Effect of vent opening and insect screens on greenhouse microclimate distribution
The objective of this work was to experimentally investigate the influence of vent type (side, roof or both) and of an anti-aphid insect screen on airflow and temperature distribution of a mono span greenhouse round arch roof with vertical side walls. The greenhouse was equipped with two side roll-up vents and a flap roof vent. A tomato crop planted in double rows was cultivated inside the greenhouse. The three components of air velocity were measured by a 3-D sonic anemometer and simultaneously air temperature and relative humidity were recorded in several positions inside the greenhouse. Concerning the effect of insect screens, it was found that the mean value of the normalised air velocity was 65% lower in the greenhouse with insect screens in the side vent openings than without the screens. Furthermore, with the screen in the openings, the spatial heterogeneity of microclimate variables was reduced. As far as the vent opening is concerned, it was found that in the case of side openings only, the air velocity inside the greenhouse was characterized by a strong air current near the greenhouse ground and low air velocity near the roof while the combination of roof and side openings increased air velocity and decreased air temperature inside the greenhouse but increased also the spatial heterogeneity of the greenhouse microclimate. The most homogeneous climate conditions were achieved by roof only openings.