Very high RH level within assembly

[Lxr_Energy]

Hello,

I'm using WUFI 2D to do a moisture simulation for an assembly. The assembly is just put in the air, meaning boundary climates are surrounding. And I select the bottom surface with "rain load calculation" (since in real life the bottom surface is facing up to get the rain).

Within my assembly, there are a few layers that are not vapor permeable at all, such as glass, POE encapsulant, etc. So I'd expect very low RH within the assembly. However, the results show that the RH within each layer is very high, about 80-90% and somewhere exceeding 100%. but the water content M% is very low - about 0.01% or so. How could that possible? It seems like the RH results does not match with the water content results.

Thanks,
Ray

[Christian Bludau]

Hi Ray,
in general, WUFI is calculating a continuous field of temperature and relative humidity for the whole construction / calculation grid. So also for more or less materials a RH has to be assigned and will adapt depending on the µ-value of the layer. After each calculation step the RH is transformed into a water content using the moisture storage function. If a material has no moisture storage function defined, an internal one is created based on the porosity.
So for materials with a low porosity high RH may occur, but the water content can be low.
See also program help "topic 14" or search for "mositure storage function".
Christian