DISCHARGE COEFFICIENTS OF GREENHOUSE WINDOWS WITH INSECT- PROOF SCREENS

摘要

The main purpose of this study was to quantify the reduction of ventilation rate caused by three kinds of screen of different thickness: anti-trip (0.18x0.18 mm), anti-aphid (0.4x0.4 mm) and shading net of 60% light transmission. Discharge coefficients of rectangular openings located in the central span and the side span of a multitunnel (3-bay) greenhouse were measured using the procedure outlined by Bot (1983) and de Jong (1990). Measurements were taken in a 1:3 scale model built inside a larger greenhouse to avoid disturbance caused by open-air wind action. For each type of window (central and lateral span) and for each type of screen material, a discharge coefficient expression was derived as a function of the aspect ratio (length/height). Results showed higher efficiency for a window situated in the lateral span than for one in the central span, Windows equipped with anti-trip screens had a discharge coefficient approximately half that of the same window without any screen.