Influence of internal heat sources on thermal resistance evaluation through the heat flow meter method

Abstract

Buildings energy performance is evaluated using codes which reproduce the building behavior, employing technical information about the structure. Wall thermal resistance can be measured using a heat-flow meter in compliance with the ISO 9869, which suggests avoiding proximity to particular points such as thermal bridges, but it does not give suggestions about how to deal with internal heat sources. Thermal resistance measurements are based on 1D models and the internal heat sources cause the departure from one-dimensional conditions. In this study we employ a FEM code to reproduce the heat-flow meter method within a 2D model. Walls include an internal pipe, inside which hot/cold water flows. Models were generated considering different stratigraphies and heat-flow plate positions along the inner side of the wall, in order to reproduce the thermal conditions that affect the flowmeter and the wall, respectively. Thus, it is possible to compare the thermal resistances of the different walls and to find the best heat-flow plate positions in order to minimize the influence of the internal heat source. A preliminary experimental evidence of the problem has been finally presented and the results of this case study have been compared with those of its corresponding FEM model.