Wageningen University (WUR) published a new report on greenhouse screening. WUR has done research on the use of high insulation screens at cucumber cultivation. The test results are very promising; in comparison to a normal greenhouse with a single energy screen, 44% less energy was used to heat the greenhouse from January till May. As an installer of greenhouse screening, Holland Scherming notices a growing demand for double greenhouse screening. More and more growers discover the advantages of the new cultivation (HNT) and adapt their greenhouse screening systems.
In 2014 a greenhouse experiment was executed with a high-wire cucumber crop to measure the impact of a multiple layer system of energy screens. The screen systems that have been tested were: • 2 layers of aluminized cloth with a 5 cm cavity operated by a single sliding system closed all night. • 1 layer of high transparency, non-porous PVDF film on a second sliding system, closed all night and when heating was required, usually below an outside radiation level of 150-200 W/m2. • 1 layer of perforated transparent PE film, mounted alongside the double screen, closing as soon as the double screen opened and opening above an outside radiation level of 100-150 W/m2 to reduce the PAR light losses. The result was a 44% reduction in heating energy in the period of January to May compared to a glasshouse with a single energy screen. Production and product quality were comparable. The intense use of screens influenced the greenhouse climate. Plant temperature remained high because the radiation losses were limited. Since the opening and closing of the screens were very gradual, no shocks in plant temperature or vapour deficit occurred. This greatly reduces the risk of condensation on the leaves leading to botrytis or to a sudden drop in transpiration leading to plant cell damages. This test shows the positive effects of a highly insulated greenhouse and the chances to regain sensible and latent heat comprised in the ventilation losses of transpiration.