Simulation of the urban thermal comfort in a high density tropical city: Analysis of the proposed urban construction rules for Dhaka, Bangladesh

Abstract

The thermal comfort in urban canyons of a high density city is a very challenging issue for urban planners and designers, especially in hot humid tropical zone. The present study aims to evaluate the effects of a newly promulgated building construction rules in respect of thermal climate for Dhaka, Bangladesh, a region characterized by high density area with tropical climate. Three different urban canyons from three areas were considered which almost represents the whole city. Measurements were carried out to assess the existing thermal climate in the city canyons. Further, three model canyons were configured according to the new rules of ground coverage, floor area ratio (FAR) and site setback. A three-dimensional numerical model with high spatial and temporal resolution was used to investigate the microclimatic changes within the urban environments. Model calculations were run for a typical summer day. The thermal climate was evaluated based on air temperature Ta, surface temperature Ts, relative humidity RH, and wind speed in the existing and model canyons. For thermal comfort assessment the temperature humidity index (THI) was considered in this study. The results showed that the outdoor spaces of the study areas are thermally uncomfortable and the new building construction rules hardly improve the conditions in general. However, THI decreases in a canyon where sky view factor (SVF) decreases in the model canyon than the existing one. In addition, the surface temperature Ts and air temperature Ta do not show the same picture. Furthermore, the wind speed increases in all the model canyons as the site setback allows wind flow uniformly inside the canyons. Keywordssimulation, urban canyon, sky view factor (SVF), thermal climate, air temperature, relative humidity, temperature humidity index (THI)

Urban heat island and wind flow characteristics of a tropical city

“…Many of the investigations provide strong evidence and findings limited to building-to-building relationships, defined as different ratios (Kakon et al, 2009;Giannopoulou et al, 2010;Hwang et al, 2011;Abreu-Harbich et al, 2013). This paper, therefore, aspires to bridge the gap in micro-climatic research related to urban design and give insight on how different urban configurations may impact temperature and wind variations.…”

Review of studies on outdoor thermal comfort in warm humid climates: challenges of informal urban fabric

“…Several studies (Emmanuel and Johansson 2006;Emmanuel et al 2007;Johansson and Emmanuel 2006;Johansson et al 2013Johansson et al , 2018Kakon et al 2009;Sharmin et al 2015) have examined the influence of the urban fabric on the microclimate within urban canyons in different neighbourhoods in warm humid tropical climates. In the tropical rainforest climate of Colombo, Sri Lanka, Emmanuel and Johansson (2006) found that urban-rural temperature differences were more significant by day than by night.…”

“…Variations in building height play a role in creating higher turbulence around high-rise buildings, thus enhancing urban ventilation (Emmanuel et al 2007;Sharmin et al 2015). Parallel arrangement of buildings combined with setbacks to increase the distance between buildings (lowering the H/W ratio) facilitates and increases the wind speed (Emmanuel et al 2007;Kakon et al 2009). Moreover, asymmetrical aspect ratios may increase wind flow in urban canyons when tall buildings confront wind direction (Qaid and Ossen 2015).…”

“…The influence of the urban fabric on microclimate and outdoor thermal comfort in the warm humid tropical and subtropical regions is reported by several studies. In the humid subtropical regions, for example, studies by Assis and Frota (1999), Johansson et al (2013), Kakon et al (2009), Kakon et al (2010), Lin et al (2010), Sharmin et al (2015), Tan et al (2017), Yang et al (2011) and Yang and Lin (2016) are available. In the tropical rainforest regions, examples of studies include those of Emmanuel and Johansson (2006), Emmanuel et al (2007), Johansson and Emmanuel (2006) and Qaid and Ossen (2015), and, in the tropical savannah regions, studies of De and Mukherjee (2018), Ndetto and Matzarakis (2013), Rodríguez-Algeciras et al (2016) and Yahia et al (2018) exist.…”

Building neighborhood emerging properties and their impacts on multi-scale modeling of building energy and airflows

“…For example, for the CFD simulations traditionally PHOENICS [28], Fluent [20,21], CFX, and OpenFOAM [46,86] [113,114], (4) Virtual PULSE [115], and (5) Honeybee [116]. These tools have used an integrated approach to model the urban neighborhood and quantify the energy consumption of buildings in the neighborhood.…”