Posted by: @jamespa

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...  Houses have a lot of thermal mass.

Is 50C really the minimum low OAT flow temp, if so thats crazy crazy crazy and wont work at all with UFH so sounds wrong. 

Are you sure that there is not an installer setting for min permissible flow temp, which can be adjusted down.  Alternatively can you make the -10 figure even colder, which would have the same effect.  

Interestingly, being a timber framed house, all internal walls are plasterboard.  The internal walls which have an external facing are plasterboard backed by insulation backed by vapour barrier backed by brick or timber cladding.  The plaster board doesn't really retain a great deal of thermal heat in the same way that bricks do but the overall insulation is good.

Octopus give very little info on their apps so I know neither the flow rate nor if there's a way to impact the minimum and maximum cold/warm weather values: 50c-70c and 30c-40c respectively.  Defaults are 57c and 37c.  If there is an installer setting I'd have to go through Octopus to get it changed.  I don't have UFH and I suspect they would install a Daikin unit for those scenarios, but just to be clear that we are talking the same thing, I've posted the Flow Temp adjustment screen in the app.

I think internal temps are slowly dropping but there has been at least one period of time today when the Cosy wasn't running - it is again now, ticking over at around 600w.  

Posted by: @andrewj

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but just to be clear that we are talking the same thing, I've posted the Flow Temp adjustment screen in the app.

we are talking the same thing.  Its crazy if its really like that, but Octopus are, in fairness, pursuing a 'low installation cost, good enough' approach rather than the 'maximise cop at all costs' approach that many erly adopters have defaulted to. Is there an Octopus Cosy user forum where perhaps you could get some more info on this aspect, with no meaningful user manual we are all in the dark!

EDIT this may be the Cosy installation manual, if so then, as I suspected there are some possibly relevant installer settings see section 11.3.5, although its not clear whether there are hard limits on these or how they relate to what the app displays.

Posted by: @jamespa

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we are talking the same thing.  Its crazy if its really like that, but Octopus are, in fairness, pursuing a 'low installation cost, good enough' approach rather than the 'maximise cop at all costs' approach that many erly adopters have defaulted to. Is there an Octopus Cosy user forum where perhaps you could get some more info on this aspect, with no meaningful user manual we are all in the dark!

EDIT this may be the Cosy installation manual, if so then, as I suspected there are some possibly relevant installer settings see section 11.3.5, although its not clear whether there are hard limits on these or how they relate to what the app displays.

There is a Facebook group in which the lead engineer participates but he doesn't get involved in every discussion and his responses are often cryptic and I've never seen him follow up if someone asks for clarification.  Which is a shame really and he definitely doesn't advocate for SCOP chasing and holds the line that running on the Primary Pod thermostat is the right way to go.  In other words, the Cosy isn't specifically intended to run purely on flow temperature although it can do so (and I don't know if there are limitations built in to its firmware.)  It's probably why the default Flow Temp settings are how they are.  and the design specs are to the MCS specifications for room temps.

Note that the 50c relates to an OAT of -10c.  At a more reasonable (except for highlands of Scotland) -5c it's 46c and at -2c it's 44c. 

That manual correlates to the flow temp settings I pasted above.  Apart from the "Target Flow Temperature" value - I don't know if the Cosy Controller is using that in some way or what it might pertain to.  The instructions in there for installers does align with what people, including me, see in the app when installed.  Adjustments are made from there if necessary.  It's an interesting cautionary note: the Cosy 9 (not sure about the Cosy 6) cannot modulate a flow temperature below 35c so if that is indicated by the WC curve then it starts cycling (although it does that by default based on the Primary Pod sensed temperature anyway).  I currently have it set at 33c so it may be a bit low.  The Senior engineer I just mentioned recommends this is 15c above desired set temp (so, in theory, 37c in my case as I am really aiming for 22c in the living area.)  I may have to tweak that up if it cannot maintain temps at 5c (probably that end of the curve rather than the cold weather end.)  Shame it doesn't go into commissioning approach as that might give more insight into why they want customers to run it the way they do.

The problem with making changes to these "hidden" configs is (a) access; and (b) unknown implications of changing them in terms of the Cosy itself (as opposed to ASHP operation principle in general.) 

Posted by: @jamespa

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Oversizing wont affect internal temperature which depends on the flow temperature (ie the WC curve adjustment) not the capacity of the heat pump (assuming its not undersized of course).  However if your house loss was overestimated (which is quite likely) then your radiators may be bigger than is needed for the flow temperature it was designed to work at, so the house will overheat if run at that flow temperature.  Not a problem, simply drop the flow temperature (WC curve) to fix that, which will also improve efficiency. 

I was thinking about this a bit.  It's probably not a problem if they are all similarly oversized otherwise the flow temperature might be too high for some and maybe not enough for others.  Not helped that they design the system to MCS room temperature standards.  It might explain why the radiator in my study heats the room up way more than, say, the living area (a good 2c-3c) even when the LSV is only open 0.25 turns.  That might be one for a decorator cap!

Posted by: @andrewj

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I was thinking about this a bit.  It's probably not a problem if they are all similarly oversized otherwise the flow temperature might be too high for some and maybe not enough for others.  

The problem comes only if you can't turn the ft down sufficiently because of the firmware limitations.  At that point you will have to run thermostat controlled.

I fear they are trying to make it easy for installers reckoning that any loss of efficiency can be made up by tarrif manipulation.  It's not silly as an experiment, but perhaps people should be warned that they are guinea pigs.  In fairness we all are, although heat pump technology is pretty mature, installation techniques are not, not is UI optimisation for a mass market.

Posted by: @andrewj

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Posted by: @jamespa

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we are talking the same thing.  Its crazy if its really like that, but Octopus are, in fairness, pursuing a 'low installation cost, good enough' approach rather than the 'maximise cop at all costs' approach that many early adopters have defaulted to. Is there an Octopus Cosy user forum where perhaps you could get some more info on this aspect, with no meaningful user manual we are all in the dark!

EDIT this may be the Cosy installation manual, if so then, as I suspected there are some possibly relevant installer settings see section 11.3.5, although its not clear whether there are hard limits on these or how they relate to what the app displays.

There is a Facebook group in which the lead engineer participates but he doesn't get involved in every discussion and his responses are often cryptic and I've never seen him follow up if someone asks for clarification.  Which is a shame really and he definitely doesn't advocate for SCOP chasing and holds the line that running on the Primary Pod thermostat is the right way to go.

The problem with making changes to these "hidden" configs is (a) access; and (b) unknown implications of changing them in terms of the Cosy itself (as opposed to ASHP operation principle in general.) 

 

TJ's share options depend on you using lots of energy, high efficiency is not part of his or Octopuses brief. They installed heat pumps as a loss leaders to grab market share, knowing they would make it up on the long tail of winter kWh. 

First cold snap, and it's already mayhem, been in the Cosy user group all day today trying offer some kind of help. Some people are going to have to choose between big bills, or being cold.

Dread to think what the running costs of Turbo installs will be like at -3c. I already sense an air of descent in the group. Some talk of going back to gas, but there is no going back, Octopus has them by the balls. 

Posted by: @dansus

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First cold snap, and it's already mayhem, been in the Cosy user group all day today trying offer some kind of help. Some people are going to have to choose between big bills, or being cold.

People have to get used to the fact that, while running costs are certainly high during (rare) very cold periods, that balances out over the whole season. 

With gas, and particularly with oil, nobody ever looked at daily consumption (if they had then it too would be scary), with heat pumps people do, but probably only for the first year!

Some gentle comforting and encouraging people to run their heat pumps efficiently, to the extent thats possible given the apparent limitations of the Cosy range (minimum cold weather flow temp of 50 - where does that come from?). is probably the way forward.

@jamespa I agree.  

It's not to say that some people probably do have problems but the commissioning side of the install is where Octopus let themselves down.  My installers failed to finish the work at 8:30pm on a Friday and did nothing but test that radiators got warm - it was middle of May so heating wasn't an issue per se.  Two weeks later, a couple of engineers came to finish the install and they finished work at around 5:30pm.  I had an engineer out around the middle of October who came and balanced the rads to deltaT 5c and adjusted the flow rate which he said was incorrect.  As this thread testifies, I'm left to work it out with the help of this forum's members and slowly getting there.  As I said to my wife: "can you imagine the people who can't really do this?"

I think they should have a commissioning team that visits the installs afterwards to complete the commissioning, turning up for an hour a day until it's set up correctly.  That's going to be expensive of course so really just a pipe dream.  Basically, this part of installation is no better than the bang-em-in boiler heating engineers that we've got so used to and love.

Apart from that, it clearly works well as I'm maintaining a hot house with a COP of 3.75 - 4.0 in this cold weather.  At least I have a problem with a hot house rather than a cold one.

Having not made any adjustments since 4am yesterday, this is the state of play this morning (attached pic.)  Just us getting up and on with the day has raised temps a bit since 8am, 0.2c-0.3c in some rooms.  However, upstairs has cooled down a bit.  The Bed1 and en-suite are a bit misleading because of course they have been used by two people (IIRC, these were around 24.2c at 7:30ish.)  OAT was down to 1.6 at 7am.

So still too warm but closer to downstairs (also still too warm.)  I'm going to leave things alone again today, as it's due to get colder tonight and into early Thursday, and see what happens.  Potentially looks like I need to tweak down the Warm Temperature setting of 33c as I have no room to manoeuvre at the Cold Temperature setting of 50c.  I may need to try the decorators caps on the Study and Landing radiators as well. 

As an aside, would it be a great problem if I turned off the landing radiator at some point - I just don't think the house needs it frankly.

Posted by: @andrewj

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So still too warm but closer to downstairs (also still too warm.)  I'm going to leave things alone again today, as it's due to get colder tonight and into early Thursday, and see what happens.  Potentially looks like I need to tweak down the Warm Temperature setting of 33c as I have no room to manoeuvre at the Cold Temperature setting of 50c.

I doubt that tweaking the warm OAT setting will make much difference but its worth a try!  My guess is you may well need a cold end setting lower than 50 which, other possibly than through the installer menu, you cant do.  Thats disappointing as every degree you drop the cold OAT end is worth about 2.5% efficiency improvement.  This seems to me to be an unnecessary limitation!  If it turns out you do need a low OAT end FT that is lower than you can dial in, your remaining options are to use the  thermostat/pod to limit the temperature (ie by setting it to the temp you want) or heat part time, its counterproductive to turn down all the LSVs.

That landing radiator is certainly looking as if its surplus to requirements.  In principle its a shame to take it out because it adds system volume, but you have a fair few rads so I doubt thats a problem.  This being the case then yes I would turn it off.

It feels to me as if we might be heading for the conclusion that your loss was, overestimated resulting in oversized rads for the min 50C FT.  However you are getting good COP so not really a serious concern, just watch it doesn't drop if you re-introduce the thermostat.  I suspect Octopus have designed the system for easy install and have possibly 'tweaked' it (to the extent it can be tweaked) so that it delivers good cop over a wide range of conditions rather than excellent COP over a narrower range of optimised conditions.  Thats a valid design approach!

Posted by: @jamespa

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I doubt that tweaking the warm OAT setting will make much difference but its worth a try!  My guess is you may well need a cold end setting lower than 50 which, other possibly than through the installer menu, you cant do.  Thats disappointing as every degree you drop the cold OAT end is worth about 2.5% efficiency improvement.  This seems to me to be an unnecessary limitation!  If it turns out you do need a low OAT end FT that is lower than you can dial in, your remaining options are to use the  thermostat/pod to limit the temperature (ie by setting it to the temp you want) or heat part time, its counterproductive to turn down all the LSVs.

That landing radiator is certainly looking as if its surplus to requirements.  In principle its a shame to take it out because it adds system volume, but you have a fair few rads so I doubt thats a problem.  This being the case then yes I would turn it off.

It feels to me as if we might be heading for the conclusion that your loss was, overestimated resulting in oversized rads for the min 50C FT.  However you are getting good COP so not really a serious concern, just watch it doesn't drop if you re-introduce the thermostat.  I suspect Octopus have designed the system for easy install and have possibly 'tweaked' it (to the extent it can be tweaked) so that it delivers good cop over a wide range of conditions rather than excellent COP over a narrower range of optimised conditions.  Thats a valid design approach!

I think I have plenty of system volume in the radiators plus the volumiser, as you say.  I will try dropping the warm temp end to see the effect and I may then call Octopus and see if there is something they can do in respect to the cold temp end of the scale - I already have an outstanding action with them following an engineer call a couple of weeks ago.  I don't really want to go back to the Pod-as-a-thermostat running and I can live with 23c downstairs at these OATs (my wife loves it) and use the TRVs upstairs in our bedroom.  It's too warm for me but my wife would be happy to go to bed at 22c. The overall COP for yesterday was 3.75 and today so far it is running at 4.05 although that is likely to drop down as the day goes on. My SCOP since May 9th is 4.06 and we've only really been heating for a 1.5 months.  These seem eminently reasonable to me but my experience is limited.  I assume the main issue will be cycling in the shoulder months.  

Octopus are definitely targeting install price vs running cost.  In fact, I think up to earlier this year they were buying business.  Ignoring the grant, the install cost from Octopus was £14.5 including a new 300l tank and 13 radiator changes; Heat Geek were quoting £26,500 for essentially the same job (7kW Vaillant and 16 rad changes.) I don't think the actual install element is any more complicated or simple than, say, a non-Octopus installer would be forced to do.  Octopus design to MCS guidelines so different temps in different rooms at a specific design temp (21c in living room., 18c in bedrooms at -3.4c for example) and commission the heat pump to operate on a thermostat using WC; Heat Geek target the same temp across the house, 22c in our case, and commission to run constantly on WC.  For me, they quoted a SCOP of 3.6. I don't think the Octopus approach leads to a particularly comfortable house as those temperature differentials will be really noticeable and the running costs will be somewhat more (SCOP of 3.6 vs 4.0 say) but it's hard to argue with the install costs they were charging.  I'd agree they are going for a non-complex operation approach which is likely to suit the majority of customers and the running costs will turn out not to be hideous.

Apropos of nothing, here's the WC curve using the minimum flow temp settings.

@andrewj All seems rather warm, try rebalancing your rads so less energy goes upstairs, and lowering desired temp. 

Do you have the quote sheet they give you, that shows the design temp and watts need? 

Posted by: @dansus

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@andrewj All seems rather warm, try rebalancing your rads so less energy goes upstairs, and lowering desired temp. 

 

Do you have the quote sheet they give you, that shows the design temp and watts need? 

I think you may have missed the posts where its explained what he is trying to do which is get it running on weather compensation alone (as many do with heat pumps) and thus he is setting the 'desired' temperature way higher than his actual desired temperature so the thermostat/pod has no influence.

Unfortunately its beginning to look like the 'cold weather' flow temp he needs is <50 (presumably because the loss was overestimated).  For some undisclosed reason it appears that Octopus make 50 the minimum cold weather flow temperature settable, at least without going into the installer menu.  He is in the process of confirming that though.