In-situ rapid determination of walls’ thermal conductivity, volumetric heat capacity, and thermal resistance, using response factors

Abstract

Accurate determination of walls' thermo-physical characteristics is a necessity for execution of energy conservation strategies in existing buildings. In practice, such data is not available because the current determination methods are time expensive and therefore rarely used. Based on the theory of Response Factors, a rapid transient in-situ method, Excitation Pulse Method, EPM, was introduced as proof of concept in a former article. In the present article, detailed conditions for accurate application of the method in heavy and multi-layered walls are further studied. Theory, simulations, and experiments are combined to determine the method’s performance in different types of walls, with specific attention to the effects of the walls’ thermal response time and the response factors’ time interval, leading to the accuracy of Rc-value determination. It is demonstrated that the two main thermo-physical properties of a wall, thermal conductivity and volumetric heat capacity, as well as the wall’s thickness can be determined using inverse modelling of the Response Factors. The ratios of the response factors have shown to determine wall’s minimum thermal response time and to give an indication of the wall’s composition. The use of longer time intervals has shown to be advantageous in terms of the accuracy and the performance of the method. Longer experiment times as a result of long time intervals are still considerably shorter than the time required for making measurements according to the current standards and other conventional methods.