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.