Optimization of vent configuration by evaluating greenhouse and plant canopy ventilation rates under wind-induced ventilation

The effects of greenhouse vent configurations, plant existence, and external wind speeds on ventilation rates and airflow patterns in a greenhouse and plant canopy zone under wind-induced ventilation were investigated. The optimization of traditional vent configuration for a two-span glasshouse for better air renewal, especially in the plant canopy zone, was attempted by three-dimensional numerical simulations using a computational fluid dynamics (CFD) approach. The realizable k-epsilon model was used for a turbulent model, and the existence of the plants in the greenhouse was modeled by a porous medium method. Prior to the optimization, the CFD model was verified with the results of an experimental study of natural ventilation. The CFD model adequately matched those results. The ventilation rates, both in the greenhouse and in the plant canopy zone, were proportional to external wind speed. Maximum greenhouse ventilation rates were achieved when rollup type side vents were used in the side walls and both side and roof vents were fully open (case 3). For example, the ventilation rate for this vent configuration was 6.03 m3 m-2 min-1 at an external wind speed of 1.5 in s-1. The greenhouse ventilation rate for this vent configuration was almost the same as when the butterfly-type side and roof vents were fully open (case 1). However, the use of a rollup side vent considerably improved the ventilation rate in the plant canopy zone. This showed that ventilation in the plant canopy zone was significantly affected by internal airflow patterns caused by different vent configurations.