REDUCTION OF SENSIBLE HEAT EMISSION BY INCREASING ROOF SOLAR REFLECTANCE AS A COUNTERMEASURE OF HEAT ISLAND PHENOMENA

Abstract

The mean air temperature in urban areas has risen due to a change of urban structure in a long term. High reflective paints can reduce a cooling load of buildings and can also improve the thermal environment in urban areas. In this paper, field measurements were carried out in a building where two areas of rooftop were finished with high reflective paint and ordinary paint. Then, the heat flux on the urban surface was calculated on the basis of heat budget equation with measured data, and the result was compared with the artificial heat release from buildings in 23 wards of Tokyo. The results of this paper show that high reflective paint is effective to resolve heat island problem. On the other hand, short wave radiation reflected at high reflective roofs may increase cooling load of neighbor buildings. In this paper, the coupled simulations of radiation and convection around buildings were conducted to estimate the influence of solar reflection at roofs on surrounding building walls. The results show that short wave radiation from high reflective roofs to neighbor building walls is much smaller than direct radiation from sun and sky to walls.