@andrewj this is an interesting discussion.  I am curious to understand why you are asking the question.  You already have a heat pump, so surely you can experience this for yourself?  Are you finding it less comfortable than with the gas boiler?  Are you finding that the system is cycling on and off too much?

We have had our heat pump system since August.  While these are early days, my wife and I feel that the house is much more comfortable now.

Posted by: @majordennisbloodnok

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Posted by: @andrewj

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I think that concurs with what you are both saying and that I will see behaviour in line with my expectations as the weather gets colder.  I suppose that also means some rooms are likely to be cooler than others simply because of this thermostat-like behaviour.

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Yes, I think it does concur.

Regarding some rooms being cooler than others, I suspect that may have more to do with radiators not being as well balanced as they could be. There's another article - this time by @toodles - covering this and it's here. Balancing is often not done well by installers simply because it takes more time than they have available, but it's a straightforward process for a homeowner to do and gives good results once done.

 

Distinctly possible as it wasn't really feasible to test more than the radiators weren't leaking and some heat could be felt.  I did agree with Octopus that they would come back and properly balance later in the year - we shall see.  However, really I suspect it's because the heat loss is greater in some rooms than others and the impact is more obvious with the way it is running.  Once it settles down to always on then, assuming it is properly balanced, I expect things to be more consistent.

Looking at the graph Im a bit surprised it isnt running more 'continuously' at night.  Of course you could have a very well insulated house (although cosy 9 = 9kW? doesn't sound that way), the heat pump could be oversized, or it could be bouncing off the room thermostat because the cold weather FT setting is too high (57 is a very high 'cold 'FT, although in fairness I dont know what outside temperature that setting corresponds to so ).  Difficult to tell for certain until we get sustained colder weather at which point its worth tweaking the WC settings to get best performance possible.

Posted by: @grahamf

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@andrewj this is an interesting discussion.  I am curious to understand why you are asking the question.  You already have a heat pump, so surely you can experience this for yourself?  Are you finding it less comfortable than with the gas boiler?  Are you finding that the system is cycling on and off too much?

We have had our heat pump system since August.  While these are early days, my wife and I feel that the house is much more comfortable now.

I'm posting my experience really, and my confusion: it is cycling on/off rather than running continuously so to me it looks like it is operating no differently to a boiler with a thermostat control.  It could be related to the outside temperature not being that cold during the day, as mentioned in the last few posts, and it isn't really related to comfort at the moment as the house isn't cold. 

Posted by: @jamespa

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Looking at the graph Im a bit surprised it isnt running more 'continuously' at night.  Of course you could have a very well insulated house (although cosy 9 = 9kW? doesn't sound that way), the heat pump could be oversized, or it could be bouncing off the room thermostat because the cold weather FT setting is too high (57 is a very high 'cold 'FT, although in fairness I dont know what outside temperature that setting corresponds to so ).  Difficult to tell for certain until we get sustained colder weather at which point its worth tweaking the WC settings to get best performance possible.

I don't really know what I should be expecting to see as it's the first time it's been used for heating.  Last night was around 5c here; I'm trying to find out the related temperatures for "Hot Weather" and "Cold Weather" as I agree 57 seems high.  I'm reluctant to fiddle with anything until I have a better idea of how its working when its cold enough to be on more.  I don't have a setback temperature for the nighttime either, I've just left it at 22c on the basis of keeping it ticking over.

My last year's gas data was 8937kW for heating (at 21c in the living room) and 2221 for hot water and 100mm of loft insulation.  The design document was for 10000kW for heating (at various but 21c for the living room) and 2000kW for hot water with 300mm loft insulation.  I was looking for the determined heat loss for the house in the design document but it isn't there (just room-by-room): IIRC, it was something like 8200kW and Heat Geek calculated something like 8,400kW (or maybe it was vice-versa but in any case correlated.)  The house is a Finnish designed timber framed building built in 1985 so whilst the walls and floors are insulated it is still quite old; modern extremely efficient triple-glazing and passivehaus standard external doors.  It can warm up quickly and, conversely, cool down slowly: it loses around 2c over 5 hours at night during Winter which seems slow to me but I don't have much to compare it against as I've lived here for over 25 years.  Having said all that, in the old gas system, I think the radiators weren't appropriately sized for some rooms and never properly balanced so some rooms were warmer than others.

Posted by: @andrewj

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I don't really know what I should be expecting to see as it's the first time it's been used for heating.  Last night was around 5c here; I'm trying to find out the related temperatures for "Hot Weather" and "Cold Weather" as I agree 57 seems high.  I'm reluctant to fiddle with anything until I have a better idea of how its working when its cold enough to be on more.  I don't have a setback temperature for the nighttime either, I've just left it at 22c on the basis of keeping it ticking over.

Very sensible, no need to panic and no need for setback at night, in fact you want it running then as hard as possible to exploit Cosy if thats the tariff you are on 

Posted by: @andrewj

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My last year's gas data was 8937kW for heating (at 21c in the living room) and 2221 for hot water and 100mm of loft insulation.  The design document was for 10000kW for heating (at various but 21c for the living room) and 2000kW for hot water with 300mm loft insulation.

Sorry but those figures dont make much sense.  Do you mean 8937kWh (total gas consumption over perhaps a year?).  Its definitely not 8937kW (power/loss) unless your house is the size of a very large village.

If you do mean 8937kWh (total annual energy consumption) then the heat pump is well oversized, your loss is more like 3-4kW (so Cosy 6) not 9kW, which would explain cycling even when its quite cool outside as well as quick heat up/slow cool down.  How big is the house (sq m?)

@majordennisbloodnok I read the document that you shared: "Get_to_know_your_Cosy-20.2-internal".

It looks as though it automatically adjusts the weather compensation curve to meet the needs set by the Cosy Pod room thermostat and the external thermometer.  If that is true, then it may be that the customer cannot control the weather compensation curve for himself or herself.

Posted by: @jamespa

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Posted by: @andrewj

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I don't really know what I should be expecting to see as it's the first time it's been used for heating.  Last night was around 5c here; I'm trying to find out the related temperatures for "Hot Weather" and "Cold Weather" as I agree 57 seems high.  I'm reluctant to fiddle with anything until I have a better idea of how its working when its cold enough to be on more.  I don't have a setback temperature for the nighttime either, I've just left it at 22c on the basis of keeping it ticking over.

Very sensible, no need to panic and no need for setback at night, in fact you want it running then as hard as possible to exploit Cosy if thats the tariff you are on 

Posted by: @andrewj

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My last year's gas data was 8937kW for heating (at 21c in the living room) and 2221 for hot water and 100mm of loft insulation.  The design document was for 10000kW for heating (at various but 21c for the living room) and 2000kW for hot water with 300mm loft insulation.

Sorry but those figures dont make much sense.  Do you mean 8937kWh (total gas consumption over perhaps a year?).  Its definitely not 8937kW (power/loss) unless your house is the size of a very large village.

If you do mean 8937kWh (total annual energy consumption) then the heat pump is well oversized, your loss is more like 3-4kW not 9kW, which would explain cycling even when its quite cool outside as well as quick heat up/slow cool down.  How big is the house (sq m?)

 

Sorry, my mistake.  For heating, it was a total of 8937kWh and for hot water it was 2221kWh.  This was gas usage figures for Feb 24 to Jan 25 taken from my bills.  I did have a thought that given that value and the rough calculation that floats around the internet a heat loss of 3-4kW but the calculation by both Octopus and Heat Geek were within 200W of each other and they both had access to my historic usage data so....  The house is 164sqm according to the EPC.  When I say quick to heat up/slow to heat down that was with the boiler - a Veissman so good quality but banged-in by British Gas so probably not the best install.  Some rooms were better than others as I had messed around with designer radiators over the years without really knowing what I was doing! They are all gone now and I expect the system to operate a lot better now.

If it turns out to be oversized then I guess I'll have to take it up with Octopus.

Edit: I'm actually on Octopus Intelligent Go and along with the Heat Pump I've had 10kWh of Solar panels installed and a 16kWh battery system with 8kW inverter.  Hot water is overnight at 7p and currently solar is providing all the energy I need (plus an export amount) when it's generating and the battery, charged overnight, covers the evening (and now early morning) with a final export to cash in at the end of the night.   Really, I'm paying 7p for all my energy usage and up until now, more than offset by the 15p export.  Obviously that is starting to change and I expect I'll be using some peak rate in Winter.

Posted by: @andrewj

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Sorry, my mistake.  For heating, it was a total of 8937kWh and for hot water it was 2221kWh.  This was gas usage figures for Feb 24 to Jan 25 taken from my bills.  I did have a thought that given that value and the rough calculation that floats around the internet a heat loss of 3-4kW but the calculation by both Octopus and Heat Geek were within 200W of each other and they both had access to my historic usage data so....  The house is 164sqm according to the EPC.  When I say quick to heat up/slow to heat down that was with the boiler - a Veissman so good quality but banged-in by British Gas so probably not the best install.  Some rooms were better than others as I had messed around with designer radiators over the years without really knowing what I was doing! They are all gone now and I expect the system to operate a lot better now.

If it turns out to be oversized then I guess I'll have to take it up with Octopus.

Assuming that the house was actually warm previously then its definitely oversized and construction/area would be consistent with that.  Given the construction which is a bit unusual its quite possible that the survey overestimated it.  Time will tell but my prediction is that you will still be cycling when its 7C outside.  Whether that makes much difference to COP is another matter, and of course if you are heating part time to take advantage of low leccy rates you need the extra oomph to compensate.

The screenshot you posted earlier looked like a pair of user-controllable dials for WC parameters.  I read the manual posted and Im not sure it self optimises this setting, but of course the manual is so dumbed down its impossible to be certain.  When it gets colder Id try dropping the cold FT down until it doesnt heat the house enough, and I would also drop the warm weather FT to 30 or even lower. I think they have currently set it so the rads always feel warm (reduces call outs) but thats not really what you want!.  No need to rush though, get used to it first!

Posted by: @grahamf

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@majordennisbloodnok I read the document that you shared: "Get_to_know_your_Cosy-20.2-internal".

It looks as though it automatically adjusts the weather compensation curve to meet the needs set by the Cosy Pod room thermostat and the external thermometer.  If that is true, then it may be that the customer cannot control the weather compensation curve for himself or herself.

You can adjust flow temperatures as shown in my image on an earlier post but have no access to anything more granular.  Octopus would have to do that.

Posted by: @jamespa

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Assuming that the house was actually warm previously then its definitely oversized and construction/area would be consistent with that.  Given the construction which is a bit unusual its quite possible that the survey overestimated it.  Time will tell but my prediction is that you will still be cycling when its 7C outside.  Whether that makes much difference to COP is another matter, and of course if you are heating part time to take advantage of low leccy rates you need the extra oomph to compensate.

The screenshot you posted earlier looked like a pair of user-controllable dials for WC parameters.  I read the manual posted and Im not sure it self optimises this setting, but of course the manual is so dumbed down its impossible to be certain.  When it gets colder Id try dropping the cold FT down until it doesnt heat the house enough, and I would also drop the warm weather FT to 30 or even lower. I think they have currently set it so the rads always feel warm (reduces call outs) but thats not really what you want!.  No need to rush though, get used to it first!

It's difficult of course as a customer to challenge beyond showing them the historic data and whilst being informed, not being an expert in this stuff.  I took some comfort from two independent surveys coming up with the same value.  As you say, time will tell.

I'm not heating part time: my solar/batteries allow me to, essentially, take advantage of a 7p rate throughout the day - at least that's the plan. As I say, I just have it set at 22c for 24hours of the day, excepting when the water schedule is on for an hour during the night.  I've currently no intention of changing that.  As you say, once the heating season really gets going then I can see how it is operating and make some Flow Temperature tweaks - it's a shame their stats don't also show outside temperature.  If it really is oversized then Octopus will have to sort it out.  

The old system was problematic, not least because of the fiddling around I had done with radiators.  I would find that the end radiators would struggle to get really hot and if anyone worked on the system that involved  draining water it was always a so-and-so to get it properly up and running again with all radiators getting warm.  It had a massive pump that was always commented on by the service engineers ("you could pump the whole street with that" was one quip.)  Once it was "settled" it was generally ok though, particularly as I used to have it set to be always on (notwithstanding how the thermostat controlled it.)  The biggest issue, for my wife, was the inconsistency of temperatures throughout the house with some rooms being cooler than others.  It was always a problem for her to come from her warm, craft room upstairs to the living room.  It was one of the main drivers for me to get a properly designed system (which I really hope I have!)  

Posted by: @andrewj

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It was one of the main drivers for me to get a properly designed system (which I really hope I have!)  

Even if it is oversized it's very highly probably that the rads are still more or less correctly proportioned, so a bit of balancing and adjustment of the WC curve down will give you consistent heating.  Even if they aren't you can still balance them for consistent temperature.  This is trial and error unless you have the whizzo flow regulating valves @editor is keen on, but not difficult.  My heat pump was fitted in November so it was immediately cold outside (and pretty much consistently so), giving me an ideal environment to both balance and adjust flow temps. 

Lower flow temps give both better comfort and better efficiency (obviously until they are too low) so this step is well worthwhile.