Air-to-water heat pump sizing in new construction

Well, clearly much more than the 2-3m long line from the pump to the return flow. It's only about preventing the incorrect operation of closing all ERRs, even though there may be a heating demand (heating curve), from causing a short-term compressor failure. The frequent cycling of the heat pump itself is not so bad for the heat pump; the problem is when a cycle is too short and the compressor is not lubricated.

As I understand it, the 50 liters are rather for defrosting, in case all valves are closed.

Both are correct. If only there were a way to effectively prevent all radiator valves from closing... ;-)

Very simple. Dismantle actuators in the [HKV]. Saves electricity too.

If only there were a way to effectively prevent the closing of all room heating valves and also save a lot of money... ;-)

No question, that’s how I will do it and I had also told that to the HSL. But the legislator requires ERR, Vaillant wants it that way and I will eventually be able to sell my house without having to explain why I don’t have a legally compliant heating system or why the heat pump breaks down in the first winter after the sale. Most people want to use the ERR anyway, so for now it will be installed for the DAU. How I then use it doesn’t matter. The efficiency loss should, as mentioned, be limited to the 50 liters flowing through the return.