Numerical study of effect of indoor-outdoor heat exchange on urban atmospheric temperature

With the process of rapid urbanization, the climatic effect of Urban Heat Island (UHI) on the urban boundary layer is becoming more notable, especially with the energy consumption in buildings and the heat exchange between indoors and outdoors as parts of the anthropogenic heat. We use the Weather Research and Forecasting Model (WRF) with the Multilayer Urban Canopy Scheme (Building Effect Parameterization, BEP) and Building Energy Model (BEM) to study the effect of heat created by air conditioners and energy diffused through roofs, walls and grounds on the outdoor atmospheric environment. Several numerical experiments are conducted from 2 Aug to 3 Aug 2010 under the typical weather background in Nanjing, aiming to better understand the new urban canopy scheme and compare its simulated results with observations. The main purpose is to discuss the effect of air conditioners and heat and energy exchanges between indoors and outdoors on the urban atmospheric temperature. Results show that with the assumption that air conditioners are turned on throughout the day, the simulated temperature in the daytime is in good agreement with the observed. In the nighttime, the simulated temperature is higher than the observed with a deviation of about 1℃ during 22:00 to 00:00 BT. Air conditioners have tiny effects on daytime urban near-surface temperature, but they can lead to temperature increase by 0.6℃ in the nighttime, especially in densely populated areas, where a temperature increase of about 2℃ can be found from 22:00 to 23:00 BT. When the indoor target air temperature is adjusted from 25 to 27℃, total energy released from the air conditioning system is reduced by 12.66%, and the temperature decrease is the largest between 13:00 and 16:00 BT with an average of about 1℃. The denser the buildings are, the larger the temperature decreases.