Computer simulation of moisture transport in walls of residences

Well insulated walls of residences experience temperature depression in their outer layers during cold weather, causing moisture to condense on the surfaces. A predictive model capable of identifying the conditions that potentially lead to condensation or high moisture levels has been developed. The model utilized includes both moisture storage and distribution effects by utilizing the general form of the thermal energy and moisture conservation equations for each layer of a wall of typical residential construction, utilizing materials such as wood siding, insulation, and gypsum board. A finite difference numerical solution produces the transient temperature and moisture profiles for each material. The model predicts that the wood layers offer most of the storage capacity for moisture, exhibiting large delays between changes in the external conditions and response of the moisture content. When walls are exposed to various outdoor climates, the wall moisture content is greater for mild and moist climates than for cold and dry climates. Simulation of an air leak in the wall, such as that found around an electrical outlet, show that the wood moisture in the region adjacent to the leak is substantially greater than with no air leak.