ENERGY SAVING IN GREENHOUSES: OPTIMAL USE OF CLIMATE CONDITIONS AND CROP MANAGEMENT

In the last few years, energy consumption in greenhouses has gained increased interest, due to the liberalisation of the energy market and the increasing prices of natural gas. In this paper, the effects of a series of adaptations in greenhouse climate and cropping systems on crop production and energy consumption are presented. Greenhouse energy consumption is primarily determined by the temperature set points. Allowing temperatures to fluctuate, can conserve 3-13% energy, depending on the bandwidth applied. If average temperatures were kept at set point values, it hardly affected plant production. Lowering the temperature set point by 2°C reduced energy consumption by 16%, and production by 3%. Increasing relative humidity set points and reducing plant transpiration by removing leaves or applying antitranspirants could save approximately 5% energy with hardly any effect on plant growth. Increased light transmission of the greenhouse increased plant production and slightly reduced the energy consumption. Filtering out NIR had a positive effect on plant production, but negatively affected greenhouse temperatures. Substantial energy conservation could be realized by the application of an energy screen (16-20%). Optimal use of the available amount of CO₂ positively affected crop production. These results indicate that in present cropping systems, energy conservation of 25-30% seems possible without major investments and without loss of production. Characteristics of such an energy efficient cropping strategy are the use of relative low temperature set points, high humidities, use of energy screens and fluent transitions in greenhouse climate.