The Interaction Between Building Energy Consumption And Urban Weather Conditions In Beijing

With the booming economy and society in recent decades,more and more people have been living in cities,which,as a result,have been expanding rapidly and continuously.Also,the energy consumption in urban areas has been also increasing steadily.More and more attention has been paid to the urbanization-induced meteorological environmental effects such as urban heat islands(UHIs)and the interaction processes.Taking Beijing as the research area,this study investigated the interactions between building energy consumption for cooling and heating and local meteorological conditions,by using the multi-layer Building Effect Parameterization and Building Energy Model(BEP-BEM)that takes into account the interaction of the built and the natural environments.Various data sets were employed here,including actual electricity data at district levels,and measurements from 210 automated weather stations and from two meteorological towers.The main results were as follows.(1)The average UHI intensity in Beijing during summer is approximately 2.02 K,and this value reaches 3.41 K in winter.The UHI effect on building energy demands for cooling and heating was explored by using an off-line urban parameterization driven by measurements from two meteorological towers,with one located downtown and the other in the outskirt.Model validation was conducted for environmental variables and for building energy demands against surface weather observations and Energy Plus,showing good agreement in all cases.For a representative office building,cooling energy use in the urban area was about 36.53 W m^-2(30%)higher than that in the suburban area during summer,while heating energy use was approximately 95.29 W m^-2(23%)lower than that in the suburbs during winter.A residential building showed similar results,with smaller differences in cooling and heating energy demands,about 9.14 W m^-2(17%)and 92.71 W m^-2(20%),respectively.If averaged over the whole year,the UHI decreased total building energy use by about 19.93 W m^-2(8%)and 35.93 W m^-2(16%)for a representative office building and a residential building in urban Beijing,respectively.Further analysis for clear and polluted days in winter showed the impact-chain of air pollution-urban heat island-heating energy use.Heating energy use was reduced in the urban area during polluted days,corresponding to an enhanced heat island,which may be attributed to a stronger inversion and a lower wind speed.(2)The district-varying cooling electric loads due to air-conditioning(AC)systems were estimated for five consecutive summers in Beijing,by using actual quarter-hourly electricity data at district levels.A common double-peak pattern was shown in the average summertime diurnal profile of AC electric loads for most districts,respectively around 15:00 and 21:00local time(LT).With locations varying from the city core to suburban and rural districts,the evening peak turned to be more pronounced and comparable to its afternoon counterpart,especially on weekends.For urban districts,AC cooling loads on weekdays were generally higher than weekends,and the“weekday energy-use island”for cooling was due to the significant decreases in human activities and cooling demands on weekends.As the most weather-sensitive electric load component in summer,AC cooling loads were significantly influenced by urban meteorological conditions.When correlating to two peak cooling loads,the integrated factor heat index shows higher coefficients of 0.8?0.9 than air temperature and air humidity.This study also investigated the district-level sensitivities of peak cooling loads to urban surface meteorological elements.For both elements,the sensitivities were greater in the evening than in the afternoon,and decreased with locations changing from the city core to suburban and rural districts.The sensitivities to heat index for two peaks were comparable to each other.As an integrated meteorological factor,heat index tends to be more effective in estimating cooling electricity consumption for Beijing than air temperature or humidity solely.(3)The air conditioning(AC)electric loads and their impacts on local weather over Beijing during a 5-day heat wave event in 2010 were investigated by using the Weather Research and Forecasting(WRF)model,in which the Noah land surface model with multiparameterization options(Noah-MP)is coupled to BEP-BEM.Compared to the legacy Noah scheme coupled to BEP-BEM,the modeling system used here showed a better performance,decreasing the root-mean-square error of near-surface air temperature from2.8°C to 1.9°C for urban stations,and the dry bias was mitigated as well.The simulated AC electric loads in suburban and rural districts were significantly improved by introducing the urban class-dependent building cooled fraction.The incorporation of more realistic AC working schedules helped reproduce the double-peaked diurnal cycle of observed AC electric loads.Waste heat from AC systems presented a smaller effect(?1°C)on the afternoon surface air temperature than the evening one(1.5?2.4°C)if AC systems worked for 24 h and vented sensible waste heat into air.Influences of AC systems could only reach up to?400 m above the ground for the evening air temperature and humidity due to a shallower urban boundary layer than daytime.Spatially varying maps of AC working schedules and the ratio of sensible to latent waste heat release were critical for correctly simulating the cooling electric loads and capturing the thermal stratification of urban boundary layer.(4)Using WRF/Noah-MP/BEP-BEM modeling system,the impacts of uniform warming on the 5-day heat wave event discussed above were further examined,as well as changes in peak electric loads for AC cooling.Results showed an enhanced heat wave event in a future warmer climate.The increases in modeled near-surface air temperatures were proportional to the warming intensity prescribed to model initial and boundary conditions,and greater increases were shown in heat index.On average,with a uniform warming signal of+2?,near-surface air temperature was increased by 1.9??2.2?,while an increase of 4.4?was produced for the warming scenario of+4?.The impacts of uniform warming on increases in air humidity cannot be ignored.Compared to the reference run without warming signals,the daytime average heat index in urban areas was increased by 5.9?with a temperature perturbation of+4?.Accordingly,the peak electric loads for AC cooling would be significantly increased in warmer and wetter conditions,especially in urban Beijing roughly encircled by the sixth ring road.