Shows RH where no RH should be.

[avp081090]

Hello

I currently modelling a window i WUFI 2D. I am using some user-defined materials such as glass and a specific type of insulation. Neither of the two should be able to have any moisture content. Below you can see some of the material properties.

The glazing shouldn´t have any moisture content as:
porosity = 0
Water Vapour Deffusion Resistance factor = very high!
moisture storage function = Not defined (since it don´t have any)

The Insulation material is Coated with a impermable plastic surface and should therefore have a moisture content of zero as:
Porosity = 0,85
Water Vapour Deffusion Resistance factor = very high!
moisture storage function = Not defined (since it don´t have any)

So as you can see, neither of the two materials should be able to gain any moisture at all, but...The results show RH in the glass and the insulation. although the moisture content [kg/m^3] is zero. How is this possible?
How come glass can have a RH value when it has a porosity of zero? i Guess i can´t trust the results im getting out of this?

btw - at which temperature is the moisture storage functions in wufi found?

Best regards

[veitner]

The driving potential used by WUFI is R.H.
To map the R.H. to water content the moisture storage function is used.
If there is no moisture storage function defined WUFI uses an internal one (Online Help Topic 14).
Temperature of moisture functions is at 20 degree celsius and it's dependence is marginal.

Regards
Veit

[avp081090]

Okay, so when i use materials with no defined moisture storage function, WUFI defines one for numerical reasons? But does this mean that i can trust the RH value i the rest of the construction as well as the water content?

[veitner]

You could remove the glass and insulation (comment the definition using "%"), set the arising "new" boundaries to be adiabatic and compare the results to the previous one.
The results are not the same of course because of the missing heat transport through the glass and insulation but they should not be that different as long as there is no transport because of the "high" diffusion resistance. And you should get equal results if you untick "heat transport calculation" in numerical settings.

[avp081090]

okay. But i guess if i untick Heat Transport Calculation, this will also impact the moisture transport?

thanks for the answers - helping a lot

[veitner]

Yes the results will differ - but you can verify if the "suspicious" water content, RH in your glass/insulations has an effect on RH inside the rest of your construction.

[avp081090]

Okay. I have tried the following:
-With and without glass - results did differ, RH were pretty similar but the water content was evidently higher.

-With and without Glass (minus the heat transfer calculation) - This gave the exact same results.

So it proved the calculations were right. In the first case where the results differ must arise due to the heat flow trough the glass ?

I was looking at the case with the glass included. (see picture). I was wondering how come it shows RH value in the glass but not in the outer layer? both are porosity 0.

And how come you can´t have porosity 0? Wufi gives a warning when processing saying that it may give strange results.