Boundry Condition _ Ground

[LAS]

I am modeling a 2D floor-to-exterior-wall connection in WUFI 2D. The floor/slab is in contact with the ground, and I am unsure how to define the boundary condition for the ground-facing side.

I would also appreciate guidance on what temperature/RH or surface transfer settings are typically used for a ground-contact floor condition.

Thanks

[Christian Bludau]

When modeling a floor or slab in contact with the ground in WUFI 2D, the boundary condition should not be treated like a standard exterior surface with air temperature and humidity. Instead, the ground boundary needs to represent the coupled heat and moisture interaction with the soil.

A good starting point is the basement example in the tutorial “Handling of Typical Constructions” (https://wufi.de/en/service/downloads/#t ... structions) - this is for WUFI Pro, but can be transferred to WUFI 2D. This example demonstrates how to model ground-contact elements properly, including appropriate boundary conditions and domain extension into the soil. It gives a practical reference for both geometry setup and boundary definition.

In addition, the following forum discussion provides useful guidance and background information on ground boundary conditions:
https://www.wufi-forum.com/viewtopic.php?p=6056

In general terms, typical approaches include:
Extending the calculation domain into the ground and assigning appropriate soil material properties.
Using ground boundary conditions that reflect the thermal mass and moisture buffering of the soil rather than prescribing fixed indoor/outdoor air conditions.
Avoiding the direct use of constant surface transfer coefficients with air temperature/RH on the ground-facing side, since this does not represent physical reality well.

Christian