Numerical analysis of the inner climate in a mechanically-ventilated greenhouse with three spans

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One of the main problems facing agriculture in greenhouses, especially, in hot climates, is to moderate and control problems arising from increased temperatures that occurs in marked periods of the year, as they reduce the quality and quantity of the harvest. An effective method of climate control is ventilation (natural or forced) and although forced ventilation is more predictable than natural ventilation, its description is more complex and a simplification requires further knowledge of the process. The objective of this study was to validate and apply a numerical model based on computational fluid dynamics (CFD) for the climate analysis of a zenithal greenhouse of three spans without crop and with forced ventilation. Experimentally the scalar variables of air and soil temperatures along with values of heat transfer and ventilation rates under different external conditions are supplied. Analysis of results indicated that when operating the forced ventilation system, the ventilation rate is stable, regardless of external conditions. For low wind speeds (less than 3 m s-1) the mechanical ventilation becomes more important than the outside air flow due to the wind or thermal effect. As to air temperatures, in small greenhouses (30 m long) the forced ventilation system provides adequate thermal uniformity, becoming more important the position and capacity (power) of the fans, since there is a maximum fan power above which the ventilation rate is not increased.

Jorge Flores-Velázquez
Enrique Mejía-Saenz
Juan I. Montero-Camacho
Abraham Rojano