Modeling Building Thermal Loads During an Extreme Heat Event in a Dense Urban Environment

Temperature rises due to global warming, added to urban heat islands present in dense cities is resulting in increasing trends of energy consumption in cities. This energy consumption from buildings during summer times is mostly associated to use of air conditioning to maintain indoor human comfort conditions. This energy demand is further magnified during extreme heat events to a point where the electrical grid may be at risk. Given the forecasted increased frequency of extreme heat events for the future, it is imperative to develop methodologies to quantify energy demands from buildings during extreme heat events, particularly for cities. The purpose of this study is to precisely quantify thermal loads of buildings located in the very dense urban environment of New York City under an extreme heat event that took place in the summer of 2010 (July 3-6). Two approaches were used to model thermal loads of buildings for these conditions; a single building energy model (SBEM), such as eQuest, and an urbanized weather forecasting model coupled with a building energy model (uWRF). The SBEM was driven by Typical Meteorological Year (TMY) weather files and by a customized weather file built from uWRF for the specific days of the heat wave of 3-6 of July 2010. A series of simulations were conducted with the SBEM to model building energy consumption data due to air conditioning for two locations in Uptown and Midtown Manhattan, NY, which represented a low density and a high density building area within the city. A residential building was chosen and modeled for both conditions. Assumptions were made regarding the building's floor plans and operation schedule to simplify the model. Results of the ensemble of SBEM indicate there was an increase in energy consumption during the July 2010 heat-wave as compared with the TMY case. The uptown location consumed 42% more energy during the heat wave event, while the midtown location showed an increased in energy consumption of 50% when compared to a typical July summer day, reaching peak loads of close to 100 kWh. Comparison with results directly from uWRF for the energy consumption for same locations, indicate that midtown energy is twice from that of the SBEM, and half for the uptown location. This may be due to the fact that uWRF takes into account the effects of energy exchange between buildings far more efficient that the single building energy model.