WUFI

Hello everyone,

I am a beginner with WUFI 3D and I am wondering a few questions concerning the analysis of the results.

The pursposes of my study are :
- First to compare to types of indoor insulation (rockwool + vapor barrier, 10 cm, ?=0,036 W/(m.K) VS. Multipor, 10 cm, ?=0,040 W/(m.K))
- Secondly to highlight the advantages of a hygroscopic material such as Multipor in case of indoor insulation (see http://www.ytong-silka.de/de/docs/Ytong ... 2_2010.pdf). The frequent problem with indoor insulation is the condensation at the boundary between the insulation and the wall, due to the brutal decrease of the temperature and the difference of the diffusion coefficient.

Here is a schema of the current structure :



Here is a schema of the structure with indoor insulation:



1) I would like to understand the influence of the insulation thickness on the amount of water. I have been testing three thickness (5 cm, 10 cm, 15 cm). But the results are confusing me because they show that the more the insulation is thick, the least is the amount of water :



Normally it should be the opposite.

2) Then I would like to highlight the condensation process at the boundary between the wall and the insulation to prove the interest of the hygroscopic material over the rockwool + vapor barrier.
That is why I have run a simulation with 10 cm of rockwool + 0,1 cm of vapor barrier + a hole representing the non-perfect junction at the boundary.
We observe indeed the increase of the global amount of water. It is not acceptable for the durability of the structure.



But even if I focus on the boundary layer (1 cm thickness) to measure the amount of water, I have no criteria to validate or reject the studied thickness :



Does anyone have any answers to these questions ?
Thank you.

Hello lulab,

there seems to be a mistake in your plots. Maybe you marked more than the wanted grid elements. I checked the case with the different thicknesses of Multipor in 1D and get other results.
The lowest water content is shown by the 5cm Multipor, at the boundary layer it shows a RH of 94% and in the first cm of insulatiuon a maximum of about 22kg/m³ (just to get an idea, the values can be different in Wufi 1D).
The 10cm shows 28kg/m³ in the first cm, the 15 cm insulation layer shows nearly the same, slightly higher. The RH is here about 95 to 96%.
The marginal difference between the water content in 10 and 15 cm insulation layer is probably due to the higher diffusion resistance of the material.

The value of the total water content is not useful to compare, because of the different diameters of the insulation layer. Here only the course is from interest.
I doesn´t seem plausible, that your total water content shows the same start value for each case. Is this the total water content of the construction?

What did you use as initial conditions?

Greetings Christian

Hello Christian,

Maybe you marked more than the wanted grid elements.

What grid elements are you refering to? 1cm or boundary layer between the wall and the insulator?

The lowest water content is shown by the 5cm Multipor, at the boundary layer it shows a RH of 94% and in the first cm of insulatiuon a maximum of about 22kg/m³ (just to get an idea, the values can be different in Wufi 1D).
The 10cm shows 28kg/m³ in the first cm, the 15 cm insulation layer shows nearly the same, slightly higher. The RH is here about 95 to 96%.
The marginal difference between the water content in 10 and 15 cm insulation layer is probably due to the higher diffusion resistance of the material.

I obtain over 100 kg/m3 water in the 1cm layer and you obtain around 25 kg/m3. I don't think it is a problem with wufi 1D or 2D but we didn't take the same assumptions...

The value of the total water content is not useful to compare, because of the different diameters of the insulation layer. Here only the course is from interest.

OK

I doesn´t seem plausible, that your total water content shows the same start value for each case. Is this the total water content of the construction?

What did you use as initial conditions?

I used 80% RH as initial condition in all materials (all thicknesses).

Do you know the RH limit not to cross at the boundary between the wall and the Multipor to avoid condensation?

PS: I will send you a report with all initial conditions

Hi lulab,

What grid elements are you refering to? 1cm or boundary layer between the wall and the insulator?

If you start a new course in WufiGraph, make sure, that there are not the elements from the last plot marked as well (you can do this by doing a right click and choose unmark all)...

Yes, thats a big difference...

Do you know the RH limit not to cross at the boundary between the wall and the Multipor to avoid condensation?

No, i don´t know. That depends on the pore structure of the material. If I remember right, the WTA-Guidelines postulate not get higher moistures than 95% to avoid the buliding of dew water.

Christian

thank you for all your support.

Quote:
Do you know the RH limit not to cross at the boundary between the wall and the Multipor to avoid condensation?


No, i don´t know. That depends on the pore structure of the material. If I remember right, the WTA-Guidelines postulate not get higher moistures than 95% to avoid the buliding of dew water.

What WTA Guideline it is written on? it is the 6-4-09/D or 8-5-08/D?
Or a third one?

Best regards

We propose to remain below 95 % RH - the detailed limits are discussed at the moment in the second part of WTA guideline 6-4 - but there is no decision yet.

To keep some safety margin we try to establish 95 % RH. At least as monthly or three month running average.

best regards
Daniel