ᐅ Operating Costs of Air-to-Water Heat Pumps: Consumption and Defrosting

RotorMotor schrieb:

As long as you haven’t moved in yet, there’s no need to worry. While tradespeople are coming and going and doors and windows are left open, you can’t really rely on the consumption figures.

I can absolutely confirm that. The tilers leave the construction door open almost all day because they frequently need to go outside to use the angle grinder. That’s why we’ve set the supply temperature to just 19°C (66°F) to avoid cooling down the house too much. The temperature sensors inside the house show between 12 and 14°C (54 to 57°F). That’s fine since the tradespeople are constantly moving around ;-P

I would just wait until all the technical installations are fully completed and the tradespeople have left, then measure again. If necessary, you could completely shut off the upper floor at the heating distribution manifold, which should save several kilowatts. In our case, only the underfloor heating in the basement is running. There it’s 14°C (57°F), while upstairs it’s still around 12°C (54°F).

*Edit:
This approach only works because everything is already dry in our house and the humidity level is consistently at 40%.

Well, whether the room thermostats are installed or not doesn’t really matter. The key point is the "hydraulic balancing," where room thermostats are no longer relevant. The problem is that with a supply temperature of 26°C (79°F), the pump will only stop running once the return temperature reaches around 22°C (72°F). Simply put, that means you also have about 26°C (79°F) inside the house. In other words, it runs almost continuously. That’s why it’s important to know how the heating curve is set. A supply temperature of 26°C (79°F) is not unusual for a reasonable 55°C (131°F) heating curve at the given outdoor temperatures. You could try to limit the flow by reducing everything by half, but it’s always tricky during the shell construction phase.

I also hope that things will improve once everything is fully installed. However, I am still shocked that the pump’s energy consumption is significantly higher than the electric fan heaters used in the weeks before—especially since heat pumps are generally promised to have comparatively low operating costs everywhere, but here the opposite seems to be true. In the end, this is an ongoing cost factor that I obviously want to eliminate as soon as possible.

I checked the display again today. The defrost cycles have decreased (2.5 hours between defrosts), and the electricity consumption is slightly lower at just under 40 kWh. However, I still consider this to be quite high, especially since according to the display no auxiliary heaters were active over a longer period (the operating hours counter is the same as yesterday), and I had lowered the room temperature on the device from 19 to 17 degrees Celsius. Otherwise, I was able to read the following operating data and times (since last Tuesday):

• Operating Times
• Outdoor unit 111 h
• Heating 97 h
• Hot water 13 h
• Auxiliary 1 23 h
• Auxiliary 2 12 h
• Operating Data
• Heat demand 0
• Outside temperature 0°C (32°F)
• Hot water 47°C (117°F)
• Flow temperature 25°C (77°F)
• Condenser OFF 25.0°C (77°F)
• Condenser ON 22.6°C (73°F)
• Coolant 1 21.5°C (71°F)
• Coolant 2 -6.3°C (21°F)
• Pressure line 63.7°C (147°F)
• Compressor temperature 52.0°C (126°F)
• Outdoor unit ambient temperature -0.5°C (31°F)

Settings and heating curve here:

Are "Zusatz 1" and "Zusatz 2" additional heaters?

When temperatures dropped below -10°C (14°F) here a few days ago, they switched on for a few hours in my system as well. During that time, they easily consume around 6-9 kW per hour.

Until you move in, I would definitely recommend saving on hot water. Especially if the temperature is set relatively high, the heating element might turn on depending on the settings.
This can really make a difference.