Optimal moisture buffering thickness of the hygroscopic material layer : Modeling and derivation

The indoor humidity level can be passively improved by the hygroscopic material without energy consumption. Some studies demonstrate that the moisture buffering capacity (MBC) of the hygroscopic material layer is affected by the material's thickness. There exists an optimal thickness that maximizes the material's moisture buffering capacity when some hygroscopic material is exposed in a specific indoor environment. Some methods have been proposed to determine this optimal moisture buffering thickness (L_opt). However, such methods are primarily based on experimental measurements or numerical simulation. Therefore, optimal moisture buffering thicknesses are approximate values. In this paper, an analytical method was proposed to solve the theoretical L_opt based on the moisture transfer function. Correspondingly, the ideal and practical optimal thickness, which present an ideal situation and a practical situation of the indoor humidity variation, respectively, were theoretically derived and validated using numerical simulations. Moreover, the optimal moisture buffering thicknesses of some conventional building wall hygroscopic materials were derived and calculated simply and efficiently via the proposed analytical method. The proposed analytical method is based on the theoretical derivation and has many advantages in terms of computational efficiency and accuracy compared with experimental measurements and numerical simulations.