Optimization of effective moisture penetration depth model considering airflow velocity for gypsum-based materials

Abstract The hygroscopic performances of building materials have a considerable effect on the humidity of indoor environments, and this performance depends on various factors on the material (physical properties), system (ambient airflow), and room (moisture load profile in the indoor environment) levels. Thus, these three levels should be considered to comprehensively evaluate the hygroscopic performances of building materials. The effective moisture penetration depth (EMPD) model assumes a layer of constant thickness with uniform relative humidity on the material surface subjected to a periodic sine wave variation in indoor humidity. The EMPD model is commonly used by simulation software such as EnergyPlus to characterize hygroscopic performance. The computational speed of the EMPD model used in EnergyPlus is fast compared to other models such as the combined heat and moisture transfer model; however, it can provide inaccurate results. By considering the effect of the ambient airflow velocity on materials and changing the relative humidity variation from a periodic sine wave to a periodic square wave, a series of evaluation indexes is proposed to adapt the EMPD model to more practical situations. The calculated evaluation indexes are then verified through a theoretical analysis and experimental calculations. A simpler and faster method is thus proposed by modifying the original EMPD model to consider airflow velocity and square wave modification. This method is then verified using several gypsum-based materials. The optimized EMPD model is shown to provide a more realistic prediction of the hygroscopic performances of building materials in different areas, functional building types, and under different airflow velocities.