A response factor-based method for the rapid in-situ determination of wall’s thermal resistance in existing buildings

• A transient in-situ method for quick measurement of walls Rc-value is introduced.
• The Excitation Pulse Method (EPM) is based on theory of response factors.
• EPM provides identical results (less than 2% error) in comparison with ISO 9869.
• Using EPM instead of energy labeling assumed Rc-values considerably reduces error.
• Using two heat flux meters in ISO 9869 method can shorten the measurement period.

The in-situ estimation of the thermal resistance (Rc-value) of walls in buildings is of major significance to determine their energy performance. The exact construction of walls is generally unknown, especially in older buildings, making the estimation of the Rc-value inaccurate. In-situ measurement is generally not being performed because, for the current standard method (ISO 9869), generally a measurement period of more than ten days is required. In the present paper, a new transient in-situ measurement method (Excitation Pulse Method, EPM) based on the theory of response factors is derived, applied experimentally on three walls, showing that it is possible to measure the Rc-value within less than 2 h. The results are compared to the ones obtained by ISO 9869 method, showing a good agreement. Additionnally, EPM measurement technique can provide the average Volumetric Heat Capacity and thermal conductivity. It is also shown that the ISO 9869 method can be easily improved by using an additional heat flux meter. EPM is believed to make a significant contribution to the quick and accurate estimation of the thermal resistance in unknown constructions and therefore to the accuracy of the prediction of energy consumption in buildings.