Effects of different moisture sorption curves on hygrothermal simulations of timber buildings

Building energy simulations are a key tool to design high performance buildings capable of facing the future challenges and to help reaching the emissions reduction targets. Currently, thermal properties of materials used in most building energy simulations are assumed to be constant and not dependent of moisture content and temperature. Heat and moisture dynamic transfer models allow to simulate building envelope performance considering thermal resistance reduction due to moisture effects. These models are generally considered more accurate than the heat transfer models and they could be used to simulate the heat transfer (increased by water vapour storage) and the moisture buffering effect on the indoor environment. For the simulation to be performed, hygrothermal material properties should be known as functions of moisture content. Nevertheless, hygrothermal material properties are rarely available and correlations from the literature have to be used. In this study, the moisture storage curves of CLT, OSB and two types of wood fibre insulation have been measured with a dynamic vapour sorption analyser. The other hygrothermal properties are estimated from values measured in previous studies or taken from the literature. The simulations of two small single room buildings in four Italian locations are performed with the software EnergyPlus, considering an ideal HVAC system, to calculate the heating and cooling needs of the building. The HAMT (heat and moisture transfer) module of EnergyPlus is used. With the results presented in this study, it is possible to evaluate how an approximated curve affects the results of a whole-building simulation in terms of wall average water content, indoor air relative humidity and heating/cooling loads.