Articles
STUDY ON VENTILATION EFFICIENCIES OF NATURALLY VENTILATED MULTI-SPAN GREENHOUSES IN KOREA
Article number
719_38
Pages
341 – 348
Language
English
Abstract
In this study, the ventilation efficiencies of naturally ventilated multi-span greenhouses used in Korea were analyzed considering the structural types, natural climates and internal positions in the greenhouses.
The ventilation efficiencies were also analyzed locally and regionally in the greenhouses.
It is critical to set up identical primary climate conditions in order to analyze the ventilation efficiencies of greenhouses with different configurations.
However, it is impossible to control these factors in field experiments which requires a lot of measuring equipment and labor.
As one solution a CFD simulation which is able to visualize the air flows quantitatively and qualitatively was used in this study.
The accuracy of the CFD model used had previously been shown to be ±6.7%. The tracer gas decay method was used to analyze the ventilation efficiencies quantitatively to overcome the limitations of traditional ventilation measurements, and it was connected to the CFD model using UDF (User defined function) tools.
When 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, singlespan and Venlo type greenhouses.
For these cases, the wind direction was perpendicular to the sidevent of the greenhouse with a speed of 2m s-1 at a 10 m height.
The average ventilation rates with the wind parallel to the sidevents were 36%, 57%, 37% and 79%, respectively lower than with the wind perpendicular to the sidevents, and 50%, 95%, 52% and 91% with the wind 45 degrees to the sidevent.
The results showed that the 1-2W and Venlo types are less influenced by wind direction.
It was also indicated that the CFD can be a very effective and powerful tool for studying greenhouse ventilation.
The ventilation efficiencies were also analyzed locally and regionally in the greenhouses.
It is critical to set up identical primary climate conditions in order to analyze the ventilation efficiencies of greenhouses with different configurations.
However, it is impossible to control these factors in field experiments which requires a lot of measuring equipment and labor.
As one solution a CFD simulation which is able to visualize the air flows quantitatively and qualitatively was used in this study.
The accuracy of the CFD model used had previously been shown to be ±6.7%. The tracer gas decay method was used to analyze the ventilation efficiencies quantitatively to overcome the limitations of traditional ventilation measurements, and it was connected to the CFD model using UDF (User defined function) tools.
When 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, singlespan and Venlo type greenhouses.
For these cases, the wind direction was perpendicular to the sidevent of the greenhouse with a speed of 2m s-1 at a 10 m height.
The average ventilation rates with the wind parallel to the sidevents were 36%, 57%, 37% and 79%, respectively lower than with the wind perpendicular to the sidevents, and 50%, 95%, 52% and 91% with the wind 45 degrees to the sidevent.
The results showed that the 1-2W and Venlo types are less influenced by wind direction.
It was also indicated that the CFD can be a very effective and powerful tool for studying greenhouse ventilation.
Publication
Authors
L.B. Lee, S.W. Hong, H.S. Hwang, L.H. Seo
Keywords
computational fluid dynamics, greenhouse, natural ventilation, tracer gas decay, ventilation efficiency
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