Ventilation efficiency of void space surrounded by buildings with wind blowing over built-up urban area

This paper outlines methods for evaluating wind-induced ventilation efficiency in void spaces in built-up urban areas. The indices of ventilation efficiency express quantitatively the ability to deliver fresh upper-tier wind to the lower tiers of void spaces and dilute pollutants emitted therein. The evaluation of ventilation efficiency is based on detailed flow analysis. The scales for ventilation efficiency, (SVEs 1, 2, 3, and 6) were originally derived by the authors for room air ventilation and are also useful when applied to the exchange of air in void spaces in built-up urban areas. The other scales, namely local purging flow rate (L-PRF), visitation frequency (VF), and residence time (RT), were also re-defined by the authors for room air ventilation and had been applied for urban street canyons. They are based on detailed flow analysis and can be evaluated more easily with computational fluid dynamics (CFD) than flow modeling experiments. CFD simulation example is used to illustrate the concept of the proposed method and it is not meant to indicate the level of CFD set up for urban flow calculations. The effectiveness of the proposed method will be demonstrated more in future study. (C) 2009 Elsevier Ltd. All rights reserved.