Influence of moisture transfer on thermal conductivity measurement by HFM: Measurement accuracy on insulation materials and consequences on building energy assessments
M. El Assaad, Yohan Plantec, Thibaut Colinart, Thibaut Lecompte
Abstract
Knowing the value of a material’s thermal conductivity as a function of temperature and water content is useful for fine-tuning the prediction of building energy performance or hygrothermal comfort. When performing thermal conductivity measurements on moist insulating materials using steady-state methods, moisture is transferred from the warm to the cold side of the sample. This results in the release of latent heat, which has the potential to impact the accuracy of the measurements. The aim of this study is to examine the impact of these moisture transfers in various moist hygroscopic insulating materials during thermal conductivity measurements using heat flow meter method. The materials tested are aerated concrete, biobased composites, cellulose wadding and wood fiber insulation. The results are examined to predict the test duration leading to hygrothermal equilibrium within the sample, to assess the experimental moisture dependence of thermal conductivity, to quantify the errors made in case of premature interruption of the test, and finally to test methods proposed in the standards EN 12664 or ISO 10051 for reducing the number of tests. Last, hygrothermal simulations of an internally insulated wall are performed to evaluate the required precision on thermal conductivity to predict relative humidity at insulation masonry interface and heat flow at the inner side of the wall.