the second phase in July 2011; on the right the existing operation from 2008.


The greenhouse builder Bom Group in Naaldwijk, in cooperation with partner HT Glass B.V., offered Diffulite+ for the roof glass. The basic glass of Diffulite+ is low iron glass. During production, a texture that causes the diffusivity is applied to the glass with a roller. Also, the glass is provided with an AR coating on both side. As a result, light transmission increases substantially. Furthermore, the glass is supplied in a toughened version. When the greenhouse was built, there was glass available with an anticipated haze factor of approx 15%, a hemispherical light transmission of approx 88.5% and a perpendicular light transmission of at least 96%.

Cutting the knots

At the foundation of the decision-making lay the following principles. The goal was a hemispherical light increase of 6-7%. The haze factor of approx 15% was taken to be an advantage, but less account was taken of this in the calculations because the effect of such a low haze factor was difficult to estimate. Assuming that 1% light increase results in a 0.7% production increase, they arrived at a return on investment period of 8-10 years. An important aspect in their choice was the low risk associated with such an investment. The greater light gain will always be an advantage, and its yield is independent of, for example, changing market situations, legislation and the like.

The confirmation

After finishing the greenhouse, an autumn crop was planted in 2011. It emerged rapidly that under the Diffulite+ glass much higher 24-hour temperatures had to be realised than at other autumn growers to keep the crop in balance. Through the higher tempo, and particularly also the greater fruit weight realised, it quickly became clear that crops under this glass have a high production potential.
Early in January 2012, the first year-round crop was planted. Here, the choice was for the Merlice vine tomato. Due to the plentiful light, the crop rapidly became very strong, and to keep the cultivation in the right balance, the stem density was raised three times from 2.5 st/m² to 4.375 st/m², while in the other part of the operation, the stem density was 3.75 st/m² under the standard glass. The high stem density was also definitely needed to avoid getting excessive fruit weights. Despite the high stem density, the fruit weight still ended up 10-15 grams higher that for other Merlice growers.

Through the higher fruit weight and the greater number of fruits per m² – due to the greater stem density – the anticipated production increase of 6% was generously exceeded; due to this, the actual return on investment period will be about 6 years.
Koen and Luc are convinced that in the coming years, more very attractive production results can be achieved thanks to Diffulite+. They have not regretted their choice for a moment. The correct combination of high light transmission and diffusivity that Diffulite+ offers gives them every confidence in the future.

New-build project at Luc Beirinckx

While the Diffulite+ glass that is supplied at Den Berk is still mainly AR glass, and given the 12% haze a less diffuse glass, HT Glass in the meantime also has Diffulite+ glass with haze factors of 30 or 50% on the market. According to Koen and Luc’s experiences, under this type of glass, both on the productive level and even more so on the qualitative level, even better results will be possible. The greater amount of energy that enters with the plentiful light due to the AR coating will at a higher haze factor after all be better spread through the crop, resulting in a less extreme climate on hot summer days. In the meantime Luc Beirinckx is busy at his existing operation with the partial replacement and expansion of 4.2 ha new greenhouses with lighting. Due to the lighting and the experience with Diffulite+ at Den Berk, Luc opted to glaze this greenhouse too with Diffulite+ glass, but with a 30% haze factor.
During the delivery, light measurements were conducted on different samples by Wageningen University & Research centre. The light transmission results were well above the expected perpendicular light transmission of 96% and hemispherical light transmission of 88%.
NB The content of the above article was prepared by Den Berk BVBA.
For more information you may contact the companies below.

Bom Group /
HT Glass B.V. /

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11 Jan 2013