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In this study, ventilation efficiencies of naturally ventilated multi-span greenhouses being used typically in Korea were analyzed considering structural types, natural climates and positions in greenhouse. The ventilation efficiencies were also analyzed locally and regionally in the greenhouses. It was critical to primarily set up the identical climate condition to analyze the ventilation efficiencies of greenhouses with different configurations. However, it was impossible to control these factors through the field experiment while it requires a lot of measuring equipments and labors. As one of the solutions, the CFD simulation which is able to visualize the air flow quantitatively and qualitatively was used in this study. The accuracy of the CFD model used in this study has already reached to ±6.7% in error by Lee et al.(2005). Likewise, the TGD (tracer gas decay) method was additionally used to analyze the ventilation efficiencies quantitatively to get over the limitations of traditional ventilation analysis, and then it was connected to the CFD model using UDF(User defined function) tools. While the boundary layers of wind velocity and turbulent intensity were used as the inlet boundary condition of the CFD, the ventilation rates were 1.26, 1.08, 1.01 and 0.73 min-1, respectively for Widespan, 1-2W, Single and Venlo types. For these cases, the wind direction was perpendicular to the sidevent of the greenhouse with 2m s-1 of wind speed at 10m height. The average ventilation rates with the wind parallel to the sidevent were 36%, 57%, 37% and 79%, respectively lower than with the wind perpendicular to the sidevent, and 50%, 95%, 52% and 91% with the wind 45 degrees to the sidevent. The results show that 1-2W and Venlo types are less influenced by the wind direction. It also indicated that the CFD can be very effective and powerful tool to study the greenhouse ventilation.