Hi @grendy,
I’m not familiar with Daikins, but:
- Have a look at How to reduce frequency of defrosts on Daikin Altherma?. It looks like @matt-drummer is the specialist in this area!
- Several heat pump controllers (maybe Daikin also, you’d have to check) start a defrost based on the temperature of the refrigerant as it enters the evaporator as well as outdoor temperature (duration of the former may also play a part - the colder the refrigerant gets, the sooner the defrost is called for). As you note, none of these factors is within our gift to control…
Personally I’m a bit skeptical whether users can do much about defrost frequency (or duration) other than running the heat pump as gently as possible when it is cold (e.g. minimum speed - or even switched off - overnight if that is consistent with space heating requirements).