KfW 55 - Ventilation system yes/no? - Experiences

I need to follow up again, this time basically regarding the ventilation system. Meanwhile, the general contractor has provided a solution in the form of a ventilation system from Alpha Innotec in combination with a heat pump from the same manufacturer.

The reason why I even want a ventilation system is, on the one hand, heat recovery in winter and, on the other hand, protection against damage caused by moisture. At some point, I asked myself what happens in summer when the outside temperature is >21°C – that is, when it is warmer outside than you want it to be inside the house. I asked the energy consultant about this, and he told me: Option A: turn off the ventilation system during the day in summer and turn it on again when you come home. Option B: keep the ventilation running and live with high temperatures inside the house.

Seriously? Especially in summer, the humidity is particularly high, so the system should ideally keep running. But you don’t want to have 30°C inside the house when it’s really hot outside… I then mentioned the keyword “ground heat exchanger.” He advised against it (condensation?), apart from the fact that it would cost a few thousand EUR more again.

How have you solved this problem?

A heat recovery system works in both directions; if the controlled residential ventilation system can do it, the outside air is cooled. However, since the temperatures inside the house rise mainly due to a lack of shading and not because of the ventilation, the effect is not as strong.

Heat recovery works in both directions; if the controlled residential ventilation system can do it, the outside air is cooled.

How so?

I think it is unavoidable that despite the bypass, one sometimes turns it off during the day and turns it on at night in summer. But since there is no experience yet, we will only know once we have moved in and the first heatwave hits us. My feeling tells me, worse than now at corresponding outside temperatures of mid-30s and an inside temperature of about 27-28: it can't get worse. Only better.

Physics. A heat exchanger works because heat flows from warm to cold. In winter, cold outside air comes in and warm air goes out, so the heat from the exhaust air flows toward the supply air. In summer, warm outside air comes in and cooler inside air goes out, so the heat from the supply air flows into the exhaust air.

Does that help much? As many often write here, I also believe that in the end only a real climate will make a difference. But as I said, we will only know when the time comes. Maybe it will work after all.