Ventilation system in summer?

The figures are always "up to" because the efficiency depends on the volume flow. You can check on passiv.de, they have a nice list of devices certified by them.

So I can provide concrete values...

With a central system at ~150cbm and 30° outside temperature, I have a supply air temperature of 26°

Which is not much cooler and the house still heats up... after a week of 30° outside, the indoor temperatures also approach outside temperatures, but as I wrote at the beginning, our system runs continuously... because I prefer to sweat in fresh air... rather than have it a bit cooler with "heavy" air.

I can provide concrete values...

Sounds plausible and anyone should be able to believe you.

Maybe the only slight temperature difference reduces the heat recovery efficiency so that no longer 90% of the warm air is sent back out but only 50%? Could be an explanation for Mycraft’s observation. But it is without any evidence and stems from my spontaneous imagination.

Ultimately, we have here again personal well-being, fresh air vs. less heating.
One could also, for example, run at the lowest level during the day for the minimum air exchange, especially if you tend to stay outside in such weather anyway. And when it gets cooler in the evening, increase to level 2-3.
At least that’s how I would try it for us.

One could also, for example, run it during the day at the lowest setting for the minimum air exchange, especially if you are mostly outside anyway in this weather. And when it gets cooler in the evening, increase it to level 2-3.

However, this usually requires going to the system in the morning and evening...

P.S. now it is 28° supply air at 31° outside

P.S. now it's 28° supply air at 31° outside

Ha, here yesterday at 30° outside 20.5° supply air temp.

Geothermal heat exchanger rules....

SCNR

So we don’t have any problems with the temperature here. The annoying thing, however, is that with controlled residential ventilation you inevitably bring moisture into the house as well. The dew points are not reached in either the geothermal heat exchanger or the ventilation unit’s heat exchanger. So no water precipitates and the humidity in the house rises to values up to 55% in the basement and up to 60%.
Still okay, but borderline for me.
I’m already considering whether to build a bypass through a dehumidifier that can then run for a few hours.

Regarding the geothermal heat exchanger:
Of course you keep the controlled residential ventilation running in summer. You do bring heat into the house, but definitely less than through an open window. And at night you can still ventilate normally if you want to.

Best regards,

Andreas

At night, the bypass should ensure that cooler air is brought into the house. Enthalpy heat exchangers not only retain moisture but also limit it. Maybe that's worth another look.