Heat Balance Analysis for Management and Design of Urban Environment

Urbanisation is progressing rapidly in many Asian cities. The process of urbanisation has modified the land use from natural environment into built environment. It alters surface heat balance by changing sensible and latent heat fluxes, heat capacity, surface albedo and together with the use of fossil fuels, brings about a great quantity of anthropogenic sources of waste heat through air-conditioning, cars, etc. In addition, theeffect of urbanisation on urban wind environment is likewise significant. This paper reviewed the recent studies for analysing the heat balance in urban space and gave a round-up of the ways how CFD analysis of urban climate could be applied to ameliorate the urban environment for preventing further increase of air temperature due to urbanisation. The analyses of mesoscale climates of three different cities located along the coastal areas of Japan, namely Tokyo, Sendai and Haramachi, were illustrated and the influence of regional characteristics on urban climates was examined based on the results of climate analyses, by considering the heat balance mechanism in the central part of each city. It was confirmed that the major factors contributing to increase and decrease of air temperature in each city are different. The latter part of the paper described the detailed analysis of the regional characteristics of heat balance mechanism inside a city. The spatial distribution of heat budget inside Sendai was drawn, in the form of ‘heat balance map’. This map indicates area where the influence of sea breeze was larger than those of heat generated from ground surface and anthropogenic heat releases. In this area, it is effective to introduce sea breeze into urban areas by matching the building arrangement with wind conditions. Inside the urbanised area, the effects of greenery and high-albedo surfaces were relatively large, particularly the inland space of the urbanised area. On the other hand, the effects of sea breeze were more important than those of greenery and high-albedo surfaces in the coastal side. The mechanism that causes these differences was discussed by comparing the heat budgets in the four sub-domains set inside the urbanised area.