Perhaps extending the design margin on this old Ecodan to 20% if sizing on a accurate heat loss is wise.
Luckily the high end of my inferred design heat loss space heating requirement at -3C is just under this at ~3.8 kW: Though we dont seem to ever experience DT’s between internal temps and outside temps of more than 20K…
Caveat of course is that these results are not transferable to newer models based on different refrigerants! This really feels like one of those things every single model needs to be tested on.
Can HeatpumpMonitor.org partner with a test house that tests and validates capacity and SCOP values for the MCS database somehow? It would be great to understand how manufacturers and others e.g at BRE Heat pump testing - BRE Group go about testing max capacity during defrost conditions. I did try and contact BRE but was told this wasn’t something they could help me with… feels like we need to know the right person to speak to…