New Greenhouse Concept with High Insulating Double Glass and New Climate Control Strategies - Modelling and First Results from a Cucumber Experiment

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. Until now, energy losses through the covering are reduced by closing energy screens, mainly during night time. In winter even during daytime transparent screens are closed resulting in a significant reduction of light in the greenhouse. However, even higher insulation values can be reached by insulating double covering materials. In an earlier study we showed that new developed coverings using anti-reflection coatings to increase light transmission and low-emission coatings to reduce energy losses only show minor light losses and are suitable as double glazing. One of the glasses developed in an earlier study has been integrated in a total greenhouse concept of 500 m(2), 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 (tau(p)) and 79% hemispherical (tau(h)) and an u-value of 1.2 W m(-2) K-1 (compared to tau(p)=90%, tau(p)=82%, u=6.7 W m(-2) K-1 of single glass). In order to develop the optimum growing strategy scenario calculations of greenhouse climate (temperature, humidity, CO2) and energy consumptions year-round were carried out with a validated dynamic climate model. Effects on cucumber production (dry matter) were calculated. That way the optimum growing strategy in terms of low energy consumption combined with a high cucumber yield was developed. Model calculations showed that a cucumber production of 75 kg m(-2) a year should be possible with a gas consumption of 12 m(3) m(-2), an electricity consumption of 8 kWh m(-2) and a CO2 consumption of 43 kg m(-2). That way the energy consumption per kg cucumber would be reduced from 0.53 m(3) gas equivalents to 0.19. A first experiment in the new built greenhouse in Bleiswijk with an autumn crop of cucumbers seems to confirm the theoretical results.