Insect-proof screens in greenhouses: Their effect on roof ventilation and insect penetration

A theoretical model, based on mass and energy conservation, was developed for the case in which the greenhouse is ventilated only by roof windows. The model predicts the transient response of the greenhouse air temperature to the opening of the windows and the results are compared with experimental data. The experiments were carried out in two adjacent greenhouses equipped with screened roof openings that were covered by plastic curtains that could be rolled up. One greenhouse had a whitefly proof, 50-mesh screen on the roof and the other had a coarser, 22% shading screen. Air temperature and the number of trapped whiteflies were measured inside both greenhouses and outdoors. The results show that immediately after the roof vents were opened by rolling the plastic covers, the greenhouse with the 22% shading screens cooled down faster and reached a lower temperature, by about 3 degrees C on average, than that equipped with the 50-mesh screens. In both greenhouses, significantly fewer whiteflies were trapped than outdoors. However, the number of insects trapped in the greenhouse equipped with the 22% shading screen was significantly higher than in the other greenhouse.