Modeling the influences of layouts of residential townhouses and tree-planting patterns on outdoor thermal comfort in Bangkok suburb

In Bangkok, reducing the extreme heat in summer is a critical challenge for urban planners and researchers associated with the built environment. A significant cause of such extreme heat is the rapid expansion of residential development without corresponding planning and design. This work explores layout designs for residential townhouses, building geometries, and tree-planting patterns for enhancing outdoor thermal comfort in a Bangkok suburb. The microclimatic conditions of a total of 192 designs were simulated through modeling based on ENVI-met software. The climatic conditions were then transferred to the ENVI-met BioMET package to calculate the hourly physiological equivalent temperature (PET) values in a street canyon. The information was used to determine acceptable comfort conditions, as compared to an upper limit of outdoor thermal comfort from a prior work. It is found that the aspect ratio and street canyon orientation can significantly improve outdoor thermal comfort performance, as compared to increases in building density or decreases in tree-planting distance. Tree and building shade can reduce the PET value by 8.6 °C and 14.2 °C, respectively. For example, street trees can increase the outdoor thermal comfort conditions of an avenue canyon (H/W = 0.5–0.7) by up to 82%. However, building and tree shade cannot reduce the extreme conditions in E-W oriented canyons, as the overhead shade requires further protection from the angle of the sun's rays. The study's findings could assist in the development of new guidelines for the design and planning of residential townhouse projects for providing a cooler outdoor environment and comfortable conditions, especially in hot-humid areas of Bangkok.