Influence of the moisture driving force of moisture adsorption and desorption on indoor hygrothermal environment and building thermal load

To more accurately evaluate the indoor hygrothermal environment of a building, control the indoor tem-perature and humidity, evaluate the thermal comfort of occupants, and select the capacity of the heating, ventilation, and air conditioning (HVAC) system, moisture transfer from and into architectural materials should be considered. However, the most widely used commercialized software ignores the moisture effect from envelopes or adopts a simplified model based on the difference in humidity ratios between hygroscopic materials and interior zone air. In this study, the effects of the driving forces of hygrothermal models were identified and quantified. The calculated results show that the indoor humidity changes dif -fered when the moisture effect by moisture adsorption and desorption was considered in the models. Because the simplified effective moisture penetration depth (EMPD) model uses differences in the humidity ratio as a driving force, the calculated results of the indoor humidity ratio exhibit relatively con -stant tendencies. However, the thermodynamic chemical potential model corresponds to a detailed heat, air, and moisture transfer (HAM) model that uses the water potential as a driving force; this model can consider the moisture effect based on temperature and humidity changes. Therefore, the humidity ratios calculated using the detailed thermodynamic HAM model show differences of 0.01%-38.78%, and the dif-ference in relative humidity between building materials and indoor air becomes smaller; these results are comparable to those of the simplified model. Finally, the adoption of a simplified model can result in dif-ferences in the sensible heat load of 4.4%-13.8% and latent heat load of 16.1%-51.2%. Thus, this study con-firmed that a coupled HAM model, which uses the water potential as a driving force, can be employed to accurately simulate the hygrothermal behavior of building envelopes. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the impact of moisture transfer from architectural materials on indoor humidity, comparing the simplified model and the detailed thermodynamic chemical potential model. Results show significant differences in humidity ratios and heat loads between the two models, confirming the importance of considering moisture effects in hygrothermal simulations.