Posted by: @jamespa

↑

Now that really is nuts.  Hopefully tech support dont suggest to downsize the radiators!

That would be my worry.  If they insist the resolution is to downsize some radiators I may instead have to go back to a thermostat to limit the temp rises as OAT drops. That would be disappointing because it brings back all the issues I had with a gas boiler and thermostat, perhaps not as bad maybe.  Besides, I don't think I could face the redecorating again 😀 

I'm going to take a stab that the problem isn't caused by an oversized Cosy and that a Cosy 6 would have the same limitation in the app/settings anyway.  In any case, my gas usage for heating last year was 8938kW, albeit with just 100-150mm of loft insulation, and hot water 2221kW, figures I gave to the surveyor.   Checking the design doc again they determined a heat requirement of:

Net Energy required to heat property: Heating 10000kWh, Hot Water 2000kWh

Existing System Consumption: Heating 10869kWh, Hot Water 2173kWh

Not that far off really.  Heat Geek thought I'd get away with a 7kW Vaillant, perhaps with a supplementary heater in the flow/return for the really cold days, but given my rate of heat loss I don't think that would be required.  Octopus don't do Vaillants, the choice is (was) a Cosy or Daikin.

Posted by: @andrewj

↑

The engineer visited this morning and checked everything over.  He agrees that everywhere is too warm but he cannot drop the Cold Water Flow Temperature min value below 50c as the system doesn't allow it.

This is disappointing.  Surely the engineer who called would have known this before he got in his van.  I can only assume that he was expecting to find yet another uninformed end user for him to put right.

@andrewj it reads as if you really need a 6kW version or they need better turn down temperatures.

From your gas usage of 9000kW divided by rule of thumb 2900 then you really only need a 4kW max(!) pump https://protonsforbreakfast.wordpress.com/2022/04/05/what-size-heat-pump-do-i-need-a-rule-of-thumb/

Alternatively you need a software upgrade!

Posted by: @andrewj

↑

I'm going to take a stab that the problem isn't caused by an oversized Cosy and that a Cosy 6 would have the same limitation in the app/settings anyway.  

A lmost certainly yes to the first half but in a way could be caused by oversizing.  Oversizing means bigger rads.  Bigger rads means more output at any given FT.

Posted by: @andrewj

↑

If they insist the resolution is to downsize some radiators I may instead have to go back to a thermostat to limit the temp rises as OAT drops. That would be disappointing because it brings back all the issues I had with a gas boiler and thermostat, perhaps not as bad maybe.  Besides, I don't think I could face the redecorating again 😀

Another solution would be to operate it on WC, but intermittently.  'Knocking out' an hour here or there would reduce the energy delivered at any given FT.  Its stupid really, but maybe will result in greater comfort than operating on thermostat.  

@andrewj At the time I had an 8pus (I like that term!😊) survey, they only offered Daikin; their Cosy unit was still in transition from the RED design stage. I suspect some of the deciding factors in favour of 8pus supplying just the Daikin range was for simplicity in training, probably a better price from the supplier and thirdly, the fact that using R32 refrigerant meant that there would be more flexibility in the siting of the outside unit compared to pumps using R290.

I believe the guidelines have been relaxed since but at the time we had our pump installed, R32 was the only type that could be sited near drains, windows, doors and vents. (All of which we have in the only possible siting we could use.) Regards, Toodles.

I will wait to see what they say but I'm expecting to have to chase.  Service is pretty good except for the usual "we'll give you a call back" shenanigans!  In the meantime, not sure.  As it gets colder it overheats the house and burns hard - it pulled 5kW out of my battery in 2 hours to get the living area to 22.7c.  It's probably worth experimenting with an overnight set back of 21c from 22:30 to 04:00 and then letting it run on the thermostat to 21.5c.  I don't really want to skew the data that the Technical Support Engineer will have access to though.

Thought it might be of interest to post relevant pages of the design doc.  The Lounge Area, Living Room, Dining Area and Kitchen are all open plan, as are Study and Office, and the radiator positions are the original ones.  The position of the radiator in the Living room is actually under the window in the Lounge Area and the radiator in the Office Area is actually under the 1.66m window.

@andrewj it's also possible that not all cosy are the same cosy.

If I was octopus and doing a rollout like this; I would definitely have A/B hardware tests where allowed under the MCS registration for the unit. I might be wrong but I believe you could vary the main fan SKU in a cosy without issue and gather valuable real world data with some fan OEM options. This would be invisible to typical end user.

Posted by: @swwils

↑

@andrewj it's also possible that not all cosy are the same cosy.

If I was octopus and doing a rollout like this; I would definitely have A/B hardware tests where allowed under the MCS registration for the unit. I might be wrong but I believe you could vary the main fan SKU in a cosy without issue and gather valuable real world data with some fan OEM options. This would be invisible to typical end user.

A different fan might make the unit less noisy at full chat!

@andrewj some of the JS for the hub certainly suggests this, or at least labeling for 2 OEM fans, maybe it's just the 6 and the 9.

Posted by: @swwils

↑

@andrewj some of the JS for the hub certainly suggests this, or at least labeling for 2 OEM fans, maybe it's just the 6 and the 9.

JS??  The Cosys are the only HPs that Octopus can experiment on.  Are they installing Daikins now, I couldn't tell from their website?

@andrewj oh yes they offer Daikin 8kW, they tried to foist that huge monster on me, it would have blocked the rear gate access into the garden, besides Cosy6 using R290, smaller , cheaper to run, modern design, more vertical than horizontal in space envelope

Latest news.  I've still been struggling with overheating and no contact with Octopus but yesterday a manager intervened and an engineer turned up this morning (who agreed it was bloomin' warm in the house.)  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.  The Warm Weather end of the WC curve was changed back to 36c.  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.

At this point, it's another monitoring period to see if this change works.  Outside temperatures are very mild now and the house internal temp is generally good in these mild temps (up to today, 22c - 23c) so I need a cold spell in order to see the impact.  Perhaps in the future I might re-attempt running it without thermostatic intervention but for now I really need to not touch anything so they can see and resolve if necessary.  Hopefully I will get a more responsive intervention if things are problematic.

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.  Last night I was around at a neighbour's and I'd forgotten how small the radiators were originally: single panel no fin types of apparently inconsequential size - the one in the hallway was around 12" x 15"!  I only mention that because clearly they were sufficient for the heat loss with a boiler to 1980's standard.  

Anyway, it feels positive and the engineer and Design Team member were surprised that the problem was related to being too warm rather than too cold!