20% humidity in KFW 40+ new construction

But hey, Controlled Residential Ventilation is an absolute must, anyone who builds today without Controlled Residential Ventilation is building an old building! How often do you read that here daily? You build a tight house and need Controlled Residential Ventilation to pull the moisture out, so the tight house doesn't get moldy. After that, you put humidifiers in every corner to bring moisture in, so you can live in the tight house at all. I sometimes find our architect a bit too oldschool when it comes to the latest building technology, but his saying "why technically correct something that you can also get right from a building physics perspective" appeals to me more and more.

Just saying.

But hey, controlled residential ventilation is an absolute must, anyone building today without controlled residential ventilation is building an old building! How often do you read that here every day? You build a tight house and need controlled residential ventilation to pull the moisture out so that the tight house does not mold. Then you put humidifiers in every corner to bring moisture in so you can even live in the tight house. I sometimes find our architects a bit too old school when it comes to the latest building technology, but his saying "why technically correct something when you can get it right physically from the start" appeals to me more and more.

Just saying.

And how do you "physically get rid of" the moisture correctly right away?
And how is it with CO2?

And yes, controlled residential ventilation only with an enthalpy exchanger.

Stone house with good plaster and ventilation, classic indeed. For the price of a [Kontrollierte-Wohnraumlüftung] including the measures you still have to take afterwards (plants everywhere - would not be an option for us, for example, humidifiers) I can ventilate warm air out for a very long time.

Of course, a [Kontrollierte-Wohnraumlüftung] is comfortable for air quality (not for comfort!), but it is not a panacea and certainly not without problems.

Hmm, there seems to be a misunderstanding here.
If you ventilate manually correctly, you have the same dry air problem as with a [Kontrollierte-Wohnraumlüftung ohne Enthalpie-WT], but additionally more effort and more heat loss.
The dry air does not come from any technical conversion in the [Kontrollierte-Wohnraumlüftung] but because moist indoor air is exchanged for dry (because cold) outdoor air. In the [Kontrollierte-Wohnraumlüftung], at least the heat is retained by 80-90%.

If you want to achieve the same air exchange manually, you simply have the additional heat loss and have to run through the whole house at least three times two times (open and close) a day.
Most people just don’t do that and therefore have better indoor humidity. However, in case of doubt, there is still some risk of mold.

We have had this discussion many times, so I calculated it once. To heat 1 cubic meter of air by 1 degree, you need 0.33 Wh. Now you just have to plug in how often you ventilate and what temperature difference you have. Depending on the numbers, with 3 air changes (= ventilating 3 times), you get 6-10 kWh per square meter per winter. With a calculated heating demand of 35 kWh for an EH55, this is indeed a relevant magnitude.
Ventilation of any kind dries the air. Whether through [Kontrollierte-Wohnraumlüftung] or manually. The difference is that most people ventilate properly for the first time in their lives with [Kontrollierte-Wohnraumlüftung]. In addition, there is the problem with ventilation itself. In calm weather, you get poor air exchange. When it is windy, windows and doors slam shut, papers blow around. Internal corridors or rooms with small window areas often have poor air exchange.

We have had this discussion many times, so I did the math. To warm 1 cubic meter of air by 1 degree, you need 0.33Wh. And now you just have to plug in how often you ventilate and what temperature delta you have. Depending on the numbers, you end up with 3 air changes (=ventilating 3 times) resulting in 6-10 kWh per square meter per winter. With a calculated heating demand of 35 kWh for an EH55 house, this is indeed a relevant order of magnitude.

I am always a fan of calculations, but those without numbers make little sense.
The first entry of the search yields 70 kWh/m²/a, so 10-7 times higher than your value.

A main problem is probably that you calculate only air being exchanged. While that might be the case with a controlled residential ventilation system, with open windows floors, furniture, walls, etc. cool down, which then have to be reheated.
Furthermore, ventilating 3 times in a modern house is by far not enough for hygienic air.

Ventilation of any kind dries the air. Whether by controlled residential ventilation or manually. The difference is that most people ventilate properly for the first time in their lives with controlled residential ventilation. Added to that is the problem related to ventilation itself. With calm wind you get poor air exchange. With wind, windows and doors slam shut, papers fly around. Interior corridors or rooms with small window areas often get poor air exchange.

I fully agree here.