Simulation on Ventilation Flux of Solar Greenhouse Based on the Coupling between Stack and Wind Effects

doi:10.3969/j.issn.1000-6362.2016.05.005

Abstract

Abstract:

Natural ventilation is a key measure for greenhouse environment adjustment, and ventilation flux calculation involves the discharge coefficient and wind effect coefficient. So, it is necessary to analyze the air volume flux over different vent types and the corresponding coefficients. The effects mechanism of the coupling between the stack and wind effects on ventilation flux was analyzed, and a model of air exchange in a solar greenhouse was established considering two main driving forces of ventilation. The tracer gas technique using carbon dioxide was used in a scaled greenhouse (scale rateis 1:5) to identify the ventilation flux. From measurements of volumetric flow rates, climate parameters and opening width, the model parameters, the discharge coefficient and the wind effect coefficient were identified by fitting the experimental data to the model using multi-linear regression. The results showed that the ventilation flux could be calculated by the following equations,G=0.81S•（H•?T/T)^0.5 +0.078S•u，G=0.63S•（H•?T/T)^0.5 +0.067S•u and G=0.46S•（H•?T/T)^0.5 +0.058S•u , where S and H was opening area and opening width; ?T was the temperature difference between inside and outside; T and u was the outside air temperature and velocity. The identified values of the discharge coefficient were 0.78, 0.6, and 0.44, and the wind effect coefficients were 0.78, 0.6, 0.44 when the vent opening widths were 3cm, 5cm and 7cm, respectively (equal to the opening widths in an actual greenhouse 15cm, 25cm and 35cm). It was shown that the ventilation flux due to the wind effect over total ventilation flux was over 50% when the wind velocity exceeds 1.5m·s^-1 and that could be over 70% when the wind velocity exceeds 2.5m·s^-1, which indicated that the temperature or buoyancy effect could be neglected.

Key words: Chinese solar greenhouse, Ventilation flux, Discharge coefficient, Wind effect coefficient, Simulation

FANG Hui, YANG Qi-chang, ZHANG Yi, CHENG Rui-feng, ZHANG Fang, LU Wei. Simulation on Ventilation Flux of Solar Greenhouse Based on the Coupling between Stack and Wind Effects[J]. Chinese Journal of Agrometeorology, 2016, 37(05): 531-537.

References

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