Acceptable fration of time during which short cycling may occur - 7 kW or 10 kW heat pump?

[sdillenburg]

Dear all,

I am getting a Buderus heatpump installed in a few montths. My heating installer (not sure if this is the correct term, German: Heizungsinstallateur) believes the 7 kW variant would be a good fit. However, after reviewing the Buderus Planning Basis (Planungsgrundlage) I am not sure this is the best option for me. Following two things are bothering me:

1. The COP of the 10 kW variant between 0°C and 10°C is way better than the 7 kW, see page 17 and 18 in the linked document
2. At -5°C outside temperature, the maximum heating power of the 7 kW variant drops to approx. 5.0 kW ... 5.5 kW at flow temperatures of 50°C...55°C.

For my home I measured the required heating power at -9.6°C to be approx. 9 kW, see plots below.

Based on my current flow temperatures, I have determined the minimum and the maximum heating power for both the WLW-07 and the WLW-10 from the linked PDF.

7 kW

The 7 kW variant would require approx. 8% more energy (use of auxiliary heater not included in the calculation of energy consumption)
Based on the weather statistics for Hamburg, the auxiliary heater would be running 600 hours per year
The heat pump short cycles for about 1600 hours per year.

10 kW

The auxiliary heater would be running for about 18 hours per year
Short cycling would occur about 2800 hours per year, see plot.

I believe the 10 kW variant is the better option.
My question: Is short cycling for ~2800 h/a (additional 1200 h/a) OK? Short cycling starts between 7°C and 10°C, see plot.

edit:
Hydraulic balancing (German: hydraulischer Abgleich) was not yet done. Also, the current gas boiler has a minimum heating power of 6 kW, so it is probably running far away from optimum -> the actual required heating power may be less than indicated above.