Temperature dependence of sorption isotherm of hygroscopic building materials. Part 1: Experimental evidence and modeling

The knowledge of sorption isotherm is of high importance when evaluating the performance and the durability of building envelope. Whereas the influence of hysteresis was often investigated, less attention has been paid to the influence of temperature. In the present paper, a specific experimental protocol is defined to investigate the influence of temperature on relative humidity variations within three building materials (Autoclaved Aerated Concrete, wood fiber insulation and hemp concrete). The measurements are analyzed in terms of a hygrometric coefficient κ [%r.h./°C], defined as the maximal relative humidity amplitude against the maximal temperature amplitude, and are compared to three modeling approaches: temperature dependent sorption model, Kelvin equation and Clausius-Clapeyron equation. Discussions show that the third approach is relevant and that it can be used to evaluate effortless the isosteric heat of sorption and the temperature dependence of the sorption isotherm.