ᐅ Ground Source Heat Pump vs. Air Source Heat Pump

Hello forum members,

My girlfriend and I are currently planning our house construction. Last week we received the final plan from our builder. Now it’s about the heating system.
We don’t have a heating load calculation yet, but I wanted to start looking into the heating topic because it’s very important to me.
You will quickly realize that I am quite a beginner when it comes to heating technology, so I am turning to you here. Please be a bit patient if I bring up the topic for the 1000th time or seem clueless.

Now to the basic data for our house:
- approximately 200 sqm (2150 sq ft) living area
- 900 sqm (9700 sq ft) plot of land
- no basement (a boiler room is planned)
- the goal is to achieve KfW Efficiency House 70 standard
- a tiled stove will be installed (for cozy/visual/personal reasons and also possibly for additional heating)

As I said, we don’t have a heating load calculation yet.
Our builder recommends an air-to-water heat pump with an integrated ventilation system from Stiebel Eltron.
Honestly, I find an integrated ventilation system quite appealing since we both work and can hardly ventilate during the day. I know we’re not building a passive house, but I think a ventilation system is still not a bad idea.

Does anyone have experience with such dual systems?
Are there integrated ventilation systems that can also humidify and dehumidify?
I’m thinking that if the ventilation system can’t do this, it might cause problems for the respiratory system, etc. In the end, we might have issues due to a lack of humidification and be stuck in a bad situation.
Would placing a small decorative fountain inside the house help in such a case?

We have already decided to go for a heat pump. Originally, we wanted a ground-source heat pump with horizontal collectors (the plot size should be sufficient). Through our builder, I have also looked a bit into air-source heat pumps.
He said we would need a heat pump with a heating capacity of 8-9 kW.
That seems a bit too much to me. Wouldn’t 6-7 kW be sufficient?

I am now totally torn between air-source and ground-source heat pumps...
It’s clear that ground-source is considerably more expensive upfront. At Stiebel Eltron, the ground-source heat pump for heating and domestic hot water including ventilation costs roughly €8,000, similar to the air-source heat pump. However, ground-source is more powerful and cheaper to run in terms of electricity. Although the increasingly mild winters also have a positive effect on the electricity consumption of the air-to-water heat pump.
Both should fit into our budget, but will either be cost-effective?
Would it possibly make sense to separate domestic hot water heating from the main system and instead install two collectors on the roof?

What were your reasons for choosing air-source or ground-source heat pumps?
Please help me with this decision, otherwise I might burn myself here.

Many thanks in advance

So... Without knowing the heating load, the question of proper sizing cannot be answered. And without information on the location, design temperature, solar gain, plot of land, etc., it’s just guesswork.

In other words: when in doubt, consult a professional... Anything else is guessing and listening to salespeople – whether the individual requirements are met remains uncertain...

How cold does it usually get in your area, and how long does the winter typically last based on your own experience? In Bavaria, it can get quite cold and the winter tends to last for a considerable time.

Gas heating usually pays off more in the short term.
Otherwise: for heat pumps with an annual performance factor above 4.5, there is still a subsidy of 4500 € from Bafa.
It’s hard to give a general answer whether 6, 7, or 8 kW is the right size. If you’re building a glass house, even 10 kW won’t be enough – even if the building meets KfW40 standards.
I doubt that climate change can be factored into the business case.

Our location is near Neumarkt in the Upper Palatinate/Bavaria. Winters can certainly be cold, but I believe there are areas in Bavaria that are much colder during winter. Using this past winter as a reference, it was actually quite mild. There were few true frost days, and temperatures rarely dropped below -10°C (14°F). The average temperature in 2014 was just over 8°C (46°F).

So, we are not planning a glasshouse. We also decided against installing many floor-to-ceiling windows on the ground floor, as originally suggested by the builder. Now, we only have two floor-to-ceiling windows.

We do not want a gas or oil heating system. It will definitely be a heat pump heating system.

Good – the last sentence is crucial. However, you don’t necessarily have to give up on floor-to-ceiling windows...

Your design temperature (lowest temperature recorded on two consecutive days in the last 10? years) and thus the key factor for sizing your heating system is probably around -16°C (3°F) for you (both Nuremberg and Regensburg have -16°C (3°F)) – so sometimes things can be misleading.

The most cost-effective option for heat pumps is probably the trench collector – but it’s difficult if you cannot find a provider or if the plot of land is too small.

After that, in my opinion, comes drilling in the long term – unless you live directly on solid rock – and there are subsidies available for both options with new builds (if you apply before signing the contract).

In Lower Saxony, we have a state agency for mining and geology (LBEG) where all drillings are registered and freely accessible online. This was very helpful for us to assess how much wattage we could expect for heat extraction, etc. You can also talk to neighbors who have drilled wells. This probably exists in Bavaria as well.

I find an air-to-water heat pump challenging at -16°C (3°F) (although many people have a different opinion).