Paper Conference

Proceedings of eSim 2001: 1st Conference of IBPSA-Canada


Advanced Hygrothermal Models and Design Models

Achilles N. Karagiozis

Abstract: Moisture engineering is becoming an important task in the overall design of building enclosures in North America. Assessing the hygrothermal behavior of building components is important to avoid short term and long-term moisture induced damages or additional heat losses. Since experimental investigations are rather expensive and of limited transferability there is a need of heat and moisture calculations tools that give realistic results but that are also easy to use. Several methods may be used to design wall systems, and modeling is definitively the most flexible approach. Engineers and Architects are commonly asked to perform thermal and moisture analysis of building envelopes. This is increasing the demand for calculation methods to assess the moisture behavior of building components. Modeling analyses are becoming increasingly important to investigate the interrelationships between envelope systems and subsystems and environmental loads. Recently, the Oak Ridge National Laboratory (Building Technology Center) and the Fraunhofer Institute for Building Physics in an international collaboration developed WUFI-ORNL/IBP, a moisture engineering assessment model that predicts the transient transport of heat and moisture. The WUFI-ORNL/IBP model is an design tool for users in SI and IP units customized for both the USA and Canada. On the other side, more advanced models such as MOISTURE-EXPERT, developed by the author at ORNL give researchers the capability to predict the behavior of complex multi-dimensional building envelope systems and subsystems with a higher level of confidence. This hygrothermal model has been used successfully to develop design guidelines for both energy efficient and durable building envelope systems by manufacturers and state regulatory bodies. In this paper the author will provide an overview of how important both hygrothermal models (design and advanced hygrothermal) are to building science envelope assessment. The limits, assumptions and differences between hygrothermal design tools and advanced modeling is discussed. Several example cases are given to demonstrate the suitability of each model.