Heating concept for single-family house new build approx. 190m²: Split heat pump vs. ground source (brine)

Hello everyone,

We are currently preparing our building application with our architect. Since I wanted to use the time efficiently, I have already obtained a cost estimate from a heating company for the whole topic of heating/bathrooms/pipes, among other things. We were presented with two different heating concepts:

Split heat pump: Buderus Logaplus package WPLS.2 -8 (an equivalent ELCO device could also be offered here)
Ground source heat pump: Buderus Logaplus package WPS 1-1 WPS 8K-1, 1HK E plus, buffer (an equivalent ELCO device could also be offered here)

The price difference (after deducting the BAFA subsidy) is over €6,000. According to the heating company, the ground source heat pump will not pay off compared to the split unit in terms of energy costs (even though the ground source has the edge here). According to him, however, he estimates the ground source heat pump to be more low-maintenance and durable. He also frankly admits that he is more convinced by this concept. In the end, however, the statement is that both solutions are "decent."

In principle, I find the principle of geothermal energy convincing, but in practice, I would like to be able to rationally justify the €6,000 additional cost.

The whole system is to be installed in a newly built single-family house without a basement, approximately 190 m² with underfloor heating.

So is this now somewhat a matter of belief? Or are there still countless details missing for the final assessment that I have forgotten here? What questions should I still ask myself to make further progress in my thinking?

Best regards from the Ruhr area Christian

I once saw a nice illustrative graphic here in the forum from a user comparing brine/water to air/water, where you can clearly see that the brine source only pays off with large amounts of energy, which do not occur in single-family houses. In that respect, your heating installer is right. As for durability and maintenance, this should rather affect the outdoor unit in a split system; the heat pump itself is the same. I don't think that changes the equation. A bigger point in favor of brine is that you don’t have a fan unit standing in the front yard, so purely from a comfort perspective, it is justifiable.

We are currently facing the same problem. The problem: brine has a higher annual performance factor, but the stuff also somehow has to go into the ground. If we assume 150 sqm, we need about 300 sqm of brine. At a soil depth of 1-2m, that should result in about 500m³ of soil to be excavated. Excavating this amount takes a while and is extremely expensive (is that already included in the price above?). If you estimate around €7,000 now for the excavation work, you can heat with an air-to-water heat pump for just over a generation before you’ve made back the higher costs of installing the brine through the electricity savings. We will be looking at some air-to-water heat pumps in the next few weeks, mainly because of the noise. However, newer devices are supposed to be significantly quieter and less noticeable than older ones... Our heating engineer says: brine is great, always works quite consistently. The architect says: air-to-water heat pump is now similarly good – the extra cost is not worth it. Energy consultant says: brine is great and better than air-to-water heat pump. As always, you ask 5 people and get 6 different opinions.

I think this is more about ground probes rather than flat collectors. With today’s drilling costs – if permitted – this is definitely the more optimal solution compared to the complicated hassle with the flat collectors. The decision is still pending here as well. I want to take a closer look at both options. At the moment, I am leaning towards the air-to-water heat pump due to the technical developments, but only because of the costs. However, these are offset by the €3000 higher subsidy. Therefore, the current prices need to be compared accordingly.

We are currently facing the same problem. The problem: Brine has a higher annual performance factor, but somehow the stuff also has to go into the ground. If you assume 150sqm with us, we need about 300sqm of brine. Which, at a ground depth of 1-2m, should result in about 500m³ of soil to be excavated. Excavating that amount takes a while and is extremely expensive (is that already included in the price above?) If you assume about €7,000 now for the excavation work, you can heat with an air-water heat pump just over one generation until the higher costs of laying the brine are compensated by the electricity costs. We will look at some air-water heat pumps in the coming weeks, mainly because of the noise. However, newer devices are supposed to be significantly quieter and less noticeable than older ones... Our heating engineer says: Brine is great, always works quite consistently. The architect says: Air-water heat pump is nowadays similarly good - the surcharge is not worth it. Energy consultant says: Brine is great and better than air-water heat pump. As always, you ask 5 people and get 6 different opinions.

According to our heating engineer, a brine heat pump with surface collectors is not possible due to the size of the property/garden. That means my price refers to geothermal probes with a borehole depth of 70m.

Our heating engineer says: brine is great, always works quite consistently. The architect says: air-to-water heat pump is now similarly good - the extra cost is not worth it. The energy consultant says: brine is great and better than air-to-water heat pump.

Every opinion is correct. Does the heating engineer say that the air-to-water heat pump is much worse? I fully agree with the architect. Does the energy consultant say why brine is better and when it pays off? That quickly relativizes his first statement again.

The problem: brine has a higher annual performance factor, but somehow the stuff has to get into the ground. If you assume 150 sqm here, we need about 300 sqm of brine. Which at 1-2m soil depth should mean about 500m³ of soil to be removed.

I had understood the OP more as meaning that drilling would be done. Not a trench collector (which you could also lay quite easily yourself).