Ventilation: central or decentralized?

Then you have a system without heat recovery - hard to imagine with KFW 55..

According to the OP, would it even be possible without any ventilation at all? Or is the calculation then made under the assumption that no ventilation takes place? I find that hard to imagine. What I really did not consider, however, are the increased requirements since last year. I still built according to the '14 standard.

Since not much heat energy is transported through the air, not much can be lost this way either. Therefore, I generally consider heat recovery to be uneconomical. For central systems it can be sensible with moisture regulation, if you like. For decentralized ones, I do not think so. (Mind you: I BELIEVE it. I can't try it out)

As already pointed out, this is then not a decentralized ventilation system but an exhaust system.

Then we probably have to differentiate here again. It is definitely the cheapest way to ventilate one’s house. And it works well, you do the maintenance yourself and apart from a small fan, nothing can break. I wouldn't have had any money for anything else (which I could then maybe recoup after 40 years).

But yes - we digress and end up in the same discussions that have already been had here in abundance.

What is important for the OP is: what do the individual variants cost? How much energy can they possibly save? The architect should be able to answer that... Properly designed and maintained systems are always comfortable.

As already pointed out, this is then not a decentralized ventilation system but an exhaust system.

Welcome to the last century!

This technology is long outdated and offers hardly any advantages over manual ventilation. (But still, it is better than no forced ventilation at all) but I digress...

But it is the cheapest and it works. I don't care about the century.. The builders are also from the previous century.

But it is the cheapest and works.

yes, but only to a limited extent and with restrictions... but as I said, it doesn't matter... the OP is interested in a central system (or rather two), which is not to be criticized. The arguments from the seller are rather far-fetched...

the OP is interested in a central system (or rather two), which there is nothing wrong with.

No - the OP wants to know what we think about three very different options. You just want to present your preferred one as the only right solution again. We've already had this in the KNX thread. You might even be right - unfortunately, these solutions are simply too expensive/not worth the price for many.

I'll leave out all the KfW stuff. The goal is that air comes into an otherwise airtight house and air goes out. So I create an airflow by making slots in window seals at point a, and at point b a fan sucks air out. What happens is air moves from a to b. I have an uncontrolled forced ventilation and exhaust in the living space without any frills. That's something already. If the exhaust fan is humidity-controlled, it turns up a bit after showering in the morning and clears the bathroom mirror, then it hums quietly again. Karsten

How much sound insulation do you still have from the outside if you have a fan in every room? I only know this personally from bathrooms and I think the sound insulation has suffered because of it. Even if these were DIY jobs with ducting and standard fans.

Fan noise aside