Effect of vents’ opening and insect screen on greenhouse ventilation

The objective of this work was to experimentally investigate the influence of vent type and of insect proof screens on ventilation rate of a round arch plastic covered greenhouse. The greenhouse was equipped with side roll-up windows and a flap roof window and is located at the University of Thessaly near Volos in the coastal area of Eastern Greece. Microclimate variables as well as the greenhouse ventilation rate (G) were measured. Two measuring methods were used for the determination of G: (a) the decay rate tracer gas method, using N2O as tracer gas, and (b) the greenhouse energy balance method. In order to study the effect of vent type on G, in a greenhouse with an insect proof screen in the vent openings, the G was determined during periods were the ventilation was performed by (i) roof, (ii) side and (iii) both roof and side vents. Furthermore, in order to study the effect of insect proof screens on G, measurements were carried out also during periods were the ventilation was performed by side vents without a screen in the openings. The two measuring methods gave similar results, but the tracer gas method provided a better fit to the experimental data. Concerning the ventilation performance, the results showed that the most effective vent configuration was the combination of roof and side vents, followed by side vents only. As far as the effect of screens on ventilation rate is concerned, it was found that their use in the vent openings caused a greenhouse ventilation rate reduction of about 33%.