ISHS Acta Horticulturae 633: XXVI International Horticultural Congress: Protected Cultivation 2002: In Search of Structures, Systems and Plant Materials for Sustainable Greenhouse Production
THE INFLUENCE OF WIND DIRECTION ON GREENHOUSE VENTILATION |
| Authors: | B.J. Bailey, A.P. Robertson, A.G. Lockwood |
| Keywords: | wind speed, wind turbulence, air exchange, air flow, leeward, windward, ventilator opening |
| Abstract:
Wind-driven ventilation of a square 1/3 scale model of a Venlo greenhouse with roof ventilators was studied experimentally in a novel boundary layer wind tunnel. The model comprised five spans with 25 ridge hinged ventilators. The air flow in the wind tunnel was created by 56 propeller fans, the speeds of which were set to create a vertical velocity profile and the speeds fluctuated about their mean values to reproduce wind turbulence. The rates of air exchange were measured using nitrous oxide as a tracer gas and both the constant supply and decay methods were used. The gas was supplied through an array of five perforated pipes. Samples of greenhouse air were taken from five locations and mixed before measurement of the tracer gas concentration. Ventilation measurements with transverse flow were made with leeward ventilators open, windward ventilators open and both leeward and windward ventilators open. Windward ventilation gave higher rates of air exchange than leeward ventilation for the same ventilator opening, and combined leeward and windward ventilation gave higher air exchange rates than the sums of the leeward and windward exchange rates. The ventilation rate exhibited a non-linear response with ventilator opening for all three configurations. A ventilation model was developed which accounted for 97% of the variation in the measured values. Flow visualization revealed the fluctuating nature of the air flow with many ventilators exhibiting alternating inflow and outflow. In general air entered through downwind ventilators and was removed via the upwind ones. When both windward and leeward ventilators were open the former acted mainly as inlets and the latter as outlets. | |
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