Air too dry! - Replace old ventilation with enthalpy ventilation?

That's funny. For comfort, I open a window anytime - no matter what the heating cost.

It's no secret that a controlled residential ventilation system dries out the air. If everything works correctly (and is properly planned = enthalpy heat exchanger), then I don't need to open windows.
But if I have to ventilate with windows anyway (for whatever reason), then I could have done without the controlled residential ventilation system.
It's not about 50€ heating costs, but about the technical equipment.

I would first check the settings of the controlled residential ventilation system. Do I need powerful ventilation everywhere, or is a normal level enough? So possibly measure CO2, use pure basic ventilation, adjust volumes overall. 20-25% in winter is not quite easy to achieve. So far, with both central and decentral systems, I have had difficulties getting below 40% (in winter).

But there is also a mistake in reasoning. It is not the ventilation system that makes the nicely humid outside air dry due to some magical technology, but in winter the outside air is already dry (cold air holds less water) and is warmed up inside, causing the relative humidity (inside) to decrease. Normally, one only ventilates with windows much less frequently in winter, so the humid exhaled air can keep the humidity level high. Therefore, more window ventilation will only be beneficial in appropriately humid and not too cold weather, but precisely then the air will not become so dry even with controlled residential ventilation.

We still have the problem. We have a wgt400 from Schwörerhaus, which is identical to vallox or maico. I wanted to retrofit it all the time, but reducing the ventilation to level 1 at night helps a lot, so I measured 34-36% humidity. From 7 a.m. it automatically goes back to level 2.

From 7 o'clock it then automatically goes to level 2.

Depending on the life situation - not at home because of work / school - you can of course also adjust the schedule

We do not get below 42% with the enthalpy exchanger in the coldest winter. The trick is, in the laundry room we deliberately bought a heat pump dryer which runs quite frequently with 2 children. There is an extraction of the controlled residential ventilation in the laundry room. The very humid air transfers enough moisture to the dry outside air (supply air). Of course, we throttle the performance of the controlled residential ventilation to about 15%. But the ventilation runs 24/7. We never get the feeling that it does not bring in enough fresh air. 20% would not be pleasant for the mucous membranes and co. over the long term.

A moisture-stabilizing effect is also achieved with clay plaster. With a layer of only 2.5-3mm, in "typical" rooms, the plaster achieves a capacity to absorb moisture that is approximately equal to the maximum moisture absorption capacity of the air volume at room temperature - (in a 25sqm room this is about 800g of water vapor). Below 50%, the clay plaster releases moisture; above 55%, it absorbs moisture. The further the relative humidity deviates from the "neutral range," the faster this process occurs. The quite favorable ratio of about 1:1 (room air and moisture storage) may surprise some, but it can be calculated. Of course, this does not help against complete drying out of a room caused by a possibly unfavorably set controlled residential ventilation, but it is likely to have a distinctly pleasant balancing effect. Unfortunately, it is not a cheap measure to add afterwards.