Impacts of uncertainty in building envelope thermal transmittance on heating/cooling demand in the urban context

Abstract

Urban building energy modeling (UBEM) is a promising tool to evaluate building energy consumption at high temporal-spatial resolution at urban scale. However, state-of-the-art UBEMs use identical building envelope thermal transmittance according to design specifications in model characterization, which neglects the uncertainty in U-values of the building stock. To evaluate the impacts of uncertainty in U-values on heating/cooling demand at the urban scale, this study proposes a physics-based model of building envelope thermal transmittance to generate the U-value distributions of building stocks. Diversified U-values were assigned to buildings according to the building age, while identical initial U-values in the design served as a baseline. The impact of uncertainty in building envelope U-values was assessed by comparing the heating/cooling demand simulated under different U-value distributions, taking 33,222 residential buildings in Beijing as a case study. The results showed that, considering uncertain physical factors, thermal transmittance followed a right-skewed distribution, which led to an increase in the heating/cooling demand of the building stock. The annual total heating/cooling demand increased by 26% and 13%, respectively. The diversity in the heating/cooling demand intensity of the building stock was enhanced when more causes of uncertainty were considered, which was more evident in the building stock with a small range of building age or heating demand intensity. Therefore, it is advisable to consider the uncertainty in the building envelope thermal transmittance in UBEM simulations for energy evaluation and planning at the district or urban scale.