Influence of Aspect Ratio of Side Ventilation Window on Air Circulation in Terraced Greenhouses

Abstract

【Objective】 The geometry of side ventilation windows is an important design parameter of greenhouse and this paper investigates the impact of their aspect ratio on air circulation in terraced greenhouses. 【Method】 The study is based on butterfly windows of terraced greenhouses in Guangzhou, using numerical simulation and experimental data measured from a greenhouse (Window C). We modelled five aspect ratios and compared the numerical simulations with experimental data. Air circulation in the greenhouse is quantified using non-uniformity coefficients. 【Result】 The average errors between the simulated and measured temperature and wind speed are 2.48% and 8.76% respectively, and their associated root mean square errors are 1.10 ℃ and 2.1×10-3 m/s, respectively. Changes in the aspect ratio do not result in significant effect on average temperature in the greenhouses, but affect temperature variation noticeably. Among the five aspect ratios we compared, Window A gives the greatest average wind speed and highest wind uniformity coefficient. Compared with Window C, it increase average wind speed by 23% and the wind speed uniformity coefficient by 41%. 【Conclusion】 Our results show that reducing the aspect ratio of the side ventilation window as currently used by local farmers can effectively increase the uniformity of both temperature and wind speed in the greenhouse.

Keywords

• multi-span greenhouse
• aspect ratio
• natural ventilation
• numerical simulation