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Horticulturalist selects higher light transmitting polycarbonate panels for greenhouse roofing

GE Advanced Materials : 03 November, 2004  (Application Story)
Lexan ZigZag polycarbonate panels deliver light transmission even higher than single glass and the energy saving insulation of double glazing.
The first commercial application for the revolutionary Lexan* ZigZag* polycarbonate panels, from GE Advanced Materials Specialty Film & Sheet, has now been unveiled in The Netherlands. Corn. Bak BV, a world leading grower and exporter of Bromelia plants, has adopted the material for the roof refurbishment of three of its greenhouses, a total area of 3800 m2.

Selection of the Lexan ZigZag polycarbonate panels was based on extensive research by Corn. Bak, which has experience with virtually all greenhouse roofing systems including glass, safety glass, acrylate and polycarbonate, and on a special study conducted by the Dutch Agricultural University of Wageningen.

Results of the investigation showed that Lexan ZigZag offered light transmission even higher than single glass, combined with insulation values the same as double glazing. Key to this new higher level of light transmission performance is the special shape of the twin-wall panel that reflects light back into the greenhouse thereby compensating for any light loss due to the panel’s double wall.

Moreover, the double wall retains 45% more heat than single glass, providing a major advantage to growers, as using Lexan ZigZag polycarbonate panels allows greater insulation and a reduced risk of damage to crops. This improved insulation can reduce peak energy demand by up to 50%, resulting in substantial cost savings. Depending on the heat and ventilation requirements of different crops, annual energy savings can be in the region of 20-40%.

“We have always been very interested in all developments for greenhouse roofing systems and have come to the conclusion the future is not in glass”, says Peter Bak, managing director. “Energy costs will continue to rise and innovative materials like Lexan polycarbonate offer energy savings in combination with other advantages. In deciding to use Lexan ZigZag we think that this material has the potential to become the material of choice for greenhouses in the future.”

The Corn. Bak renovation includes three wide-span roof greenhouses, 12.80m wide and 96m long with a planting height of 3.50m. The work was carried out with roofing systems designed by Bosman Kassenbouw of Aalsmeer, The Netherlands. The design incorporates large double sided, continuous ventilation windows of 1,95m in length fitted with insect-proof netting. Innovative is a special profile, which allows the fitting of different types of insect-proof netting. Furthermore, for each slope of the roof only three roller curtains are installed compared to four in a standard greenhouse, thus reducing the number of roller curtain motors and girders to three per roof side.

The sides and gable ends of the greenhouses are constructed of 16mm Lexan Thermoclear X-structure panels. These panels were chosen because of their high insulation value in combination with high stiffness. Material stiffness is of special importance in ensuring the structure’s ability to withstand anticipated wind forces.

Corn. Bak’s objective is to maximise use of available daylight during the autumn and winter. The structure of Lexan ZigZag helps to achieve this by enabling light to enter the greenhouse earlier and for longer than is possible with a flat roofing panel. During the period November through to March when the sun is low, the direction of the material’s channels, from north to south, will deliver 6-8% extra light compared to a standard single glass Venlo roofing system.

“In addition to its high light permeability and excellent insulation value, LEXAN ZigZag’s 10 year guarantee against breakage, loss of light transmission and UV resistance also contributed to its selection,” explains Van der Laarse, general manager, Bosman Kassenbouw. “The guarantee includes a provision that the light transmission may not decrease by more than 2% over 10 years. We are aware that other plastic materials have caused confusion around light transmission properties in the horticultural industry, Lexan ZigZag resolves those issues. Furthermore, alternative materials such as acrylate do not meet our fire resistance requirements.”

Corn. Bak associate director, Elly Bak, responsible for human resources, also believes the material’s contribution to safety is important: “I do not want our people to work under an acrylic roof,” she says. “The risk of fire is simply too great. LEXAN offers superior fire-resistance and will not go up in flames within minutes.”

Complementing its light transmission and insulation properties, Lexan ZigZag is safe to install and it’s hail-resistant. Additionally, the panels are provided with an anti-condensation, anti-algae and anti-drip coating on the inside of the channels, and the outside of the panels are treated to protect them against the degrading effects of UV-light.

Corn. Bak is one of the world’s largest growers of Bromelia’s and developers of Bromelia hybrids. Plants from the company’s centre in Assendelft, The Netherlands, are sold to customers all over the world, from Europe to the United States and Japan.

Headquartered in Aalsmeer, The Netherlands, Bosman Kassenbouw designs and manufactures complete greenhouse systems for the global market and undertakes greenhouse building projects throughout the world. Bosman also supplies constructions for special greenhouses used in garden centres and botanic gardens. For the Lexan ZigZag polycarbonate panels Bosman has developed a new series of profiles to fit the wide-span roof greenhouse.
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