The best way to proceed, or at least the easiest we have found, is to export all the thermal zones and properties using gbXML with the green building studio / ecotect add-on and import data into ecotect. You will still need to define the materials, layers, ...
Additional geometry can be exported and imported in ecotect using 3ds files.
Since your model is complicated, as ours often are, I strongly suggest that you slit it in different functional layers then import, check and modify each of them one by one to keep it manageable.
Note that Ecotect is sometimes surprising when you import large models, so save the new versions often.
There is a document detailing the core of this procedure on Graphisoft.com. Try to search on Ecotect gbXML: that should point you to the add-on download and the how-to document.
Good luck
