Posted by: @andrewj

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He checked the settings, again, and said that the WC max temp setting of -3.2c was too warm and should be something like -10c - in other words, the max flow temp of 50c was being applied at -3.2c rather than, say, -10c.  By changing this value, actually to -7c after consultation with the Design Team, it effectively means that my Max Flow temp has been lowered below 50c at the sorts of temps I've had problems with.

Great, this is something of a breakthrough.  You could presumably reduce it all the way to -10 (or lower?) if necessary

Posted by: @andrewj

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All the radiators were rebalanced and I've been told to adjust internal house temps either by adjusting the Set Point temperature (i.e. the temp the thermostat attempts to reach) and/or the TRVs.  It would seem that Octopus are pretty adamant that their heat pumps should be thermostatically controlled.

Make no mistake and don't be fooled, thats for their convenience not your comfort or operating efficiency!

Posted by: @andrewj

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They are also going to arrange a re-survey of the house which will be interesting.  I'm really hoping that doesn't lead to a suggestion to downsize radiators.

If they do (and assuming you are happy with the physical size of the radiators) I suggest you tell them politely but firmly where they can put the downsized radiators (hint, not in your house!).

@jamespa yes, I'm under no illusions but in some respects, I've made my bed by going with Octopus.  I've sort of proved it will work without the thermostatic control, with the last element being the Flow Temp setting which I couldn't adjust further.  I think I could probably dive in and adjust that set point from -7c to -10c if needed but initially at least I need them to see it working or not.  I do have a direct line to the Design engineer who said I should call if there are problems and he can walk me though making changes in the Cosy Hub.  

The re-survey will be undertaken with version 2 software (whatever that means) so all I can do is wait to see what that comes back with.  I really don't want to get into an argument about changing radiators and would certainly prefer a flow temperature based fix but concomitantly, I don't want to be getting into arguments about support either so it may be tricky.  I would have thought that it would be cheaper for them to try and resolve with flow temp changes first before changing radiators, and in fairness to them nobody has actually specifically mentioned changing radiators!  Part of me is actually hoping they say you could get away with a Cosy 6 because it's a much smaller unit.

I'm not unhappy with Octopus (except maybe the promise-to-call-back-and-never-doing-so which infuriates me and has prolonged this experience) and I genuinely feel they want to get it sorted for me.  Anyway I will add to the tale as things progress.  What a journey!!

Recently had my follow up with octopus for the vibration / structure tied noise I've experienced since install.

They turned up with a airborne noise meter, obviously didn't show anything.

They have offered me to go visit another cosy, just to confirm its "usual" operating noise and not something wrong with my unit. Engineers seem to think it's typical noise.

Octopus have been good at handling it though to be fair, if it turns out it is inherent to the unit we will look at further isolation.

Id prefer to run it overnight in the cheap period but can't really do that at the moment.

@swwils I have my Cosy6 out the back, on a concrete plinth with no rubber isolating feet that come with daikin

i can here the noise of the pump running thru the flow pipes to the DHW tank, when it’s in water heat mode it runs noisier, so I moved DHW heat to 1pm rather than 10p

ive not finished the room that is next to the heat pump, I’m planning to install sound deadening plasterboard on the wall and sound proof insulation in the ceiling where the pipes run, and in the walls surrounding the utility room where the DHW is.

i have a sound meter which I will use before and after the sound insulation to see how effective it was

@agentgeorge unfortunately mine is a structure borne noise. 

I can't say for sure; but I think the fan is producing a harmonic booming style noise at higher speeds that is being transferred through to the structure of house, it's very low frequency so regular microphones and noise meters won't pick.it up as they have low cut filters. 

Posted by: @swwils

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@agentgeorge unfortunately mine is a structure borne noise. 

I can't say for sure; but I think the fan is producing a harmonic booming style noise at higher speeds that is being transferred through to the structure of house, it's very low frequency so regular microphones and noise meters won't pick.it up as they have low cut filters. 

Interesting.  I don't have that problem, although the fan is quite noisy when it is working hard, but my house is quite susceptible to specific frequencies.  It's a timber frame house and fireworks and nearby concerts in the park can really reverberate.  Is it not possible to recreate when an engineer is on site so they could at least personally acknowledge a problem even if they can't fix it?

@andrewj yeah we recreated it. Engineer seemed to think it was inherent to the unit.

It's hard to describe; but it's not airborne fan noise, it's an interaction between the fan and the case producing a vibration that transmits.

The leg kit helped alot, as did done Eva foam. But it's still not fully solved.

I just found this forum after watching the YouTube vids for a while, and have been on the Octopus and Facebook groups for a while. I have been playing around with the settings I can access for a while, initially tweaking the WC settings and radiator valves to get an even temp across the house. Whilst this worked for the last 6 months I found the high noise of the Cosy 6 whenever it came on to be annoying and not in-line with how the rest of the industry seems to have their heat pump operate.

For background, I run my system with a constant 21degC target across the house and a 50-60 degC DHW temp that runs at night. 

I have over the last week been running my system with a constant 23 degC target temp with the WC settings at the minimum they will go (30/50). I find that even with these settings the house never goes below 21 and often sits at 21.5. On the colder days (below 5) I see the oscillation in the power and flow temp which I thought was an underdamped control loop but reading this thread it seems there is a temperature element to flow temp.

As others have mentioned you cannot change the flow temps below 30/50 but you can change the outdoor temps for the curve to whatever you like. Normally warm weather is 12 and cold weather is -10 degC. I currently have it at 13/-10 but am going to try -20 to get the flow temp to drop a bit more when its colder outside as I am getting overheating.

I have also found that the Power Input recorded in the Cosy app and from the API is a higher than what my Shelly EM-50 records when the heat pump modulates down. I have put this down to Octopus not recording Active power and instead Apparent Power. The kWh consumption readings can be 10 kWh from the Shelly and 12 kWh from the Cosy, which has a very different COP assuming the heat output is correct.

Below picture is from a few days ago and you can see that at the lower outdoor temps the compressor starts to fluctuate.

@harrisonc mine has level 3 MID monitoring and you can see this power ramping. It's not completely weather comp control, there is a thermostatic element.

Basically the cosy should be thought of in terms of running cost and not COP. 

@swwils I can figure out how the cosy knows the energy input, but how does it calculate the energy output it sends to the house

I’ve got an open loop downstairs UFH network and a TRV regulated upstairs, I don’t use the upstairs a lot so have it set at 19C, Downstairs I have the cosy pod set at 21 during cheap cosy periods and 20 during the costly peak 4-7pm.

This has worked well for the year keeping the house cosy and saving 1/3 on the power bill since last year I had Gas.

some of that power has gone to the EV I have, used for local trips, and ive extended and  super insulated the house since having UFH so can’t directly compare to heating with Gas, but happy with the running costs so far 

Posted by: @agentgeorge

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@swwils I can figure out how the cosy knows the energy input, but how does it calculate the energy output it sends to the house

Flow rate x delta is how heat pumps monitor energy to house, no reason for cosy to be different so presumably this is what it does.

@swwils I am going to have to try putting the primary cosy pod in the airing cupboard to make it think the house is warmer than it is and see if the ramping flattens.

I have enough battery to cover the usage on a cold day, so I am just looking at efficiency, but can believe they designed the control to work best with the limited hours in each slot of the Cosy tariff. 

I can't complain that my yearly bill is £1,100 for home, heating and 20,000 miles on the car. 

Did you add the Level 3 MID yourself, and assuming you're the only Cosy 9 on HPM do you find the heat output reported by the API to be similar to that of the MID?