ᐅ Experiences with ground-source heat pumps using a borehole and water as the heat transfer medium?
Created on: 1 Feb 2023 23:05
N
NilsHolgersson
Hello everyone,
we are about to build a house (key details below). So far, a ground-to-air heat pump is planned. However, the more I read about it, the more doubtful I become whether it is the right choice: numerous reports about air-to-water heat pumps breaking down in freezing temperatures (when you actually need them), malfunctioning defrost cycles of the outdoor unit, noise emissions from the outdoor unit, and a maximum lifespan of 15-20 years.
Therefore, I am considering a ground-to-water heat pump as an alternative. Our plot is rather small, so drilling is the only option. I am aware of the disadvantages like initial and drilling costs and the requirement for a building permit/planning permission, and I accept these. In the end, I need a system that works reliably without breaking down in winter conditions (otherwise, the whole family has to wait for a week or more in a cold house until repairs are done), that operates relatively quietly, and possibly lasts a long time. A passive cooling function in summer is also attractive.
These are my considerations, now the questions:
1. Does anyone have experience with ground-to-water heat pumps with probes? Especially whether they actually work without problems?
2. The compressor would then be located in the basement along with the pump – how quiet is it?
3. Where is the drilling usually done for the probes – directly under the house or beside it? Regarding the timing – should this be completed before construction starts or can it be done in parallel next to it?
4. Approximately how long does the approval process take (possibly including water law permits)?
Key details of the house:
Thank you very much!
Best regards
Nils
we are about to build a house (key details below). So far, a ground-to-air heat pump is planned. However, the more I read about it, the more doubtful I become whether it is the right choice: numerous reports about air-to-water heat pumps breaking down in freezing temperatures (when you actually need them), malfunctioning defrost cycles of the outdoor unit, noise emissions from the outdoor unit, and a maximum lifespan of 15-20 years.
Therefore, I am considering a ground-to-water heat pump as an alternative. Our plot is rather small, so drilling is the only option. I am aware of the disadvantages like initial and drilling costs and the requirement for a building permit/planning permission, and I accept these. In the end, I need a system that works reliably without breaking down in winter conditions (otherwise, the whole family has to wait for a week or more in a cold house until repairs are done), that operates relatively quietly, and possibly lasts a long time. A passive cooling function in summer is also attractive.
These are my considerations, now the questions:
1. Does anyone have experience with ground-to-water heat pumps with probes? Especially whether they actually work without problems?
2. The compressor would then be located in the basement along with the pump – how quiet is it?
3. Where is the drilling usually done for the probes – directly under the house or beside it? Regarding the timing – should this be completed before construction starts or can it be done in parallel next to it?
4. Approximately how long does the approval process take (possibly including water law permits)?
Key details of the house:
- Semi-detached house, solid construction, not a KfW-standard house (EnEV 2016)
- Two full floors plus basement, ground floor + upper floor 68 + 68 m² (732 + 732 sq ft), plus about 30 m² (320 sq ft) of heated basement area
- Underfloor heating, controlled ventilation system (mechanical ventilation) with heat recovery and enthalpy heat exchanger
- No photovoltaic system planned primarily
Thank you very much!
Best regards
Nils
A quick question from the sidelines:
If the annual performance factor (seasonal coefficient of performance) of a ground source heat pump is 1 point higher than that of an air-to-water heat pump (median values from consumption databases: 3.82 vs. 4.72) and the cost of drilling is €8,000, doesn’t it take forever to recoup the drilling costs?
0.4€/kWh / 4.72 = 8.47 cents/kWh heating demand
0.4€/kWh / 3.82 = 10.47 cents/kWh heating demand
So the difference per kWh heating demand is €0.02.
€8,000 / €0.02 difference = 400,000 kWh heating demand before I financially benefit from the ground source heat pump. For a house with a heating demand of 15,000 kWh, it would take 26.66 years before the drilling cost is paid off.
Where is my mistake in this reasoning?
If the annual performance factor (seasonal coefficient of performance) of a ground source heat pump is 1 point higher than that of an air-to-water heat pump (median values from consumption databases: 3.82 vs. 4.72) and the cost of drilling is €8,000, doesn’t it take forever to recoup the drilling costs?
0.4€/kWh / 4.72 = 8.47 cents/kWh heating demand
0.4€/kWh / 3.82 = 10.47 cents/kWh heating demand
So the difference per kWh heating demand is €0.02.
€8,000 / €0.02 difference = 400,000 kWh heating demand before I financially benefit from the ground source heat pump. For a house with a heating demand of 15,000 kWh, it would take 26.66 years before the drilling cost is paid off.
Where is my mistake in this reasoning?
SoL schrieb:
Where is my mistake in reasoning?No external unit, no noise, possibly longer lifespan because it is not exposed to weather conditions.Michilo schrieb:
No outdoor unit, no noise, possibly longer lifespan because it is not exposed to weather conditions.Yes, I am aware of the advantages; my concern is only the financial aspect.
SoL schrieb:
Yes, I am aware of the advantages; my concern is only the financial aspect.There is a very thorough study from Switzerland on this topic:"Life Cycle Costs of Heat Pumps".
It is very helpful for this kind of question. Just search for it on Google. But be careful: the summary alone is 57 pages. So it’s more suitable for long winter evenings.
W
WilderSueden3 Feb 2023 08:54Basically, you are right. A ground-source heat pump only pays off through energy savings after a long time and in new buildings most likely not within the owner’s lifetime. The exact differences in consumption naturally also depend on the local climate. Here in Konstanz, it is always 3-4 degrees warmer than at the construction site (250 meters (820 feet) lower altitude and mild climate due to the lake), so you will probably get somewhat different values than the median. Still, we would probably have built more economically with an air-source heat pump and chose the ground-source heat pump mainly because it is the standard installed by the general contractor.
The difficulty with monetary comparisons is that you also have to consider the lifespan. If you assume the same lifespan for both options, the air-source heat pump clearly has the advantage. According to reputation, the ground-source heat pump should last significantly longer because it can operate at a relatively constant input temperature. That would be another financial advantage.
The difficulty with monetary comparisons is that you also have to consider the lifespan. If you assume the same lifespan for both options, the air-source heat pump clearly has the advantage. According to reputation, the ground-source heat pump should last significantly longer because it can operate at a relatively constant input temperature. That would be another financial advantage.
AxelH. schrieb:
There is a very good study from Switzerland on the topic:
“Life Cycle Costs of Heat Pumps.”
This is very helpful for this question. Just look it up on Google. But be careful: the summary alone is 57 pages long. That’s more for long winter evenings.Thanks, I’m reading it right now. @WilderSueden: The aspect of service life is also included there.
Thanks to all of you!
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