Ventilation: central or decentralized?

Hello,

I am planning to build a KFW-55 two-family house. The living area on the ground floor is about 100m² and on the upper floor 90m². The house will be fully basemented. I will live on the ground floor myself and rent out the upper floor.

I have now visited various construction companies to get offers for turnkey construction. I have heard many different opinions about ventilation systems, far more than I expected. The topic of ventilation was the dominant issue in all conversations, even though I want a fairly complex KNX installation.

Basically, it comes down to the following statements:

Central ventilation system
Since it is to be a two-family house, this is apparently not so easy because of soundproofing. There was also the idea to install two smaller systems, one for each apartment. Furthermore, I was advised against a central ventilation system because it would have to be thoroughly cleaned at least every 2 years, which costs at least 3,000 euros. Otherwise, mold would form in the pipes, leading to illnesses.

Decentralized ventilation system
I was recommended a decentralized ventilation system several times. Since there are no long pipes here, maintenance would be much easier. However, I am not a fan of this, because then I would be moving the noise of the fans from the basement into the living areas. Furthermore, I would like to avoid having outlets in the facade.

No ventilation system at all
The energy consultant said I should simply skip the ventilation system, as KFW-55 can also be realized without it. Of course, manual ventilation is possible, but if I leave for work in the morning after showering, nobody closes the window again. So I don’t really see that as an option.

So now I have the choice between three bad options. I would prefer a central system, as then the noise, if any, occurs in the basement.

I would be very grateful for tips, opinions, and experiences.

Two central systems. Always keep the system running, never leave it idle, change filters regularly, F7 filters in the supply air, filter bags/pouches in front of every exhaust air opening.

The seller is telling you fairy tales. Two central ventilation systems and that's it.

It does not need to be cleaned extensively.

and above all not every two years either...

The noise problems from decentralization shift to rooms where one does not "live". That means to the utility room and the bathrooms. Therefore, this is not disturbing.