Is a brine-water heat pump still worthwhile with KfW 40+?

The drilling costs are completely unclear. However, they would be crucial for a calculation. One aspect might also be that you don’t want to have the stupid split parts lying around somewhere. What about the service life? Faster amortization and faster failure does not have to be the cheaper solution.

Thank you for your answers. The estimate for drilling is around ~10000-13000€ Euro. [Ringgrabenkollektor] might possibly be an alternative. Unfortunately, I cannot answer how the lifespan is. Maybe the air heat pumps break down more often?

Question to the experts: I have always understood the efficiency calculations to assume the optimal operating condition. Now, the air-to-water heat pump loses efficiency as the outside temperature decreases, while the conditions for the brine-to-water heat pump remain fairly constant. How is this accounted for in the consumption cost calculation? I think in an area with a lot of frost, the brine-to-water heat pump will perform significantly better in terms of energy consumption despite higher construction costs – maybe that is why it is quite common in Switzerland...

How is this taken into account in the consumption cost calculation?

The temperature is considered in the annual performance factor calculator. Roughly speaking, you are right: the colder the standard and the higher the building's heating energy demand, the greater the advantage for brine.

The topic creator should rather invest their money in a properly designed underfloor heating system and a wall heating system in the bathroom. If using brine, then with a horizontal trench collector.

The temperature is taken into account in the annual performance factor calculator. Roughly speaking, you are right, the colder the standard and the higher the building's heating energy demand, the greater the advantage for brine.

The topic starter should rather invest his money in a properly designed underfloor heating and a wall heating in the bathroom. If brine, then with a horizontal trench collector.

Thank you very much. I live in the Eifel, at an altitude of 496m. So it can sometimes get very cold in winter ;) But even here temperatures below -5 degrees are very, very rare.

The most important argument for the brine-water heat pump is actually that you cannot find a suitable location for the air-water heat pump. ;-)