Study on non-isothermal moisture transfer characteristics of hygroscopic building materials: From parameter characterization to model analysis

Abstract

The heat and moisture transfer in building materials has significant effects on the energy consumption and indoor thermal comfort. In this paper, an improved heat and moisture transfer model based on temperature gradient coefficient (TGC) and phase change criterion (PCC) was built. The effects of relative humidity and temperature on liquid water conductivity, moisture diffusivity and TGC were considered and discussed. A new moisture transfer characteristic index called the temperature gradient factor (TGF) was proposed. It presents the ratio between the moisture flux due to temperature gradient and the total moisture flux. The PCC was introduced to quantify the significance of the vapor flux relative to the total moisture flux. Based on the improved model and two moisture transfer characteristic indexes (i.e., TGF and PCC), two series simulations were conducted to investigate the non-isothermal moisture transfer characteristics of cellulose insulation. The results showed that the liquid water conductivity was independent of temperature. The liquid water transfer could be ignored when the relative humidity in the cellulose insulation was less than 60%. Also, the liquid water transfer due to temperature gradient could be ignored when the relative humidity was larger than 60%.