Sole-water heat pump with ground probe experiences?

Just a question from the sidelines:
If the annual performance factor of a brine heat pump is 1 higher than that of an air-to-water heat pump (consumption database median 3.82 vs. 4.72) and a drilling costs €8,000, then it takes forever to make up for the drilling cost, 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 before I am monetarily better off with the brine heat pump. For a house with a heating demand of 15,000 kWh, I would thus only break even on the drilling cost after 26.66 years?

Where is my flaw in reasoning?

Where is my mistake in thinking?

No outdoor unit, no noise, possibly longer lifespan because not exposed to the weather.

No outdoor unit, no noise, possibly longer lifespan because it is not exposed to the weather.

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

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

There is a very nice study on the topic from Switzerland: "Lebenszykluskosten von Wärmepumpen". Very helpful for this question. Just enter it in Google. But be careful: the summary alone has 57 pages. That is more for long winter evenings.

Basically, you are right. A brine-to-water heat pump only pays off through consumption very late and most likely not within a lifetime in new buildings. The exact consumption differences, of course, also depend on the local climate. Here in Konstanz, it is always 3-4 degrees warmer than at the construction site (250 meters lower altitude and mild climate due to the lake), so you certainly get somewhat different values than the median. Nevertheless, we probably would have built somewhat more economically with an air-to-water heat pump and chose the brine-to-water heat pump mainly because the general contractor installs it as standard. The difficulty with monetary comparisons is that you also have to take the lifespan into account. If you assume the same lifespan for both variants, the air-to-water heat pump is clearly advantageous. According to reputation, the brine-to-water heat pump should last significantly longer because it can be designed for a fairly constant input temperature. That would also be a monetary advantage.

There is a very nice study from Switzerland on the topic:

"Life cycle costs of heat pumps".

Very helpful for this question. Just enter it on Google. But be careful: the summary alone has 57 pages. That’s more something for long winter evenings.

Thanks, I am just reading through it.
: The aspect of lifespan is included there as well.

Thanks to you all!