The effect of insect-proof screens in roof openings on greenhouse microclimate

Experimental data from a wind tunnel, was used to compare three available methods to predict the pressure drop through screens. Advantages and drawbacks of each method are discussed. Two of the methods are based on equations that were derived for flow through porous media and the third is based on Bernoulli’s equation. It is shown that comparing different screens by plotting their pressure drop versus the upstream velocity may be misleading. Experiments in a roof-ventilated greenhouse with leeward roof openings revealed the obstruction offered by fine mesh screens to flow through the openings, and the resulting higher temperature and humidity within the greenhouse.