Assessing impact of urban densification on outdoor microclimate and thermal comfort using ENVI-met simulations for Combined Spatial-Climatic Design (CSCD) approach

Future urban planning requires context-specific integration of spatial design and microclimate especially for tropical cities with extreme weather conditions. Thus, we propose a Combined Spatial-Climatic Design approach to assess impact of urban densification on annual outdoor thermal comfort performance employing ENVI-met simulations for Singapore. We first consider building bylaws and residential site guidelines to develop eight urban-density site options for a target population range. We further classify annual weather data into seven weather-types and use them as boundary conditions for the simulations. Comparing such fifty-six combined spatial-climatic simulation outputs by analyzing Outdoor Thermal Comfort Autonomy, we report the influence of site geometry is nominal on air temperatures but significant for mean radiant temperatures and physiological equivalent temperatures. Neighborhoods with taller (20% increase in mean height) buildings and narrower footprints exhibit better thermal performance compared to short and wider (12-58% decrease in mean width) buildings, due to less radiative heat gain during solar noon. For a high density tropical urban context, like Singapore with high sun angle and solar radiation, mutual shading and presence of wind enhances thermal comfort. Results provide useful and actionable recommendations on ideal building profile for heat responsive neighborhoods in low-latitude hot-humid cities similar to Singapore.