Abstract
Ventilation efficiency (VE) indices for indoor environments are widely used to evaluate the ventilation performance and air quality of indoor domains. These indices are considered effective for outdoor air quality assessments too. In this paper, application of the ventilation efficiency indices for indoor environments to urban domains is presented and their effectiveness is confirmed. Three indices for indoor VE indices are considered here: the purging flow rate (PFR: the effective airflow rate required to purge pollutants from the domain), visitation frequency (VF: the number of times a pollutant enters the domain and passes through it) and residence time JP: the time a pollutant takes from once entering or being generated in the domain until its leaving), which can be calculated by means of computational fluid dynamics (CFD) simulations. Two examples for evaluating the air quality of urban domains in terms of the VE indices were presented. In the first, CFD simulations were carried out using a two-building model to assess the effects of urban street width and street building heights on the VE indices of a domain located within a street. In the second example, numerical simulations were carried out to estimate the influence of the arrangement of building arrays on the VE indices of selected domains located within these arrays. The results of the study showed that the ventilation efficiency indices of indoor environments appear to be a promising tool in the assessment of the air quality of urban domains as well. One of the features of applying these indices is that it is not necessary to consider the location of the pollutant source within the study domain. In addition, the VE indices are able to describe the pollutant behavior within the domain, which is very important for obtaining a complete assessment for the wind ventilation performance within urban domains. (C) 2007 Elsevier Ltd. All rights reserved.