I have the next build-up with water repellent and foil faced PIR in both sides modelled as vapor retarder (sd=1500).
is it right?
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Evaluating the WC in the PIR I have observed irregular, non-periodic changes in the total water content what makes me think that something can be wrong in the results. any thoughts about this change in trend?
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However there are no larger differences in balances as it can also be recognized in part by the total
water content curve above
The steep vertical increases in water content are obviously not correct. However, in the total balances these problem remain unvisible - this may be because the issue is simply a slightly incorrect distribution of moisture within the building component, which is not apparent either in the total water content or in the surface moisture fluxes.
In any case, you can assume that no moisture accumulation will occur between two layers with an sd value of 1500 m. And ss the total error ist only 0,01 kg or 10 g (0,1 kg/m³ * 0,1 m³) over 10 years, the influence on the neighbour materials remains completely negligable.
In other words, to sum up: You can perform a normal evaluation.
best regards
Daniel
Dr.-Ing. Daniel Zirkelbach, Deputy Head of Department Hygrothermics, IBP Holzkirchen
1- Could the "Assessing the Risk of Interstitial Condensation Runoff" guideline be applied for a foil face PIR insulation which is between an unventilated cavity and concrete?
for the case we have unventilated air layer facing in one side with a brick and the other side with a face foil aluminum PIR insulation, which value should we take? the one from the column Rmet to calculate µ* and lambda*?
Hi Alberto,
regarding your questions:
1) yes, the condensation in air layers part
2) yes, the Rmet values - these should always be used if there is at least one metallic surface connected to the air gap
Christian
would it be possible to model this case just with one vapor barrier (between PIR and unventilated cavity, the most critical condensation surface)?
As we see in the top-left of the image below, the water content in the PIR, I think that the trend is a consequence of putting a double vapour barrier and creating a vapour sandwich. it is the result of the "ping pong" effect between the vapour barriers. it looks that WUFI cannot cope well with two vapour barriers like that. I have modelled a new case (just one vapour barrier between unventilated cavity and PIR) and observed that despite the water content profile of the concrete (in the WUFI film) hardly change in both cases, however, the water content increases a lot in the case with just one vapor barrier. This make me think that interstitial condensation will occur in the case with just one vapour barrier if we see the high number of convergence failures (3146) and trend of water content in the PIR (correct me if I am wrong). why is this not observed in the case with double vapor barrier? I think I should see an increase of water content in the outermost part of the concrete as the moisture from indoor should be trapped by the vapor barrier between concrete and PIR.
any thoughts?
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do you know what is the reason of this error message when I open wufi graph...This only occur when I open wufi graph including the second case where I model just one vapour barrier.
