Heat and moisture transfer in wall-to-floor thermal bridges and its influence on thermal performance

Abstract

A significant portion of the cooling or heating load of buildings is contributed by relatively large heat flux through thermal bridges. Water vapour concentration significantly alters thermal conductivity and heat transfer characteristics within the thermal bridges, affecting building energy consumption, particularly in humid climates. Moreover, the condensation on the building envelope is highly related to the temperature and moisture distribution, which threatens the safety of the building structure. The heat and moisture transfer presents strong coupling effects. Nevertheless, the coupled heat and moisture transfer (HAMT) within thermal bridges and its influence on the building energy consumption were less studied. In this study, field experiments and validated numerical models were conducted to investigate the heat and moisture transfer in the wall-to-floor thermal bridge (WFTB) in a humid and hot summer cold winter region of China (Hangzhou city). The results show that the heat transfer is underestimated if the moisture is not considered. The differences in heat transfer between the WFTB and the main part of the wall were reduced when considering the coupling effect of heat and moisture transfer, as the thermal performance of the wall is more sensitive to moisture than that of the WFTB region. Furthermore, if the significant moisture transfer is considered, the overall thermal conductivity of the WFTB has a risk of counterintuitively increasing when a thermal insulation layer is added. The reason for this is that the thermal insulation layer may raise the moisture content in the WFTB region, subsequently increasing the thermal conductivity.