THERMAL ENVIRONMENT AND ENERGY EVALUATION FOR HEAT ISLAND COUNTERMEASURE IN DIFFERENT RESIDENTIAL AREAS Kazuki Yamaguchi*, Tomohiko Ihara**, Yukihiro Kikegawa***, Yutaka Genchi**, Yasuyuki Endo* *Tokyo Electric Power Company, R&D Center, Yokohama, Japan **National Institute for Advanced Industrial Science and Technology, Tsukuba, Japan ***Meisei University, Tokyo, Japan Abstract Various countermeasures to urban heat island applied in the residential areas are evaluated for thermal environ- ment improvement and year-round energy performance, using an urban canopy model coupled with a building energy model. The simulation shows that a combination of surface cooling measures and installation of heat pump water heater can lower the nighttime air temperature and reduce the annual energy consumption effectively. For the area with smaller and poorly insulated buildings, the surface cooling shows larger potential for reduction of the energy consumption for air-conditioning. For the area with larger and densely populated buildings, the heat pump water heater shows larger potential for nighttime cooling effect. Key words: Urban Heat Island, Greening, Heat Pump Water Heater 1. INTRODUCTION To mitigate the urban heat island (UHI) phenomenon, improvements in urban surface in terms of reducing heat accumulation by measures such as solar reflective coating, greening and water-retentive paving are considered to be effective. A massive installation of heat pump water heaters, which absorb heat from the outdoor air, can also be expected to have cooling effects (e.g., Tamura et al. 2003), which was verified by means of meteorological observation around an inhabited apartment building (Yamaguchi et al. 2009). The effects of these measures on thermal environment and energy demands are thought to depend on characteristics of targeted city areas, such as street geometry and construction of buildings. Based on this viewpoint, in this study, various countermeasures applied in two residential areas with contrasting characteristics are evaluated for their influence on urban thermal environment during summer in conjunction with year-round energy performance for buildings, using an urban canopy model two-way coupled with a building energy model (Ihara et al. 2008). 2. DESIGN OF EXPERIMENT 2.1. Areas for evaluation In order to examine the effects of UHI countermeasures that depend on characteristics of city areas, two con- trasting residential areas, each located in central Tokyo, were selected. The areas were designated Area-A and Area-B. As shown in Table 1, Area-A is a newly devel- oped district of apartment units, and Area-B is an old low-rise district of apartments and detached houses. Buildings in Area are all four-story high with larger build- ing area and smaller floor area per dwelling unit, and highly thermal-insulated outer walls, while those in Area- B are about two-story high with smaller building area, * Corresponding author address: Kazuki Yamaguchi, Tokyo Electric Power Company, R&D Center, 4-1, Egasaki- cho, Tsurumi-ku, Yokohama, 230-8510, Japan; e-mail : Yamaguchi.ka@tepco.co.jp Table 1. Street geometry and building construction of the evaluated areas. Area ID A B Gross building-area ratio [%] 31 21 Gross floor-area ratio [%] 122 44 Averaged building story 4 2.1 Avelaged buildig area [m 2 ] 365 108 Floor area per dwelling unit [m 2 ] 50 81 Thermal resistance of roofs [m 2 K/W] 1.5 0.4 Thermal resistance of walls [m 2 K/W] 1.4 0.2 Table 2. Simulation setup for countermeasure cases. Cases Conditions Rooftop greening Coverage: 86% area of rooftop, Soil thickness: 20cm, G s *: 3.0 (summer), 0.9 (winter) Rooftop solar reflective coating Coverage: 100% area of rooftop, Albedo: Doubling (from 0.2 to 0.4) Sidewall solar reflective coating Coverage: 100% area of sidewall except for windows, Albedo: Doubling (from 0.2 to 0.4) Shade planting with tall trees Shade coverage: 50% area of the ground and sidewalls during summer Water-retentive paving (or lawn planting) Coverage: 100% area of the ground except for buildings, G s *: 2.5 (summer), 0.0 (winter) * G s : Latent heat transfer conductance [mm/s] 0.0 0.5 1.0 1.5 Area-A Area-B [GJ/m 2 ] Appliances Lighting Cooling Heating Hot water Fig. 1. Annual primary energy consumption per floor area for control runs. The seventh International Conference on Urban Climate, 29 June - 3 July 2009, Yokohama, Japan