Hi @OlgaT,
Yes I agree that there are currently very few good / inexpensive solutions for 3D Thermal Bridge tools - its probably the biggest missing piece of our toolkit at the moment in our office and if anyone knows any good ones I’d personally love to know more. I know several folks who are using Heat3 for this purpose as well as Trisco and Psi-Therm but they are all (in my experience) quite clunky to actually model in. If there was a solution which connected to Rhino that would be terrifically useful. The simulation math seems to be relatively straightforward and outlined quite clearly in ISO 10211.
And yes, there are some super expensive ones out there like NX Thermal and Comsol too but I haven’t ever gotten my hands on those.
There is an open source tool named ‘Elmer’ but I haven’t personally used it and not sure if it would work for this issue. It may be worth investigating if you are interested though.
To your other point about approximating 3D heat flow with multiple 2D ‘slices’ - while I don’t think anyone would tell you it was ‘correct’, I can certainly say that we’ve done it plenty of times as a better-than-nothing solution to these kind of things.
Within the tool we use the most for 2D simulation (Flixo) there is also some limited functionality for simulating ‘effective’ 3D bridging from small elements which is good for screws and the like. There is also a whole methodology within the ISO 6946 (used to be Annex D: Corrections for Mechanical Fasteners but in the new version I think its in Annex F now) which shows a simplified equation for calculating a U-Factor ‘supplement’ (added to the base U-Factor of the assembly) based on some input data about fastener material, spacing, size, etc…
best of luck with it.
-Ed