Experiences with brine heat pump

September
4 people, 190 sqm living area, KFW55 Energy Saving Ordinance 2014
Heating: 4 kWh electricity (unfortunately I can only limit the AT shut-off temperature to 10 °C, so the heating has probably already started)
Water: 24 kWh electricity
Household electricity: 140 kWh electricity

October 4 people, 190 sqm living space, KFW55 Energy Saving Ordinance 2014 Heating: 123 kWh electricity (according to heating display - real including everything according to submeter it is probably ~ 15% more) Water: 29 kWh electricity Household electricity: 155 kWh electricity

Okto-Bär 180 sqm heated, additional 65 sqm in the insulated basement, 4 persons, KFW70 energy saving ordinance 2009 Heating and hot water together 92.8 kWh (according to meter, not heat pump)

Hats off. I believe it’s a mix of your boiling brine and the mild temperatures where you are.

Yes, I always cook my eggs in brine in the morning.
Here is a diagram showing how cold it was at my place (ground level, wind-protected in the shade). The values are the daily degree number (good for comparing heating values between buildings in different regions - for me, the required heating energy in the last two years has been almost exactly proportional to the daily degree number). So if the value on October 16th is, for example, 10, it means that the average difference between indoor and outdoor temperature over the day is 10°C (I log outdoor/indoor temperatures as well). Indoors, it is around 21°C for me, with only minor deviations (less than 1 degree).
This results in an average temperature of 10.5°C for October at my place.
How cold / warm is it where you are?

Where did you get the graphic from?
I found daily averages and minima:

Minima: