Sole-water heat pump with ground probe experiences?

Yes, I am aware of the advantages; I am only concerned with the monetary aspect.

If the decision is based solely on this aspect, then the gas heating is probably still the better choice.

For us, it was not necessarily the economic motives behind it, but the already mentioned potential advantages. And last but not least, of course, the electricity prices that exploded in 2021, which triggered the switch in planning from air to ground-source heat pump.

Thank you, I am currently reading through it. @WilderSueden: The aspect of lifespan is also included there.

Yes, Axel posted in while I was writing my article. However, one must also say at this point that a lot is currently happening with air-to-water heat pumps. This can have a positive effect on durability or not. The only thing that is certain is that usable figures for current models will only be available in 15-20 years.

Today I discussed the topic with our construction company (GU): the heating engineer from GU (contractor) only does it with air-water heat pumps, so a brine-water heat pump would be a self-performed task. I have now done a bit of research – there are a few companies in the region that do deep drilling/ground probes. The question is whether everything typically runs from a single source (i.e., drilling + pump installation and commissioning) or if I should look for a suitable heating engineer for that. How was it with you? Since it potentially becomes the self-performed task, it might be necessary to create few interfaces.

A question from the sidelines:
If the seasonal performance factor of a brine heat pump is 1 higher than that of an air-water heat pump (consumption database median 3.82 vs. 4.72) and a borehole costs €8,000, then it takes ages to recoup the cost of the borehole, right?

€0.4/kWh / 4.72 = 8.47 ct/kWh heating demand
€0.4/kWh / 3.82 = 10.47 ct/kWh heating demand

Thus, the difference per kWh heating demand is €0.02.

€8,000 / €0.02 difference = 400,000 kWh heating demand until I am monetarily better off with the brine heat pump. For a house with a heating demand of 15,000 kWh, it would take 26.66 years for the borehole to have paid off?

Where is my thinking wrong?

In new builds, the expensive part is not the consumption, but the system or investment costs.
And this also explains the financial advantage compared to the air-water heat pump. If the air-water heat pump breaks down, you purchase a heat source (the outdoor unit) again in the second investment cycle, whereas the borehole outlasts a human lifetime. Especially with air-water heat pumps with an outdoor unit, it is also likely that these could cause premature failure of the heating system (weather exposure, mechanical parts) and thus incur repair costs. The borehole as a heat source is virtually maintenance-free.
Possibly, the borehole is also eligible for subsidies. Of course, that is an "artificial" factor, but my brine-water heat pump cost only €1-2k more in total than an air-water heat pump.

Today I discussed the topic with our construction company (general contractor): the heating installer from the GC (contract partner) only does air-water heat pumps, so brine-water heat pump would have to be done as own work. I have now done a bit of research – there are a few companies in the region that do deep drilling/ground probes. The question is whether everything typically runs from a single source (i.e., drilling + pump installation and commissioning) or if I should look for a suitable heating installer separately. How was it with you guys?
Since it will potentially be own work, maybe fewer interfaces need to be created.

My personal experience is that heating installers can indeed offer "complete" solutions, but due to lack of detailed calculations in the offer phase, they do so in a lump sum manner or with safety factors. By splitting the trades of drilling and heat pump, I saved several thousand euros.
The coordination effort was not a big deal because the transfer point is easy to define. The driller creates the probe, leads it into the house and hands it over at a shut-off valve. He also delivers the brine mixture and fills it up to the shut-off valve. The heating installer connects there and fills the rest of the system.
The heating load is calculated by the heating installer, who then deduces the drilling depth in consultation with the driller based on geological conditions (=heat extraction rate per meter).

I also advocate for one borehole >100m instead of several. Saves material, time, and above all drilling meters and thus your money. The application process takes longer, though.

By the way, the clay that you might have confirmed from your soil report (which checked 2-7m deep) does not play a relevant role in a probe borehole. The extraction rate per drilling meter increases with depth, so the near-surface drilling meters are insignificant for the extraction capacity of the entire probe anyway.

Today I discussed the topic with our construction company (GU): the heating engineer from GU (contractor) only does it with an air-water heat pump, so a brine-water heat pump would be a self-performed task. I have done a little research - there are a few companies in the region that do deep drilling/ground probes. The question is whether it is typically all handled from one source (i.e. drilling + pump installation and commissioning) or if I should look for a suitable heating engineer for that. How was it with you? Since it will potentially be self-performed, you might have to create few interfaces.

Rather uncommon - drilling contractors are highly specialized. They usually deliver everything up to the interface shut-off valve/distributor brine line (either inside or outside, depending), including filling with brine. After that, it is the heating engineer’s business (who can in turn offer everything as a package, with the drilling company then acting as a subcontractor).

You definitely have to think carefully regarding the heat pump as a self-performed task - very, very few heating engineers do only "heat pumps". Usually, they also want to implement all other related trades (underfloor heating, ventilation, possibly DHW/air conditioning).

The question is whether everything typically comes from one source (i.e. drilling + pump installation and commissioning) or if I should look for a suitable heating engineer for that. How was it with you?

We had the drilling company for the probe. Then the general contractor came with the mini excavator, exposed the brine hose, and brought it into the technical room via core drilling. Now the heating and sanitary installer will come and install the rest from the brine connection.