Decentralized ventilation system that is hardly visible on the exterior facade

Quieter, but not by much. Can be almost invisibly installed in the window recess. Outside noise is only an issue in loud environments. Ditto for decentralized. The ventilation output is correctly calculated for both variants and is identical. ... over 90% for decentralized. Nonsense!

Of course a central system is 100 times quieter than a decentralized one? Why do you think that is nonsense???

Of course a central system is 100 times quieter than a decentralized one? Why do you think that's nonsense???

Because I have used both myself in recent years. So from practical experience. Therefore, I allow myself to make that judgment ;-)

Currently living in a KFW 55 apartment built in 2016/2017 with decentralized ventilation from Aereco, which the company installs as standard. I do not perceive the system acoustically at all, and the air quality is, in my opinion, always very good. Therefore, I decided to use the system again in the new building without much thought, since I am building with the same company that also constructed the apartments. Visually, I do not notice the devices, but that is always subjective. In my case, I would have seen no reason to upgrade to a central system, as, as mentioned above, I have not noticed anything negative so far.

What I always find lacking in such comparisons is that the devices play an extreme role. There were model houses where I could clearly hear both the central and decentralized ventilation systems, and vice versa. I mean: there is indeed a difference in the quality and effectiveness of the devices.

The system question did not explicitly arise for the OP. The actual noise development depends more on the model and installation than on the principle. I can imagine that the hole will become a feature with the appropriate decor. When I think of the dragons spitting water from the roofs of late medieval government buildings, I immediately have an idea: Each hole gets its own individually crafted dragon head made of tinplate or copper (or ceramic). Maybe it huffs really impressively in cold weather.

From a purely technical perspective, it is of course much smarter to house the mechanics and the fan(s) in an enclosed space and decouple them with silencer elements, rather than slapping a buzzing little annoying fan into an open wall hole in a decentralized manner. That it is more efficient and powerful than having 8 individual small fans due to limited installation space is also no rocket science.

Since a single-family house does not require a ventilation system, a compromise would be to equip the bathrooms each with a decentralized device and, if a very quiet device can be found, also the bedroom. These are the rooms from which the user benefits the most.

If one has the money, install a central system and enjoy the many advantages :). Everything said.