Coupled Heat and Moisture Transfer in Two Common Walls

In order to optimize building energy consumption, it is essential to reduce the heat losses and gains through the building envelope by selecting proper materials which are often porous. However, heat transfer and moisture transfer are often highly coupled, so coupled heat and moisture transfer in two common walls (aerated concrete wall and red brick wall) were studied in this paper. Aerated concrete wall is made up by aerated concrete block, cement mortar, and lime-cement mortar. It is widely used now for the superior thermal insulation of aerated concrete block. Red brick wall is made up by aerated concrete block, cement mortar, and lime-cement mortar. It was frequently used in China decades ago, and many existing building are made up by red brick wall. After a simple review of the development of models for coupled heat and moisture transfer in porous media, a dynamic model was proposed which takes into account most of the main hydrothermal effects. It takes temperature and air humidity ratio of the porous media as the critical driving potentials. Then the model was used to simulate coupled heat and moisture transfer in both aerated concrete wall and red brick wall and then analyzed comparatively. Results show that aerated concrete wall can reduce more heat transfer than red brick wall. However, aerated concrete wall may accumulate moisture and cause moisture damage more easily.