Cooling naturally ventilated greenhouses in the tropics by near-infra red reflection.

摘要

High temperatures and humidity inside greenhouses located in the tropics is one of the major constraints to protected cultivation in areas, such as central Thailand. Studies were conducted in 2 naturally ventilated greenhouses, clad with insect-proof nets on the sidewalls and roof ventilation openings, with tomatoes as a crop, to investigate the effect of near infrared (NIR) reflecting pigments on the greenhouse microclimate and plant growth. A polyethylene film was used to cover the roof and gable of the greenhouse, while a white plastic film was used as a mulching material. A shading paint containing a NIR-reflecting pigment (ReduHeat, Mardenkro B.V., Baarle-Nassau, the Netherlands) was applied on the roof of one of the greenhouses ("Trt"). This led to the lowering of the greenhouse air temperature by up to 4 degrees C when the crop was young corresponding to 18% reduction in transmission of global radiation. However, when the crop was mature at 57 days after transplanting during the rainy season, transpiration cooling minimized air temperature differences between the 2 greenhouses. Shading reduced plant water requirement, power consumption of the fans and the number of blossom-end rot affected and parthenocarpic fruits, in both dry and rainy season. A slight reduction in marketable yield and an increase in the number of cracked fruits were observed in Trt. The results revealed that the combination of natural ventilation and NIR-reflection may provide a solution for cooling greenhouses in areas with high ambient humidity and high solar radiation levels.