Question about everyday life with a controlled residential ventilation system

If you want to sleep with the window open, then you have to turn off the system.

You don't have to do anything!
Controlled residential ventilation can be left on while opening the window.
In winter, opening the window lets the cold in and the energy out. You should internalize that, and eventually you won't need window air anymore, the ventilation air will be enough. That is fresh air too, it just doesn't come from the window, but from the wall.
If you still don't want to give up opening the window, then you should keep the bedroom door closed so that the thermostats don't go crazy and heat additionally against the cold from the window.

Is ventilation mandatory according to the minimum standard Energy Saving Ordinance 2016? Or only from Kfw55 onwards?

You don't have to do anything at all!
Running the controlled residential ventilation system and opening windows works

Yes, but one should not do that because it promotes the wear of the system. With closed doors/windows, the system is in balance.

As soon as a window is open, the balance is disturbed and the system tries to compensate by constantly adjusting the speed of the fans up and down...

Yes, you shouldn't do that because it promotes wear and tear on the system. When doors/windows are closed, the system is in balance.

As soon as a window is open, the balance is disturbed, and the system tries to compensate by constantly adjusting the speed of the fans up and down...

I just want to take away the fear of a controlled residential ventilation system from the skepticism.
Once you have it, it's easy to live with...

We also turn it off when the need arises. But that's rare.

Then air out...done. No mold so far and here the water sometimes really runs down the walls

Then have fun. In a KFW40+ or even better without controlled residential ventilation. I can only advise you: First get properly informed about the topic before you compare new construction in the Kfw40 + x class with your current old place. Where your moisture in the "old hovel" still somehow escapes today: in the planned building it will rather not anymore or only poorly. Your window ventilation action diametrically contradicts all your ideas of efficiency. Especially in winter + transitional seasons. You are an engineer. So a smart man! In another thread here you talk about heat contributions from refrigerators in a passive house and saving a heat pump and heating directly electrically.....And then wanting to ventilate by opening windows. Yes: great. You: That doesn’t fit together for me. You want to build something here that won’t work. At least not in your sense. Well, it is/will be your house. The later problems with it without controlled residential ventilation you will then just have to solve. I say this—unusual for me—uncharismatic and blunt. Best regards Thorsten

He is quoting someone else!

On the topic of controlled residential ventilation and large window fronts.

Do you lower the shutters every time? In my case, the tiles heat up so much that by noon I already have 25-26 degrees on the ground floor.