Measurement and analysis of air exchange rates in a greenhouse with continuous roof and side openings

The results of natural ventilation measurements carried out in a plastic greenhouse with continuous roof and side openings are presented. Both the static and turbulent pressure differences were taken into account. The results show a strong dependence of air exchange rate on wind velocity and total ventilator opening area as expected, but no important dependence on wind direction could be found for the conditions in which the experiments were conducted. Wind induced ventilation seems to become dominant when the wind speed exceeds about 1.8 m/s that is, the thermal buoyancy effect can be neglected. When the wind speed is lower than 1.8 m/s, although the thermal buoyancy effect is minor it cannot be neglected. Roof only and roof and side ventilator configurations are always more efficient than side only ventilator configuration. The best results for the calculated ventilation flux were obtained by a model that takes into account both thermal buoyancy and wind effects. (C) 1996 Silsoe Research Institute