ᐅ Experiences with ground-source heat pumps using a borehole and water as the heat transfer medium?
Created on: 1 Feb 2023 23:05
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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
SoL schrieb:
Yes, I am aware of the advantages; for me, it’s only about the financial aspect.If the decision is based solely on this aspect, then a gas heating system is probably still the better option.In our case, the reasons were not necessarily economic, but rather the potential benefits mentioned above. And, not least, the electricity prices that skyrocketed in 2021, which led to the change in planning from an air-source to a ground-source heat pump.
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WilderSueden3 Feb 2023 09:24SoL schrieb:
Thanks, I’m just reading through it now.
@WilderSueden: The aspect of service life is included there as well. Yes, Axel replied to me while I was writing my article. At the same time, it’s worth noting that there is currently a lot of development happening in air-to-water heat pumps. This could have a positive effect on their durability, or it might not. The only certainty is that reliable data on current models will only be available in 15 to 20 years.
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NilsHolgersson3 Feb 2023 15:20Today I discussed the topic with our general contractor (GC): the heating engineer from the GC (contractual partner) only works with air-to-water heat pumps, so a ground-source heat pump would be a self-performed task. I have done a bit of research – there are a few companies in the region that carry out deep drilling/ground probes. The question is whether this is typically handled by one company (i.e., drilling plus pump installation and commissioning) or if I should look for a specialized heating engineer for that. How was it in your experience?
Since this will potentially be a self-performed task, it might be necessary to minimize the number of interfaces.
Since this will potentially be a self-performed task, it might be necessary to minimize the number of interfaces.
SoL schrieb:
A quick question from the side:
If the annual performance factor (COP) of a geothermal heat pump (ground source heat pump) is 1 point higher than that of an air-to-water heat pump (median values from consumption database: 3.82 vs. 4.72) and drilling costs are around €8,000, doesn't it take ages to recoup the drilling costs?
€0.4/kWh / 4.72 = 8.47 cents per kWh heating demand
€0.4/kWh / 3.82 = 10.47 cents per kWh heating demand
So the difference per kWh heating demand is €0.02.
€8,000 / €0.02 difference = 400,000 kWh heating demand before a geothermal heat pump is financially better. For a house with a heating demand of 15,000 kWh, it would take 26.66 years before the drilling cost is amortized?
Where am I wrong? In new construction, the expensive part is not the energy consumption but rather the system and investment costs.
This also explains the financial advantage compared to an air-to-water heat pump. If the air-to-water heat pump breaks down, you will buy a new heat source (the outdoor unit) in the next investment cycle. In contrast, the borehole lasts a lifetime. Especially with air-to-water heat pumps that have an outdoor unit, there is a high chance these components cause premature system failure (due to weather exposure, mechanical parts), leading to repair costs. The borehole as a heat source is virtually maintenance-free.
The borehole may also be eligible for subsidies. This is, of course, an "artificial" factor, but overall my geothermal heat pump cost only about €1,000-2,000 more than an air-to-water heat pump.
NilsHolgersson schrieb:
Today I discussed the topic with our general contractor (GC): the heating engineer hired by the GC only works with air-to-water heat pumps, so installing a geothermal heat pump would be a DIY effort. I did some research—there are a few companies in the region that do deep drilling/ground probes. The question is whether this is typically handled by one provider (drilling + pump installation and commissioning), or should I find a suitable heating engineer separately? How was it for you?
Since this might be a DIY job, minimizing interface points might be important. My personal experience is that heating engineers can offer a "complete" package, but during the offer phase they often use rough estimates or safety margins because they don’t perform detailed calculations. By separating drilling and heat pump installation, I saved several thousand euros.
The coordination effort was minimal since the handover point is clearly defined. The driller installs the probe, brings it into the building, and hands over at a shut-off valve. The driller also supplies the brine solution and fills it up to the shut-off valve. The heating engineer connects from there and fills the rest of the system.
The heating load is calculated by the heating engineer. Based on this and geological conditions (heat extraction rate per meter), the driller determines the depth of the borehole.
I also recommend a single borehole deeper than 100 meters (330 feet) rather than multiple shallower ones. This saves material, time, and especially drilling meters — meaning less cost for you. However, the permit approval process takes longer.
By the way, the clay layer that your soil report may show (typically tested down to 2–7 meters [7–23 feet]) does not play a relevant role for borehole probes. The heat extraction per meter increases with depth, so the upper few meters near the surface have little impact on the total heat extraction capacity of the probe.
Today I discussed the topic with our general contractor (GC): the GC’s heating engineer (contractor) only installs air-to-water heat pumps, so a ground source heat pump would be considered self-installation. I have done some research—there are a few companies in the region that perform deep drilling/ground probes. The question is whether everything typically comes from a single source (i.e., drilling plus pump installation and commissioning) or if I should look for a suitable heating engineer separately. How was it for you?
Since it might be self-installation, it may be necessary to minimize the interfaces.This is rather uncommon—drilling contractors are highly specialized. They usually deliver everything up to the shut-off valve/distributor for the brine circuit (either inside or outside, depending on the setup), including filling the brine. After that, it is the heating specialist’s responsibility (who can also offer the entire package and then subcontract the drilling company).
You definitely need to think carefully about the heat pump as self-installation—very, very few heating specialists handle only heat pumps. Usually, they also want to manage other related trades (underfloor heating, ventilation, possibly domestic hot water/air-to-water systems).
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WilderSueden3 Feb 2023 15:55NilsHolgersson schrieb:
The question is whether everything is usually handled by one contractor (that is, drilling plus pump installation and commissioning) or if I should look for a suitable heating specialist separately. How was it for you? We hired the drilling company for the borehole. Then the general contractor came with a mini excavator, exposed the brine pipe, and brought it into the utility room using core drilling. Now the heating and plumbing installer will come and complete the installation from the brine connection.
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