In-situ characterization of walls' thermal resistance: An extension to the ISO 9869 standard method

Accurate and reliable in-situ characterization of buildings' thermal envelope is of high significance to determine actual energy use and thermal comfort. In this context, walls' thermal resistance is one of the most critical properties to be identified. Regardless the numerous studies being carried out to accurately measure the actual thermal resistance of walls on site, the heat flow meter method suggested by the ISO 9869 standard is the one being applied the most. The method requires one heat flux sensor and two thermocouples to measure and estimate the average thermal resistance over a sufficiently long period. Despite the advantages of this method, two problems have been seen in practice: long duration and precision problem. The present article describes and demonstrates how modifications to this standard method can improve the results of the in-situ measurements in terms of duration and precision. Simulations and experiments have been applied to show the effect of using an additional heat flux sensor, opposite to the first one. The modified method aids in obtaining the thermal resistance with a higher precision in a shorter period of time.