I think it takes a while for the juices to equalise and reach equilibrium before it’s running at max efficiency. You don’t want a duty cycle of say 15mins. You want say 1.5hrs. Something like that. (Numbers very hand wavy this is not my field directly) With an over designed system it stops and starts too quickly and this invalidates the warranty on commercial systems.
Modern heat pumps drive the VFD and circulation pumps as needed (i.e. the pumps run slower when the heat demand is low).
The main factor for good efficiency is low output temperature- underfloor heating works at ~35 deg C, radiators work at ~55 degC (because of smaller surface area).
I sized my heat pump based on historical data of heating oil /diesel consumption- since I had the data of past two winters, I could reliably determine the maximum continuous heat requirements for my house.
It also makes the environment itself uncomfortable in many cases - excessively drying the air, or causing weird moisture/condensation issues (as it won’t fully cycle the air in the house before stopping).
Essentially, you want your HVAC system to run for long enough it’s a gradual transition in temperatures inside and the equipment can run for awhile each time it needs to run to avoid the start/stop problems and let it ‘settle in’.
