Comparison between heat-flow meter and Air-Surface Temperature Ratio techniques for assembled panels thermal characterization

Abstract

Walls thermal characterization is fundamental for the evaluation of the energy performance of buildings and for the energy certification practice and simulations. The evaluation of the thermal characteristics of building walls can be achieved through mathematical calculations (when the stratigraphy is known, and technical data are available) or non-destructive techniques (when wall layers are unknown, and they cannot be altered).Starting from this, the aim of this study is a critical analysis of the basic principles related to heat-flow meter (HFM) and Air-Surface Temperature Ratio (ASTR) methods. In particular, the heat flow meter method was tested during summer, comparing the obtained results with a previous measurement campaign, conducted in the same university lab during winter, and theoretical value; then the heat-flow meter method was compared with the Air-Surface Temperature Ratio technique, considering the indoor air temperature vertical profile. The influence of the constant total internal heat transfer coefficient (hi) suggested by ISO 6946 (generally used) was investigated, providing a simple data elaboration for assessing the actual total heat transfer coefficient. In addition, the influence of the reciprocal positions of the temperature probes on final results was analyzed, finding significant deviations.Comparing the hi constant value suggested by the standard and the ones obtained experimentally, percentage differences, ranging from about 40% to about 143%, were obtained.