On modelling moisture buffering when evaluating humidity controlled HVAC systems

As most building energy simulation programs focus on the thermal response of the building, the relative humidity of the indoor air is often calculated in a simplified way. One of the main shortcomings is the isothermal calculation, which may have a strong influence the predicted relative humidity. In this paper the use of a simplified effective moisture penetration depth (EMPD) model is compared with a coupled TRNSYS-HAM-model. First, an estimation of the load for humidification and dehumidification is made. Results showed that the EMPD-model underestimates the humidification load because the model disregards non-isothermal effects. Secondly, calculations showed that the indoor and surface relative humidity of an office room with a gypsum cooled ceiling are overestimated using the EMPDmodel. Furthermore, due to not including nonisothermal effects the peak load for dehumidifying the ventilation air may be underestimated using an EMPD-model.