Influence of Heat Flow Meter sensor type on the thermal conductance measured in presence of vapor flow

• Experimental and numerical study of thermal conductance assessment for a vapor-permeable light earth wall. • Influence of moisture transfer on thermal conductance measurement is assessed. • Heat flux sensor (HFS) blocks moisture flow, leading to measurement inaccuracies. • Hygrothermal simulations confirm the influence of vapor flow in real climate conditions. Knowing the thermal conductance of a wall is essential for accurately assessing the energy needs of a building. With the increased use of bio-based and vapor-permeable walls, it is essential to study the full influence of moisture on thermal conductance measurement measurements. This study examines the influence of moisture transfer on the thermal conductance measurement for a vapor-open light earth wall. Experiments were conducted in a bi-climatic chamber under summer and winter steady-state conditions to evaluate the impact of moisture flow and assess the accuracy of the Heat Flow Meter (HFM) method in capturing the actual thermal performance of the walls. The results show that vapor flow significantly influences thermal conductance measurements, causing deviations of up to 28% depending on the directions and the magnitude of the vapor pressure gradient. Additionally, the heat flux sensor (HFS) was found to obstruct moisture flow, leading to errors in thermal conductance evaluation. Numerical simulations in transient real-life conditions confirmed the experimental findings under steady-state conditions. The findings of this paper highlight the influence of moisture flow and the need for improved measurement techniques that account for coupled heat and moisture transfer in hygroscopic materials, ensuring more reliable thermal performance evaluations.