Effect of measurement conditions on the in-situ determination of the thermal resistance of a wall

Abstract

The determination of the actual thermal resistance of walls is of importance to help reduce the performance gap between design and real energy consumption, both in case of new built and renovation works. To evaluate the thermal efficiency of building envelopes, the norm ISO 9869-1 gives a methodology to determine the in-situ thermal resistance of walls. However, literature reports difficulties and uncertainties in the results, associated with other factors to the environmental conditions of measurements. The aim of the present paper is to show how the measurement conditions can affect the results. Measurements were done on two test façades, in winter and summer, the same façades being oriented alternatively to the North or to the South. The determined thermal resistances are compared among them, and to theoretical values. Results show that the method can give reliable results, if a period of time long enough is used, even for South-oriented walls.