Enhancing Outdoor Thermal Comfort in High-Rise Housing: The Impact of Asymmetrical Canyons and Building Heights in Ahmedabad

The rapid growth of high-rise buildings in urban areas, driven by population growth and urbanization, significantly contributes to the Urban Heat Island (UHI) effect. Most high-rise structures, designed as symmetrical canyons, absorb heat during the day but fail to reradiate it at night due to the reduced sky view factor, raising nighttime temperatures. In contrast, asymmetrical canyons with varying building heights improve thermal comfort by enhancing air circulation and shading, which helps reduce heat buildup and promotes cooling. In Ahmedabad, India’s seventh-largest metropolis, the UHI effect is exacerbated by rapid urbanization and increased high-rise housing in its hot and dry climate. This research investigates the impact of asymmetrical canyons with varying building heights on outdoor thermal comfort in high-rise housing in Chharodi, Ahmedabad. A preliminary study found that typical high-rise housing in Ahmedabad has an aspect ratio between 2 and 3. For the study, a high-rise neighbourhood with four 30-meter blocks and an aspect ratio of 2 was chosen. Field measurements were collected to assess thermal comfort, and the neighbourhood was simulated in ENVI-met. Six scenarios were developed considering orientation, varying heights, and shading between blocks, and these were compared with the base case scenario for the summer and winter months. The results revealed that asymmetrical canyons offer better thermal comfort than symmetrical ones. Shading was identified as a crucial factor in improving Mean Radiant Temperature (MRT) and Physiologically Equivalent Temperature (PET). A 3:2 aspect ratio with an NW-SE street orientation provided the best year-round thermal comfort. This suggests that improving outdoor thermal comfort in high-rise housing in Ahmedabad is possible by relaxing the height and ground cover restrictions while maintaining the permissible Floor Space Index (FSI).