Dear forum members,
Despite various research efforts, I am still missing reliable information. Therefore, I am posting my question here in the hope of receiving some feedback.
We are planning a KFW 55 house in Oranienburg with 150 sqm (1,615 sq ft) of living space and a general contractor. The contract originally included a geothermal solution with deep drilling and a 6 kW Junkers system (STM 60). This system is intended for both heating and hot water supply. However, the local water authority has blocked this plan and does not allow deep drilling. We are permitted to drill up to a maximum depth of 3.5 m (11.5 ft) without a permit. According to the soil report, there is about 30 cm (12 inches) of topsoil, followed by loose sands. From 2.6 m (8.5 ft) depth, flowing groundwater is present. Nearby, there are reportedly private wells used for drinking water extraction.
My question is: Considering these conditions, which ground collector solution (ground, basket, or trench collector) would be sensible, and what land area should be expected for installation?
Thank you in advance for your support and best regards!
Despite various research efforts, I am still missing reliable information. Therefore, I am posting my question here in the hope of receiving some feedback.
We are planning a KFW 55 house in Oranienburg with 150 sqm (1,615 sq ft) of living space and a general contractor. The contract originally included a geothermal solution with deep drilling and a 6 kW Junkers system (STM 60). This system is intended for both heating and hot water supply. However, the local water authority has blocked this plan and does not allow deep drilling. We are permitted to drill up to a maximum depth of 3.5 m (11.5 ft) without a permit. According to the soil report, there is about 30 cm (12 inches) of topsoil, followed by loose sands. From 2.6 m (8.5 ft) depth, flowing groundwater is present. Nearby, there are reportedly private wells used for drinking water extraction.
My question is: Considering these conditions, which ground collector solution (ground, basket, or trench collector) would be sensible, and what land area should be expected for installation?
Thank you in advance for your support and best regards!
Hello,
Trench collectors can be a cost-effective alternative if you can contribute significant DIY effort. When done by contractors, the price is similar to vertical drilling. However, companies usually have little or no experience with these systems. Be aware that this method will make the garden look like a “battlefield.”
The third option is ground baskets (spiral collectors), which extract heat very efficiently with minimal space requirement. Unfortunately, they are quite expensive.
For all collectors, the local groundwater level affects installation costs (possibly requiring dewatering).
The required installation area must be calculated precisely based on the heat pump’s cooling capacity. There are no general assumptions.
A 6 kW capacity for a KfW 55 house seems a bit high to me. Is there a heating load calculation?
As a last alternative, an air-source heat pump could be considered. This saves the cost of expensive ground loop installation, but you have to accept a somewhat lower annual performance factor. For a KfW 55 house, this should not be a problem. The difference can be calculated exactly.
Important for all heat pump systems: Exact calculation of the heating load, room heating loads, air volumes (if mechanical ventilation with heat recovery is planned), heating surface areas, and pipe hydraulics.
Heat pumps only achieve high annual performance if the system is optimized accordingly; otherwise, it risks becoming a money pit.
Best regards.
mikberl schrieb:That’s actually close to me.
...We are planning a KfW 55 house in Oranienburg with 150sqm (1615 sq ft) of living space and a general contractor.
mikberl schrieb:The general contractor should have known this!
...The contract originally included a geothermal solution with deep drilling and a 6kW Junkers system (STM 60). ...Now the local water authority has blocked this plan and does not allow deep drilling.
mikberl schrieb:There are several alternatives, but they all require appropriate space, especially the surface collectors, as the name implies. It’s important to know that the supply temperature curve to the heat pump follows outdoor temperature more closely due to the shallow installation depth. This results in greater fluctuations compared to vertical drilling. Additionally, especially in moist locations, longer frost or icing periods on the affected areas can occur in spring.
...My question here is: which solution (ground collector, basket collector, trench collector) is reasonable given the conditions, and what building area should be expected?
Trench collectors can be a cost-effective alternative if you can contribute significant DIY effort. When done by contractors, the price is similar to vertical drilling. However, companies usually have little or no experience with these systems. Be aware that this method will make the garden look like a “battlefield.”
The third option is ground baskets (spiral collectors), which extract heat very efficiently with minimal space requirement. Unfortunately, they are quite expensive.
For all collectors, the local groundwater level affects installation costs (possibly requiring dewatering).
The required installation area must be calculated precisely based on the heat pump’s cooling capacity. There are no general assumptions.
A 6 kW capacity for a KfW 55 house seems a bit high to me. Is there a heating load calculation?
As a last alternative, an air-source heat pump could be considered. This saves the cost of expensive ground loop installation, but you have to accept a somewhat lower annual performance factor. For a KfW 55 house, this should not be a problem. The difference can be calculated exactly.
Important for all heat pump systems: Exact calculation of the heating load, room heating loads, air volumes (if mechanical ventilation with heat recovery is planned), heating surface areas, and pipe hydraulics.
Heat pumps only achieve high annual performance if the system is optimized accordingly; otherwise, it risks becoming a money pit.
Best regards.
Hello €uro
Thank you for the quick feedback. I have requested the documents for the thermal protection certificate from the general contractor. At the moment, I cannot say whether a heating load calculation is included. I will follow up on that. What interests me most is the fact of the low groundwater level. Is it possible to use this positively? For example, if the circulation pipes (e.g., as a coil) are installed in flowing groundwater, would this result in better heat exchange? Or am I mistaken with this approach?
Best regards!
Thank you for the quick feedback. I have requested the documents for the thermal protection certificate from the general contractor. At the moment, I cannot say whether a heating load calculation is included. I will follow up on that. What interests me most is the fact of the low groundwater level. Is it possible to use this positively? For example, if the circulation pipes (e.g., as a coil) are installed in flowing groundwater, would this result in better heat exchange? Or am I mistaken with this approach?
Best regards!
Hello,
Dry soils (e.g., sand) provide significantly less annual heat extraction compared to “wet” substrates. Sometimes having “wet feet” can be an advantage for energy supply, although it is usually a disadvantage in basement construction!
Best regards.
mikberl schrieb:The thermal insulation certificate (Energy Saving Ordinance/KfW certificate) does not replace a heating load calculation according to DIN 12831! Also, the sizing of a heating system based on this certificate is not possible and not intended by law!
I requested the documents for the thermal insulation certificate from the general contractor.
mikberl schrieb:Yes, because water is an excellent energy storage medium and heat conductor! It is no coincidence that H2O is used on the secondary side for heat distribution and transfer in most heating systems! Only with passive houses can this be omitted.
...What interests me significantly is the fact of the low groundwater level. Could this possibly be used advantageously?
mikberl schrieb:Absolutely correct! An interesting factor here is the flow direction of the groundwater, if known. However, it is not always necessary to reach deep into the groundwater because the adjacent soil layers benefit from the heat transport and exchange caused by the groundwater.
...So, if the circulation pipes (e.g., in a coil) are installed in flowing groundwater, resulting in better heat exchange. Or am I mistaken with this approach?
Dry soils (e.g., sand) provide significantly less annual heat extraction compared to “wet” substrates. Sometimes having “wet feet” can be an advantage for energy supply, although it is usually a disadvantage in basement construction!
Best regards.
€uro schrieb:
Dry soils (e.g., sand) provide significantly less annual heat extraction capacity compared to "wet" substrates.If we apply this information to my specific situation... So sandy soil with groundwater flowing at a depth of 2.50 m (8.2 ft)... Are these conditions suitable and practical for a geothermal solution, and if so, which type would be recommended, considering minimal space requirements?
mikberl schrieb:
....Are these now practical and usable conditions for a geothermal solution, and if so, which type (considering minimal space requirements)? Good conditions, geothermal baskets.
Best regards.
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