Ground source heat pump vs. air source heat pump

We are getting an air-to-water heat pump from Weishaupt with 9 KW (I think it is called WWP L9 A). I don’t know the exact price, I believe it’s around 12,000 euros. (Including storage tank and accessories for the heating system) We have a heated area of 180 sqm in the house. (Entrance hall in the basement and study room in the basement are also heated). But it doesn’t necessarily depend only on the size, but also on your heating load. So, for example, how well the walls and windows are insulated and how much energy is "lost".

It is also the case that the better insulated a building is, the less important an efficient heating system becomes. Otherwise, it is usually the case that geothermal energy is somewhat more expensive to install (depending on the source, such as drilling, collector, etc.) but cheaper to operate. For a purely financial, somewhat realistic comparison, all construction data and some lifestyle habits regarding temperature, daily bathtub use, the climate location of the building owner, and so on are needed... There is no universal answer. Then, in the end, ideological factors also come into play, for example, whether one wants to place such a large heat exchanger in the front yard or next to the terrace, and so on.

Since we are building turnkey with a GÜ, I unfortunately don't have an individual price on hand. A colleague has ground collectors and complains every spring that the snow stays on his place so long while his neighbors are already experiencing spring blooms. Since the street will be in the south, the outdoor installation can fortunately be hidden behind the house and no one will see it.

I am now also facing a decision (must be decided by Monday), air-to-water heat pump or ground-source heat pump with earth collector. The facts are as follows: €4000 (including subsidies, etc.) extra for a ground-source heat pump instead of an air-to-water heat pump, both from Nibe.

According to the annual performance factor calculator, the air-to-water heat pump should have 4.17 APF / ground-source heat pump 5.05 APF. 8kW are needed, construction project is in the region of Hesse, Rhein-Main area, Wetterau. The fan noise of the air-to-water heat pump is really tolerable, I was able to listen to it, but of course it would be very nice without it. I am now assuming savings of €200-250 per year with the ground-source heat pump compared to an air-to-water heat pump, does that sound about right?

In your opinion, is the investment worthwhile? What do you think about Nibe?

The savings depend, as written, on >10 factors. How are we supposed to say that without information? Even for the COP, the information about which temperature difference is missing. For example, my ground source heat pump has a COP of 4.98 specified at B0/35, but my brine temperature was always above 6°C over the winter, and the underfloor heating was below 30°C, so the annual performance factor exceeds 6... However, an air-water heat pump, when power is needed, also often has intake air below 0 degrees.

OK. Then please be so kind and tell me the most important factors needed to answer my question. Then I will provide them afterward, thank you.