Effects of frontal area density on outdoor thermal comfort and air quality

Abstract

This paper systematically investigates the effects of the frontal area density of various three-dimensional (3D) array building models on the thermal comfort and air quality at the pedestrian level above four sidewalks (north, south, east and west). The buoyancy force for natural-convection flows and the realistic solar irradiance at local solar times (LSTs) from 0700 to 1700 are considered with five different frontal area densities (λF = 0.0825–1.25). By a combination of the Rayman model and the ANSYS Fluent® software, the CO concentration and physiologically equivalent temperature (PET) are solved numerically. The simulated CO concentration and PET results are considered as outdoor parameters of the air quality and thermal comfort. A critical λF is obtained for urban development by applying multivariable regression analysis to a group of dimensionless parameters. This analysis will facilitate the choice of building density and simultaneously enhance the air quality and thermal comfort. The results reveal that with an increase in λF, the PET decreases above most of sidewalks during the daytime, while only is a steady reduction of air quality observed above west and east sidewalks of spanwise streets. According to the multivariable regression analysis for Hong Kong, the building density should have a λF value between 0.82 and 0.84 to basically realize a PET <38 °C and CO concentration <30000 μg/m3 simultaneously in the daytime in June.