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      CommentAuthordjh
    • CommentTimeMay 4th 2019 edited
     
    I've just come across another U-value calculator - https://www.ubakus.de/u-wert-rechner/?

    It looks professional and works out condensation and decrement delay and suchlike to EU standards.

    It has an English language option, but only some of the content is in English. The rest remains in German. So if anybody with better German with me wants to have a go and see how useful it is, that would be helpful.

    PS It might be better to use it before brexit, from some of the statements on the site about access within the EU.
    •  
      CommentAuthordjh
    • CommentTimeMay 4th 2019
     
    I managed to make a crude model of my walls. The main limitation (apart from quite how to access all the materials etc) seems to be the one-dimensional calculations. So it calculates the average properties of a mixed layer like my straw + posts and uses that in the overall calculation. Not much problem with my walls but it leads to some interesting results if you put timber nearer the outside edge because it spreads the condensation uniformly whereas in reality it probably concentrates nearer the timber.
  1.  
    Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?

    It looks professional and works out condensation and decrement delay and suchlike to EU standards.


    I had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator, maybe you have to register.
    •  
      CommentAuthordjh
    • CommentTimeMay 5th 2019
     
    Posted By: PeterStarckI had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator,

    The U-value calculator just calculates and displays it?
  2.  
    Posted By: djh
    Posted By: PeterStarckI had a look at that a couple of months ago to calculate decrement delay but I couldn't find the calculator,

    The U-value calculator just calculates and displays it?

    Thanks
  3.  
    Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?


    +1 for u-bakus. Previously called U-wert.

    I've been using it for a few months and it remains my go-to calculation software for testing theoretical wall build-ups.

    djh, curious to know what you think about the 'drying time' calculation it performs, given what you mention about the condensation predictions vs. where it would actually occur. Is this also a slightly flawed (i.e. simplified) approach?
    • CommentAuthorbhommels
    • CommentTimeMay 7th 2019
     
    A whole new world has opened up to me. Really good find, thanks for posting!
    • CommentAuthorgravelld
    • CommentTimeMay 7th 2019
     
    Ah, thanks for re-discovering this. I remember seeing it before but I completely forgot about it.
  4.  
    Thomas, the condensation calculation here is very simplified (following a simplified DIN standard method), because it assumes condensation will happen as soon as the dewpoint line is reached, somewhere deep inside the insulation layer, as stated on pg2 of djh's download. This is a common misconception, which messes up the 'drying time' calculations.

    In reality the vapour molecules have a 'choice' whether to condense or to carry on diffusing until they reach an even colder place, such as the cladding, they will always 'choose' to condense at the coldest (lowest energy) point they can easily reach, always at the outside edge of an insulating layer or the inside edge of a low permeability layer.There's some nice photos explaining this at https://www.buildingscience.com/documents/insights/bsi-049-confusion-about-diffusion

    Once condensation does occur, it will wick and drip away through the material, not sit still in a discrete blue layer until next summer.

    I would use this website as it is intended, a nice and handy u-value calculator, for constructions where condensation will never occur, but if condensation amount and drying time are important to you, then use a more appropriate tool such as WUFI.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 7th 2019
     
    Interesting, Will - thanks
    •  
      CommentAuthordjh
    • CommentTimeMay 7th 2019
     
    Posted By: WillInAberdeensomewhere deep inside the insulation layer, as stated on pg2 of djh's download

    Actually, it's showing condensation within the render, not the straw, I think, since that's where the dewpoint line crosses the temperature line. So it's not too far from the truth in this particular case.

    In another model I did (attached), that had some timber immediately behind the external render, it did predict a thick blue layer throughout that layer of insulation, whereas I believe it would concentrate on and around the timber and the render.

    Once condensation does occur, it will wick and drip away through the material, not sit still in a discrete blue layer until next summer.

    It will certainly spread by capillary action to some degree in both the straw and lime (they are intimately coupled so both materials will be involved regardless of where the condensation first occurs. But I wouldn't expect much in the way of free water that could drip. Indeed I have a theory that some of the condensate may be carried all the way back into the interior of the building.

    I think the assumptions it makes are generally conservative (i.e. pessimistic) so if it says something is safe, I would generally trust it. But as you say, a more accurate tool, especially one that uses 2D or 3D flow would be better.
  5.  
    Sorry, I was referring to this paragraph on pg2, which states the assumption/simplification/misconception. The Lstiburek piece I linked to explains why this is rather a simplification.

    Quote:

    "The dew-point indicates the temperature, at which water vapour condensates. As long as the temperature of the component is everywhere above the dewpoint, no condensation occurs. If the curves have contact, condensation occurs at the corresponding position." End quote

    To be fair they do include this disclaimer:
    Quote:"Convection and the capillarity of the building materials
    were not considered. The drying time may take longer under unfavorable conditions (shading, damp / cool
    summers) than calculated here" end quote

    Just to be clear, I think this is a really neat u-value calculator, and for checking that condensation will never occur, but I wouldn't use a u-value calculator for drying calculations.
    •  
      CommentAuthorfostertom
    • CommentTimeMay 7th 2019 edited
     
    Posted By: djhwhereas I believe it would concentrate on and around the timber and the render
    That's talking about two different kinds of 'simplification' -
    the first being what Will was talking about
    Posted By: WillInAberdeenwhether to condense or to carry on diffusing until they reach an even colder place
    where it 'carries on' along the in-out axis to the render;
    the second being that it will concentrate somewhere laterally, around the timber rather than in the insulation between - simply a limitation of a 1D model, where only that in-out axis exists. A 2D modeller such as super-WUFI or whatever it's called would handle that side-to-side axis.
  6.  
    Posted By: djhI've just come across another U-value calculator -https://www.ubakus.de/u-wert-rechner/?" rel="nofollow" >https://www.ubakus.de/u-wert-rechner/?

    It looks professional and works out condensation and decrement delay and suchlike to EU standards.


    I ran ubakus and also the Dynamic Thermal Properties Calculator written by Arup for the Concrete Centre and using the same data got very different results for decrement delay. I wonder if the decrement delay models are modelling the effect very accurately. Results following.
  7.  
    Ubakus
      Decrement Delay Ubakus.jpg
  8.  
    Arup
      Decrement Delay Arup.jpg
    • CommentAuthorSilky
    • CommentTime7 days ago
     
    +1 for this tool, have used extensively and would have been lost without it
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