Recommendation air-water heat pump vs. local near heating network KFW40 new building

Hello everyone,

we are just about to start construction on our single-family home.

Key data:
2 full floors
200 sqm
no basement
KfW40 standard
3 people
Photovoltaic system 7-9 kWp (depending on heat pump or district heating), storage optional
underfloor heating throughout the house

There are two concrete alternatives for energy supply that have been offered to us:

Option 1: District heating

Technology: transfer station, meter and downstream combined storage for heating and hot water (CS Solar KS-R 1000), plus two 3kW heating rods with control for feeding photovoltaic power. Supply temperature via district heating network: 65-80 degrees

Basic price kWh independent 300 euros + 9.95 cents/kWh
One-time connection fee including transfer station: 14,000 euros

Option 2: Air-to-water heat pump

Technology: iDM ALM 4-12 with integrated storage (100l heating, 295l hot water)

Comparison price: 18,000 euros

The total costs over the term and an assumed lifetime of the heat pump of 15 years favor district heating.

However, two questions are currently on my mind:

I am just not sure whether a combined storage tank makes sense with district heating, especially in summer. For example, does the entire buffer always have to be heated to temperature for showering, even though the heating water is not needed? Could I possibly also have problems with legionella here?

Furthermore, the claim that a photovoltaic system works more efficiently with an air-water heat pump than with a heating rod, since at the time of the heat demand probably no 3-6 kW are available from the photovoltaic system.

Does anyone have experience with one or the other option or an answer to my two questions?
Also happy to hear any possible improvement suggestions :)

Thank you very much!

I would choose the heat pump with such a small difference. This way you are more independent. How much is the cost difference per year according to your calculation?

At just under 10c for local heating, I would tend to go for the heat pump. At 30c/kWh electricity, you only need a seasonal performance factor of 3, which is easily achievable in new buildings. Besides, you are not tied to a monopolist. Who knows what prices will be charged for local heating in 5 years.
On the technical side, local heating is quite inefficient due to the high temperature. 35 degrees supply temperature is sufficient in new buildings; strictly speaking, you don’t even need 65 degrees for hot water. You would run the photovoltaic electricity through heating rods instead of through the heat pump with a COP of 3-4. Especially during the transitional period, that makes quite a difference.

Hi, the ALM 4-12 has a minimum output of 4kw according to the website, which seems oversized to me. What does the heat load calculation say then? The smaller one should already be big enough. Is the storage tank a combination buffer or are the domestic hot water and heating sides separate? Have them make an offer for one/the smaller ALM and recalculate. Apparently, you don't have a connection obligation. How long are the prices for the local heating guaranteed? Regards from Hamburg

Which senior specialist planned the 12 kW heat pump for you? "KfW40" houses, even with 200 sqm, have "difficulty" utilizing 5 kW heat pumps, and that only happens if they have to heat at NAT for weeks (in other words: never). To compare sensibly, you need to try to have a significantly smaller heat pump offered – ideally one that can modulate down to 1.5 kW. And please, without a buffer – you don't need it, it only adds costs and efficiency losses.

Do you also want to cool in summer? The option is obvious, especially if you have a photovoltaic system.

I would choose the heat pump with such a small difference. That way you are more independent. How high is the cost difference according to your calculation per year?

According to my calculation, the difference is about 250-300 euros in favor of the heat pump with 30 cents electricity price and 10 cents local heating. On the other hand, there is about 700 euros higher depreciation for the heat pump, which makes local heating approximately 400 euros per year more advantageous overall – assuming that the usage prices do not change.