IBP / Software / WUFI-ORNL/IBP-ORNL/IBP / Tour 1

Software / WUFI-ORNL/IBP / Tour 1

This short tour through WUFI-ORNL/IBP shows you a calculation example and compares the results with experimental data.

Outdoor experiment and simulation

The ORNL and the branch Holzkirchen of the Fraunhofer Institute for Building Physics is performing laboratory and field tests in order to assess the thermal and hygric behaviour of building materials and components. These experiments tend to be lengthy and expensive so that only a small number of variants can be examined.
A suitable simulation method can replace some of these experiments. After validation and calibration by experiment it can be used to test further variants.

Experiment

External thermal insulation composite systems (EIFS) with expanded polystyrene (EPS) and mineral wool (MW) insulation were applied to the west-facing lime silica brick walls (initial water content: 10 vol.%) of a test house. The drying-out of the wall was monitored for three years by gravimetric testing of drill samples.

Simulation of Experiment by WUFI-ORNL/IBP calculation

Component Assembly and Numerical Grid

The individual layers of the component and their respective thickness are entered into a table.

The component is then divided into numerical grid elements whose widths are chosen according to the temperature and moisture variation expected for the respective location.
The manual grid definition is done by entering the desired number of grid elements per layer and an expansion factor which describes the ratio of the sizes of successive grid elements.
Steep temperature and moisture gradients may especially be expected close to the layer interfaces. Splitting a layer into two layers allows the grid to expand and subsequently contract within a material layer.
Optionally, WUFI-ORNL/IBP creates an automatic grid (coarse, mean or fine) which is adequate for most applications.

Material Data

The hygrothermal material data for each layer can be read from WUFI-ORNL/IBP's database. As a minimum, WUFI-ORNL/IBP requires the bulk density, the porosity, the specific heat capacity, the heat conductivity (dry) and the diffusion resistance factor (dry).

Depending on the object and the purpose of the calculation, additional data can be entered: the moisture storage function, the liquid transport coefficients for suction and redistribution, the moisture-dependent heat conductivity and the moisture-dependent diffusion resistance factor.

For the present example, material parameters from the educational database were used. The users are cautioned when using material properties from this educational database. ORNL is working on providing a reliable database with the new hygrothermal laboratory facilities.

Weather Data

The boundary conditions acting on the building component are the temperature and relative humidity of the interior and exterior air and the rain and radiation loads, both depending on inclination and orientation of the building component. These data can be derived from a database. ASHRAE provided the raw data for the development of a moisture design year for 50 city.

The time steps for the climate data and the calculation may be selected at the user's discretion; for most cases hourly values are appropriate.