Waste Heat Heat Pump vs. Ground Source Heat Pump

Why shouldn’t a ground-source heat pump be considered for a single-family house ... have I overlooked something significant?

Because costs and benefits are not in an attractive ratio. Those who choose a ground-source heat pump for a single-family house do so not for economic reasons, but for ecological considerations. As you have already correctly written, the performance of ground-source heat pumps and air-source heat pumps does not differ significantly – BAFA subsidies are possible for both heat generators, but the drilling risk is eliminated with the air-source heat pump. Rhineland greetings

Because costs and benefits are not in an attractive ratio. Those who choose a ground-source heat pump for a single-family house do so not for economic reasons, but for ecological considerations.

As you already correctly wrote, the performances of ground-source heat pumps and air-to-water heat pumps do not differ significantly – BAFA funding is possible for both heat generators, but the drilling risk is eliminated with the air-to-water heat pump.

Rhine regards

However, this cannot be left like that – even if it is factually correct due to a certain unintended mistake. The performance of all heat generators does not differ, as you always buy a device with suitable capacity for your construction project. The efficiency and running costs, however, are very different. Especially with air-to-water heat pumps vs. ground-source heat pumps, it very much depends on the region and the construction project. The longer/colder the winter is, the (significantly) worse an air-to-water heat pump performs compared to a ground-source heat pump. On the other hand, air-to-water heat pumps win in warm regions thanks to the lower acquisition costs. Similarly with exhaust air heat pumps, although these are much more sensitive to cold regions/too much heating load. In construction projects, it is usually the case that a ground-source heat pump becomes more worthwhile the higher the heating load – because the consumption costs are usually significantly lower than air-to-water heat pumps, so that the higher acquisition costs can then also be worthwhile. Even if you cannot always directly compare it (usage behavior etc.), our neighbors with (split) air-to-water heat pumps have had three times the electricity consumption in recent years for the same size house (if I don’t count my basement) compared to my ground-source heat pump. And the winters weren’t particularly cold.

In construction projects, it is usually the case that a brine heat pump becomes more worthwhile the greater the heating load - because the operating costs are generally significantly lower than those of an air-water heat pump, so that the higher initial costs can also pay off.

D'accord.

Even if you cannot always directly compare it (usage behavior, etc.), ...

That is why I also avoid such terrain :D Rhineland greetings

We are still undecided whether to choose a brine-water heat pump or an air-water heat pump. Of course, this depends on the costs, but the brine-water heat pump also has other advantages that are not purely ecological.

The heat pump component seems to be roughly the same price for both the brine-water heat pump and the air-water heat pump, with a slight advantage for the brine-water heat pump. This is because there is no outdoor unit, etc., which can result in price advantages. However, the drilling is of course expensive. And this becomes very individual, depending on the region, the required heating load, and thus the drilling depth, etc.
In an initial conversation with the energy consultant, it was suggested that one single borehole of 100-110m would suffice, as our heating load is not very large. Accordingly, the system can be dimensioned small. The price was estimated at 6-7k€, which would not be incurred with an air-water heat pump.
On the other hand, the brine-water heat pump is more efficient, meaning the annual costs are lower (but it is far from recovering the 6-7k€ investment). However, the brine-water heat pump is subsidized by [BAFA] (4.5k€) and the borehole ideally lasts one or several lifetimes, meaning that when a new heat generator is needed in 20-30 years, replacing the unit in a brine-water heat pump system is expected to be cheaper.
The brine-water heat pump also supports passive cooling, whereas the air-water heat pump only does so modestly. It also has the advantage of regenerating the heat source.
The brine-water heat pump does not require space for an outdoor unit. Therefore, one does not have to see or hear such a unit constantly (opinions on this do vary).
Those who implement a brine-water heat pump with a trench collector, which usually involves self-installation, can avoid drilling, spend about 2.5k€, and still receive [4k€ BAFA] — making it even profitable compared to an air-water heat pump.
Last but not least, the brine-water heat pump is also significantly (20-30%) more efficient on paper than an air-water heat pump, which is reflected in the energy demand calculations and can be helpful in meeting [KfW] standards and the like, which in turn are linked to further subsidies.

Therefore, in my opinion, the brine-water heat pump is always worth considering. It is clear that the investment is higher than for an air-water heat pump, but the brine-water heat pump offers more both functionally and non-functionally, and in the best case, it is a break-even comparison.

Get a quote for a drilling. They can also be more expensive... It is more efficient not only on paper.