ᐅ Air-to-water heat pump including ventilation system vs. ground-source heat pump including ventilation system

Hello dear forum community,

We are currently planning the heating system for our new build (135 sqm [1450 sq ft] living area, KfW 55 standard). So far, we thought we wanted an air-to-water heat pump with a central ventilation system featuring heat recovery. The KfW application has been submitted and approved for the air-to-water heat pump.

Now we had a meeting with a heating contractor who strongly recommended a ground-source heat pump. This also sounds logical to us... better annual performance factor (seasonal coefficient of performance), since deep underground it never gets too cold... therefore, there is no “risk” of the electric heating element kicking in with the air-to-water heat pump, which would drastically reduce the seasonal performance factor.

In terms of price, both systems are fairly similar after subsidies (the ground-source heat pump is 1500 Euros more expensive after BAFA support).

With the ground-source system, there is the option of a decentralized ventilation system that only exhausts air centrally from the kitchen, bathroom, guest toilet, and utility room, while fresh air is supplied through mechanical openings in the windows (this option would even be 1500 Euros cheaper than the air-to-water heat pump).

Now the questions:
1. Does anyone have experience with these heating systems and can explain why they chose one of the two options?
2. Would I need to change the KfW application if I decide on the ground-source heat pump, even though it offers a better seasonal performance factor?
3. We definitely want a ventilation system with heat recovery, but the decentralized solution sounds a bit odd to me... does anyone have this? Would it be better to go with the central system?

Thank you very much for your answers :-)
Bauer2018

We are still in the planning phase, but ground source heat pumps are generally the better system where they can be used and drilling is affordable (like in your case, according to your offer). The efficiency is not mainly due to the electric heating element but primarily because of the closer temperature range between the warm side (heating water) and the cold side (ground loop or outside air). However, with an effective price difference of €1500 (about $1600), the investment pays off relatively quickly. It’s also nicer since the annoying outdoor unit is eliminated.

The choice of ventilation system is completely independent of the selected heat source; it seems you might be mixing this up in your mind…

By using decentralized fresh air supply (without heat recovery!!!), you end up losing the efficiency you gained.

This is just an estimate, but it would need to be calculated. Still, I believe my assumption is close to the truth.

toxicmolotow schrieb:
By using decentralized fresh air supply (without heat recovery!!!), you are negating the efficiency gains you achieved.

… also: Who wants to have their exterior wall pierced in every room where a decentralized ventilation system is installed, just to make space for the unit? Visually, this solution is also not very appealing.

AxelH. schrieb:
… also: Who would want to have the exterior wall drilled in every room where a decentralized ventilation system is installed just to make space for the unit? Visually, this solution is not really attractive either.

I would have expected something more like window reveal ventilation.

Bauer2018 schrieb:

In terms of price, both systems are quite similar due to the subsidy (the brine system is then 1500 euros more expensive after the BAFA grant).

If that is actually the additional cost compared to the air-to-water heat pump and the conditions are met, I wouldn’t hesitate for long. However, the price difference seems a bit low to me. How much does the drilling cost for you? How many meters do you need to drill? Or are you talking about ground collectors?
A further note on the brine-to-water heat pump: please also check your soil’s regeneration capacity beforehand. If you have a high clay content in the soil, that could potentially be an issue. Otherwise, if everything fits, I would invest the 1500€ (about $1600) immediately – if only for aesthetic reasons.

Regarding controlled residential ventilation: I believe choosing a decentralized system is false economy.