ᐅ Recommendation: Air-to-Water Heat Pump versus Local District Heating Network for KFW40 New Construction

Hello everyone,

We are about to start construction on our single-family house.

Key facts:
2 full floors
200 sqm (2,150 sq ft)
No basement
KfW40 standard
3 people
Photovoltaic system 7-9 kWp (depending on heat pump or district heating), battery storage optional
Underfloor heating throughout the house

There are two specific energy supply options we have been offered:

Option 1: District heating

Technology: Transfer station, meter, and downstream combined storage tank for heating and hot water (CS Solar KSR 1000), plus two 3 kW heating rods with control for feeding in photovoltaic electricity. Supply temperature from the district heating network: 65-80 degrees Celsius (149-176 degrees Fahrenheit)

Flat price per kWh independent of consumption: 300 euros + €0.0995/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 tanks (100 l (26 gallons) heating, 295 l (78 gallons) hot water)

Comparable price: 18,000 euros

Overall costs over the service life, assuming a heat pump lifespan of 15 years, favor district heating.

However, I have two questions:

I am not sure whether a combined storage tank is really practical with district heating, especially in summer. For example, do you have to heat the entire buffer tank to temperature for showering even if the heating water isn’t needed? Could this possibly lead to issues with legionella?

Also, there is a claim that a photovoltaic system works more efficiently with an air-to-water heat pump than with a heating element, because the PV system likely does not produce 3-6 kW at the time of the heat demand.

Does anyone have experience with one of these options or answers to my two questions?
I would also appreciate any suggestions for improvement.

Thank you!

With such a small difference, I would go with the heat pump. It makes you more independent. According to your calculations, how much is the cost difference per year?

For district heating at just under 10°C (50°F), I would lean towards a heat pump. With electricity costs of 30 cents per kWh, you only need an annual performance factor (COP) of 3, which is easily achievable in a new build. Besides, you’re not tied to a single supplier. Who knows what district heating prices will be like in five years.

From a technical perspective, district heating is quite inefficient due to the high temperature. A supply temperature of 35°C (95°F) is sufficient for new builds; strictly speaking, even 65°C (149°F) isn’t necessary for domestic hot water. You would be using photovoltaic electricity through electric heating rods instead of achieving a COP of 3–4 with a heat pump. This difference is especially noticeable during transitional seasons.

Hello,
according to the website, the ALM 4-12 has a minimum output of 4kW, which seems oversized to me.
What does the heat load calculation say? The smaller one should be sufficient. Is the storage tank a combined buffer or are the domestic hot water and heating circuits separate?
Get a quote for the smaller ALM as well and recalculate. Apparently, you are not required to connect. How long are the prices for the district heating guaranteed?
Best regards from Hamburg

Which specialist planned the 12 kW heat pump for you? "KfW40" standard houses, even those with 200 m² (2,150 sq ft), typically have trouble fully utilizing 5 kW heat pumps, and that’s only if they need to heat continuously at natural temperature mode for weeks on end (which is practically never). To make a meaningful comparison, you should ask for an offer with a significantly smaller heat pump—ideally one that can modulate down to 1.5 kW. And please, without a buffer tank—you don’t need it, it only causes extra costs and reduces efficiency.

Do you also want to cool during the summer? That option is obvious, especially if you have a photovoltaic system.

CC35BS38 schrieb:

With such a small difference, I would go for the heat pump. It makes you more independent. According to your calculation, what is the annual cost difference?

According to my calculation, the difference is about 250-300 euros in favor of the heat pump, assuming an electricity price of 30 cents and a district heating price of 10 cents. On the other hand, the heat pump has approximately 700 euros higher depreciation costs, which means that overall, district heating is about 400 euros more cost-effective per year—assuming the usage rates stay the same.