Posted by: @andrewj

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I don't know how else to ask this and I sometimes think I must be speaking Martian as even on the Facebook Octopus group I can't get an answer: is your Cosy running continuously (i.e. ALL THE TIME, low and slow) or does it go on/off based on the temperature read by the Primary Pod letting the temp drop and thing bringing it back up again?

This will differ from house to house depending on how it's set up.  Because the octopus user manual is heavily dumbed down it's impossible to tell what the actual algorithm is.  This is probably why you won't get a clear answer!

Try the following:

Increase the target temperature by 3C above what you really want on the room temp control 

The house will probably overheat 

Then gradually, a degree at a time, and not more than once ever 12 hrs, turn down the WC curve at the low outdoor temp end.

Eventually you should get to a point where the house is either at the right temp or a bit too cool.

If the latter turn the WC up a degree.

This will have the effect of optimising your WC settings unless there is some sort of auto adapt of the WC, in which case it becomes more complex.

Before you do anything note the settings so you can reset if necessary.  

The objective is just to match the heat loss of your house with the heat supplied by the radiators by getting to a WC curve that just matches these two, by getting the relationship between flow temp (which determines radiator energy output) and OAT(which determines house loss and therefore energy needed to keep it at constant temperature) correct.  If it's matched the thermostat (pod) won't do anything, because it doesn't need to and it so happens doing this is both the most efficient and most comfortable operating pont in most circumstances.

Forget anything you learned about controlling boilers, it was mostly wrong for boilers and wholly wrong for heat pumps. 

Lots more detail can be found / provided if you want it, it's unfortunate we didn't adopt weather compensation in the UK for boilers, unlike some more enlightened european countries.  As a direct result you have almost certainly been paying 10% more for your heating up until now than you needed to, and been less comfortable, and (as if that wasn't enough) have a steep learning curve to adapt to heat pumps. 

Keep asking questions and read the ABC guide to heat pumps in 'articles' on this site.

I have the cosy 9 and full MID monitoring. I also have technical insights to details about them.

I got octopus to deliberately chuck in a cosy 9 knowing it would be oversized. Zero radiator changes, as quick as possible job.

Ask away.

Someone signed the PCB!

@swwils that PCB is signed by Dr. Jason Cassells, former managing director of Renewable Energy Devices (RED) and unknown heat pump manufacturing legend. RED made high-end heat pumps and they were acquired by Octopus. We had the honour of interviewing Jason years ago before he sold to Octopus. 

I have to say watching the intro is uber cringe! 🤣 

Posted by: @swwils

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I got octopus to deliberately chuck in a cosy 9 knowing it would be oversized. Zero radiator changes, as quick as possible job.

That's interesting.  I suppose youbl are experimenting with/testing how to get the best out of an oversized heat pump.  

If so are you in a position to share any insights and associated explanations.  There has been some discussion here (and in the other place) about this and a bit of theirising, but as yet no conclusions that have been soundly backed up by experiment.

In a similar vein there are discussions here how to deal with a situation where a buffer tank has been fitted unnecessarily (other than the obvious which is often negated by circumstances).

@swwils Sounds like you could be useful on this Cosy thread 😀 Do you have any insights in to the control choice that Octopus took with these models?  I’d be very interested in how you have yours set up to run - have you had it installed for long?  @jamespa has given an approach which might alter the way the Cosy runs - I haven’t tried yet as I’m still interested in how others have theirs set up.

@jamespa I haven't bothered at all. The system isn't even balanced.

The cost to me was less than the gas valve that just got replaced on the oversized system boiler it replaced. The biggest "cost" to the whole thing was me buying an induction hob. 🤣.

Hot water COP improved significantly at the end of August as they rolled a new firmware, you can tell it now has ramp feedback on high loads. I charge 300L to 55C because going without hot water not allowed and see COP of 4.

Heating COP is also way above 4, near 5, they don't like being below 34C, so I have the linear curve 34 to 50, which is the lowest it will go unless you inject commands into the modbus or mess around in the hubs "OEM" menu which is separate to the engineering mode.

Internally it's a emnerson copeland scroll with the newer higher frequency drive, so the cold weather performance should really be quite good.

The modbus between the unit and the hub is pretty standard, the internals of the cosy had more care than the hub did. The hub is very similar to a hive.

I would think one under the 6 would be good and a 12. As is a proper "eco" mode, which isn't even implemented yet.

My unit has the leg base, which I guess will become common soon.

@editor most senior engineers ocotpus send will have good experience with the limited numbers of red installs out there.

Reds were interesting units.. absolutely fantastic for large low flow temp underfloor homes. Ridiculously loud though. I believe they had a quite neat secondary vapour injection that helped performance? Abit similar to some larger mitsubishi units.

Overall ive found it fantastic. It's almost magic. Running it off 8p stored electric 😂.

My house was originally supplied with a ridiculous oversized system boiler (30kW, minimum modulation 8.6kW) that never modulated. It didn't even get a chance to cycle since the light up sequence would do an overheat cutoff. So mine is a real beautiful use case for a "quick" heat pump install.

Despite my boiler being commissioned at 80C flow - the rads were significantly over sized by pure chance.

Posted by: @swwils

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Overall ive found it fantastic. It's almost magic. Running it off 8p stored electric .

With 8p electric you can't go wrong!  I can't quite make the case for a battery work so get 7 hrs of electric at 7p and the rest full price, on eon next drive.

On the octopus heat pumps is the weather compensation curve adapted in any way by the unit in response to the measured IAT.  Some heat pumps have some autoadaption of the WC curve, but it's not clear if octopus does or not.  People often ask questions here the answer to which depends on this question.

@jamespa I rolled my own storage. £40 per kWh.

I am not privvy to the exact control algorithm, but it definitely seems to have some room temp influence... but not directly as far as I've seen - the unit will occasionally ramp up past the minimum modulation point, check the result on room temp then ramp back down again. This is outside the usual, constant dT modulation.

I haven't really had any non-cyclic loads for it yet, so my data is very limited... My house has massive solar gains (every room is south facing with floor to ceiling glazing) and the primary stat is in the room with largest heat loss. A perfect system would be multi zoned and WC downstairs but RAT everywhere else, but to be honest I am happy just running it in one large open WC loop. There is real value in just set and forget and I think for the majority of people noone cares about how the heating works.

Once I get some time I'll balance the whole system properly, but I've been meaning to switch to new flow control valves that will make that easier.

Im happy with just the WC performance really, there is also value in having the volumeiser in every system, mine must be something like 200L+ system and still has it.

Posted by: @swwils

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£40 per kWh.

OK thats cheap, the commercial price seems to be £400 per kWh.

@andrewj Bear with me, this is my first post on this forum although I have lurked for a while, and have just come across this thread.  Given the number of Cosy ASHPs installed, I am puzzled by the low interest, I am sure the other Cosy users must be 'talking' somewhere!

Anyway, I share your aim to achieve constant low and slow running rather than mimicking a gas boiler.  My Cosy 9 is currently set to achieve 19c 24/7, with a WC of 30/50 (the lowest either variable can be set.  When the OAT hits 12c or less, the pump runs every hour however I have no way of knowing whether within each hour there is constant running or stop/starts.  Today for example the OAT is 10.4c (as at 15:00) and the pump has run each hour consuming 6.06kWh at a COP of 4.47.  This includes a water boost.  Was it continuous...I suspect not.

This is the closest I have come to 'continuous running' and I suspect that if I raise my target temp slightly I might achieve it (though at higher cost but also greater efficiency?).

If we compare data, the standouts are your target temp of 22c and WC of 36/57 compared to mine of 19c at a WC of 30/50.

I believe that the aim is to run at the lowest WC settings that enable the pump to hit the target temp and, if it can't quite get there, it will theoretically 'tick over' as it tries to do so.  

My thoughts are that your pump has plenty of heat to play with and is hitting its target temp with ease.  So you might want to gradually lower your WC settings and see what happens.  Doing so would mean that your pump would have less heat to play with and would therefore need to be running for longer...you get my drift?

These are the ramblings of a fellow Cosy user, I am obviously no expert, and if nothing else this post has enabled me to think through my own settings, which I'll no doubt tweak as the OAT drops.

I would be interested in your thoughts and indeed, those of anyone else reading this.