A study of annual moisture variation in an internally insulated building wall under a mild climate using a small-scale model and the similarity laws

• Published in: Energy and buildings 1991, Vol.16 (3), p.933-945
• Main Authors: Matsumoto, Mamoru, Fujiwara, Seiji
• Format: Article
• Language: English
• Subjects: Accuracy; Climate; Construction; Exteriors; Mathematical models; Reliability; Similarity; Temperature distribution; Variations; Walls; Water
• ISSN: 0378-7788
• DOI: 10.1016/0378-7788(91)90088-K

In order to evaluate the durability and the thermal/moisture design of a building wall, it is necessary to know the moisture distribution and variation, especially the maximum value of the moisture content in it. These can be predicted with a certain degree of accuracy by solving the nonlinear simultaneous heat- and moisture-transfer equations with suitable boundary conditions. The physical parameters, such as moisture conductivities and moisture capacity, in the equations depend strongly on dependent variables, namely moisture content and also temperature. Furthermore, these parameters are usually sensitive to the microstructure of the materials used. For the reasons mentioned above, sufficient data for the predictions are limited in the present state. Predictions of the moisture content and evaluation of building walls using the results of field measurements or experiments under real boundary conditions are still required. Experiments using a real-scale wall usually require a very long time (several years) and are very expensive. In this paper, an experimental method using a small-scale model of the building wall and similarity laws based on the governing equations of simultaneous heat and moisture transfer through porous media are presented. With the assumption that the small-scale model is composed of the same materials as the real building wall and that the boundary values are the same as in a real wall, simple similarity relations are obtained, in spite of the dependency of the physical parameters on dependent variables. From the similarity relations, the time scale in the small-scale experiment is reduced to l 2, where l is the ratio of the characteristic length of the small-scale model to that of the real building wall. Using the similarity relations, experiments using a small-scale model of an internally insulated exterior building wall are performed under various boundary conditions. The period of variation of the boundary values corresponds to one year in the real system. The results of the experiments are presented in terms of the variations of moisture and temperature distributions. The accuracy and reliability of the experiments are discussed by comparing the results of the experiment with the results of a numerical solution of the governing equations in which the values of the physical parameters are independently measured values. As a comparison, converted values from the small-scale model to the real system are used. The experimental resul