20% humidity in KFW 40+ new construction

Hmm, there seems to be a misunderstanding here. If you ventilate manually properly, you have the same dry air problem as with a controlled residential ventilation system without an enthalpy heat exchanger, but with additional effort and more heat loss. The dry air doesn’t come from any technical conversion in the controlled residential ventilation system but rather because moist indoor air is exchanged for dry (because cold) outdoor air. In the controlled residential ventilation system, 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 at least three times twice (open and close) through the entire house per day. Most people just don’t do that and therefore have better indoor humidity. However, there is still some risk of mold.

When ventilating manually, you can control it better. You just close the window when the desired humidity is reached. You also don’t have to run through the house; you can just walk normally ;). You only have a mold risk if you don’t observe the whole process and don’t adjust accordingly.

Depending on the numbers, with 3 air changes (=3 times airing), you get 6-10 kWh per square meter and winter

In the heating load/energy class calculation of our house without controlled residential ventilation,
the heat losses through ventilation are about 1/4 of the total losses.
3/4 are all other components, such as the floor slab, walls, windows, roof, etc.

In the heating load/energy class calculation of our house without controlled residential ventilation, the heat losses through ventilation are approximately 1/4 of the total losses. 3/4 are all other components, such as the floor slab, walls, windows, roof, etc.

And that is about 500 to 600 kWh per year. How many kWh does the controlled residential ventilation consume per year? And what did it cost to purchase?

For us, ventilating twice (morning and evening) plus once more when lighting the fireplace in the living room is more than enough to maintain a comfortable humidity level. You shouldn't forget either that the front door is opened several times a day, letting fresh air in.

With manual ventilation, you can control it better. You just close the window once the desired humidity is reached.
You also don't have to run through the house; you can walk normally ;).
You only have a risk of mold if you don't observe the situation and adjust accordingly.

Oh man, now windows can also be "controlled" better than a device designed for it, equipped with sensors and control technology.

For us, airing twice (morning and evening) plus once more when lighting the fireplace in the living room is more than enough to maintain comfortable humidity. You also must not forget that the front door is opened several times during the day, letting in fresh air.

Are you only concerned about humidity?
Yeah, fits well with this thread, but:
CO2, VOC, other pollutants don't matter to you?

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

A main problem is probably that you calculate that only air is exchanged. While that might be the case with controlled residential ventilation, with an open window floors, furniture, walls, etc. cool down, which then have to be heated up again.

I don’t know the calculation. But I would be interested under which assumptions you arrive at that range.
For me, the assumptions are approximately as follows:
100 days x 20 degrees difference x 3 air changes x 2.5m room height x 0.33 Wh -> 5 kWh (winter)
90 days x 10 degrees x 3 air changes x 2.5m x 0.33 Wh -> 2.2 kWh (transition period)
That would be, in this example, about 7.2 kWh/m². That should be quite close to the range that officially calculated. Of course, this is only an approximation. Cooling of the furniture is not included, while at the same time the furniture also reduces the air volume. With correct shock ventilation (as long as it is possible with the wind conditions), almost only air is exchanged. Of course, if someone showers in the morning, then opens the bathroom window and returns after half an hour of breakfast, that has little to do with the calculation. Likewise tilted windows, etc.
Whether 3 air changes are sufficient is debatable. But more than 3 times airing out is certainly unrealistic. For most people, I would even assume 2 times a day. See Silke ;)

I don’t know the calculation. But I would be interested in under which assumptions it arrives at that range.
For me, the assumptions are approximately as follows:
100 days x 20 degrees difference x 3 air changes x 2.5m room height x 0.33Wh -> 5 kWh (winter)
90 days x 10 degrees x 3 air changes x 2.5m x 0.33Wh -> 2.2 kWh (transition period)
That would be 7.2 kWh/sqm in this example. That should put me quite accurately in the range that officially calculated. Of course, this is only an approximation. Cooling down of the furniture is not included, at the same time the furniture also reduces the air volume. With proper shock ventilation (if wind conditions allow), almost only air is exchanged. Of course, anyone who showers in the morning, then opens the bathroom window and comes back after half an hour for breakfast has little to do with the calculation. The same applies to tilted windows, etc.
Whether 3 air changes are sufficient is debatable. But more than 3 ventilation times is certainly unrealistic. For most people, I would even assume twice daily. See Silke ;)

But the counter calculation is still missing, what the controlled residential ventilation itself consumes.
I have googled a bit now and found values from 200 to 500 kwh/year. So even assuming 200 kwh to 500 kwh for ventilation, I would save 300 kwh, which is 60 euros per year. Economically, it would no longer pay off in my lifetime, even if electricity prices rise.