Quiet decentralized ventilation for new single-family house

The heat recovery is based on a heat exchanger. This also works in reverse when it is warmer outside than inside. Then the outside air is cooled down. What is missing, however, is the bypass circuit, which ensures that cool air comes directly inside at night.[/QUOTE]

How can the bypass circuit be implemented, or is it only available in central systems?

Through insulation, a new roof or new windows and doors, the airtightness is only achieved, which could then subsequently lead to mold. This strongly limits natural infiltration.

I can briefly explain how it will be in summer...
I usually install systems in a north/south or east/west direction. This way, part of the fans is always on the cooler side. I now recommend my customers to set the system to ventilation mode in summer.
Provided the fans are correctly connected (changing the rotation direction afterwards is always possible), the fans in the north and east run permanently on supply air and those in the south and west permanently on exhaust air.
This effectively allows the heat recovery to be switched off, since a heat storage requires the change of air direction to realize heat recovery.
Of course, one should not expect air conditioning. The system cannot do that. But it is possible to lower the temperature by 1 - 3 °C in this way. Only an air conditioning unit itself can achieve better results.
I do not know how it is with central systems.

How can the bypass circuit be activated, or does it only exist in central systems?

Proper bypass circuits normally only exist in central units. In decentralized ones that recover heat through direction change, it is possible as M.O. wrote by disabling the direction change.

Only through insulation, a new roof or new windows and doors is airtightness achieved, which could subsequently lead to mold. This strongly limits natural infiltration.

Sort of, yes through a new roof, windows and doors, but insulation has nothing to do with it there. When the mentioned things are replaced, airtightness is naturally considered during implementation. New windows/doors are of course airtight, but independently of their insulation value.
Airtightness in doors/windows is achieved through seals, in the roof by vapor barrier foil, transitions by bonding etc., and in walls by the interior plaster. In the roof, insulation lies above the vapor barrier, and in the walls outside the interior plaster.

Simply replacing windows and doors, without insulating the roof and walls, already requires a change in previous ventilation behavior.

30% renewal of the window area or even just 30% insulation of the existing roof area makes it necessary to have a new ventilation concept created.

That's true, I have to agree with you so far, DerBioern... The insulation alone is not responsible for that, but the overall package.

hi everyone,

has anyone of you had any experience with the decentralized WRG of Viessmann Vitovent 200-D.
We are currently considering whether to have this installed in our new build.

Unfortunately, I have no experience with it, but I haven't heard anything good about it either. There are other decentralized systems that are better.