On coupling 1D non-isothermal heat and mass transfer in porous materials with a multizone building energy simulation model

Hygroscopic materials available in the interior of buildings such as wood, gypsum, paper etc, are able to absorb moisture if the relative humidity of the room increases and release it again if the relative humidity decreases. This moisture buffering phenomenon is often accounted for in a simplified way in Building Energy Simulation programs (BES) e.g. TRNSYS, which limits their applicability. Nevertheless several building applications require an accurate prediction of the indoor relative humidity already from the design stage. This paper presents the development and possibilities of a coupled TRNSYS-HAM model which allows to account for the response of a multizone building on moisture buffering effects in a more detailed way. The HAM (Heat, Air and Moisture) model describes one dimensional transient coupled heat and mass transfer in porous materials. The coupled model agrees well with the analytical solution of two verification exercises. The model is applicable for the design and evaluation of relative humidity controlled HVAC (Heating, Ventilation and Air Conditioning) systems and can be employed in numerous building applications. To illustrate this an evaluation of gypsum cooled ceilings was made using a simplified model and the coupled model. The results show that when non-isothermal vapour transfer in the gypsum layer is neglected, the buffering effect is largely underestimated.