In large Asian tropical or subtropical cities where anthropogenic energy demand is concentrated, urban heat island effects cause the increases in building energy demands for cooling. The recent increase rate of summer electric power demand is estimated up to 3%°C in the Greater Tokyo, this means the fact that about 1.6GW of additional demand is required as the regional air temperature increases by 1.0 °C. This huge demand for summer electricity creates additional waste heat, which would further intensify Tokyo urban heat island. From the viewpoint of the reduction of anthropogenic CO2 emission to mitigate the global warming, this additional energy demand should be reduced through the control of the urban heat islands. In order to analyze the above-mentioned vicious interaction between urban thermal environment and cooling energy use on city-scale, and to evaluate the technologies and measures for urban warming alleviation, we have been developed a new multi-scale numerical simulation system.

In this study, our system was improved and validated for the yearlong numerical prediction of the regional air-conditioning energy consumption in several types of urban districts. Then, the improved system was applied to Tokyo urban canopies to assess the yearlong impacts of heat island countermeasures on urban thermal environment and building energy consumption.