Influence of exhaust wind cowls on wind driven ventilation

doi:10.3785/j.issn.1008-973X.2023.03.017

Journal of ZheJiang University (Engineering Science)

2023, Vol. 57

Issue (3): 591-597 DOI: 10.3785/j.issn.1008-973X.2023.03.017

Influence of exhaust wind cowls on wind driven ventilation

Guo-qing HE(

),Yi-tian TANG

College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China

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Abstract

A scaled model of solar chimney building was designed and tested in a wind tunnel, to investigate the impact of wind pressure related factors and wind cowls on the discharging performance of high exhaust of a building. A comparison study between a common elbow outlet and two wind cowls (a louver type and a baffle type) was conducted to investigate their influences on wind pressure distributions and the resulting ventilation rate. Results show that under the gradient-profiled wind, the influence of the net height difference between the inlet and outlet on the ventilation rate cannot be ignored. The resulting wind pressure at the high exhaust was in general greater than that of the lower inlet. When the roof-mounted elbow outlet was facing the wind, the reverse flow occurred, which was against the chimney flow and weakened the stack ventilation design. Both wind cowls prevented the reverse flow. However, the baffle type was superior to the other. It produced the largest ventilation rate among the three outlets except for the side-wind case, where its flow rate was 28% lower than that of the elbow outlet case. The flow rate of the baffle type outlet was 57% and 33% higher than that of the elbow outlet in the windward and leeward directions, respectively. In the design of building ventilation systems with high exhaust, such as solar chimneys, the inlet needs to be placed at windward side as much as possible, while the outlet needs to be placed as high as possible. And the baffle type wind cowl is recommended.

Key words： wind cowl solar chimney wind driven ventilation wind tunnel test gradient wind openings arrangement

Received: 21 February 2022 Published: 31 March 2023

CLC:

TU 18

Fund: 国家自然科学基金资助项目（51678518）

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Cite this article:

Guo-qing HE,Yi-tian TANG. Influence of exhaust wind cowls on wind driven ventilation. Journal of ZheJiang University (Engineering Science), 2023, 57(3): 591-597.

URL:

https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2023.03.017 OR https://www.zjujournals.com/eng/Y2023/V57/I3/591

风压通风中排风风帽的影响

为了研究建筑高位排风口排风时风压影响因素以及风帽的作用，设计太阳能烟囱建筑缩尺模型，通过风洞试验，对比普通弯管出口和2种风帽（百叶型和挡板型）对建筑风压分布及烟囱内通风量的影响. 结果表明：在梯度风下，进出口高度差对风压通风的影响不可忽视，当出口位置高于入口位置时，出口处风压往往大于入口处风压. 当屋顶普通弯管出口遇到迎面风向时，产生的与烟囱热羽流方向相反的倒灌通风会破坏烟囱的气流组织设计. 2种风帽均可阻止气流倒灌，其中挡板型风帽综合性能更优. 通风量除了在侧风向低于弯管出口28%外，在迎风和背风方向上均为三者最大，并分别高出弯管出口57%与33%. 在包括太阳能烟囱在内的建筑高位排风设计中，除了入口应尽量处于主流风向的迎风面外，出口应布置在高位，并推荐使用挡板型风帽.

关键词： 风帽, 太阳能烟囱, 风压通风, 风洞实验, 梯度风, 开口布置

Fig.1 Wind tunnel test layout

Fig.2 Solar chimney building model and distributions of measuring points

Fig.3 Wind cowl models and distributions of measuring points

Fig.4 Five wind profiles in wind tunnel test (reference height is 0.45 m)

Tab.1 Comparison of wind pressures at center of inlet and outlet (reference velocity is 5 m/s)

Fig.5 Comparison of surface pressure coefficients between two models under gradient wind

Fig.6 Pressure coefficients of cube model under uniform flow ^[21]

Fig.7 Layout of room inlet and outlet and four tested wind directions

Fig.8 Volume flow rates under different layouts of inlet and outlet

Tab.2 Measured pressures at inlet and outlet of room with different exhausts (reference velocity is 5 m/s)

Fig.9 Volume flow rates versus reference velocity at three exhausts


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