SE—Structures and Environment: Effect of Ventilator Configuration on Wind-driven Ventilation in a Crop Protection Structure for the Tropics

A laboratory method for studying wind-driven natural ventilation was applied to a single-span greenhouse with side-wall and roof ventilation openings, a design common to crop protection structures used in tropical countries. A 1:15 scale model replica of the greenhouse, made from clear Perspex, was immersed in a flume tank filled with water. A steady mean flow generated by the flume simulated wind flow past the model. The flow inside the model greenhouse was examined for four different ventilator configurations and ventilation flow rates compared in each case. Neutrally-buoyant particles seeded in the flow allowed for clear flow visualization and these particles were tracked using a digital image analysis system from which detailed velocity measurements were obtained. Flow patterns observed in the scale model agree qualitatively well with full-scale observations. Predictions of the flow at full scale inferred from measurements of pressure and flow speed made at the side-wall openings of the model differed by less than 10% and 28%, respectively, from measurements made in the full-size greenhouse. For all ventilator configurations using side-wall openings an incoming jet-like flow crossed the greenhouse and established a circulating flow. The greenhouse with roof ventilation only had the lowest ventilation rate and the maximum rate was achieved with combined side-wall and roof openings. The results of these studies are detailed and design recommendations to improve the ventilation of tropical greenhouses are suggested.