Hello everyone,
Today I received an offer for the ground drilling and need some help interpreting the data.
I was given the following information 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 ground temperature 9.7 °C (49.5 °F)
Specific thermal conductivity of geological layers 2.2 W/(m*K)
Number of boreholes 2
Depth per borehole 60 m (197 ft)
Flow type Turbulent
Probe type Single U-tube 40
Energy output: Your borefield generates 8.2 MWh (megawatt-hours) per year
According to the engineering office’s calculation, my house has a heating load of 4,297 W (without domestic hot water).
There is a mistake with the planned heat pump; it should be the Nibe S1255-6-PC, not the F1255-6. However, I don’t think this makes a difference here.
Is it normal to size the probes based simply on the maximum heating capacity of the heat pump (6 kW)?
I don’t understand the two values given for annual heating energy demand and domestic hot water energy demand. Why is 6,450 kWh being used now?
An annual domestic hot water energy demand of 4,000 kWh for a three-person household also seems very high to me, doesn’t it?
Can someone clarify this?
In the end, I am surprised by the two boreholes and the associated estimated costs (almost 14,000 €).
I had actually hoped to manage with just one borehole due to the relatively low heating load. According to the map from the state of Berlin, the ground in my area should provide about 35 W/m.
Best regards
Today I received an offer for the ground drilling and need some help interpreting the data.
I was given the following information 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 ground temperature 9.7 °C (49.5 °F)
Specific thermal conductivity of geological layers 2.2 W/(m*K)
Number of boreholes 2
Depth per borehole 60 m (197 ft)
Flow type Turbulent
Probe type Single U-tube 40
Energy output: Your borefield generates 8.2 MWh (megawatt-hours) per year
According to the engineering office’s calculation, my house has a heating load of 4,297 W (without domestic hot water).
There is a mistake with the planned heat pump; it should be the Nibe S1255-6-PC, not the F1255-6. However, I don’t think this makes a difference here.
Is it normal to size the probes based simply on the maximum heating capacity of the heat pump (6 kW)?
I don’t understand the two values given for annual heating energy demand and domestic hot water energy demand. Why is 6,450 kWh being used now?
An annual domestic hot water energy demand of 4,000 kWh for a three-person household also seems very high to me, doesn’t it?
Can someone clarify this?
In the end, I am surprised by the two boreholes and the associated estimated costs (almost 14,000 €).
I had actually hoped to manage with just one borehole due to the relatively low heating load. According to the map from the state of Berlin, the ground in my area should provide about 35 W/m.
Best regards
JaiBee07 schrieb:
Is my assumption correct that a single borehole of 120m (394 feet) would be cheaper than two boreholes of 60m (197 feet) each?
(I understand that this probably cannot be simply calculated based on the performance of the ground probe).
Are two boreholes advantageous in any way? You won’t need a full 120m (394 feet) if you drill two 60m (197 feet) boreholes—in fact, you will need less total depth, because the extraction capacity per meter increases with depth.
However, a single borehole of the same total depth is cheaper to install. The drilling rig does not need to be moved, the entire process is done once rather than twice. You also save space on the property, benefit from a shorter and more direct pipe layout, and won’t need an inspection chamber where the two probes would join.
Two boreholes offer an advantage over a single borehole in terms of reliability. From an efficiency perspective, a single deeper borehole is preferable to two shallower ones. Based on my experience, the general statement that a deeper borehole is always cheaper to install cannot be confirmed. This depends on the specific ground conditions in the subsurface, for example, if there are rocky layers at greater depths.
Regarding the questions in the initial post: heating load and annual heating energy demand including domestic hot water are different concepts. However, it is correct that these calculations already include a safety margin. Therefore, the heat generator (heat pump) should not be oversized for better efficiency, as this would reduce efficiency.
On the other hand, oversizing the heat source (i.e., a deeper borehole) increases efficiency by lowering the operating costs of the heat pump. Whether this benefit justifies the higher drilling costs is not easy to calculate and must be decided individually. But in general, a few extra meters of drilling are a good thing.
Regarding the questions in the initial post: heating load and annual heating energy demand including domestic hot water are different concepts. However, it is correct that these calculations already include a safety margin. Therefore, the heat generator (heat pump) should not be oversized for better efficiency, as this would reduce efficiency.
On the other hand, oversizing the heat source (i.e., a deeper borehole) increases efficiency by lowering the operating costs of the heat pump. Whether this benefit justifies the higher drilling costs is not easy to calculate and must be decided individually. But in general, a few extra meters of drilling are a good thing.
X
xMisterDx15 Nov 2023 11:22Yes, exactly. Just because you can drill 60 meters (197 feet) deep doesn’t mean you can reach 100 or 200 meters (328 or 656 feet). The risk of hitting rock increases with every meter.
Are there any local experiences you can refer to?
Why does the company want to drill twice at 60 meters (197 feet) instead of once at 100 meters (328 feet)? Have they had bad experiences with deeper drilling in your area or know that it might not be possible?
Just because it worked in location X and Y doesn’t automatically mean it will work in location Z...
Are there any local experiences you can refer to?
Why does the company want to drill twice at 60 meters (197 feet) instead of once at 100 meters (328 feet)? Have they had bad experiences with deeper drilling in your area or know that it might not be possible?
Just because it worked in location X and Y doesn’t automatically mean it will work in location Z...
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