There was a peak of 5 kW here. That supports the statement that the 2-8 kW version is more than sufficient.
That supports the statement that the 8 kW version is 40% too large. Even with domestic hot water, 5 kW will suffice on 99% of the days. And in that case, the heat pumps have an integrated 3-5 kW heating element that can provide additional heating. Those two hours per year are cheaper than running an oversized heat pump all year round. However, it is important not only to consider the maximum value but especially the minimum value (as you already recognized). At Viessmann there is also no alternative that goes below 2.1 kW. Generally, there are few options. Cycling above 5 degrees is acceptable and only possible otherwise with higher heat demand.
Does anyone have an opinion on district heating – if I decide on it, would you recommend adding a combined storage tank after the transfer station here or possibly just working with a domestic hot water storage tank? The district heating water comes in at about 70-80 degrees at the transfer station.
District heating would have the advantage, independent of the price and monopoly discussion, that you wouldn’t have to worry about your heating hydraulics and the installation spacing of your underfloor heating. If in doubt, just turn it up 2-4 degrees higher.
There are surely technical connection conditions from the provider (TABs). These usually also specify transfer stations or types. They usually specify a small buffer to reduce the connection load. Otherwise, only domestic hot water storage tanks.
For district heating, I would look into who operates it and what other networks they have, and check if I can find prices there.
There are municipal/local utility companies that have operational reliability and moderate prices as a service objective in the sense of public provision, and then there is the other kind. This can also be the case with larger operating companies, but usually the rule is: the more private, the less influence you have and the more expensive it usually gets for the customer.
Furthermore, he writes that a value of 7 kW is assumed for domestic hot water preparation.
Did he assume that as a heating engineer? On what basis? I would doubt it, but it does not matter for the heat pump choice. The minimum value should be more decisive.
Even the 2-8 version doesn’t really run efficiently at temperatures above 5 degrees, or am I mistaken?
No, you are right, it then starts cycling. But this is the case somewhere with every design. The point should just be as “warm” as possible.
In the control, you can then extend the cycling intervals afterwards by, for example, not heating at night during the transition period or setting long hysteresis times / blocking times.
