Ventilation in new buildings (central vs. decentralized), noise disturbance

Thank you very much for all the answers here. Currently, I tend to install decentralized devices from Meltem. Three times each over the two-room system, so that a bathroom/WC is ventilated and another room (bedroom, children's room, study) is ventilated. In addition, a standard device in the living room. Then I’m at about 5k€ for material costs and think that the installation is very quick and easy (flush-mounted set --> install directly into the wall + lay 2-3 pipes). This way I have all rooms at least partially covered, meet my minimum requirements, stay within budget, and don’t have to lay pipes all over the place (or have them laid) and accordingly box out ceilings. Am I being too naive here? Are the installation costs actually higher, so that in the end I come close to a central system, and do I perhaps even have to be careful with the statics if I lay pipes between the rooms? Or do I have to consider more when installing the fans than simply covering all rooms? I think the details like air exchange rates / air quantities etc. are not fully covered here (but as I said, I’m also not afraid to ventilate additionally with the window if necessary). Also, I can imagine it being unpleasant if, for example, I’m in the study and the demand ventilation in the guest WC kicks in, and suddenly much more air is blown into the study or the fan gets louder. Also: Do I have to cut slots into the individual doors so that air can circulate between the rooms? Many thanks! Kiri

And my statement was just that, in my opinion, the controlled residential ventilation is not suitable for bringing enough cool air into the house

so terrace doors are gladly left open. And then the place heats up...