ᐅ Comparison of Geothermal Heat Pump and Air-to-Water Heat Pump

I would have preferred to use a brine-water heat pump, but it is not possible in my case due to the drinking water protection area.

T_im_Norden schrieb:

And?
For all heat pumps, the efficiency decreases as the temperature drops.

The key factor for funding is the result given by the annual performance factor calculator.

Yes, that’s how it is.

Sorry if it was unclear that I was referring to the value from the annual performance factor calculator. That’s what counts for the BAFA subsidy.

I would have preferred a ground source heat pump (e.g., with a horizontal trench collector). But when you subtract the house from a small plot, then the terrace and driveway, and also consider the required setback distances... at best and with a lot of luck, only vertical installation remains. Or a borehole. Both options are not ideal and are again complicated and expensive.

guckuck2 schrieb:

Yep. However, you can use heat sources that are less affected by seasonal variations. These tend to be the least efficient exactly when they are most needed. But this depends on the region and the winter conditions.

Our assumption was that the issue of especially cold days will likely become less significant in the coming decades. Looking at global climate trends, truly cold winters in our North Sea region are expected to decrease rather than increase, with temperatures around 0°C (32°F) in the coldest months becoming more likely than deep subzero temperatures.

T_im_Norden schrieb:

So?
With all heat pumps, the efficiency decreases as it gets colder.

Not exactly. The discussion here is about air-to-water heat pumps versus ground-to-water heat pumps, and with ground-to-water heat pumps, the ground temperature is largely independent of the outside air temperature.

kati1337 schrieb:

Our assumption was that the issue with exceptionally cold days will likely diminish over the coming decades. Considering global climate trends, really cold winters here by the North Sea will probably become less frequent rather than more, and temperatures around 0°C (32°F) in the coldest months seem more likely than deep subzero temperatures.

That may be true, although my understanding is that climate change mainly means more extreme weather. So both extremes are expected to increase.
In fact, the last winters have been very mild (NRW), so my consumption example was based on a mild winter. That means if it gets colder, the load on a ground-source heat pump will be even higher.

The COP of an air-to-water heat pump in January with 3.5 was already chosen by me in favor of the air-to-water system. In a truly cold winter month, which we haven’t seen here for a long time, that value is probably just wishful thinking. Even for the newest air-to-water heat pumps, which are more efficient according to their specifications.

HAL06120 schrieb:

Not at all. The discussion here is about air-to-water heat pumps versus ground-source heat pumps, and for ground-source heat pumps, the ground temperature is largely independent of the outside air temperature.

Well, it does change by a few degrees throughout the year, and also within the heating season.
At the start of winter or the heating period, the ground source flow temperature is a few degrees higher than at the end of the heating season. In my case, we’re talking about roughly 9°C (48°F) at the beginning and 5°C (41°F) at the end of the heating period.

guckuck2 schrieb:

COP and calculated annual performance factor are theoretical values. The fact is, they are constantly improving, at least in the lab. Practical results are yet to be seen since the models are quite new.
Perhaps it is time for BAFA to adjust its criteria.

Yes. However, you can use heat sources that are less affected by seasonal fluctuations. These tend to be least efficient precisely when they are needed the most. But that depends on the region and the winter conditions.

During the last heating season, January 2020 was the month when we consumed the most heat energy at home: 1641 kWh of heat including hot water. With a seasonal performance factor (including pumps and controls) of 4.69, corresponding to 350 kWh of electricity.
If I consider that a common air-to-water heat pump might have achieved about 3.5 in that period, that would have meant over $30 more in electricity costs to heat the house that month. And we had five such months this season...

In the last calendar year, I kept a four-person household with about 200sqm (2150 sq ft) warm, including hot water, using 2200 kWh of electricity. That corresponds to roughly €572 per year, or about €48 per month, using regular household electricity rates (no heat pump tariff). This is not entirely accurate, since part of the consumption comes from my own photovoltaic system, so the actual energy costs are even lower. Maintenance costs are zero.

I am therefore still very satisfied with a ground-source heat pump using drilling.

For the sake of completeness: How much did the drilling cost you? If there are actually €150 (about $150) in additional annual expenses, one could make a sample calculation.