I'm curious about the proposed solution. I have two independent plans from Zehnder and I'll just say... they're very straightforward. But it could be resolved with discussions.
A slot in the exterior wall is by far not enough. You might get a flat duct in there but you need one per room. Or two 160mm(?) pipes go to the upper floor and there connect to a distributor (where to?!) and from there into the rooms. There are also distributors that can be cast into concrete, but that has to fit, be clarified with the structural engineer... and in the upper floor leads to floor outlets and the expensive flat duct system under the screed.
I really appreciate my flat concrete roof, where the cheaper round duct with ceiling vents can easily go in or on the concrete.
Or do you maybe have suspended ceilings on the upper floor?