Numerical modeling of outdoor thermal comfort in 3D

Abstract

With the rise in urban air temperature, heat stress and thermal discomfort are challenging the livability of urban environments. To respond to this concern, we employ numerical modeling to evaluate the spatial and temporal variabilities of thermal comfort and introduce a simulation tool: outdoor thermal comfort in 3D (OTC3D). The model builds upon the work by Nazarian et al., 2017, and is a) extended to evaluate realistic urban configurations, b) validated against measurements, c) enabled to intake a wide resolution range of microclimate parameters (modular approach), and d) made available on an open-source platform. Using OTC3D, we evaluated outdoor thermal comfort (OTC) in two urban configurations: idealized and realistic. In the realistic configuration, we demonstrate the functionality of the model in presenting the variability of OTC in an urban neighborhood. Using the idealized configuration, on the other hand, we performed sensitivity studies regarding the effects of urban density and realistic surface heating. First, we observed that thermal comfort changes non-monotonically with urban density, as the ensuing change in wind speed and radiation patterns have counteracting effects on thermal comfort. Accordingly, to achieve the desired thermal comfort in hot climates, strategies to enhance urban ventilation are favored in higher densities, while strategies to minimize radiation are needed for lower urban packing densities. Furthermore, we observed that realistic distribution of surface temperature is critical when urban density is high (e.g. λp = 0.44). Therefore, approximations of surface temperature found in existing thermal comfort models are not suited for high-density urban areas. This further motivates the modular approach to improve the accuracy of thermal comfort analysis.