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)