Heating of the supply air in the pipe

I cannot understand the comments. If you have a heat exchanger for active cooling in front and the bypass works, cool air MUST flow out. Nothing can warm up in the short pipe. We have a [LErdwärmetauscher], theoretically, cool air of 12-16 degrees should flow in during summer. The heat capacity of the air is so low that no miracles can be expected here, that is another story. But at the outlet, you must be able to measure cool air.

That's what I also thought, the supply air is at about 16 degrees after maximum cooling, at the air distributor after the bypass it reaches 17.5 degrees, and in the living room after the short double-walled pipe with about 15m3/h flow velocity it is then 23 degrees now and almost 26 degrees in summer.

If you don't want to be warm in a modern house during the summer, you install a proper air conditioner. We are not the only ones here who have done that. You could retrofit one.. definitely possible.

@TE

No, your basic understanding is wrong... the heat exchanger is primarily intended for winter to save heating energy... and that works quite well... gains of 15-20K are common there...

The bypass is then for summer but it's just a flap... the warm air from outside enters the warm system and goes through the warm house... without active cooling, nothing cooler can come out...

It is simply a ventilation system and not an air conditioning unit... the primary function is to suck out used air and provide fresh air. These systems do no more and no less.

OK, thank you very much, I really expected more, especially since even the statement from the manufacturer (Paul) of the ventilation system says that the typical warming of the supply air in the entire system up to the outlet is about 1-2 degrees. So temperatures of up to nearly 10 seem quite high to me. But if it is like that for everyone, then it seems to be part of the system.