Urban wind environment and its impact on indoor environment-Acceptable wind features of void space surrounded by buildings

To deal with a stochastic wind environment in urban areas, this study introduces exceedance probability analysis to evaluate low-speed wind properties. As wind environment can be evaluated in terms of both ventilation performance and thermal comfort, two representative indices were adopted: the local air change rate (N) and the space-averaged kinetic energy of wind (KE). The former was used to express the ability of airflow to exhaust contaminants generated within a given space, and the latter to represent the ability of airflows to cool the human body. The exceedance probability (EP) was calculated based on the wind speed distributions described by the Weibull function for 16 azimuths and then used to indicate the exceedance probability of a given air change rate. The exceedance probability of the kinetic energy of wind in the void space was also evaluated in the same way as the local air change rate. Acceptable values of the exceedance probability for both local air change rate and kinetic energy in the void spaces were then suggested, based on acceptable indoor environmental indices, which were often worse than those found outdoors and also affected by the outdoor environment.