Only joined the forum today and have found this thread very informative. Thanks everyone.
I'm curious to find out if there is a simple way to monitor more parameters than the Octopus app currently displays for the Cosy 9.
I currently don't receive any notifications of pump failures resulting in the red flashing light on the control panel. Only finding out there is an issue when I open the app to check performance.
Any advise on how additional parameters and system performance prior to failure would be greatly appreciated.
@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.
Sorry, only just seen this I don't know why. I was speaking with an Octopus Engineer last Tuesday and he said that the Cosy 9 can only modulate down to 35c so that presumably is the lowest you can actually achieve, even if the app is set to 30 at 12c - have you taken any actual measurements? We've had a number of 12c-15c days recently and I've been keeping a track of internal temps in the rooms at the current settings so that I had some baseline - as you point out, you get no useful data from the app except that during "this" hour, the heat pump ran and consumed nkW of electricity. Next I'm going to wait for some colder weather and keep track again. Following that I might have some useful info that I can make a decision around - e.g. drop the flow temp from 36c to 35c and see what impact that has across the rooms - not scientific obviously as the OAT isn't remaining stable and it might possibly be quite a bit colder.
I want to be able to better balance the radiators as I currently run at around 23.5c-24.0c upstairs and around 21.8c - 22.3c in most rooms downstairs (hysteresis) but unless I can keep it running at a stable temp I don't really know what temps the radiators can achieve. For example, it runs a lot more overnight and in the morning one of the downstairs rooms is reading 20.2c but by early afternoon this is down to 19.5 and by the end of some days, 17.5c so I know it can get to temp if allowed to do so.
I have had some sort of confirmation that it is possible to run it at a target temp of, say, 30c (a temp it couldn't possibly achieve) and that the Cosy would run continuously but (a) there was some mumbling about "until it loses DT" without really explaining what that means; (b) specifically stating that having the Cosy running all the time wasn't very efficient and that chasing SCOP over cost was not wise. I wish someone at Octopus would just give me a straight answer as I've reached a point where I think they don't really know!! Anyway, I'm neither chasing COP/SCOP nor price - I'm on Intelligent Go with 16kW of battery and 10kW peak of solar (admittedly not generating much now) and what I'm actually chasing is "comfort".
I'm still on at Octopus to speak to engineers to find out how this thing actually works and an informed "art of the possible" before I follow some of the advice previously given by other members on the forum. Fortunately, I'm not doing this from a position of being cold! Since the beginning of October my weekly COPs have all been over 4.25, a couple of weeks over 4.7 and the recent week 4.85. I've even had a day with a COP of 5.12. Mind you the temps have been warm so it probably doesn't mean much.
I’ve just got the link for this thread from @editor, here’s my experience with the cosy6.
firstly it’s not 6kW, only 5.6kW. That nearly sank my installation, more later.
I had a professional heat loss survey on my house (not by octopus) as it would be after the renovations, and a cosy6 seemed what I wanted.
Octopus didn’t want to install a HP in a property that was being renovated; I deduced that when I tried to ask them for a quote. They form you used declined everytime until I fibbed and said I wasn’t renovating.
So Octopus arrived for the survey and nearly left when they found the property was being renovated, it had built a large extension on the front, side and rear of the house. Fully sealed with roof, windows but no drywall.
I argued my case and the manager turned up and allowed the survey to go ahead. In each area I showed them what insulation would be added and it was recorded and a calc was done.
Even though I asked for a cosy6, a dented used Daikin turned up. I spent ages on the phone complaining I wanted a Cosy 6kW not a Daikin 8kW. New R290 gas, newer design, it ticked my boxes.
I dug my heels in and stopped the install, as I was getting the runaround from “Sales”, next day the area manager arrived and promptly told me the Cosy 6 wouldn’t work with my install and I wouldn’t get the BUS grant, so I’d need to pay an extra 7.5k to get the cosy or stick with Daikin.
Well they soon found where I wanted them stick their dented Daikin. I launched into a complete engineering review of the renovations and demonstrated their heat calc was flawed; they had the wrong room sizes!
This is where they admitted the cosy 6 isn’t 6, but 5.6kW capacity. This would be an issue later but for now we agreed to proceed with the install.
I had it fitted Dec16th, yes dumb now as there was no heating in the house that week, but they said it would be fitted by Xmas.
By day 4 they threw 5 engineers on my install as it was getting close to Xmas break for everyone.
They got it working Dec 19th for 1h then it gave up, Friday 20th they fiddled with the settings and left at noon with it working, it lasted 1h then “red flashing light”
I had 5 engineers out over 5 days and they couldn’t figure the fault as the system was new to all of them. I had a new hub, and several reboots of the HP.
Eventually an experienced heating engineer came out and asked how to get into the diagnostics menu of the HP. You link your phone to the Hub thru Bluetooth by pressing the secret button for 3 seconds, you need the secret password to get in which no one knew, so we guessed it was either Greg’s name or the company name; bingo. We were in and could see the pump had a flow rate issue.
The pump has to see 12L/min or it reports a blocked flow, this would be important later. But for the moment we had a correct diagnosis.
What they failed to do when fitting a delicate HP to an old Gas system was flush the old system; they emptied the water but no further.
Next day, the man turned up and power flushed the whole system, took 5h and a lot of sludge and calcium flakes came out. This was a real heating engineer but he’d never worked on a Cosy6, so had no training on restarting the HP, that’s where I came in, I’d already got hold of the installers manual, and knew the secret password to get into the Hub; there’s a lot of settings in the HP they don’t want you adjusting so we only used the Initialisation Menu section.
So the HP worked for the next week, red light flashing at least 8 times a day; I kept a log which came in useful for the last issue I had: Flow Rate Errors.
As revealed earlier, Cosy6 needs a 12L/m flow rate. If you have flow restrictions on every radiator and UFH circuit, when each room gets to temp, the Flow Rate plummets and the Cosy6 falls over.
After much experimenting I found leaving the main UFH loop open always gave the minimum to keep system almost happy. It still records flow rate issues but not severe enough for the flashing red light.
The final hurdle was to get the heat flow rate into the remaining upstairs radiators acceptable.
Again Octopus said it was all down insulation missing, but by this time I’d installed all the 150mm cavity, floor and ceiling blocks so that’s not the problem; it was the microbore pipe that Octopus said would work, that was now limiting the amount of heat/minute that can reach each radiator.
I withheld the final payment as I wanted this rectified, and it took several weeks before they agreed that my flow rate calcs showed the pipework needed increasing from 10 to 15mm.
As part of renovation to the whole heating system I wanted no radiators downstairs, so I’d dug out the floor, insulated it and fitted UFH 16mm pipework, it works very well with a HP with a flow temp of 37C and you can throw the mixer pump away as well.
I’d watched a Heat Geeks video of how bends, joins, dead pipes all disrupted the clean flow of water thru the pipes. This can also cause noise. I spent the summer replacing all the dead 10mm with 15mm, upgraded the Towel Rail to 15mm, and swapping 2 radiators between bedrooms.
Id noticed that Octopus had labelled the Bedrooms as B1 B2 and Office. I had a home office when I ran my Company, but it’s now a store room. Octopus had set that Office temp to 21C so the radiator was truly oversized. I rebalanced to room to 19C and put the larger rad in the granny annex; knowing elderly people like it warmer and it worked a treat.
I've had the system running for a year now, I’m getting a decent COP of 4.5. Using the Cosy 8h cheap tariff linked with 5kW battery allows the house to store energy at cheap rate and deliver it during the peak rates of 4-7pm.
I’ve learnt that the Cosy6 can manage my installation if I leave it running a constant temp 24h a day. I have it boost the house during the off peak times, so the UFH slab is nice and warm by 7am, there is good solar gain helping the HP stay quiet till it’s needed in the evening.
Ive helped several friends adopt HP themselves, none have used Octopus but that wasn’t my influence, just their choice of fitter. What I have done is pick up on the issues like pipe sizing, rad sizing and positioning and no buffer tank!
I’ve learnt that the Cosy6 can manage my installation if I leave it running a constant temp 24h a day. I have it boost the house during the off peak times, so the UFH slab is nice and warm by 7am, there is good solar gain helping the HP stay quiet till it’s needed in the evening.
That's some story. How did you set it to keep it running constantly?
I’ve learnt that the Cosy6 can manage my installation if I leave it running a constant temp 24h a day. I have it boost the house during the off peak times, so the UFH slab is nice and warm by 7am, there is good solar gain helping the HP stay quiet till it’s needed in the evening.
... which is usually how to run almost any heat pump BTW, and how heat pump systems are generally designed.
@andrewj when I referred to the HP running constantly, I didn’t mean the pump was running 24h a day, I meant the system was on 24/7, with no setbacks overnight like how a Gas Boiler would be set up.
When I had Gas heating, I had a 24/7 timer with usual pattern of 18C overnight, 21C 6-7am and 4pm-9pm, so house felt warm when you got up and home from work.
With the Heat Pump, I have the Cosy6 schedule set like this:
I have hot water on at 13h which is when the outside air temp is warmest and the HP uses less energy to heat the DHW tank.
I did try heating DHW during the 4am and 10pm cheap slot but it used more energy and the HP kicking in on full heat was audible in the bedroom; I’m part way thru renovating the lounge and there’s no ceiling so noise transfer is an issue I will address later.
Here is what my usage looks like with the HP using the Cosy cheap periods it’s very efficient at a COP of 5 gives 2.6p/kWh
I hope members enjoyed reading my tale of the challenge to get what I wanted and not what the installer tried to convince me was a finished solution.
The story I shared here was an abridged version, I kept a log every day of how the installation progressed and every day after with number of faults as reported by the Cosy Hub.
Octopus never walked away from my Installation and never said they wouldn’t do anything, unlike some of the tales we’ve read on the forum about smaller companies, but they were hoping I’d give in and stop calling up every day when the system faulted and stopped due to flow rate too low error. If I wasn’t an experienced Electronics Engineer I would have been without heating for weeks while they tried to sort out their issues; once I got access to the diagnostic menu, it quickly became obvious there was a flow rate issue, had caused by me having the UFH on a controller that shutdown areas when they got to temperature, and half by Octopus who at the time did not have “flush the system if it’s old” in their installation manual. To their credit they took all my comments on board and implemented improvements to their installation manual, which is available online if you know where to look and have the Octupus Energy password.
with the UFH, the time it takes for a room to heat up is easily calculated knowing the length of pipework in that loop, times diameter to give volume of water in the loop. Working on a DeltaT of 10C which I see on the manifold Temp in 37C, Temp out 27C, you can work out the heat transfer rate into the room.
A room with 100m of pipework will need 2X the energy as one with 50m. So I balanced the UFH loops so the biggest area gets 1.5L/m flow rate, next room 1L/m and the small rooms 0.5L/m. This gives similar heat up times for each room for a 1C change. The correlation in heating times is similar to a Gas heating system except as Spock said, If days were hours, it takes 2 days to get a small room warm with UFH.
You can do a similar test with a room with a GCH radiator. Open the TRV to 5, set the Gas Boiler to 60C and time how long it takes for the room to increase by 1C, with the temp measuring done in centre of the room at 1m off floor. Then repeat next day at 50C, then next day at 40C.
You can also read the gas used in this experiment and you will see at 50-55C the condensing boiler uses less gas than at 40C or 70C
To eliminate a variable, do the test at same time each day, record OAT and any solar gain.
I did this over a 2 week period to assess heat gain vs loss in a room from GCH so I had a base reference for how big a heat pump the house needed, too big and it would be cycling inefficiently.
Here is what my usage looks like with the HP using the Cosy cheap periods it’s very efficient at a COP of 5 gives 2.6p/kWh
It's good that you can keep the whole house warm with the heat pump only producing heat at that period - during those gaps, a lot of the rooms in my house would cool down a lot. Mind you, the OAT is quite high so it may well struggle to maintain the flow temp/deltaT. Now it's become a bit colder, my heat pump is on a lot more and it's slower to warm up the room with the Primary Pod and thus other rooms stay warm - some are over heating. It feels like I ought to be able to balance things out a bit to even things up. My current COPs are running at 4.7-5.15 right now so pretty pleased with that.
Octopus never walked away from my Installation and never said they wouldn’t do anything, unlike some of the tales we’ve read on the forum about smaller companies, but they were hoping I’d give in and stop calling up every day when the system faulted and stopped due to flow rate too low error.
What I've found with Octopus is difficulty getting to speak to someone who actually knows how these things work in practice - i.e. not in a generic heat pump sense, but an actual Octopus Cosy 9, Cosy Controller, Primary Pod sense. So far, all I've been able to get from them is that it is perfectly normal for the heat pump to work like an on/off thermostatically controlled system; it feels like they don't want to "blind me" with science or some such as even getting them to explain "what would happen if I set the target temp to 30c and just let it run on flow temperature?". The last time I spoke to an engineer he wandered off (metaphorically) into radiator sizing and wanting to refer it back to the design team, but I never heard any more and following up no notes were made on my account. Still not heard anything in 5 days. It's a bit frustrating.
I’ve learnt that the Cosy6 can manage my installation if I leave it running a constant temp 24h a day. I have it boost the house during the off peak times, so the UFH slab is nice and warm by 7am, there is good solar gain helping the HP stay quiet till it’s needed in the evening.
... which is usually how to run almost any heat pump BTW, and how heat pump systems are generally designed.
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