Thermal screens — Environmental and plant studies

Abstract

The microclimate and yield of an early tomato crop were studied in a glasshouse fitted with a thermal screen, which could be pulled over the crop each night to save energy. The screen was made of aluminised polyester material, slightly permeable to air, and it gave an estimated saving of 31% of the “unscreened” energy costs. The parked screen caused a radiation loss of 3–5% during the day. At night, the humidity under the screen was slightly higher than in the unscreened control, depending on outside temperature, but there was little difference in leaf—air temperatures between the plants of the 2 treatments. One important effect of the screen was the lower heat input, which reduced the convectional distribution of heat. A vertical thermal gradient developed such that young plants were 2°C colder than those in an unscreened house set to the same temperature, based on temperature-control sensors in an aspirated screen 1.5 m from the ground. Under the screen, fruiting was slightly delayed compared with the unscreened crop, possibly due to the temperature differences referred to above. Final yields were slightly higher from the screened house, but the trial was not replicated, and because of the temperature differences, the crops were not strictly comparable.