ISHS Acta Horticulturae 710: International Symposium on Greenhouses, Environmental Controls and In-house Mechanization for Crop Production in the Tropics and Sub-Tropics
DETERMINATION OF GLOBAL WIND COEFFICIENTS FOR THE DEVELOPMENT OF SIMPLE VENTILATION RATE CALCULATION MODELS FOR A PARRAL MULTISPAN GREENHOUSE |
| Authors: | J.J. Pérez-Parra, J.I. Montero, E.J. Baeza, J.C. Lopez-Hernandez |
| Keywords: | natural ventilation, ´parral´ greenhouse, wind global coefficient, anti-insect screen |
| Abstract:
The parral greenhouse is the most important greenhouse structure in the coastal southeast of Spain, with 25.000 ha only in the province of Almeria. Despite its great importance and increasing use in other parts of the world (North Africa, North and South America) no studies of natural ventilation performance of this greenhouse type had been made until very recently. The aim of this study was to estimate wind global coefficients (Cw) of a 5 span symmetric parral greenhouse, and to develop simple calculation models to estimate the ventilation rate at different wind velocities. The experimental greenhouse, located at the “Las Palmerillas” Experimental Station of Cajamar was equipped with both roof and side ventilation. Ventilation rates for different wind speeds and directions (windward or leeward) and for different ventilator configurations (rolling vs. flap type; anti-insect screen vs. no screen) had been previously estimated using the tracer gas decay rate method. Discharge coefficients for the continuous vents were estimated from published models. It was found that the wind global coefficient values varied with wind speed for each ventilator configuration. Cw could be expressed as a function of wind speed using a simple power law of the type Cw=a u-b with regression coefficients (R2) which ranged from 0.64 to 0.89. Wind direction also showed a big influence on Cw values for the roof flap vents, the windward coefficients were bigger than the leeward ones, in agreement with other authors. The presence of an anti-insect screen in the roof rolling vents decreased Cw values in relation to the absence of screen. A simple ventilation rate calculation model was developed for the different ventilator configurations and wind directions that depended only on the external wind speed. | |
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