I think that’s a separate issue, we are definitely seeing low initial starting performance on these daikins, at least that’s my impression?
It’s peculiar in that it doesn’t have the profile of a defrost (I’d expect flow to go lower), and the electrical input is way higher that the rest of the cycle (immersion?). There is a little spike of heat afterwards.
There’s also a bit of resistive heating at the start - note how flow jumps up when the pump starts.
For hopefully some peace of mind for @matt-drummer, here’s mine at similar outside temps. COP 3.2 getting to 46C flow, Matt achieved 3.4 COP up to 46C flow temp, including that defrost
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I’ve noticed that on @ColinS’s system as well. Compressor being heated up in preparation?
What is a ‘Hermetically sealed swing compressor’ @marko ?
Yes good point, that’s unusual for a defrost and no dip in flow temp, so yes unlikely to be a defrost, perhaps as you say a brief bit of immersion/booster heater kicking in.
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From asking around I have been told it is preheating the heat exchanger to reduce the thermal shock post the three way valve switching over (as any water in the coil will likely be warmer than the radiator circuit).
@Timbones How did you compare the systems and make the scatter graph, is there a feature I am missing or is the data exported and manipulated?
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Octopus have told me today that my heat pump is the right size for my house and that I should be happy with a SCOP of 3.30 All the other houses are different to mine and the heat pumps are built differently and I probably use more hot water than the other homes???
But it’s OK as when it gets really cold I’ll need it and it will probably do better.
I am not sure I need this?
So I have a 9kW heat pump as that is what I need but it seems to need even more electricity.
I am just about to investigate what the cause of the increased electricity consumption is, I assume it is the back up heater.
And so it is, 3.5kW of back up heater and it’s 4.4c outside.
Is this normal?
I’d be better off with night storage heaters, this cannot be what is supposed to happen?
Honestly, flip the breaker for backup heater (BUH) and disable in settings. I did mention this before in another thread that I did this very swiftly after Octopus 
finished.
I’ll really only consider putting it back on if we have a fault. Although let’s face it the fault will be such that the BUH will be irrelevant!
You can then fundamentally rule out BUH (and sort out/turn off Booster Heater (tank immersion for Legionnaires)!
You can always undo these actions (take note of parameters and values prior to changing them), but these heat pumps really don’t need them (that I can see - and I have neither switched on since Octopus commissioned the system and left and we got through the whole winter ‘22/‘23)
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Thanks Stephen.
Just a bit of a surprise to see when I got home.
The thing is a useless pile of junk in my opinion, not fit for purpose.
I thought the back up heater was for when things get tough.
I have a 9kW heat pump that I don’t need that now requires 3.5kW of back up heater to provide 6.575kW of heat.
At least I’ll be OK when it gets really cold according to Octopus 
It really depends on the commissioning values. Octopus seem quite conservative in them. I’m really not sure they’re needed - especially given the oversizing context in your specific case.
You may have a fault, but either way, your property suits the smaller (4/6/8 kW) unit I would say regardless. The unit (9/11/14/16 kW) on minimum modulation is still too high an output for our property- circa 40-50% more m2.
Octopus have told me this afternoon that although they originally surveyed my conservatory with a heat loss of 827w and yesterday it turned out to be actually 2,300w that they haven’t really made a mistake because they also got the rest of the house wrong at the original survey to compensate, the mistakes cancelled each other out and there really wasn’t any mistake at all???
So despite the heat loss of my conservatory going up by 1,500w the heat loss of the whole house has only gone up from 7,300w to 7,400w because the rest of it had been overstated by 1,400w.
Convenient good news all round, my heat pump is exactly the right size and my SCOP of 3.30 is really good as it is better than the 2.80 the MCS require.
Apparently, if I wanted better I should have paid more money!!!
There was more but I think the above really sums it up.
The heat pump was running fine up until 18:00, and then stopped for a little nap. Restarting at 18:30, it struggles to get that heat output back; COP is 2.7. The heat pump can sense that something’s not right, and turns on the BUH to boost the heat. It then reduces the compressor to the point where there’s only 1.2kW input + 3.5 kW for the BUH. Discounting the BUH, the underlying COP is still around 2.6 at 19:20.
At 19:25 there’s a defrost, keeping the BUH running for additional heat until 19:30. We then have a normal looking cycle that starts with that COP of 2.6 and gradually climbs to a respectable 3.6.
Feels like it decided to use the BUH to keep the heat pump running, rather than do a regular defrost at 18:50. 
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And give Octopus some more of my money 
Octopus also told me this afternoon that because I have replaced four radiators upstairs (that are on my radiator schedule as being P+ even though they were actually K1s) I have changed their design and they are no longer liable for it in any way.
That’s the crux. Are all Daikins doing this, turning the backup on at the drop of a hat, or could there be some sort of fault on this installation?
The oversize unit is annoying but should only hurt performance and not totally tank it.
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You didn’t admit that change on the record, did you? 
If you’d already told them their schedule was wrong, then they’ve no idea what was there if they didn’t replace them.
I did, I’m honest and I don’t care.
I don’t really want them to replace the heat pump. I know this one heats the house, I have no idea whether a replacement would and I would prefer not to take the chance.
I never wanted a Daikin and I will never have another one, I have no faith in the company or their products.
I didn’t want anything from Octopus other than an explanation of how they arrived at the heat loss and what the mistakes were, I now have my answer.
I will make the heat pump work as best as I can as I am the only person I can rely on, although I need a bit of help at times from the nice people here
What I have learnt today, from the horses mouth, is that Octopus install heat pumps to a budget, they are only interested in achieving a low level of efficiency that meets MCS requirements, if you do better then you got lucky but they are not aiming for mid to high efficiency, just comparable running costs to a gas boiler.
They told me that if you want better performance then you need to look elsewhere and pay more money as all they are offering are cheap installations, fair enough, at least we know.
If you are not satisfied with the performance and try to make it better then you are on your own as they wash their hands of any responsibility for the installation.
I don’t disagree with any of it, it’s their business and they run it how they like. As I told them, I would never have used them as an installer if I could have found anybody else to do it, mainly because I didn’t want a Daikin heat pump, I wanted a Vaillant but couldn’t find a willing installer.
So I have what I have and I will make the most of it.
What Octopus have gained from this is a very dissatisfied customer who will pass on his experience of the company to anybody that is interested in listening. I won’t be telling lies or advising anybody to avoid them or Daikin but I do feel quite within my rights to share my experience of both companies and the performance of my heat pump.
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I wouldn’t have lied about it. I wouldn’t have volunteered that, though. Even though you did, it seems completely reprehensible of them to refuse liability because you actually improved part of your system that they’d mismeasured anyway.
I don’t think they’re allowed to do that, but ordinarily MCS seem as useful as a whelk in a whirlwind. However, Octopus have been treading on their toes saying they’d accept non-MCS solar installations (I think. Might have been battery), so they might fancy acting.
You have my sympathy. I still feel lucky that we went for Mitsubishi, knowing as little as we did back then. It’s not perfect (but it seems none are) and the installers definitely weren’t, but we got it working reasonably. I don’t think Daikin were high on our list, but Grant were and I really don’t like what I’ve read about those since.
It’s also sad that octopus seem to be trashing their reputation with some iffy Daikin installs before their own brand pumps are in full production.
I hope you get it running well. I find your process fascinating. I’m sorry I don’t have more help to offer.
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Thanks @mjr
It wasn’t so much not telling lies or volunteering the information, I had already told them that I really wanted to make this heat pump to work and that I had started increasing radiator sizes to handle the heat produced at a lower flow temperature to improve efficiency.
I still would have told them what I was doing as I think it is the right thing do but I agree that it is totally reprehensible to hold that against me, they are bigger radiators, nothing more and nothing less.
I think they were expecting me to make monetary demands or force a replacement and they have been on the defensive as soon as they realised the errors in the original heat loss survey.
They refused to talk to me for a day and have formulated this story that the heat loss was wrong but not wrong in this time. In March the conservatory needed to be excluded from the heat loss but then didn’t as he mucked it up but now it must be included as it is a habitable room.
Either way they must be wrong as now it is included the radiator isn’t big enough and so they have not met MCS requirements. I think this is why they have decided to disown the system for my radiator changes as this has now absolved them from having to come and rectify the conservatory radiator(s).
They did offer to pay for and install a radiator in the conservatory but I declined the offer, I already have two of their radiator replacements here that I need to fix as the workmanship is atrocious!
It would be nice to say I have documented this to help others, I did a bit but being honest it has been nice to vent a bit and I welcome the advice and assistance I have received, it is very much appreciated.
Having said that, I do hope a lot of this lasts and it can become a bit of a lesson about how important the heat loss survey and the system design is, they are the most important parts and if it is wrong it’s quite difficult and costly to fix but hopefully not impossible in my case.
I have learnt a lot in the last six weeks and hope to learn more although some of the things I have learnt I wish I hadn’t had to if you know what I mean.
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