Newly built single-family house KfW55 standard - How to heat?

Then your heating design is simply shit. Sorry for the harsh words. The consumption is a total disaster. I currently have such costs per square meter in my 60s apartment with normal radiators.

So you are welcome to express your subjective opinion, I have no problem with that. For 210m2 of heated space (including basement) that is not a bad value according to forums, acquaintances, and heat pump database. Where exactly the disaster should be is a mystery to me. A brine system unfortunately only pays off after 25 years. That's why they are so rare in new housing developments.

If at all possible and also really really planned and executed correctly, then definitely preferable to an air-water heat pump or air-air heat pump.

The question was whether it is worthwhile. You can estimate. The additional investment minus higher subsidies. Then calculate how much more electricity the air-water heat pump will consume compared to the ground-water heat pump. Then you know after how many years you have saved the additional investment. You could still save with the ground-water heat pump option if you install a horizontal trench collector yourself instead of drilling boreholes.

We have a brine-water heat pump instead of an air-water heat pump in our offer. Costs about €7,500. Does anyone have experience with a brine-water heat pump? It is supposed to be drilled 2x 90m deep. The question is whether the additional costs pay off? For me, still a layman, it seems logical that it is better to transport heat from the ground than from the air, especially in the winter months.

It is not worthwhile. If I take our house, kfw55 with an air-water heat pump, I could save about 400 kWh of electricity per year with a well-running brine-water heat pump – currently about €80-100 per year considering photovoltaics, ergo 70-100 years until amortization (calculated without interest, without subsidies).

Doesn't pay off. If I take our house, kfw55 with air-to-water heat pump, I could save about 400 kWh of electricity per year with a well-running ground-to-water heat pump - currently about 80-100€ per year considering photovoltaics, so 70-100 years until amortization (calculated without interest, without subsidies).

Good, thanks. Then the question about air-to-water heat pumps. Is it better to have an outdoor "fan" or can it also be inside in the utility room? And is the thing inside the house noisy?

Good, thanks. Then the question about air-to-water heat pumps. Preferably with an external "fan" or can it also be placed inside the utility room? And is the thing that stands inside the house loud?

Placement as desired. Just not in the living room. I have one for indoor installation. The utility room is located directly next to the living room, the children's room directly above. We do not hear it in our timber-framed house (only in the utility room can it be heard).
The selection of units for indoor installation is smaller, also regarding performance classes.

Always keep in mind that sound is not calculable and difficult to predict. If you are sensitive to it, you should definitely avoid an indoor installation. It can go well like with Daniel, but what do you do if there is a buzzing etc. in the house? Then it gets really expensive...