Hello and thank you very much for the information.
In the meantime, I have spoken with a few ventilation installation companies and indeed, an installation in the concrete ceiling would have been most sensible. Most now recommend installation in the floor structure with flat ducts. But here, with a 10cm floor structure, we hardly have any space left.
I have now come up with another alternative that I would like to put up for discussion:
Since the house is only 1.5 stories, I would have the air outlets on the ground floor run through the basement and the air outlets in the attic run through the loft.
This means the ventilation unit would be located in the basement (or in the loft) and the connection between the basement and the attic would be made with an installation shaft.
Pipes would run in the basement almost surface-mounted under the basement ceiling. The air outlets into the rooms on the ground floor would be routed through openings made by core drilling.
From the loft, the rooms in the attic can be ventilated. Here, there is no need for core drilling as the ceiling is made of wood.
This way, there is no need to lower the ceiling (the basement is just a utility basement and not a living basement) nor to go into the floor structure.
What do you think?