In-Situ Measurement and Evaluation of Thermal Transmittance Value by Means of Temperature-Based Method

Thermal transmittance (U-value) of building envelope is one of the most important parameters when assessing the actual energy performance of buildings and even slight changes in this value can significantly affect building energy demand. Over or underestimation of building wall U-values, mainly responsible for the energy losses through the building due to the largest share in surface area, can result in misguided assessments of energy refurbishment and implementation of energy-saving measures in terms of building technology selection, time, and costs. Therefore, to obtain data close to reality and to plan optimal refurbishment interventions, it is necessary to perform in-situ measurements for an accurate evaluation of U-value, i.e., thermal performance of buildings. In this paper, U-value assessment based on in-situ temperature measurements was applied using temperature-based method (TBM) and compared to theoretical values calculated following international standards. The viability of the method has been analyzed under different measurement conditions and for two types of walls before and after retrofitting. The findings presented in the study show a very good agreement between measured U-values and estimated ones for uninsulated walls, while further studies are still needed for insulated walls.