Hello everyone,
I have a small problem and would like your opinion.
House details:
Semi-detached house with four occupants
142 m² (1,528 sq ft) living area
335 m² (3,606 sq ft) plot size
140 m² (1,507 sq ft) usable area for ground baskets
Solid clay soil
We hired a construction company to build our semi-detached house. We bought the house with KfW 70 standard, underfloor heating, and a ground source heat pump, for which I pay an additional €15,000.
They initially told us that they would try to install the heating system using a deep borehole and probe, but they weren’t sure if that would work because we are building in an area where drilling permits are most likely not granted, as it is part of the Carolinen Brunnen water protection zone. However, they said using ground baskets would be 100% certain, and those would be installed instead of drilling.
It turned out that drilling is not allowed, so 19 ground baskets with a diameter of 45 cm (18 inches), which the heating installer produces himself, are to be installed at a depth of 6 m (20 ft) with a spacing of 3 m (10 ft).
The air-to-water heat pump was supposed to be:
Viessmann Vitocal 300-G, BWC 6 kW
Now, while excavating the basement, they found a layer of shale stone at about 3 m (10 ft) depth, and suddenly they say they cannot drill into this layer. The heating engineer told me today that he wants to discuss the option of an air-to-water heat pump instead, to see if it might be suitable for us.
He said he would choose the market leader for air-to-water heat pumps, which is:
Mitsubishi Zubadan PUHZ-HRP71VHA2 8.1 kW
Additionally, I would pay €2,000 less for the heating system.
He also explained that the air-to-water heat pump is, compared to the ground source pump, more efficient because it can operate down to –20°C (–4°F) without needing an electric heating element. The ground source heat pump, on the other hand, was not sufficient during freezing temperatures like we had last year, and then the electric heating element has to kick in, which can cost several hundred euros over a two-month frost period in winter.
He also calculated that, with an annual heat demand of 15,000 kWh and an electricity price of about €0.15/kWh, I would pay approximately €600 per year for the ground source heat pump and about €780 for the air-to-water heat pump. Compared to gas heating at around €1,200, this is still a saving.
So much for the background, and now my questions:
Thanks a lot!
dimah
I have a small problem and would like your opinion.
House details:
Semi-detached house with four occupants
142 m² (1,528 sq ft) living area
335 m² (3,606 sq ft) plot size
140 m² (1,507 sq ft) usable area for ground baskets
Solid clay soil
We hired a construction company to build our semi-detached house. We bought the house with KfW 70 standard, underfloor heating, and a ground source heat pump, for which I pay an additional €15,000.
They initially told us that they would try to install the heating system using a deep borehole and probe, but they weren’t sure if that would work because we are building in an area where drilling permits are most likely not granted, as it is part of the Carolinen Brunnen water protection zone. However, they said using ground baskets would be 100% certain, and those would be installed instead of drilling.
It turned out that drilling is not allowed, so 19 ground baskets with a diameter of 45 cm (18 inches), which the heating installer produces himself, are to be installed at a depth of 6 m (20 ft) with a spacing of 3 m (10 ft).
The air-to-water heat pump was supposed to be:
Viessmann Vitocal 300-G, BWC 6 kW
Now, while excavating the basement, they found a layer of shale stone at about 3 m (10 ft) depth, and suddenly they say they cannot drill into this layer. The heating engineer told me today that he wants to discuss the option of an air-to-water heat pump instead, to see if it might be suitable for us.
He said he would choose the market leader for air-to-water heat pumps, which is:
Mitsubishi Zubadan PUHZ-HRP71VHA2 8.1 kW
Additionally, I would pay €2,000 less for the heating system.
He also explained that the air-to-water heat pump is, compared to the ground source pump, more efficient because it can operate down to –20°C (–4°F) without needing an electric heating element. The ground source heat pump, on the other hand, was not sufficient during freezing temperatures like we had last year, and then the electric heating element has to kick in, which can cost several hundred euros over a two-month frost period in winter.
He also calculated that, with an annual heat demand of 15,000 kWh and an electricity price of about €0.15/kWh, I would pay approximately €600 per year for the ground source heat pump and about €780 for the air-to-water heat pump. Compared to gas heating at around €1,200, this is still a saving.
So much for the background, and now my questions:
- Is the cost difference of €600 versus €720 plausible?
- Does anyone know the Mitsubishi air-to-water heat pump and, especially, how is the noise level? The heating installer told me it is not disturbing if the unit is installed outside. I have triple glazing and so on but am not sure if the unit is loud because I have read differing opinions online.
- Is the pump really powerful enough to operate reliably down to –20°C (–4°F) without issues?
- Would you accept the deal with the €2,000 discount, or do you think it’s possible to negotiate a better deal with the company?
Thanks a lot!
dimah
Since I assumed that the technical terminology would be used correctly in this forum, here is a clarification of the term "heat demand" (not "energy"):
Heat demand (Qa in kW) = Living area: A (in sqm) * specific heat demand QH (in kW/sqm) = kW
(as of today, however, as Mr. € pointed out, it actually refers to heat (?) in kWh).
To calculate the annual performance factor, it is advisable to use a calculation based on the COP of the cooling system, but this is where the difference between amateurs and professionals becomes apparent.
With this, I say goodbye to this discussion with a smile, knowing that for the repair of the heat pump’s refrigeration circuit, once again a "layman" (refrigeration technician) will be called in to fix the system ... because he knows how to do it.
Heat demand (Qa in kW) = Living area: A (in sqm) * specific heat demand QH (in kW/sqm) = kW
(as of today, however, as Mr. € pointed out, it actually refers to heat (?) in kWh).
To calculate the annual performance factor, it is advisable to use a calculation based on the COP of the cooling system, but this is where the difference between amateurs and professionals becomes apparent.
With this, I say goodbye to this discussion with a smile, knowing that for the repair of the heat pump’s refrigeration circuit, once again a "layman" (refrigeration technician) will be called in to fix the system ... because he knows how to do it.
omlo schrieb:
Since I assumed that the technical terminology is used correctly in this forum, here is again the definition of the term "heat demand" (not "energy"):
Heat demand (Qa in kW) = living area: A (in m² (square meters)) * specific heat demand QH (in kW/m² (kW per square meter)) = kW It should be well known to a professional by now that the incorrect term "heat demand" (DIN 4701) has been replaced for years by the precise term "design heating load" = power (DIN 12831) ;-)
Best regards
Hello, regarding the additional price of 15,000 EUR you mentioned for a ground source heat pump, this is generally in line with what we have been quoted by construction companies.
1. If you calculate a demand of 15,000 kWh, with 600 EUR at 15 cents per kWh, the annual performance factor (COP) for the ground source heat pump would be 3.75 and for the air source heat pump 3.125. This is basically within a realistic range. However, I would expect a ground source heat pump with probes to have a significantly higher performance factor. Also, this electricity price assumes special heat pump tariffs. In our area, heat pump electricity costs over 17 cents plus around 55 EUR extra annual base fee, and it is definitely not green energy.
2. In the municipality where we are buying our plot (the house is still in planning), you cannot just install an air source heat pump. This also involves consideration of how much the noise might disturb the neighbors.
3. No. An air source heat pump is completely inefficient at -20°C ( -4°F) outside temperature. Additionally, with a heat pump using ground probes, the temperature at the depth where the heat is extracted remains constant throughout the year. In Berlin, this zone is at about 20 to 30 meters (65 to 100 feet) deep. From there down, the temperature remains constant year-round and even increases slightly with greater depth. So, for the ground source heat pump, it doesn’t really matter if it is -20°C or +20°C (68°F) above ground.
4. Basically, he is not wrong when he says there is slate and does not recommend probes. Drilling would be very expensive here. According to the conversations we have had so far, an air source heat pump is more than 10,000 EUR cheaper than a drilled ground source system. Since drilling was not planned here, the extra 2,000 EUR could be reasonable. I can’t really judge that.
Depending on the region where you live (we want to build near Berlin), I would never install an air source heat pump because they become extremely inefficient at sub-zero temperatures, which is precisely when you need heating the most (who actually heats in summer?).
However, the ground source heat pump also becomes less attractive in our current planning. We want to build sustainably and environmentally friendly, but not at the expense of living quality. In other words, if we invest huge amounts of money in ecological solutions, there will be no money left for, for example, a nice kitchen. We are not that "eco" after all.
Assuming the stated 600 EUR for the ground source heat pump compared to 1,200 EUR for gas is correct, then with extra costs of 15,000 EUR you get a simple payback period of 25 years! This, in a simplified way, assumes gas and electricity prices rise equally. But electricity (which powers the heat pump and is only needed in small amounts by a condensing boiler) has increased significantly more. You can also be environmentally friendly with gas, after all, there are plenty of biogas providers as well as green electricity suppliers. Our current consideration is therefore leaning towards a condensing boiler as backup combined with a large solar system with a very large storage tank.
P.S. Why do I only focus on drilling above? In my opinion, investing in a ground source heat pump only pays off if you can drill deep because otherwise the advantages are lost and the investment costs remain much higher than for an air source heat pump. At a depth of 6 meters (20 feet), it is also colder in winter, making the heat pump less efficient than it could be.
1. If you calculate a demand of 15,000 kWh, with 600 EUR at 15 cents per kWh, the annual performance factor (COP) for the ground source heat pump would be 3.75 and for the air source heat pump 3.125. This is basically within a realistic range. However, I would expect a ground source heat pump with probes to have a significantly higher performance factor. Also, this electricity price assumes special heat pump tariffs. In our area, heat pump electricity costs over 17 cents plus around 55 EUR extra annual base fee, and it is definitely not green energy.
2. In the municipality where we are buying our plot (the house is still in planning), you cannot just install an air source heat pump. This also involves consideration of how much the noise might disturb the neighbors.
3. No. An air source heat pump is completely inefficient at -20°C ( -4°F) outside temperature. Additionally, with a heat pump using ground probes, the temperature at the depth where the heat is extracted remains constant throughout the year. In Berlin, this zone is at about 20 to 30 meters (65 to 100 feet) deep. From there down, the temperature remains constant year-round and even increases slightly with greater depth. So, for the ground source heat pump, it doesn’t really matter if it is -20°C or +20°C (68°F) above ground.
4. Basically, he is not wrong when he says there is slate and does not recommend probes. Drilling would be very expensive here. According to the conversations we have had so far, an air source heat pump is more than 10,000 EUR cheaper than a drilled ground source system. Since drilling was not planned here, the extra 2,000 EUR could be reasonable. I can’t really judge that.
Depending on the region where you live (we want to build near Berlin), I would never install an air source heat pump because they become extremely inefficient at sub-zero temperatures, which is precisely when you need heating the most (who actually heats in summer?).
However, the ground source heat pump also becomes less attractive in our current planning. We want to build sustainably and environmentally friendly, but not at the expense of living quality. In other words, if we invest huge amounts of money in ecological solutions, there will be no money left for, for example, a nice kitchen. We are not that "eco" after all.
Assuming the stated 600 EUR for the ground source heat pump compared to 1,200 EUR for gas is correct, then with extra costs of 15,000 EUR you get a simple payback period of 25 years! This, in a simplified way, assumes gas and electricity prices rise equally. But electricity (which powers the heat pump and is only needed in small amounts by a condensing boiler) has increased significantly more. You can also be environmentally friendly with gas, after all, there are plenty of biogas providers as well as green electricity suppliers. Our current consideration is therefore leaning towards a condensing boiler as backup combined with a large solar system with a very large storage tank.
P.S. Why do I only focus on drilling above? In my opinion, investing in a ground source heat pump only pays off if you can drill deep because otherwise the advantages are lost and the investment costs remain much higher than for an air source heat pump. At a depth of 6 meters (20 feet), it is also colder in winter, making the heat pump less efficient than it could be.
Hello,
Best regards
P.S. Generally: the higher the actual demand for heating/domestic hot water, the greater the requirements for the efficiency of the technical solution!
Chris82 schrieb:The achievable annual performance factor of heat pumps depends on the boundary conditions of the individual building project, not on self-imposed or wished-for values ;-)
....Regarding point 1. If you calculate with a demand of 15,000 kWh, for the ground-source heat pump at 600 EUR with 15 cents per kWh, an annual performance factor of 3.75 would result, and for the air-source heat pump, 3.125.
Chris82 schrieb:That is a very one-sided view. The electric backup heater share of well-designed air-source heat pump systems accounts for only about 0.2 up to a maximum of 2% of the annual heating demand. Mostly negligible compared to the remaining 99.8% or 98%! ;-)
....Regarding point 3. No. An air-source heat pump is completely inefficient at -20 °C (−4 °F) outdoor temperature.
Chris82 schrieb:In milder climate locations, shallow horizontal trench collectors are advantageous because they benefit more from solar radiation effects than one or more expensive vertical boreholes, which can hardly or only minimally participate in this.
....In addition, for a heat pump with boreholes, the temperature at the depth where the heat is extracted remains constant year-round.
Chris82 schrieb:That is a misconception, especially if you completely ignore the annual balance!
...Depending on the region where you live (we want to build near Berlin), I would never install an air-source heat pump because they become extremely inefficient at sub-zero temperatures, and that is exactly when you need them (who heats in summer anyway).
Chris82 schrieb:If a gas condensing boiler is chosen, I would advise against a solar thermal system (the 15% rule). Solar thermal systems are hardly economically viable for a "standard" single-family house. If you disagree, have a heat meter installed and compare the "actual yield" with the additional investment—then report here on the "success" of the measure! ;-)
...Our current consideration is therefore in the direction of a condensing boiler for backup and a large solar system with a very large storage tank.
Chris82 schrieb:Completely wrong! Horizontal trench collectors, whether narrow or wide design, can be implemented cost-effectively (with a high share of self-performed work possible). Any lower efficiency is usually more than compensated for by the significantly lower investment costs.
...In my opinion, investing in a ground-source heat pump only makes sense if you can drill deep ...
Best regards
P.S. Generally: the higher the actual demand for heating/domestic hot water, the greater the requirements for the efficiency of the technical solution!
There are more factors to consider with trench collectors than just the cost savings compared to deep drilling when looking at the initial installation expenses. First of all, you need a sufficiently large plot of land. Large plots are naturally more expensive, and you probably wouldn’t buy a bigger property just because of a shallow collector (which would mean exorbitant extra costs). If you do have a large plot, it must be free of trees. You can’t install a collector under tree roots. Removing trees costs money, and replanting costs money as well.
An air source heat pump, no matter how well designed, cannot be planned against below-freezing temperatures unless you heavily oversize the unit so it can still operate in sub-zero conditions. Achieving 100% solar coverage is practically impossible, and you are completely right about that. However, for half the additional investment of a ground source heat pump, you can already reach 40-50% solar coverage (based on price quotes from providers).
Gas, on the other hand, is considerably cheaper than electricity (which the heat pump needs) and is subject to less severe price increases. Additionally, due to climate change, northern Germany is actually tending to get colder! This means air source heat pumps will become even less efficient in the future (although it is uncertain how quickly climate change will proceed), and the same also applies to ground source systems to some extent. Solar systems, however, only need sunlight and even operate significantly more efficiently at low temperatures.
An air source heat pump, no matter how well designed, cannot be planned against below-freezing temperatures unless you heavily oversize the unit so it can still operate in sub-zero conditions. Achieving 100% solar coverage is practically impossible, and you are completely right about that. However, for half the additional investment of a ground source heat pump, you can already reach 40-50% solar coverage (based on price quotes from providers).
Gas, on the other hand, is considerably cheaper than electricity (which the heat pump needs) and is subject to less severe price increases. Additionally, due to climate change, northern Germany is actually tending to get colder! This means air source heat pumps will become even less efficient in the future (although it is uncertain how quickly climate change will proceed), and the same also applies to ground source systems to some extent. Solar systems, however, only need sunlight and even operate significantly more efficiently at low temperatures.
Chris82 schrieb:
There is more to consider with trench collectors than just the cost savings compared to deep borehole drilling regarding the initial installation expenses. First of all, you need a sufficiently large plot of land. How large exactly? Chris82 schrieb:
... An air heat pump, no matter how well designed, cannot be planned against subzero temperatures, ... No, not against them, but the respective climatic parameters (average temperature profile) are taken into account in the planning! ;-) Chris82 schrieb:
A 100% solar coverage is practically impossible, you are absolutely right about that. But for half the additional investment of a ground source heat pump, you can already achieve 40-50% (I am basing this on supplier price quotes). 40–50% of what exactly? Marketing claims or optimistic calculations, or is it actually contractually guaranteed? Then try to get the respective representatives to commit to a definite kWh/year yield, which, as you know, is hardly possible due to the known circumstances :-) Chris82 schrieb:
... Solar systems, on the other hand, only require sunlight and even operate significantly more efficiently at low temperatures. Which ones? Solar thermal systems or photovoltaic panels? What reliable results do you base this insight on?Regards
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