Energy model of a building with FreeCad

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yorik
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Re: Energy model of a building with FreeCad

Post by yorik »

Yes, using openstudio/energyplus with FreeCAD model would be awesome! I started coding a gbXML exporter some time ago, but fell short, it was never finished...

Basically the main issue is that we need an analytic model. An analytic model is very different than a "normal" BIM model. Some apps like openstudio do try their best at converting, but it very often fails and your BIM model must be very carefully and specifically modelled.

An analytic model for structural analysis is basically only lines, connected by their nodes. An analytic model for energy analysis is basically only spaces, which may or may not share faces with other spaces, and these faces may contain openings.

So the main question we have is: How to obtain such a model from FreeCAD. Obviously, we could, and probably should, use arch spaces for that.

Some questions to solve, then:
  • How to know when 2 spaces share a face. Should they always be modelled with their faces touching? In most cases people will place spaces inside walls. We need therefore an algorithm that "decides" if two spaces close to each other should be considered as sharing a face. But I can think of a number of weird cases where this algorithm could easily fail
  • We could get wall information and openings from surrounding walls and structural elements (slabs, etc). But there too it could fail easily (ex a space is surrounded by other kind of objects (stairs, etc...) where it is unclear).
  • Should this be done manually then? For each space, one should manually give a list of adjacent spaces, and the walls or other boundary objects attached to it? This seems cumbersome and prone to error (the model will change and one will forget to update the space data)
Basically that's where I stopped last time :)
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Re: Energy model of a building with FreeCad

Post by carlopav »

topologic seems to be made exactly for that... AFAIK you can ask a cell of a cellCompex about the neightbourh cells and about the outside faces... @paulee is following the topic more than me i think.
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paullee
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Re: Energy model of a building with FreeCad

Post by paullee »

Yes, using Sketch as floor layout - that's why I stick to Sketch :)

[ArchSketch Workflow] - Creating ArchWall + CellComplex on 1 ArchSketch

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yorik
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Re: Energy model of a building with FreeCad

Post by yorik »

carlopav wrote: Thu Jan 27, 2022 5:23 pm topologic seems to be made exactly for that... AFAIK you can ask a cell of a cellCompex about the neightbourh cells and about the outside faces... @paulee is following the topic more than me i think.
Yes. But we still need to model accordingly. Topologic would still have a hard time "deducing" an analytic model from a common IFC file. But you are right, there is definitely convergence work to solve exactly that problem. @paullee's approach might be an excellent one too. There is maybe even the possibility to deduce a big unified sketch from an IFC model? (ex. starting from a plan generated by ifcopenshell)

Hence my idea in another thread to enable Arch to support different kinds of "engines" ;)
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johnwang
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Re: Energy model of a building with FreeCad

Post by johnwang »

yorik wrote: Thu Jan 27, 2022 10:24 am Basically the main issue is that we need an analytic model. An analytic model is very different than a "normal" BIM model. Some apps like
I haven't figured out how IFC is functioning. For steel frame, an analytic model could be created by tools like column and beam. For a beam, the tool just needs to draw a single line at the same time.
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yorik
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Re: Energy model of a building with FreeCad

Post by yorik »

johnwang wrote: Fri Jan 28, 2022 11:11 am I haven't figured out how IFC is functioning. For steel frame, an analytic model could be created by tools like column and beam. For a beam, the tool just needs to draw a single line at the same time.
What you describe a is an analytic model for structural analysis. Indeed those are basically made of lines connected by nodes. Note that this is fully supported by the IFC format already, and by the FreeCAD multithread IFC exporter (enable it in the IFC preferences). Unfortunately, few structural analysis apps seem to support that already.

An analytic model for energy analysis is basically made of spaces connected by their faces.
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Re: Energy model of a building with FreeCad

Post by ragohix769 »

yorik wrote: Fri Jan 28, 2022 10:21 am There is maybe even the possibility to deduce a big unified sketch from an IFC model? (ex. starting from a plan generated by ifcopenshell)
This is a very interesting idea.
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Re: Energy model of a building with FreeCad

Post by carlopav »

yorik wrote: Fri Jan 28, 2022 10:21 am There is maybe even the possibility to deduce a big unified sketch from an IFC model? (ex. starting from a plan generated by ifcopenshell)
I think this would imply some assumptions on how the model Is made... For example if the walls are IfcWallStandardCase It should be possibile to extract the outer or inner face quite easily (i Remember moult showing something like this in a video)...
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Re: Energy model of a building with FreeCad

Post by paullee »

carlopav wrote: Fri Jan 28, 2022 10:12 pm I think this would imply some assumptions on how the model Is made... For example if the walls are IfcWallStandardCase It should be possibile to extract the outer or inner face quite easily (i Remember moult showing something like this in a video)...
All those edges may be 'disconnected', and maybe in the first place (before Topologic intervention), how to determine which side is inner or outer... :roll:

yorik wrote: Ping
FC seems also export to IFC the 'base line' of the ArchWall if exists, with all 'extrusion information', then it is basically all edges in a Sketch right ?
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johnwang
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Re: Energy model of a building with FreeCad

Post by johnwang »

paullee wrote: Fri Jan 28, 2022 10:21 pm FC seems also export to IFC the 'base line' of the ArchWall if exists, with all 'extrusion information', then it is basically all edges in a Sketch right ?
Instead of exporting to ifc, why not export directly to what you want.
Though ifc is good, other fea software needs some effort to import it.
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