Yes, that is fine with the window open, I can understand that. However, you will hardly place much value on a perfectly insulated efficiency house, that was what this was about.
There is a lot of arguing here again, people say you "don't have to" ventilate thanks to controlled residential ventilation. Sounds like ventilating is a terrible burden. I only know my/our living habits, but basically we always have windows open in the bedrooms when we/the child are inside. From spring to autumn also in many other rooms.
I find that absolutely wrong especially in winter...and yes, I do see it as a burden when I come home and first have to open windows everywhere because the air just isn't fresh...and then the tilted or open windows cool down the house and I have to heat expensively again. Why build KfW whatever houses if the benefits partly dissipate because you have the windows open or have had slots cut in?
We are also the type to open windows for people. When I get up in the morning, I first go to the living room and kitchen, open the windows, make myself a coffee and feed the cat. And I also enjoy this flash love fresh air in winter. I think in the morning, with the warmth of the bed in your body, you don’t get cold so quickly.
First of all, it is not forbidden to open windows.
What might not be so clear to the non-KWL user is this: with controlled residential ventilation, you have fresh air all night long, constantly, always and continuously. You wake up, the air is just as fresh as when you fell asleep. If you open the window, it might become colder, but not "fresher".