The urban heat island (UHI) phenomenon has been more accelerated and the outdoor air temperature (OT) has become higher. Such OT rise is posing an increase in electricity consumption (EC) for air conditioning. Nowadays, the UHI countermeasure such as green roofs is developed and installed in order to decrease OT and reduce energy consumption for air conditioning. However, the countermeasure can bring adverse effects on the society. For example, green roof increases outdoor air humidity. It can increase EC for air conditioning through lowered efficiency of air conditioners due to dew condensation. Therefore, we need to understand a quantitative relationship between the energy consumption and the meteorological elements such as OT and air humidity throughout the year for reasonable installation of the UHI countermeasures. Thus, we aimed at quantifying sensitivities of EC to meteorological elements in city-block scale, which are residential and business districts. Moreover, we compare previous studies which analyzed sensitivities of EC to OT before the Grate East Japan Earthquake because some studies reported the relationship between EC and OT was changed due to this earthquake.
Two apartment residential, one detached residential, and two business districts in Osaka city, which is the second largest city of Japan, were chosen as the target districts in this study. The district sizes are 1 to 3 km2. We installed meteorological instruments to the rooftops of five primary schools in the five target district so that we measured the meteorological data which are OT, and relative humidity from April 2013 to March 2014. We also obtained hourly electricity consumption data in the target districts. Then, we calculated the sensitivities of EC to OT and specific humidity (SH) using the multiple regression (hockey stick regression) analysis. We analyzed branch points and sensitivities of summer OT and SH during only summer.
Our analysis showed that the branch points of summer OT in the business districts were 7°C lower than those in the residential districts. It is suggested that occupants and appliances in the business districts lead to the air conditioning demand. The branch points of winter OT in the business district were similar to that in the residential districts. In the residential districts, the sensitivities of EC to summer OT in early morning is the smallest and that at night is the largest during a day. The sensitivities of summer SH were the similar tendency of those of summer OT because dehumidification on the fan coils in the air conditioner occurs and leads to EC.
We compared our results with the previous studies' results before the Great East Japan Earthquake (March 11, 2011). Sensitivities of EC to winter OT in our result were similar to those in the previous studies, however, those to summer OT in our analysis were 50-60% smaller than those in the previous studies. People is considered to conserve electricity in summer by not introduction of energy-saving appliances but change in their behaviors.