Ventilation Simulation in a Large-scale Greenhouse Based on CFD

doi:10.3969/j.issn.1000-6362.2017.04.003

Abstract

Abstract: To solve the problem that the inner available space of the traditional Chinese solar greenhouse is usually small, a new-type large-scale greenhouse which was tunnel type and had a wide span with steel frame and south-north orientation was designed. The?distribution?of airflow and temperature patterns, the effect of vent openings under different outdoor wind speed conditions on airflow and temperature patterns in a naturally ventilated large-scale greenhouse were studied. Firstly, simulation model of the airflow and temperature patterns in a naturally ventilated large-scale greenhouse was established by means of three-dimensional computational fluid dynamics (CFD). Secondly, the model was validated via the comparison with the field experimental results at the same locations where 13 temperature sensors were installed under the typical sunny day when the vent opening degree was 50%. The comparison between simulations and measurements showed that the absolute error was within 2.8℃, the square error was within 1.6℃, the maximum relative error was less than 9.9% and the average relative error was around 4.1%. An agreement existed between simulated and experimental results. Finally, the model which was validated was used to study the effect of vent opening degree (25%, 50%, 75% and 100%) under different outdoor wind speed (1, 2, 3, 4m·s-1) conditions on airflow and temperature patterns. The results showed that, the average temperature of the top of the greenhouse was higher than the bottom of the greenhouse, and the colder air outside went into the greenhouse from the west side vent, so the average temperature of the west of the greenhouse was lower than the east of the greenhouse. From south to north, the average airflow rates decreased in the greenhouse. Because of the west and east vents, the average air velocity in the center of greenhouse was lower than the side. When both top and side vents full opened, the airflow in greenhouse was relatively low. Temperature distribution was uniform in the large-scale greenhouse when the vent opening degree was 100%. The outdoor wind speed had a significant positive correlation with the ventilation rate when vent opening degree was kept constant. For the purpose of cooling, the optimum vent opening degree was 75%-100%. If the temperature of the greenhouse was suitable for crop growth and the outdoor wind speed was faster than about 3m·s-1, the optimum vent opening degree should be less than 75%.

Key words: CFD model, Model, Temperature field, Air flow field, Ventilation rate

ZHANG Fang, FANG Hui, YANG Qi-chang, CHENG Rui-feng, ZHANG Yi, KE Xing-lin, LU Wei, LIU Huan. Ventilation Simulation in a Large-scale Greenhouse Based on CFD[J]. Chinese Journal of Agrometeorology, 2017, 38(04): 221-229.

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