A study of natural ventilation in an Almeria-type greenhouse with insect screens by means of tri-sonic anemometry

The wind coefficient of an Almeria-type greenhouse has been calculated from direct estimation of airflow at the openings by means of three-dimensional sonic anemometry. Measurements were taken with a strong northeast wind (Levante) and with a weak westerly wind (Poniente). For the model considering only the wind effect, the coefficient of effectiveness obtained was E-V = CdCw0.5 = 0.050, and the values of the mean and turbulent wind coefficients were C-w = 0.066 and C-w' = 0.029, respectively. Two important characteristics of the Almeria-type greenhouse analysed in this work make natural ventilation difficult: the presence of mature tomato plants inside the greenhouse and of an obstacle close to one of the side openings, which affected the air movement throughout it. Discharge coefficients due to the presence of screens in the greenhouse (C-d,C-phi = 0.156-0.245) were calculated from wind-tunnel measurements, obtaining a total discharge coefficient of C-d = 0.193. Use of the anti-aphid screen in the openings can cause an approximately 71% reduction of C-d and consequently of the wind-related coefficient E-V. Winds perpendicular to the axis produce an inflow through the side opening free of obstacles and an outflow through the roof vents. in qualitative terms, this airflow pattern is in good agreement with previous simulations using Computational Fluid Dynamics. (C) 2009 IAgrE. Published by Elsevier Ltd. All rights reserved.