Examples of irregular, non-periodic changes in the total water content

[Alberto Morales]

Hi,

I have a historical wall made of:

outdoor (bottom of the image)
Granite stone
Unknown material
Brick
Air cavity
Timber
Indoor (top of the image)

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The unknown material has been modelled as 3 potential cases:
1- Solid calp limestone
2- Calp limestone/mortar/calp limestone (following Joseph Little's approach Stone/Mortar/Stone from Assessing risks in insulation retrofits using hygrothermal software tools)
3 - Brick

The only difference in the 3 models is just the unknown material, the rest is the same (orientation, initial condition, climates, etc)

The total water content I get is showed below:

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My concern is about the sharp increase of water content for the case where the unknown material has been modelled as a brick.

Following "Guideline for the Evaluation and Assessment of hygrothermal Calculation Results", it is mentioned that "Examples of irregular, non-periodic changes in the total water content Almost certainly impossible to evaluate meaningfully!" which would be my third case, however, I cannot find a way to improve it as the balances and convergence failures look good as you see below.

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The only conclusion I can make is that there is permanent moisture accumulation in the construction, however, dynamic equilibrium is reached.

Any thoughts or advice? What would you recommend I modify in my model, and are there any other aspects of the results that I should check?

Thanks in advance

[Alberto Morales]

On the other hand, I tried to analyze the effect of the air layer in the CASE 3 of the previous message so,

I created 3 subcases:

Subcase 1- Air layer 25 mm
(Convergence failures: 9, balance 1: 205.53, balance 2:206.20)

Subcase 2- Air layer 25 mm, without moisture capacity
(Convergence failures: 2, balance 1: 43.35, balance 2:43.56)

Subcase 3 - 1mm Air layer 25 mm
23 mm Air layer 25 mm, without moisture capacity
1 mm Air layer 25 mm
(Convergence failures: 20, balance 1: 205.0, balance 2:208.87)

What I have observed in WUFI film that for Subcase 1 and 3, the results are pretty the same with brick being saturated in water content and reaching RH 100% all the time. For the case 2 the water content is much lower than the other cases what can make an impact in the conclusion of the build-up. You can see a well in the "check of numerical quality), although the obtained does not match with what is mentioned in the next links (I read as a reference):

https://wufi.de/en/service/wufi-forum/? ... b371df865f
https://wufi.de/en/service/wufi-forum/? ... 4586bd401

wufi film-imageonline.co-merged.png (245.78 KiB) Viewed 8 times

For both Subcase 2 and 3 (top row of pictures), the outer side of the air layer is at RH 100% which can reach dew point (left and right picture).

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For the inner part of the air layer, Subcase 2 (right picture) and 3 (left picture), the risk is with the oak that can cause wood rot (see local hygrothermal load pictures above)

So, my question is: what would be the best approach to define the air layer? it has an impact in the total water content as you see below although it seems that the build-up wall has issues.

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