20% humidity in KFW 40+ new construction

But the counter-calculation is still missing, what the controlled residential ventilation itself consumes.
I googled a bit and found values from 200 to 500 kWh/year. So even assuming 200 kWh to 500 kWh due to ventilation, I would save 300 kWh, that's 60 euros per year. So it wouldn't pay off in my lifetime, even if electricity prices rise.

What are you comparing against? Your 2 air changes per day or the 5+ air changes that you get on low setting and should have at least?

What are you calculating against? Your 2 air changes per day or the 5+ air changes you get at a low level and should have at least?

Who says I should have at least that? I use the values assigned in my heat load calculation by an energy consultant (1/4 of my heating energy demand). Apparently, experts consider that sufficient. And that is not even correct, I simply took the electricity consumption of my heat pump, which even includes domestic hot water preparation; if I subtract that as well, there is probably almost no economic advantage left for controlled residential ventilation. If YOU regard controlled residential ventilation as a comfort benefit, that’s fine. That is subjective and certainly true. It is not necessary, it does not pay off financially, and I assume that the majority of houses currently being built do not have it. Even though a different impression may arise here, but the masses of home builders are not active here.

You should have received a ventilation concept from your planner that specifies how often ventilation is required. Otherwise, just use the big search engine and look for recommended air exchange rate or minimum air exchange. Then you will find 0.5 air changes per hour or 12 per day everywhere. I also find that quite high, but with windows you don’t even come close to that. 2 air changes are definitely far too few. Even in old buildings with not-so-tight windows, you as a tenant can have problems if you have only ventilated twice a day and it gets moldy.

You should have received a ventilation concept from your planner that specifies how often you need to ventilate. Otherwise, try using the big search engine and look for recommended air exchange rate or minimum air exchange. Then you will everywhere get 0.5 air changes per hour or 12 per day. I also find that high, but with windows you don’t even come close to that. 2 air changes are definitely far too few. Already in old buildings with not so tight windows, tenants can have problems if they only ventilate twice a day and it gets moldy.

I just checked my ventilation concept. The minimum requirement for moisture protection is 0.1. That fits with my twice ventilation plus bedroom window open at night plus opening doors several times a day.

This is the wrong section. I have looked up the three relevant levels for you. Moisture protection is the ventilation you need when you are on vacation. You have to look at rated ventilation, which is for everyday life with people in the house, cooking, showering, and so on. And I can promise you that there will be much more than 0.1 air changes per hour.

The core element of the DIN 1946-6 standard is the distinction of four ventilation levels of different intensities, which we present to you here in more detail:

Ventilation for moisture protection (FL)
This ventilation level is intended to achieve adequate ventilation of the building depending on the respective thermal insulation level. The aim is to avoid building damage due to moisture even when the occupants of the room are temporarily absent and the moisture loads are reduced, for example, because drying laundry is consciously avoided. This means: A correspondingly designed ventilation must therefore operate independently of the user.

Reduced ventilation (return flow)
This ventilation level must also be largely independent of the user. It must be ensured that even when the occupants are only absent for a short time due to, for example, their job, the ventilation meets hygienic minimum standards and building protection.

Rated ventilation (NL)
The so-called rated ventilation means the air supply necessary to comply with hygienic and health standards as well as building protection when the apartment is used normally. The rated ventilation level can partially involve the occupant actively in the ventilation concept, for example, with their manual window ventilation.

That fits with my 2x airing plus bedroom window open at night plus several times a day doors open.

plus working in the garden, plus sitting on the terrace with doors open for hours ;)