ᐅ New single-family house construction, gas heating or heat pump, target KfW55 energy efficiency standard

Hello Forum,

I have been reading here for some time and am very impressed by the quality of some of the answers, so I hope to get the right guidance for myself as well.

I am currently planning my single-family house with 171m2 (1840 sq ft) of living space to KfW 70 standard.
Through the developer, I would get a gas condensing boiler with solar hot water and a Zehnder ComfoAir residential ventilation system.
Through a heating installer friend, I could get an Ochsner air-to-water heat pump GMLW9 plus VX with split outdoor unit Millennium MSV 14 for heating,
and an Ochsner Europa 323DK air-to-water heat pump with integrated residential ventilation. This pump would be installed in the utility room and extract warm air from the hallway and bathroom; fresh air would be supplied back to the rooms via membrane flaps on the window.

I would get both options at the same price.

About the house:

Setback floor, 171m2 (1840 sq ft) living space
Underfloor heating with supply temperature approx. 35°C (95°F)
2-layer wall construction: 17.5cm (7 inches) Ytong, 14cm (5.5 inches) insulation, brick veneer
10cm (4 inches) perimeter insulation
Triple glazing, 6-chamber profile, Ug value 0.7

Results of the energy assessment according to DIN 4108-6 and DIN 4701-10
Annual primary energy demand 56.92 kWh/m2
Transmission heat loss 0.27 W/(m2K)
Building envelope area 534.65m2 (5752 sq ft)
Building volume 705.65m2 (7598 sq ft)
Heated air volume 536.29m2 (5772 sq ft)
Usable building area 225.81m2 (2430 sq ft)
A/V ratio 0.76 1/m
Window area 39.36m2 (424 sq ft)

Ground slab U-value 0.23 W/(m2K)
Exterior wall U-value 0.17 W/(m2K)
Wood beam ceiling U-value 0.19 W/(m2K)
Ceiling to outside air above U-value 0.23 W/(m2K)
Ceiling to outside air below U-value 0.22 W/(m2K)

Absolute heating demand 10,704 kWh/year
Absolute hot water demand 2,823 kWh/year

I hope this is enough for now.

My questions:

Which of the above heating systems makes more sense?
Are these values reasonable?
Would I possibly reach KfW 55 with the heat pump system combined with a 5 kWp photovoltaic system?

I look forward to your answers.

Thank you
Elektriker

One more thing about the heat pump:
including cooling function and a buffer tank for the planned photovoltaic system

Hello,

Elektriker schrieb:
....Through the developer, I would get a gas condensing boiler with solar thermal hot water and a Zehnder ComfoAir mechanical ventilation system.

The usual setup, where a solar thermal system is compulsory even though it is usually uneconomical in single-family homes :-)

Elektriker schrieb:
....Through a heating installer friend, I would get an Ochsner air-to-water heat pump GMLW9 plus VX with a split outdoor unit Millennium MSV 14 for heating and an Ochsner Europa 323DK air-to-water heat pump for domestic hot water with integrated mechanical ventilation. This pump would be installed in the utility room and extracts warm air from the hallway and bathroom; fresh air is supplied back to the rooms through membrane flaps in the windows.

Whether a supply air temperature of -12 to -25°C (10 to -13°F) in winter makes sense is for each person to decide ;-) Also, why use two heat pumps instead of one air heat pump for heating and domestic hot water plus a separate controlled mechanical ventilation system with heat recovery?

Elektriker schrieb:
...
Result of the energy consultation according to DIN 4108-6 and DIN 4701-10...

These are standardized boundary conditions for primary energy performance verification, nothing more. It is not allowed to use these for dimensioning the heating system!

Elektriker schrieb:
...With this heat pump model and a 5 kWp photovoltaic system, would it possibly achieve KfW 55?

That depends on where the weak point is! Either Ht′ or qp″! If qp″ is the "critical factor," it is quite certain that KfW 55 can be achieved.
What a buffer tank, which usually reduces efficiency with heat pumps, has to do with photovoltaic systems is unclear to me ;-)

Best regards

Hello €uro,

thank you very much for your reply, but unfortunately I am not much wiser than before :-(

Two heat pumps for the following reason:
If the heating and domestic hot water demand were to be covered by a single heat pump, the system would tend to overshoot due to the two different temperatures (35°C (95°F) for heating and 65°C (149°F) for hot water).
A supply temperature of 35°C (95°F) can be easily maintained even in the coldest winter.

The hot water heat pump extracts about 20°C (68°F) warm indoor air, which means less energy is required to reach the 65°C (149°F) water temperature, and at the same time solves the issue of indoor ventilation.

Our main concern is the cost; I do not want to spend more on the entire heating system than the budget specifies, and with this model, we have achieved that.

Which DIN standard should be used for the heating load calculation?
Does this mean the heating installer cannot use any of the data from the calculation?

The buffer tank ultimately serves as an energy storage for the photovoltaic system and is intended to increase self-consumption.

According to the manufacturer, the COP of the heating heat pump is 4.0 at L2/35W.
The heating capacity of the hot water heat pump is 2.2 kW at L21/W15-55, according to the manufacturer.

If you really have a general contractor, you probably aren’t allowed to have anyone else install the heating system.

I don’t understand how two heat pumps could be cheaper than one slightly larger one.

As for the logic: To make it easier for the water-source heat pump, it draws heat from inside the building? Where does that heat come from? Right: from the second heat pump that supplies the underfloor heating. Sorry, but that doesn’t make sense!
Why heat the water to 65°C (149°F) anyway? With an air-source heat pump, it would probably even need to be supplemented with an electric heating element.

According to Ochsner, a heating element is not required up to 65°C (149°F).
The second pump is mainly for the residential ventilation system.
Heat pump for heating and domestic hot water plus residential ventilation = more expensive?