UHI and Thermal Performance of Office Buildings in Bangkok

Urbanization has an impact on thermal environment of Bangkok. Besides receiving a great deal of solar radiation like other hot-humid cities, the effect of urban heat island (UHI) further adds to discomfort as well as increases the cooling loads of buildings in Bangkok. In order to keep building occupants thermally comfortable, most buildings in Bangkok rely primarily on air-conditioning systems which consume enormous amount of energy. Office buildings, in particular, are the major energy consumers of the city. Therefore, it is important to study the impact of UHI on thermal performance of office buildings and find ways to improve their conditions. Moreover, UHI intensity (UHII) in each area is influenced by local height-to-width ratio (H/W ratio). In order to study UHII of areas representing different densities and H/W ratios and their effect on thermal performance of office buildings, the research is divided into 2 parts. The first part is aimed to investigate UHII in relation to H/W ratio of medium and high density areas. The second part is aimed to investigate thermal performance of office buildings in such areas. Results from field measurement including indoor and outdoor air temperatures, surface temperatures and mean radiant temperatures (MRT) were analyzed along with energy consumption and cooling degree hours (CDH). Results show that H/W ratio has an influence on UHII. However, it is not always the case that higher H/W ratios yield higher UHI intensities. UHI intensities from the medium-density area with low H/W ratios tend to be higher than those from the high-density area with high H/W ratio as the maximum UHII difference between the two areas is 2.57 K. Even though energy consumption of each building does not show a direct relationship with UHII and H/W ratio due to incomparable building sizes, operational time, energy management, and design factors, the increase of CDH tends to follow the increase of UHI intensity.