Is it no longer allowed to open the windows with a ventilation system?

Ventilation system is comfort Most people do not do shock ventilation several times a day - especially during the cold season. It cools down the whole house

With a ventilation system you may and can open the windows at any time without problems, often there are just no reasons.

Because terrace doors are installed in the kitchen, living room, and bedroom, people open them more often for a few minutes - at least I think so. Now we live in a house without terrace doors, the windowsills are all fully occupied. Therefore, we only open the windows on tilt at most.

No, you don't, because you don't have time. Ventilating the bedroom on Saturday morning is not enough.

Besides, you don't build according to the Energy Saving Ordinance because of a loan, but you get the loan because you build according to an enhanced Energy Saving Ordinance. Many do this out of conviction or because of the energy savings. For the same reason, you keep the windows closed in winter so that the energy does not escape outside.

Friends of ours built a normal house and after the Blower-Door-Test they practically had a passive house - and that without controlled ventilation.

Now they can first make sure that the place doesn’t get moldy.

and then we would never be allowed to open the windows again

That is completely correct. That is why only fixed windows and patio doors without handles and opening options are installed in modern houses. It has the huge advantage that you save a lot of money with it.

Apart from the fact that it is complete nonsense not to be allowed to open the windows, I just noticed that the fan tends to run faster when one or two windows are slightly open.

Yes, because then the pressure conditions change and the systems try to compensate for that.