Influence of an aluminized thermal screen on greenhouse microclimate and canopy energy balance

Abstract

Greenhouse microclimate, energy savings, and crop transpiration were investigated during winter in a glass-covered greenhouse cultivated with a rose crop and equipped with an aluminized thermal screen. Air temperature and humidity profiles were recorded at 0.3, 0.8, and 1.8 m heights inside the greenhouse. Net radiation over and under the rose crop, heating pipe temperature, canopy temperature at 0.3 and 0.8 m, and transpiration rate were simultaneously measured and recorded. When compared to unscreened conditions, it was found that the thermal screen provided a more homogeneous microclimate and increased the average air temperature and canopy temperature at 0.8 m by about 2.5°C and 3.0°C, respectively. The latter result was attributed to the observed increase (about 100%) in the net radiation absorbed by the canopy, along with reflection of long-wave radiation by the thermal screen. Higher canopy-to-air vapor pressure deficits (+0.3 kPa) were observed in the lower layer (bent shoots) under screened conditions. Canopy transpiration rate was of the same order of magnitude in both cases. Energy savings due to the screen was estimated to be about 15%. The body of results underlines that the basic effect of the studied screen on crop behavior was the doubling of the net radiation absorbed by the canopy, with positive consequences on both air and canopy temperature, and therefore on growth, development, and sanitary conditions of the rose plants.