Central ventilation system - is moisture recovery necessary?

One must be allowed to question the practical relevance. I'm still interested in how the CO2 level usually looks like in old buildings.

I agree with you, but just read a few studies. The values are not pulled out of thin air (haha pun). As for old buildings... no idea, just measure at someone's place. yes, that will probably be because the recommended limit is 1500, so you don't necessarily need to know how much higher it is then. Many people also sleep with the window open because otherwise it feels too stuffy, even in old buildings. I don't like that at all, and in that respect, controlled residential ventilation is already a blessing.

Here is a graphic from 1988. It fits well with the old building.



Source:
Fig. 6: Measured carbon dioxide concentration trend over a week in the bedroom of a residential building (Mack et al. Physical Institute University of Tübingen)

The comfort limit according to DIN is exceeded by twice, the Pettenkofer recommendation even by three times.

Window ventilation is entirely the responsibility of the users. Although it could achieve sufficient air exchange, the window ventilation procedure is not practical in certain rooms and at certain times. Therefore, window ventilation is not considered a ventilation strategy for low-energy houses.

We talked about the ET yesterday at the construction meeting with the [Sanitär] and [GU]. Both are of the opinion that the ET is not necessarily needed for the new build at first because you actually want to keep the building dry. After 1-2 years, we will then consider it.

But this only applies to solid construction. It looks different again with wood.

Well, I would definitely rely on enthalpy. The hut will dry out anyway. The shock ventilators manage it, and no one can tell me that they all at least achieve the 0.3. After a few years, invest a few thousand again for another WT?

We talked about the ET at the construction meeting yesterday with the plumber and the general contractor. Both are of the opinion that the ET is not necessarily required at the new build initially, because you basically want to dry out the building first. After 1-2 years we will then consider it.

Then my experience from practice: We have now been in the house for 25 months, built solidly, with flowing screed. So already with a lot of building moisture. We have a Zehnder Q350 with ET and actually struggled with air that was too dry in the first winter. In the meantime, we have a Venta LW45 and thus relatively constant ~50% humidity.