CFD study of the natural ventilation performance of a parral type greenhouse with different numbers of spans and roof vent configurations.

摘要

The majority of the studies of greenhouse natural ventilation, both field and laboratory experiments, have been performed on small greenhouses, mainly for economic reasons. Therefore, information on commercial size greenhouses is very scarce. In the present work, two dimensional CFD simulations have been performed to study the effect of the number of spans in a parral type greenhouse (2, 3, 5, 7, 10 and 15 spans) with four different roof vent configurations: windward flap vents, leeward flap vents, alternate flap vents and double flap vents. The simulation model was previously validated using experimental ventilation rate data for a 5 span greenhouse. All configurations showed an important decrease in the ventilation rate (vol/h) as the number of spans increased, but the values increased again for the 10 and 15 span models with the alternate and double vent configurations. For the 15 span model, the double vent configuration provided almost 5 and 3 times more air exchange than the single leeward and windward vents configurations. The double vent configuration also provided the best air movement in the lower part of the greenhouse for any greenhouse size. The alternate vent configuration generated the highest air velocities but only in the upper part of the greenhouse. According to the results, the double vent configuration ensures that ventilation rate values do not decrease when the greenhouse size increases and it also provides the best air movement in the crop area..