Individual room control with air-water heat pump and underfloor heating

But that does not change the fact that the "fiddling around" is simply totally counterproductive for effective heat pump operation. After a hydraulic and thermal balancing, there is no longer any overheating.

When it comes to a cooling function, the whole thing might look different again. An ERR can certainly make sense there (whether with or without KNX is initially irrelevant)

Could you maybe say more about that? Or give me links to further literature/websites (search term)?
I am interested in the background.

What would the usage profile look like then?
In winter, everything on "manually off with power cut", as described by Michert, and in summer only the room to be cooled is turned down?
With "manually off with power cut", wouldn't the other rooms also get the cool water?

But that doesn't change the fact that the "constant adjusting" is simply totally counterproductive for an efficient heat pump operation. After a hydraulic and thermal balancing, there is no more overheating.

How do you come to that assumption? In my house, this statement definitely does not apply. As mentioned, solar gains and usage measurably warm up rooms. A thermal balancing is constant, but life is not, and neither is the weather. From my point of view, controlling here is very useful. What use are the solar gains to me otherwise if I continue to add heat through the heating? What many confuse here, I think, is that a good COP/annual performance factor is placed above everything else. But the total consumption is much more important to me, because that is what harms the environment and the wallet.

In winter, everything on "manually off" as described by Michert, and in summer only regulate down the room to be cooled?

With a heat pump with cooling function, the desire about where water should flow and where not changes twice a year. That is quite annoying manually.

Your considerations in the initial post are largely correct.

The ERR is great for old buildings with radiators to save energy. In new buildings with underfloor heating, on the other hand, it is rather rubbish.

However, it can make sense for the cooling function. However, I don't really consider the few degrees possible to be actual cooling, but at most a slight tempering. Everyone has to decide for themselves whether it is worth it.

You transport the solar gains throughout the house with a running heating system; if it is off, then not. The room overheats due to the solar gains and not because of the underfloor heating. Throttling the heat pump then doesn't help at all.

You transport the solar gains throughout the house via an operating heating system; if it's off, then not. The room overheats because of the solar gains and not because of the underfloor heating. Turning off the heat pump doesn't help at all in that case.

If the sun only falls on the floor, that might even be true, but I don't assume that.
If, on the other hand, the sun falls on walls or furniture, kitchen countertops, etc., the room would have to overheat through the supply temperature to transport heat via the underfloor heating. So that's rather nonsense.

And regarding people: while I work, I contribute 100W as a person, plus the computer and monitors.
So 300W of heating power. The underfloor heating also provides that. So if I'm not in the room, I need the underfloor heating; if I am in the room, I definitely don't need it.