On the indoor hygrothermal regulation ability of earth building walls

A coupled finite element model has been developed to investigate the ability of earth walls to regulate indoor hygrothermal conditions. The model simulates heat and water transfers across earth walls, accounting for pore water phase changes and the associated latent heat fluxes. The constitutive laws adopted in this study are grounded in the thermodynamics of porous media and the mechanics of unsaturated soils. All the hygrothermal properties of the earth are expressed as functions of material porosity and water retention characteristics. Therefore, the hygrothermal response of earth walls is fully described by only six parameters, which greatly simplifies sensitivity analyses. The model has been used to explore the effects of latent heat fluxes on the evolution of moisture and temperature inside an idealised room enclosed by two infinite earth walls. In the absence of indoor heat and moisture sinks or sources, the results demonstrate that latent heat buffering intensifies with increasing relative humidity gradients between outdoor and indoor environments. For instance, during cold and humid winters, vapour condenses in the colder outer layers of the wall, generating a local peak in latent heat flux. The condensed moisture then migrates inward toward the warmer core of the wall, where it re-evaporates, thus promoting further condensation at the outer surface. The overall latent heat exchange, which is governed by these hygroscopic processes, becomes more pronounced in walls with higher porosity, steeper retention curves and greater saturation levels.