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Energy Assessment: Thermal Bridge Modelling - which software would you recommend?

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      CommentAuthorfostertom
    • CommentTimeSep 7th 2013 edited
     
    •  
      CommentAuthorSteamyTea
    • CommentTimeSep 7th 2013
     
    Neither Tom, was about the affects of insolation on thermal mass, both passive and active. All within an insulated envelope.
  3.  
    Steamy,
    1) we won't have any more valves etc than if it were a "bog-standard" central heating system.
    2) running pipes under the roof has proven only minimally more expensive than not bothering ... (granted it's a new roof)
    3) we're on a slope, and deep digging not an option, so this is also testing the use of insulation to force a long path from ground to slab
    4) once it's commissioned we'll have, at the very least, a series of fuel bills to compare before-and-after ... not a game changer I know, but informative nonetheless assuming other variables like occupancy, unit price and weather have been taken into account.
  4.  
    Can anyone please shed light on appropriate boundary conditions, specifically film coefficients, as they pertain to materials which are not immersed in air e.g. EPS to soil, sand blinding or Hardcore etc? I gather that surface resistance does not manifest the same way in this application? At the moment I've created a new boundary condition and taken a tabulated soil resistance of 1.5m2K/W (from Dansk Standard 418 page 37) to give a coefficient of 0.66W/m2K but I'm really just stabbing in the near darkness!!!
    • CommentAuthorEd Davies
    • CommentTimeJan 9th 2022
     
    AFAIK “film coefficients” only apply when at least one material is a fluid. Are you sure that number given in the Dansk Standard is not an assumed resistance for the bulk soil?
  6.  
    Hi Ed

    I'm not sure no, but I suspect your hunch is probably correct as the tabulated value is given for:

    "Ground supported floor, from 0.5 m above to 0.5 m below the terrain"

    I attempted to extract this coefficient from the 1.5m2 K/W resistance given in the table (1/1.5=0.666W/m2K?)

    The first thing I tried was simply to delete the film coefficient for the elements in contact with the ground however the isotherms don't look even vaguely correct when I did this so I reasoned that I needed to find some value to attribute to that boundary condition order to generate a vaguely plausible result.

    <blockquote><cite>Posted By: Ed Davies</cite>AFAIK “film coefficients” only apply when at least one material is a fluid. Are you sure that number given in the Dansk Standard is not an assumed resistance for the bulk soil?</blockquote>
      Screenshot 2022-01-09 at 12.06.09.png
  7.  
    Zero coefficient
      Zero coefficient.png
  8.  
    0.66 coefficient
      0.66 coefficient.png
    • CommentAuthorEd Davies
    • CommentTimeJan 9th 2022 edited
     
    Certainly looks like that 1.5 m²K/W (and the other values in their table 6.9.1) is supposed to be used as the net resistance of the whole soil-to-air path so makes sense as your boundary condition, so not really a “film resistance” like that Rsi [¹] figure.

    It's odd how they have the resistance increase from 0.2 to 0.8 m²K/W as the depth down the outside wall increases from 0 to 2 metres then suddenly jumps to 2 m²K/W. I wouldn't expect an exact match as this is all presumably a simple approximation to extending the finite-element model out into the soil but it does seem quite a big jump anyway.

    [Ă‚Âą] Irritating how Rsi for the internal surface resistance clashes with Rsi for resistance specified in SI units as opposed to in US customary units.
    • CommentAuthorlineweight
    • CommentTimeSep 12th 2023
     
    This thread was started ten years ago - is the situation substantially different now?

    As far as I can make out:

    - Most of the commercial packages are very expensive
    - There's nothing free/cheap that will run natively on a mac.

    It looks like THERM is probably the best option for someone who doesn't want to pay for expensive commercial software. And it looks like it can probably run on a mac (using parallels) although who knows how long that will be the case.

    But what about the time investment to learn to use it properly, that is, to be confident enough in its use that results can be used to make meaningful real-world design decisions?

    My situation is that I often work on small-ish refurb/extension projects where there's (currently) no requirement under building regs to do the kind of detailed SAP calculations that look at thermal bridging issues. And this means that getting professional modelling done is an "extra" cost that isn't budgeted for.

    Working within those constraints I try and do the "best possible" which means trying to make judgements on design details without quantifying heat loss.

    If there were a relatively easy-to use package (that runs on a mac, because that's what I use) that could let me get even a rough idea of the difference a certain detail decision would make, it would make my life much easier. But each time I look at this, I end up coming to the conclusion that such a thing doesn't really exist.
    •  
      CommentAuthordjh
    • CommentTimeSep 12th 2023
     
    I think you're right that Therm is the best possibility for software. There are some documents and tutorials for it so I'd say just download it and see how you get on.

    Another approach might be to invest in a book of thermal bridge details. There are several around. There's the grand daddy - https://www.amazon.co.uk/Passivhaus-Bauteilkatalog-OEkologisch-Konstruktionen-Ecologically-Constructions/dp/3035616868/ - and there are several other books written about PH details. There are also some about 'normal' details e.g. https://greenbuildingencyclopaedia.uk/wp-content/uploads/2016/10/ZCH-ThermalBridgingGuide-Screen_0.pdf or https://www.brebookshop.com/details.jsp?id=190683 or many others.
    • CommentAuthorlineweight
    • CommentTimeSep 15th 2023
     
    Posted By: djh
    Another approach might be to invest in a book of thermal bridge details. There are several around. There's the grand daddy -https://www.amazon.co.uk/Passivhaus-Bauteilkatalog-OEkologisch-Konstruktionen-Ecologically-Constructions/dp/3035616868/" rel="nofollow" >https://www.amazon.co.uk/Passivhaus-Bauteilkatalog-OEkologisch-Konstruktionen-Ecologically-Constructions/dp/3035616868/- and there are several other books written about PH details. There are also some about 'normal' details e.g.https://greenbuildingencyclopaedia.uk/wp-content/uploads/2016/10/ZCH-ThermalBridgingGuide-Screen_0.pdf" rel="nofollow" >https://greenbuildingencyclopaedia.uk/wp-content/uploads/2016/10/ZCH-ThermalBridgingGuide-Screen_0.pdforhttps://www.brebookshop.com/details.jsp?id=190683" rel="nofollow" >https://www.brebookshop.com/details.jsp?id=190683or many others.


    Thanks. I'm familiar with some of these.

    The difficulty is with the kind of one-off details that don't appear in these books. Or details that aren't uncommon for certain types of projects but tend not to be covered in books. It's in those situations where it would be good to feel that it was possible to do a bespoke calculation oneself, and be confident enough in the results to make decisions beased on them.
    •  
      CommentAuthordjh
    • CommentTimeSep 15th 2023
     
    As I said, I think the answer to that is to download Therm and get stuck in.
  14.  
    Not one that I've tried myself, but this interface certainly looks friendly than THERM.

    https://www.accasoftware.com/en/thermal-bridge-software

    They are priced on a subscription basis, but there is a free trial available too.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 15th 2023
     
    From Euro84/yr looks OK, if it's any good, and less clunky than Therm (that shouldn't be difficult)
    • CommentAuthorlineweight
    • CommentTimeSep 15th 2023
     
    Posted By: Doubting_ThomasNot one that I've tried myself, but this interface certainly looks friendly than THERM.

    https://www.accasoftware.com/en/thermal-bridge-software" rel="nofollow" >https://www.accasoftware.com/en/thermal-bridge-software

    They are priced on a subscription basis, but there is a free trial available too.


    Unfortunately for me, Windows only.
    • CommentAuthorwookey
    • CommentTimeOct 23rd 2023
     
    I'm quite sure that FreeCAD can be made to do decent thermal modelling with a lot less aggravation (and on more platforms) than THERM. But it needs some work to experiment and document how.

    People already use it for thermal modelling, just not quite the sort we want:
    https://www.youtube.com/watch?v=hUS7T9hrn4k
    https://forum.freecad.org/viewtopic.php?f=18&t=16749&start=40#p133612

    FreeCAD doesn't cost anything and runs on Windows, Linux and MacOS. And it's proper 3D parametric CAD. Like all 3D CAD tools (argulably excepting sketchup and SweetHome3D) it requires some investment in learning how to drive the damn thing. But it is very flexible. https://www.freecad.org/

    Working out how to do this, adding any missing bits, and documenting it, is on my list, but has been for more than a year with no progress so far. Here is someone else with similar ideas, starting on adding temp constraints and material properties: https://forum.freecad.org/viewtopic.php?t=11494

    Getting your building model into it should let us calculate and model various other things too (like making air-volume calcs for airtightness tests easy, for example).

    If you want to see what it can do, there are plenty of architecture tutorials as both text and video:
    https://wiki.freecad.org/Arch_tutorial
    https://wiki.freecad.org/Video_tutorials_for_architectural_design

    There is now loads of good free FEM software, like Calculix and Sparselizard. A lot of what they do is way more complicated than we need for simple steady-state thermal modelling of constructions. But once we have that working, we ought to be able to do dynamic modelling too.

    One other nice tool is Energy2D, which is very easy to drive and has quite a sophisticated physical model. But it doesn't have any concept of boundaries to measure fluxes across so you get great visualisations, but no numbers. Also it seems to me that making this work for 3D gives us the 2D case for free so that seems a more fruitful case to concentrate on.
    https://energy.concord.org/energy2d/ (it's great fun to play with the examples)
    • CommentAuthorlineweight
    • CommentTimeOct 31st 2023
     
    Posted By: wookeyWorking out how to do this, adding any missing bits, and documenting it, is on my list, but has been for more than a year with no progress so far.


    That would be great, if you ever manage to do it!

    I use 3d CAD every day (Vectorworks) and I'm not sure there's enough space in my brain to learn another package. But a how-to might make it manageable. Especially if I could use my own software to build the 3d geometry, import it and just do the thermal bit in something else.
  19.  
    Many of us have under-employed Raspberry Pi's about the house, which come bundled with a free copy of Wolfram Mathematica.

    This can do finite element heat transfer models, 2D3D, dynamics, etc. If GBF falls apart, I'll use my new free time to learn how to work it.

    https://reference.wolfram.com/language/PDEModels/tutorial/HeatTransfer/HeatTransfer.html

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