Dense urban environments are exposed to the combined effects of rising global temperatures and urban heat islands, a thermal gradient between the urban centers and the less urbanized surroundings suburbs. This combination is resulting in increasing trends of energy consumption in cities, associated mostly to air conditioning to maintain indoor human comfort conditions. The energy demand is further magnified during extreme heat events to a point where the electrical grid may be at risk. Given the anticipated 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.
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 4–8). Two approaches were used to quantify thermal loads of buildings for these conditions; a single building energy model (SBEM), such as the US Department of Energy eQUEST and EnergyPlus™, and an urbanized weather forecasting model (uWRF) coupled to a building energy model. The SBEM was driven by Typical Meteorological Year (TMY) weather file and by a customized weather file built from uWRF’s weather data for the specific days of the heat wave. A series of simulations were conducted with both SBEM software 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. Assumptions were made regarding the building’s floor plans and operation schedule to simplify the model and provide a close comparison to uWRF.
Results of the ensemble of SBEM indicate there was an increase in energy consumption during the July 2010 heat-wave when compared with the central park TMY case. The uptown location consumed 137% more energy during the heat wave event, while the midtown location showed an increased in energy consumption of 125% when compared to a typical July three day period, reaching total loads of close to 9812 kWh for a 20 m height building. Comparison of the results directly from uWRF for the energy consumption for same locations, indicate that for the midtown location both SBEMs underestimated the total energy consumption within a factor of three. This may be due to the fact that uWRF energy model takes into account urban microclimate parameters such as anthropogenic sources and waste heat interactions between surrounding buildings.