THERMAL SCREEN EVALUATION IN SOILLESS TOMATO CROP UNDER GLASSHOUSE

The first objective of this study was to determine the value of the SLS 10 (Ludvig Svensson) thermal screen in cutting energy costs in a soilless tomato crop under heated glasshouse. The second one was to improve climate control under a thermal screen. The thermal screen was mostly used during the night in the 2001 trial with a decrease of the night temperature setpoint (- 0.5°C). It was used intensively in the 2002 trial with an increase of the night temperature setpoint (+ 0.5°C from January to March) and day ventilation temperature setpoint (+ 1.0°C). It was also used intensively in the 2003 trial with an increase of the night temperature setpoint (+ 0.7°C during January and February) and day ventilation temperature setpoint (+ 1.5°C). In the 2001 trial, the average inside night temperature decrease of 0.2°C and the use of a thermal screen for 52% of the time during the spring period led to 22% energy savings, less precocity and greater fruit weight with a thermal screen at the beginning of harvest. In the 2002 trial, the average inside night temperature increase of 0.3°C and the use of a thermal screen for 58% of the time during the spring period led to 30% energy savings with little effect on quality and yield. In the 2003 trial, the average inside night temperature increase of 0.1°C, the average inside day temperature increase of 0.3°C and the use of a thermal screen for 58% of the time during the spring period led to 27% energy savings and no effect on quality nor yield. These results obtained for the Nantes area showed that it is possible to optimize an intensive use of a thermal screen by an adjustment of inside night temperature setpoint and day ventilation temperature setpoint. 30% energy savings were obtained with no effect on quality nor yield. These trials also enable us to calculate a profit earning capacity of 2 to 4 years for a thermal screen in a soilless tomato crop. However, it will be difficult to apply this intensive use of a thermal screen in the West of France because of high night relative humidity under thermal screens.