Software / WUFI-ORNL/IBP / Introduction

Besides the thermal properties of a building component and their impact on heating losses, its hygric behaviour has to be considered, too. Permanently increased moisture content in the component may result in moisture damages. Elevated surface moisture levels in living rooms can lead to hygienic problems and health risks due to mould growth.
In addition, thermal and hygric behaviour of a building component are closely interrelated: an increased moisture content favours heat losses; the thermal situation affects moisture transport. Therefore, both have to be investigated together in their mutual interdependence; the research field of hygrothermics is dealing with these problems.

The Dew-Point method as detailed in ASHRAE has been a common method to assess the moisture balance of a building component by considering vapour diffusion transport in its interior. However, this method does not allow for the capillary moisture transport in the component, nor for its sorption capacity, both of which reduce the risk of damage in case of condensation. Furthermore, since the method only considers steady-state transport under heavily simplified boundary conditions, it cannot reproduce individual short-term events or allow for rain and solar radiation. It is meant to provide a general assessment of the hygrothermal suitability of a component, not to produce a simulation of realistic heat and moisture conditions in a component exposed to the weather prevailing at its individual location.

The menu-driven PC program WUFI-ORNL/IBP developed by IBP and ORNL and validated using data derived from outdoor and laboratory tests, allows realistic calculation of the transient hygrothermal behaviour of multi-layer building components exposed to natural climate conditions.

WUFI-ORNL/IBP is based on the newest findings regarding vapour diffusion and liquid transport in building materials.

WUFI-ORNL/IBP only requires standard material properties and easy-to-determine moisture storage and liquid transport functions.

WUFI-ORNL/IBP can use measured weather data - including driving rain and solar radiation - as boundary conditions, thus allowing realistic investigations on the behaviour of the component under exposure to natural weather.

WUFI-ORNL/IBP can be used for assessing

• the drying time of masonry with trapped construction moisture
• the danger of interstitial condensation
• the influence of driving rain on exterior building components
• the effect of repair and retrofit measures
• the hygrothermal performance of roof and wall assemblies under unanticipated use or in different climate zones.

WUFI-ORNL/IBP is a tool for developing and optimising building materials and components. For example, it was used as a development tool for the smart vapour retarder.

WUFI-ORNL/IBP is directed at manufacturers of building products, consultants, designers, engineering offices and experts in the field of hygrothermics.

WUFI-ORNL/IBP may be used as a teaching aid or advertising tool because of the instructive visualisation of its calculation results.

WUFI-ORNL/IBP runs on PCs under Windows NT4, 95, 98 and 2000. The comprehensive on-line help and documentation amounts to ca. 200 A4 pages. WUFI-ORNL/IBP is available in an English version. A free Research and Education version for USA and Canada is available for download.
Proper application of WUFI-ORNL/IBP requires experience in the field of hygrothermics and some basic knowledge in the use of numerical calculation methods.