A study of thermal comfort in outdoor urban spaces in respect to increasing building height in Dhaka

Thermal environment of urban spaces plays a great role on the quality of life in a city. It directly affects people’s behaviour and usage of outdoor spaces. Therefore, an environmentally conscious urban design solution should give high priority to the thermal comfort implications of urban microclimate. Deterioration of urban microclimate due to unplanned construction of built forms which is largely the outcome of uncontrolled urbanization is a major concern in Dhaka. Regarding the context of Bangladesh where climate change is a crucial issue, a proper arrangement of urban blocks with comfortable outdoor spaces can positively contribute to mitigate the harmful impacts of urban climate. The study of urban thermal environment and outdoor comfort demands an urgent thought specially due to the introduction the new building construction rule 2008. The rule encourages a high density urban development through a relaxed building height and plot coverage rules and regulations. Building height, distance between buildings and street widths are important design features which need to be considered at the design stage of urban outdoor spaces. The impact of the rule is being reflected in the recent high-rise characters in city’s residential and commercial areas. The commercial areas in particular are being hastily filled up with high-rise structures under fast urban expansion. It is becoming increasingly difficult to ignore the unfavourable impact of built forms on urban micro-climate. These high rise buildings built to achieve the highest commercial benefits with least consideration for climatic issues are a large contributor of urban heat islands. Uncomfortable urban microclimate not only affects urban life on outdoor spaces but also increases energy demand of buildings. This study attempts to examine the role of physical configuration of urban canyons in controlling the microclimate. For this study, a number of existing urban canyons in Dhaka city have been chosen which are generated by two rows of high-rise structures with varied high H/W ratio and solar orientation. It will observe the air temperature, humidity, mean radiant temperature, mutual shading, sky view factor and wind speed which represent the microclimatic characteristics of the canyons. Finally, the aim of this study is to explore the role of urban planning and urban design in creating favourable urban micro-climate so that the experts are aware of its consequences at the early design stage. Integration of climatic considerations into city planning and design can thus contribute to sustainable urban development as well as mitigation of the adverse impacts of climate change