Influence of sorption isotherm hysteresis effect on indoor climate and energy demand for heating

In order to investigate the effects of sorption isotherm hysteresis on indoor climate and energy demand, a new module for precise representation of mass transfer in materials in contact with indoor air, called Humi-mur, was developed and implemented in the energy performance simulation tool, TRNSYS. This extended whole-building HAM (Heat–Air–Moisture) simulation tool was then used to investigate the impact of the moisture-buffering effect on indoor conditions in a room. Two modelling approaches were compared: including/excluding moisture-buffering effect and including/excluding hysteresis in sorption isotherm. In addition, two ventilation strategies were used: constant airflow ventilation (CAV) and relative humidity sensitive ventilation (RHS). The simulation showed that for the CAV system, the use of moisture-buffering materials did not change energy demand but improved the indoor conditions. For the RHS ventilation system, the use of the buffering materials led to a higher energy demand, but the indoor relative humidity comfort was significantly improved. The results also showed that hysteresis of the sorption isotherm impacts on indoor conditions, even if the effect is smaller for the studied material than the average moisture-buffering effect.