ISHS Acta Horticulturae 659: VII International Symposium on Protected Cultivation in Mild Winter Climates: Production, Pest Management and Global Competition
MODELLING NATURAL VENTILATION IN A "PARRAL" GREENHOUSE WITH CONTINUOUS FLAP VENTS USING COMPUTATIONAL FLUID DYNAMICS AND WIND TUNNEL MEASUREMENTS |
| Authors: | J.J. Pérez-Parra, E.J. Baeza, G. Zaragoza, J.C. López, J.I. Montero |
| Keywords: | greenhouse, ventilators, pressure coefficients, CFD, LDA. |
| Abstract:
The “parral” greenhouse structure comprises 84% of the total greenhouse area in Spain. Its use is increasing in other Mediterranean countries, most notably in Morocco, and also in Mexico and South America. “Parral” greenhouses are naturally ventilated. There is minimal scientific information available concerning natural ventilation for this greenhouse structure. This study used laser doppler anemometry (LDA) with a 1:20 scale model in a wind tunnel, and two-dimensional computational fluid dynamics (CFD) simulations to develop a detailed understanding of natural ventilation of a 5-span “parral” greenhouse with continuous flap roof vents in each span. Vertical air velocity profiles for each roof vent were obtained using both LDA and CFD. These demonstrated the important role of the first vent facing the wind, which was the only vent that functioned clearly as an inlet, the rest functioning largely as outlets. From wind velocity profiles, pressure profiles were obtained which were used to calculate individual external pressure coefficients for each vent. The pressure coefficients were used to develop simple mathematical models that estimated in-flow and out-flow through the five individual roof vents relative to the directly-incoming external wind velocity. There was good agreement between pressure coefficients calculated using LDA and CFD. The ventilation rates calculated with the models based on pressure coefficients agreed well with those measured with a tracer gas technique in the actual greenhouse that was used as the basis for the CFD simulations and the model for the combined LDA-wind tunnel approach. | |
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