GREENHOUSE CONCEPT WITH HIGH INSULATING DOUBLE GLASS WITH COATINGS AND NEW CLIMATE CONTROL STRATEGIES; FROM DESIGN TO RESULTS FROM TOMATO EXPERIMENTS

Abstract

The goal of the Dutch horticultural sector is to build new greenhouses in 2020 without the use of fossil energy and reduce CO2-emissions with 45% compared to 1990. Closing several screens, mainly during night, is in practice the most common way to reduce heat loss through the cover. In winter during day time transparent screens are closed resulting in significant reduction of light at plant level. Insulating double covering materials can reach higher insulation rates compared to the use of single glass with screens. In an earlier study we showed that new developed coverings using anti-reflec-tion coatings to increase light transmission and low-emission coatings to reduce energy losses only show minor light losses and are suitable as double glazing. This high insulating glass has been integrated in a total greenhouse concept of 500 m2, realized in summer 2010 at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk. The glass used has a light transmission of 88% perpendicular (tp) and 79% hemispherical (th) and an u-value of 1.2 Wm-2 K-1 (compared to tp=90%, tp=82%, u=6.7 Wm-2 K-1 of single glass). In cooperation with growers an optimum growing strategy scenario is devel-oped. Special attention is taken for an energy saving technique for dehumidification while it’s known that condensation at double glass will decrease compared to single glass. Two years of tomato growing have showed that energy savings up to 60% of energy use at commercial nursery farms is possible without affecting the production level. In the second year the dehumidification system has been improved and the final result is an energy use of only 456 MJ for heat and 6 kWh electricity to run fans with a tomato production of 72 kg m-2, cultivar ‘Komeett’. In that way the energy consumption per kg tomato would be reduced from 18.5 MJ kg-1 to 6.6 MJ kg-1