Building envelope designers and architects provide expert advice during the selection of building envelope systems. Until recently, a limited hygrothermal engineering analysis was performed to determine performance of a selected wall system other than review the details of wall systems and subsystems. Infrequently, a glaser or dew point method analysis may have also been performed, but this kind of analysis is only steady state in nature and ignores the hygroscopic effects, such as nonlinear dependencies of hygroscopic material properties, moisture storage, freeze-thawing mechanisms, liquid transport, latent heat, and transient nature of moisture loads at the boundaries. The main reason for not performing a thorough moisture engineering analysis was the lack of an easy-to-use hygrothermal model that integrated the physics and that was accompanied by a material property database and a set of realistic hygrothermal environmental loads for both the interior and exterior of the envelope. Recently, the increasing demand for better performing calculation methods to assess the moisture behavior of building components prompted an international collaboration between the Oak Ridge National Laboratory (USA) and the Fraunhofer Institute in Bauphysics (Germany) to develop a hygrothermal design tool named WUFI-ORNL/IBP. This hygrothermal design model can assess the response of building envelope systems in terms of heat and moisture loads and can also provide a very useful and fair method for evaluating and optimizing building envelope designs. This state-of-the-art model is discussed in detail in this paper and is also available in North America free of charge at www.ornl.gov/btc/moisture.

Authors: Achilles Karagiozis, Ph.D.; Hartwig Kuenzel; Andreas Holm

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001