Air exchange rates and air quality - understanding

That should not be misunderstood, I am also very satisfied. Anything under 1000ppm is a good value and absolutely within the green range. I am only interested in the behavior of the systems and which volumes you have set.

I could also run the system permanently at level 2, it is still very quiet there. But I actually don't see the need...

The technology is now quite good if it is properly adjusted and sensors for the control system are sensibly placed. When building, I would always prioritize the following basic factors even before the technology:

[*]Rooms with large air volumes [*]natural building materials [*]Arrangement of windows and doors that allow good manual ventilation by opening them briefly

You can accept 200ppm in the indoor air if you have a plastic floor. The limit values are often a compromise between what is technically and economically desired and what is health-wise sensible. Experience shows that the limit values of yesterday are the "disasters" of today. However, we like to believe that we are safe when we orient ourselves to the limit values of "today."

You will not catch peaks like those described (two people in a small space for hours). Because the rooms cannot be controlled individually. The result would only be that the system would have to run constantly at a higher level.

Theory and practice... It works so well here that I didn't even install all the sensors as I originally intended. The system only rarely runs at full load and certainly not when there are only two people in the house. I also do not understand two people in a small space for hours as a peak but as normality, and sensors handle that very well.

In controlled residential ventilation systems without automatic room control, central sensors, in my opinion, bring little benefit.
At night in the bedroom 2000 ppm CO2, in the rest of the house 400 - the system receives 600-700 and everything is in the green zone.

We have a CO2 sensor in the bedroom and living room - it doesn’t cost much and you can objectively adjust the air quality to your needs.

In our case, the system runs at about 80% for an hour in the morning (device with 500), low during the day, and on a medium level at night.
This way, we usually have around 400-500 ppm in the house, at night it stays below 800-1000 in the bedrooms, and the air also feels good.

If you have several people visiting, you can always activate the party mode at the push of a button - or alternatively add a sensor for the system in the living room, which I have already considered - but it costs 300-400€ just to save pressing a button 2-3 times a month.

Theory and practice... It works so well here that I didn’t even have to install all the sensors as I originally intended. The system only rarely runs at full capacity and definitely not when only two people are in the house.

I also don’t consider two people in a confined space for hours as a peak, but rather as normal, and sensors handle that very well.

I hope the system never runs at full capacity; that would be neither economical nor comfortable for the occupants. The control range must of course be much narrower.

The situation with two people is actually the starting point for Bookstar. He measured in this constellation and would like to change something about the result. As Lumpi also wrote, a central measurement won’t change anything in this state because the result gets too diluted. If the entire house shows poor values, the basic setting is wrong. Leaving aside individual results like raclette with 30 people on New Year's Eve.

If you measured decentrally, as Bookstar does, the only reaction to the increased value would be to significantly increase ventilation for the entire house. Not very effective for the measured spot, uncomfortable (and unnecessary) for the whole house. Not economical either; despite heat recovery, of course heat energy is lost.

In my opinion, it is therefore important to have a suitable basic setting in the system that can be slightly and temporarily increased when needed. If even necessary at all. I have therefore had no need for it so far; the green cable is therefore unused on the system.

In my opinion, it is therefore important to have an appropriate basic setting in the system that can be easily and temporarily increased if necessary. If at all required.

Exactly. Sensors are usually used for this purpose and this works very well. The demand can then range from 0-100% without the need for the resident to perform any actions.