On validation of hygric characteristics for heat, air, moisture models

Lack of reliable material characteristics remains a major roadblock in the development of integrated testing and modeling approach for the enhancement of durability of building enclosures. This paper takes a very broad look and provides an update on three-prong approach to achieve the progress needed in the development of reliable material characteristics. The first prong involves an improved description (definition) of the tested material. Even the best test method with a well-defined measurement uncertainty, will not provide precise results if the specimen is not adequately defined. In such an instance, the variability attributed to differences in test specimens cannot be separated from the measurement errors. The second prong involves improvements of test methods used to generate data for input into HAM models. Hygric characteristics measured in different laboratories (Roels et al 2004) showed that some frequently used tests, considered to be well standardized e.g., water vapor permeance or free water uptake tests, were not as precise as initially thought. Furthermore, hygrothermal data in a handbook may not represent the actual material. Therefore, the third prong, called here "material validation", compares the results of HAM model with the measured values. Effectively, these three elements constitute the methodology of generation of adequate material characteristics.