Influence of an Aluminized Thermal Screen on Greenhouse Microclimate and Canopy Energy Balance

Greenhouse microclimate, energy savings, and crop transpiration were investigated during winter in aglass-covered greenhouse cultivated with a rose crop and equipped with an aluminized thermal screen. Air temperature andhumidity profiles were recorded at 0.3, 0.8, and 1.8 m heights inside the greenhouse. Net radiation over and under the rosecrop, heating pipe temperature, canopy temperature at 0.3 and 0.8 m, and transpiration rate were simultaneously measuredand recorded. When compared to unscreened conditions, it was found that the thermal screen provided a more homogeneousmicroclimate 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 thecanopy, 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 thesame order of magnitude in both cases. Energy savings due to the screen was estimated to be about 15%. The body of resultsunderlines that the basic effect of the studied screen on crop behavior was the doubling of the net radiation absorbed by thecanopy, with positive consequences on both air and canopy temperature, and therefore on growth, development, and sanitaryconditions of the rose plants.