Interpretation of Earth Drilling Experiences

Hello everyone,

I received an offer for the ground drilling today and need some support with the evaluation of the data.

The following was provided to me in a document:

Your heat pump: Nibe Systemtechnik GmbH: NIBE F1255-6
planned heating capacity 6 kW
annual heating energy demand 6,450 kWh
annual domestic hot water energy demand 4,000 kWh
annual heating profile Standard new build load profile

YOUR GEOLOGICAL CONDITIONS

undisturbed site-specific soil temperature 9.7 °C
specific thermal conductivity of the geological layers 2.2 W/(m*K)

Number of drillings 2
Depth per drilling 60m
Flow type Turbulent
Probe type Single U-probe 40

Energy output: Your drilling field generates for you (in megawatt hours) p.a. 8.2 MWh

According to the calculation by the engineering office, my house has a heating load of 4297W (without domestic hot water).
There is an error in the planned heat pump; it should be the Nibe S1255-6-PC, not the F1255-6. However, I think this makes no difference here.

Is it normal to simply size the probes according to the maximum heating capacity of the heat pump (6 kW)?
I don't understand the two values specified for annual heating energy demand and for domestic hot water energy demand. Why is 6450 kWh used now?
A domestic hot water energy demand of 4000 kWh for a 3-person household also seems extremely high to me, doesn't it?
Can someone shed some light on this?

In the end, I am surprised by the 2 drillings and the associated estimated costs (almost €14,000).
I had actually hoped to manage with 1 drilling due to the rather low heating load. According to the diagram for the state of Berlin, the soil in my area should provide about 35W/m.

Best regards

4000kWh for hot water is not much. Remember, they are talking about heat, not electricity.

But yes, I would insist on a borehole, a double U probe. It shouldn't be more than 100m (and even if it is, you simply go deeper than 100m instead of installing two probes).

But online I find surcharges of 600-800kWh per person for hot water. For 3 people, that would rather be in the range of 1800 to 2400kWh. Here almost double is indicated. On other sites, however, it says that some do not include any surcharge here at all, because the standards for heating load calculation already include so much reserve (e.g. solar gains) that it is not necessary. Besides, the heating never does both, but prioritizes hot water preparation.

But I first want to understand the numbers so that I can then argue with them. Does anyone have an idea where the heating energy demand of 6450kWh p.a. is derived from?

PS: Drilling over 100m apparently is not possible, then you are in the mining area and need completely different approvals that no one will give you.

From 100m on, the application process is more extensive, yes, but of course it's possible. We have done it too. It's just significantly cheaper.

I can confirm, I also have "only" a 110m borehole for the house. An Alpha Innotec WZSV 62K3M (1.25 - 5.95 kW incl. PC) was installed.

Is my assumption even correct that a borehole with 120m would be more cost-effective than 2 boreholes of 60m each? (I am aware that you probably cannot simply calculate this based on the performance of the ground probe). Are 2 boreholes in any way advantageous?