4.5 Using WRF-Urban to Assess Summertime Air Conditioning Electric Loads and their Impacts on Urban Weather in Beijing

Xu, Xiaoyuu, Nanjing University of Information Science and Technology, Nanjing, China, IUM, Beijing, China, and National Center for Atmospheric Research (NCAR), Fei Chen, NCAR, Shiguang Miao, IUM, Beijing, China, and Michael Barlage, NCAR

The air conditioning (AC) electric loads for Beijing during a 5-day heatwave event in 2010 are explored by using the latest WRF-Urban modeling system, in which the Noah Land Surface Model with Multiparameterization Options (Noah-MP) is coupled to the Multilayer Building Effect Parameterization and Building Energy Model (BEP+BEM). The modeled near-surface meteorological elements (i.e., 2-m air temperature and humidity, and 10-m wind speed) are validated against measurements from 210 automatic weather stations, which show a reasonable model performance at both urban and rural sites. Additionally, the simulated AC electric loads averaged over city built-up grids are able to reproduce the observed ones in each district in Beijing. The simulation results show that the high electricity consumption for AC cooling is concentrated in the urban districts encircled by the 6th ring road with a common double-peak at 3 pm and at 9 pm and a minimum at 5 am local time for each of those five days, and its spatial distribution pattern agrees well with the classification of urban land use as well as the urban heat island (UHI). Although a stronger UHI occurs in the evening, the most significant differences of AC electric loads between urban and rural areas occur in the afternoon due to a prevalent lower air temperature after sunset. The double-peak phenomena in the diurnal variation profile of observed AC electric loads for each district is captured by WRF-Urban to some extent by using different time schedules of AC systems as well as different diurnal cycles of equipment heat gain and occupation ratio for commercial/residential buildings. A number of WRF-Urban sensitivity simulations are conducted with varying the areas covered by AC usage together with UHI mitigation methods such as green and cool roofs to assess their impacts on electricity consumption and urban weather.