Air pump more efficient than ground pump, noise disturbance?

Hello everyone,
I have a small problem and need your opinion.

Information about the house:
Semi-detached house with four people
142 m² living space
335 m² plot size
140 m² usable area for the earth baskets
Solid clay soil

We commissioned a construction company to build our semi-detached house. We bought the house with Kfw 70 standard, underfloor heating, and geothermal heat pump, for which I pay an additional €15,000.
At the time, they told us they would try to realize the heating with a deep drilling and probe, but they were not sure if it would work because we are building in an area where there is most likely no drilling permit, as it belongs to the water protection area of Carolinen Brunnen. But with earth baskets it is 100% certain, and these will be used instead of drilling.
It turned out that we are not allowed to drill, and 19 earth baskets with a diameter of 45 cm, which the heating installer manufactures himself, should be installed to a depth of 6 m and at a distance of 3 meters.
The air heat pump was supposed to be the following:

Viessmann Vitocal 300-G, BWC 6 kW

Now, while the basement was being excavated, they came across a layer of slate stone at about 3 m depth, and suddenly it is said that they cannot drill through such a layer, and the heating installer told me today he wants to talk to us about an air-water heat pump to see if it would be an option for us.
He says he would also take the market leader in air-water heat pumps, which is:

Mitsubishi Zubadan PUHZ-HRP71VHA2 8.1 kW
Additionally, I should pay €2,000 less for the heating system.

He also said something like the air heat pump is more efficient compared to the ground heat pump because this unit does not need an electric heating rod down to –20 degrees, and the ground heat pump is not sufficient at freezing temperatures like we had last year, and then the electric rod has to support it, which costs several hundred euros for an operating time of 2 months of continuous frost in winter.
He also calculated that with a heat demand of 15,000 (k)W per year and an electricity price of about 15 cents/kWh, I have to pay about €600 per year for the ground heat pump and €780 for the air heat pump, which is still a saving compared to gas at about €1,200.

That's the story so far, and now my questions:

[*]Can the cost difference of €600 to €720 be correct?
[*]Does anyone know the Mitsubishi air heat pump and especially how is the noise level? The heating installer told me it is not disturbing when the unit is outside. I do have triple glazing and so on, but I don't know if the unit is still loud, as there are different opinions to be read online.
[*]Is the pump really so powerful that it has no problems down to –20 degrees?
[*]Would you accept the deal with €2,000 discount, or do you think you can get more out of the company?

Thanks to you all!
dimah

Hello,

....Details about the house:.....

They are quite nice but:
- What is the actual energy demand for heating and hot water?
- What is the required power in each case?
- Which climate data are relevant for the location?

....They told us back then, they would try to realize the heating with a deep borehole and probe, but they were not sure if it would work, because we are building in an area where there is most likely no drilling permit, as it belongs to the water protection area of Carolinen Brunnen.

A bit strange in hindsight! ;-)

....Now, while the basement was being excavated, they encountered a layer of slate at about 3 m depth and now suddenly they say they cannot drill into such a layer ...

Was there no soil survey for the construction project? Do inconsistencies always only become apparent afterwards here?
If applicable, a trench collector might be possible, that doesn’t require 3 m depth :-)

....He said something like the air pump would be more efficient compared to the ground pump, since the unit does not need an electric heating rod up to –20 degrees, and the ground pump does not suffice at frosty temperatures like we had last year, so the electric heating rod has to step in, which costs several hundred euros for a 2-month continuous frost period in winter.

Send that expert into the desert!

....He also calculated for me that with a heat demand of 15,000 (k)wh per year ...

Only heating or also hot water? How does he arrive at this number?

....and with an electricity price of approx. 15 cents/kWh I have to pay about 600 € per year for the ground pump and 780€ for the air pump

Both numbers are completely off, assuming the 15,000 kWh should be correct! ;-)

Regards

Hello, the heating engineer is talking about 15kw heating demand, not electrical power.... therefore the numbers are quite plausible. I would definitely buy the air heat pump! Regards C.Lotte (Kälteanlagenbauermeister)

....the heating engineer is talking about 15kw heating demand, not electrical power.... so the numbers are quite plausible.

A master refrigeration engineer should actually be able to distinguish between energy and power!:(

Best regards.

A master refrigeration engineer should actually be able to distinguish between energy and power!:(

v.g.

I couldn't recall having spoken of energy.
The text mentions a heat demand of 15 kW: Quote: "Wärmebedarf von 15.000 (k)w"
If this means the "annual heating energy demand" (unit would then be: kWh), even better.
And don't forget: The mentioned heat pump is specified with a COP of about 4.4.

I couldn't remember talking about energy.
The text states a heat demand of 15 kW: Quote: "Wärmebedarf von 15.000 (k)w"

Heat is always = energy (kWh). A layperson might sometimes confuse that ;-)

And don't forget: The mentioned heat pump is specified with a COP of about 4.4.

Which one?
Especially with air source heat pumps, individual COP values only play a minor role; what matters to the user is the achievable seasonal performance factor. That's where the wheat is separated from the chaff ;-)

best regards