Numerical simulation of ventilation efficiencies of naturally ventilated multi-span greenhouses in Korea

In this study, the ventilation efficiencies of naturally ventilated multi-span greenhouses typically used in Korea were analyzed considering structural types and natural climate factors such as wind direction. It was critical to set up identical, stable climate conditions for fair analysis and comparison of ventilation efficiencies in regards to different configurations. However, these ideal conditions do not exist in reality. Therefore, computational fluid dynamics (CFD) simulation, which is able to visualize the airflow quantitatively and qualitatively, was used in this study to reduce the effect of variations between greenhouses and locations. The CFD model used in this study had an established ±6.7% error. In addition, the tracer gas decay (TGD) method was used to analyze ventilation efficiencies quantitatively to overcome the limitations of traditional ventilation analysis. The TGD results were then connected to the CFD model using user-defined function (UDF) tools. The ventilation rates computed by the TGD method showed a 16.7% average difference compared to rates determined using a conventional method. When the wind direction was perpendicular to the greenhouse side vent with 2 m s-1 wind speed at 10 m height, overall ventilation rates computed by TGD were 1.30, 1.23, 1.02, and 0.74 AC (air exchange) min-1 in summer conditions for widespan, 1-2W, widewidth, and venlo type greenhouses, respectively. The average ventilation rates with the wind parallel to the side vent were respectively 32%, 52%, 30%, and 75% lower than when perpendicular to the side vent, and respectively 50%, 89%, 47% and 94% lower than with the wind 45° to the side vent. The results indicate that 1-2W and venlo type greenhouses were less influenced by wind direction, likely due to the effect of roof openings.