Ventilation system in the warm summer

And I am destroying the environment with my gas heating... yeah yeah

And I destroy the environment with my gas heating... yeah yeah

That is correct.

I cool exclusively with photovoltaic electricity.
Since I have a KFW40+ house, I am "affected" by the 60% curtailment.
That means I can use the other 40% for free or it is not generated at all.

Any combustion (whether oil, gas, or wood) for heating in newly built residential buildings is absolutely nonsensical and definitely disproportionately destroys the environment. This has nothing to do with air conditioning.

As I wrote above, I take pure photovoltaic operation even a step further, i.e. I actively control the heat pump depending on the weather forecast, photovoltaic power reserve, and photovoltaic power forecast.

Oh yes: For seasonal storage systems, cooling in summer is even strongly recommended. Unfortunately, it often happens that people think they save electricity in summer by turning off the air conditioner. Well, then the solar thermal system does not provide enough, in autumn the storage is far too cold, and in winter the heating element burns continuously.

Technically, all heat pumps should be capable of cooling because they also need to be able to defrost. Unfortunately, not all manufacturers implement this or they charge extra for licenses. The regulation is rather more problematic.

Could you please explain that in more detail? For example, I'm getting a Daikin Altherma 3, but how does it look there?

In the 3M I read "Heating and Cooling". but: it must of course also be installed accordingly. So you need the controller, the additional sensor for condensation, and the cooling-capable room thermostats. It also has to be set up and configured – and that is not exactly trivial, the manufacturer technician has already been on site three times because the switch between summer and winter operation did not work automatically.

Cooling or at most buffering via the floor has many disadvantages. Cold feet, cold stays at the bottom, dew point no dehumidification, etc. Better to have a proper air conditioning system. Better controllable, dehumidification, cooling is properly distributed, powerful… You cannot effectively cool through a normally sized [Kontrollierte-Wohnraumlüftung]. It has to be significantly larger dimensioned. Chiller, refrigeration machine with buffer. Uncommon in single-family houses. We have something like that. The waste heat goes into the pool.