ENERGY SCREENS IN TOMATO: DETERMINING THE OPTIMAL OPENING STRATEGY

Abstract

In general, the use of energy screens is a good means to reduce the energy consumption and to lower peaks in energy use in greenhouse horticulture. In tomato, experience with screens is limited since the use of screens is not so widespread as in other fruit vegetable crops. In this study effects of different screen opening strategies on greenhouse climate, energy consumption and crop production were quantified by means of an experiment and model calculations. In the experiment, two treatments were compared, i.e. opening the energy screen (SLS 10 Ultra plus) at 5 or at 50 W m-2 outside global radiation. Plant dry weights and tomato production did not differ between the treatments. Due to the larger number of screening hours, energy consumption in the 50 W m-2 treatment was 3.5% lower during the experiment than when screens were opened at 5 W m-2. With a greenhouse climate model and a crop growth model, effects of different screen opening criteria on greenhouse climate, energy consumption and crop growth were simulated. Application of a screen during the night reduced the energy consumption by 16% without affecting crop production. When screens were opened at higher levels of outside global radiation (up to 150 W m-2), energy consumption decreased by 1.6 m3 gas m-2 year-1 and crop production by 0.3 kg m-2 year-1. Financial considerations between energy saving and production loss were discussed. Screen opening based on a combination of global radiation and outside air temperature reduced the energy use, but increased the number of hours with high humidities. Screen opening based on the temperature difference below and above the screen performed comparable to the temperature and light strategy. Opening the screen caused a temporarily decrease in greenhouse air temperature. Increasing the number of opening steps before the screen was opened completely, decreased this temperature drop. This study provides growers with information to determine their screening strategy. However, screen use could be further optimized by offering growers a decision support tool that, given outside weather conditions and prices of gas and tomatoes, gives daily advice on the optimal moment of screen opening.