Evaluating the accuracy of in-situ methods for measuring wall thermal conductance: A comparative numerical study

In-situ measurement of wall thermal conductance is a complex task due to the transient conditions resulting from the variability of environmental factors. The literature offers numerous methods, each based on different as-sumptions, which are not always valid. This paper aims to compare the accuracy and test duration of the main methods by testing them on various walls and climatic conditions. The study is numerical and carried out on virtual walls, modelled using the finite difference technique. The walls have different characteristics, including thermal capacity, conductance, and insulation position. The simulations are conducted using real environmental variables such as temperature and wind speed. The theoretical errors due to the non-fulfillment of the as-sumptions of the methods are evaluated. The study reveals that the most commonly used method (HFM) yields high errors when heat flow meter is on the surface opposite the insulation. The same limitation is also found in its evolution, the SHB-HFM. The dynamic method, described in the UNI ISO 9869-1 standard, is inadequate when temperatures change abruptly. The study highlights the primary criticalities of the main methods and can assist technicians in selecting the most appropriate one to use.