Thanks David
Assuming 180 m2 x 2.35m ceiling height = 423 m3 building volume.
Air change rate = 4551W / (0.336 x 423 m3 x 23K) = 1.4 ACH average.
Given that you have new windows, doors and have taken care with draughts etc that suggests a fairly air-tight building, do you have any special ventilation beyond intermittent extract fans?
Sounds like it might be plausible that the air change rate is half of this maybe 0.5-0.7 ACH, you could calculate what your minimum ventilation requirements should be based on part F building regs and cross check this with a blower door test if you wanted to delve into it deeper… You might be interested in reading the thread here: Measuring air change rates with CO2 sensors for heat pump heat loss calculation.
0.7 ACH would give 2275W reducing total heat loss to 7365W.
@ColinS’s experience with defrost performance with a EDLA11DA3V3 (ASHP sizing for Freezing Conditions) is that you cant rely on more than 7.5 kW from this unit (without the backup heater). It doesn’t give the 10.8 kW or so at -3C as quoted on the MCS database. Octopus are likely aware of this and are probably suggesting this unit so that you have capacity to cover periods below zero.
You can see the data for Colin’s heat pump here https://heatpumpmonitor.org/system/view?id=27.
The 9kW EDLA09DA3V3 has the same compressor as the 11 kW as far as we understand and so the low end modulation is not necessarily improved until you get down to the 8kW model… I dont think we know what the real world capacity of the 8kW model is under defrost conditions but if it was similar to the 11kW model it would likely leave you a fair bit short?
Do other Daikin owners think this is a fair reflection of our understanding?