Impacts of UHI on variations in cooling loads in buildings during heatwaves: A case study of Beijing and Tianjin, China

The frequent occurrence of extremely high temperatures and heatwaves (HWs), combined with the urban heat island (UHI) effect, significantly affects building energy consumption. This study is performed to investigate the impacts of UHI on building cooling demand during HW periods in megacities. Thus, we examine a typical HW event in late June and early July of 2018, which is classified into HW and non-HW periods, in the two megacities of Beijing and Tianjin. Based on hourly meteorological observation data and rural weather stations selected using satellite-based methodology, the impacts of the UHI on the hourly cooling loads of typical residential and office buildings are evaluated by simulating the hourly cooling loads during the HW event. The results show that the hourly maximum urban heat island intensity (UHII) in Beijing and Tianjin reached 8.4 degrees C and 5.7 degrees C during the HW period, respectively. The cooling load of the buildings as well as the urban-rural load difference increased significantly when HWs occurred. The urban-rural hourly load difference of the office buildings is greater than that of the residential buildings. During nighttime, the urban-rural hourly load difference of the residential buildings increased, and the peak value occurred between 02:00 LST and 04:00 LST, which is more evident in Beijing than in Tianjin. For every 1 degrees C increase in the UHII, the hourly cooling load of the residential buildings (office buildings) in the urban areas increased by 0.5 x 10-3 kWh/m2 (1.4 x 10-3 kWh/m2) compared with that in the rural areas. These findings should be considered in the building design and operation regulation of energy saving, particularly the impacts of extreme HWs and UHI on peak loads, to reduce energy consumption and carbon emissions in other megacities located at similar latitudes and with similar conditions as those of Beijing and Tianjin.