Combined effects of sorption hysteresis and its temperature dependency on wood materials and building enclosures-part II: Hygrothermal modeling

Abstract

Hygroscopic materials such as wood and wood based materials have been widely used as insulation and surface moisture buffering materials due to their low thermal conductivity and high moisture capacity. And their hygrothermal performance is mainly dependent on the moisture properties, such as sorption isotherm and water vapor permeability etc. Instead of a univalued function of relative humidity, sorption isotherm of wood materials is not only affected by sorption history, but also temperature dependent. This work is devoted to a better understanding of the effects of temperature dependent sorption hysteresis on moisture transport in wood and wood based materials under ambient temperature and relative humidity variations through experimental investigations and numerical modeling. In part I, the formulated hygrothermal model based on local thermodynamic equilibrium assumption and Frandsen’s hysteresis model are experimentally validated. In this part, the effects of sorption hysteresis and its temperature dependency are investigated under several dynamic conditions through numerical modeling. Hysteresis should be taken into account in determining the moisture buffering capacity, and temperature dependency should be considered to investigate the RH variation in the material when it is subjected to drastic temperature fluctuation. Then heat and moisture transport through a roof assembly under natural climate conditions is further modelled to show the effects of temperature dependent sorption hysteresis in practical applications.