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Open AccessArticle

Effects of Unstable Stratification on Ventilation in Hong Kong

Insitute of Meteorology and Climatology, Leibniz Universität Hannover, 30419 Hannover, Germany
School of Architecture, The Chinese University of Hong Kong, Hong Kong, China
Institute of Future City (IOFC), The Chinese University of Hong Kong, Hong Kong, China
Institute of Energy, Environment and Sustainability (IEES), The Chinese University of Hong Kong, Hong Kong, China
Author to whom correspondence should be addressed.
Atmosphere 2017, 8(9), 168;
Received: 3 August 2017 / Revised: 24 August 2017 / Accepted: 6 September 2017 / Published: 8 September 2017
(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)
Ventilation in cities is crucial for the well being of their inhabitants. Therefore, local governments require air ventilation assessments (AVAs) prior to the construction of new buildings. In a standard AVA, however, only neutral stratification is considered, although diabatic and particularly unstable conditions may be observed more frequently in nature. The results presented here indicate significant changes in ventilation within most of the area of Kowloon City, Hong Kong, included in the study. A new definition for calculating ventilation was introduced, and used to compare the influence of buildings on ventilation under conditions of neutral and unstable stratification. The overall ventilation increased due to enhanced vertical mixing. In the vicinity of exposed buildings, however, ventilation was weaker for unstable stratification than for neutral stratification. The influence on ventilation by building parameters, such as the plan area index, was altered when unstable stratification was considered. Consequently, differences in stratification were shown to have marked effects on ventilation estimates, which should be taken into consideration in future AVAs. View Full-Text
Keywords: convective boundary layer; LES; street-level ventilation convective boundary layer; LES; street-level ventilation
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Gronemeier, T.; Raasch, S.; Ng, E. Effects of Unstable Stratification on Ventilation in Hong Kong. Atmosphere 2017, 8, 168.

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