Simulation of heat and moisture transfer in construction assemblies

Moisture in building components is mostly attributed to diffusion and condensation of indoor air humidity. Practitioners know that the Glaserm method is a steady state design tool to avoid interstitial condensation problems . There are, however, other moisture sources like rain water penetration, rising damp and construction moisture which may affect historic and also new buildings. These phenomena cannot be accurately dealt with by the Glaser-diffusion model because they include liquid transport as well as moisture retention. The same holds for transient effects like summer condensation, freeze and thaw cycles, humidity buffering and heat losses by water evaporation which can cause damage or higher energy consumption. In order to determine the real moisture behavior of building components hygrothermal simulation models have been developed and experimentally validated in recent years. One of the commercially available models widely used in Germany, Eastern Europe and the United States is the PC-program WUFI. The deficiencies of the Glaser-method and the advantages of hygrothermal simulations has been recognized by the CEN committee TC 89. Therefore a new task group was formed in order to overcome the lack of official guidelines for modern simulation tools. Since many manufactures are prepared to have their products tested more thoroughly in order to provide the necessary material data a more wide-spread application of hygrothermal simulations will be feasible in future. In order to convince an increasing number of practitioners to use simulation tools, the user-interface has to become simple and foolproof. This has been the emphasis for the development of the third version of WUFI which has been available since November 2000. The simulation results help to understand the hygrothermal processes in building assemblies. However, the interpretation of the results requires practical experience. In order to quantify moisture related effects, such as mold or algae growth, corrosion, frost or salt damage post-process models have to be developed which derive the damage probability from the hygrothermal simulation results