In-situ U-value measurements of typical building envelopes in a severe cold region of China: U-value variations and energy implications

Building energy consumption in the severe cold regions of China is an important consideration in building energy conservation because of the high amount of energy consumed by heating. As an important thermal parameter, the thermal transmittance (U-value) of building envelopes can directly affect the operational energy consumption of buildings. Understanding the U-values of buildings in severe cold regions is important to predict building energy accurately. However, the U-values of envelopes fluctuate constantly due to environmental impacts. Therefore, this study aimed to examine the influence of dynamic U-values on building energy efficiency. To achieve this, this study focused on the in-situ measurement of the U-values of two typical building envelopes in Harbin from winter to summer in 2023 to determine the average and dynamic U-values of the tested envelope, comprising a brick envelope and reinforced concrete (RC) envelope. The building energy simulation results based on theoretical U-values were compared with the measured average and dynamic U-values of the tested envelopes. The findings revealed that the fluctuations in the U-values were significant. In the dynamic U-values of tested brick and RC envelopes, the U-values in winter were 159.8% and 30.8% higher than those in summer, respectively. Furthermore, the dynamic U-values significantly influenced heating energy consumption, with an increase of up to 15.9%.