Airflow at the openings of a naturally ventilated Almeria-type greenhouse with insect-proof screens.

摘要

The main objective of this particular study was to determine the wind coefficient of an Almeria-type greenhouse equipped with insect-proof screens from the ventilation airflow by measuring air velocity through the openings with a tri-directional sonic anemometer. Measurements were taken with a strong north-east 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=C_dC_w0.5=0.050, and the values of the mean and turbulent wind coefficients were C_w=0.067 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 and an obstacle close to one of the side openings. Discharge coefficients due to the presence of insect-proof screens in the greenhouse (C_{d, phi} =0.156-0.245) were calculated from wind tunnel measurements, obtaining a total discharge coefficient of C_d=0.193. Use of the screen in the openings can cause approximately a 71% reduction of C_d. Winds perpendicular to the axis produce an inflow through the side openings and an outflow through the roof vents. In qualitative terms, this airflow pattern is in good agreement with previous simulations of Computational Fluid Dynamic in the greenhouse.