I think this is the basic problem/error by Octopus. Specifying a system to run at 50/45 means specifying a low efficiency system. Sure the heat pump can do this - especially if it is oversized.
However you will find the the most efficient units (lowest running costs and carbon footprints) on Heatpumpmonitor.org all run at something closer to 35/30, most but not all with underfloor heating, I know of at least two who achieve these numbers with standard radiators. Now with rads that does mean a large increase in size which might not always be possible or desirable. In my bedrooms I have not changed my rads - so they are undersized I know, but I do not like hot bedrooms so it is not a problem and anyway if my downstairs is warm it gives some underfloor heat to the upstairs. Downstairs I have massively increased the radiator sizes and used fan assisted radiators as well when I wanted them to be less visible - my aim was 40/35 on the coldest days.
Just to clarify - my 4.6kw minimum is on continuous running. You can get lower with cycling on and off but it seems that the Daikin units are not that efficient when cycling (other units are much better at this if you look at Heatpumpmonitor.org). The Daikin control theory does allow many variables to be changed and I suspect this is to try and get the units running continuously. So if you set them up to get continuous running you will achieve efficiencies close to the best of the other systems.
That is the neat thing about modulation vs weather dependant curves. With the latter you make a best guess at what the flow temp should be and the heat pump just has to try and obey your command. But with good modulation the system works out what the best temp is by itself. In your case it finds that the radiators are not putting enough heat out to move the room thermostat fast enough when the flow is below 42c so it is adjusting for your radiator systemā¦ at least thatās my theory, until corrected by those more expert.
I should add that when it gets really cold outside the house will cool faster and the system will find that 42c is not warm enough to keep the room thermostat satisfied. So it will modulate the temperature up when it gets colder = weather dependency via modulation and (not by the owners best guess).
I think Glyn does more or less the same thing, settles on a flow that works and is efficient and lets it turn on and off as necessary to keep the set room temperature.
My problem doing that is my radiators canāt handle this heat pump at its most efficient.
I am also struggling with what appears to be inconsistent behaviour.
My DHW is all over the place and now what was working yesterday and this morning is not going so well this afternoon.
Itās ok playing with settings when you have a predictable base setting but when everything seems to be moving all the time itās hard for me to get a grip of.
I love motorcycle racing and this has lots of the same elements in terms of set up, you need a good solid basic set up that works and that you can fine tune. If the base set up is off you are lost. Itās how I feel right now.
This is great stuff you are sharing here, thanks. My system has been cycling like made today, gradually dropping the LWT. I have it setup to run continuously at the weekend and itās too hot in the house, now 22C and it hasnāt shut off.
Iām going to try changing to fixed LWT and see whether I can improve things based on the feedback here. If you want to help on my system Iād love to go through the same process over on my post.
Maybe as I think you have said earlier focusing on COP is too narrow. If your house is warm enough and you can gradually lower your energy bills then thatās the real objective! Small incremental adjustments from now onā¦
Itās 8.4kW, vs. the 9.9kW radiator output, so the radiators are in principle too big, but then the heat calcs donāt account for thermal bypass generally and some dodgy tiled areas! And of course, itās sometimes colder than -2.
How did you do that from the data you have, since it didnāt include a -2 period?
I suspect Iām in the same situation! Some of them could have gone bigger, but weāre bumping up against the āreasonable retrofit impact on house interiorā in a few places.
Yeah, hindsight is a wonderful thingā¦ But itās hard to have the courage of your convictions, if they could even be classed as that until you have more evidence - but that takes an installation!
I donāt know that thatās immediately obvious from the specs, so how would you know? It would come down to Octopus, as the people installing container shipsā worth of Daikin ASHPs, hanging around to collect proper data and act on it. If you consider that you and I are otherwise pretty ok with the actual in-house result, and my wife now thinks Iām a genius for making this happen, if thatās the result they get with 90% or more of their customers, along with scrapping all those gas boilers, job probably done.
At least you will be making compromises based on a proper understanding of the parameters and their effects.
Yeah, that is weird. Mine seems fine, admittedly without proper data, I had it on schedule and reheat, but we donāt seem to need the reheat, so I dumped it for now. Maybe with the extra guests over Xmas Iāll switch back.
Still considering this. As you can see from my screenshot, the water temp lasts a pretty long time and avoids at least one scheduled warmup! We probably need it because we use so little water.
No, a summary is really helpful, especially for those just starting on such a huge and confusing thread.
May, so like you it wasnāt until 14/15 October that we it turned on at all, and we still havenāt really seen sustained low temps to test the bottom end setup, and thus the full power of the āfully operational Death Starā! For a big lump of stuff on the patio, it looks pretty cool though
Sigh. I kinda know that, maybe you can DM me about your OEM installation to give me more confidence about going for it. My only concern is a possible pipe-cutting requirement and refilling without excessive air.
BTWā¦
I was referring to the ESPaltherma monitoring facility you mentioned acquiring in your previous monitoring thread - I think it uses ModBus via a serial port. Thatās tempting too, especially as itās pretty standalone and doesnāt get one involved with other components like the P1P2 interface.
Hereās to warm and cosy, with an eye on the environment!
Heat loss is a linear regression ( I think that is the correct terminology)
If I know what it is at one set of temperatures I can plug that into the formula to work out what it will be at any other temperature.
For example if I use 36kWh of heat to keep my house at 21c for the day whilst it is 10c outside I know my heat loss with a delta t of 11c is 1.5kW per hour.
So if it is -2c outside and I remain at 21c indoors the delta t is now 23c
So 1.5kw x 23/11 = a heat loss of 3.14kW
I would need 75.36kW to keep my house at 21c when it is -2c outside.
And that is about what it is historically .
The most gas I ever used was 110 kWh and that was when it was an average -5c for a day. That included DHW and boiler inefficiency so something like 85-90 kWh of heat required.
All this information was available to my installer but they went with a heat loss of 7.3kWh and sized the heat pump based on that.
Hence my problem.
The OEM install is straightforward plumbing wise if you have enough space. Mine area was a bit confined but I managed it with ease.
Draining the heat system was easy and refilling was no trouble at all with automatic bleed valves. The heat pump has a air purge cycle you can run in installer settings and if you have a back up heater then the bleed valve in the heat pump is automatic as well.
There are some pictures of my install in this thread.
I made sure I had some spare pipe and compression fittings just in case I messed up!
I think the ESPAltherma is good if you are OK with home assistant. It just plugs into a serial port inside the heat pump. I have not read of any issues with it with regard to damaging the heat pump.
But as with everything I am concerned with warranties. I tried to get Octopus to fit the OEM system for me but I never gt a straight answer from them, as far as I know their technical team are still looking at it for me!
Apparently Octopus did fit this to 50 systems so that they could monitor some.
It is a shame that they donāt offer it to every customer as a cost option, it would have been a lot easier to fit at install.
Thanks @matt-drummer! Since my house was previously very irregularly heated, so I canāt really use that situation as a comparison, Iāve just taken
todayās heat output figure from the MMI (64kWh) over 23 hours => 2.78kW loss rate
the average outside temp (7.5deg)
the average inside temp (the room with the lowest temp, so over-egging a bit) (21deg)
=> dT of 13.5
=> new outside temp of -2
=> new dT of 23
=> new loss of 2.78 * 23/13.5 or 4.74kW!
=> daily requirement of 113kWh at -2deg
ā¦so my HP is possibly a bit on the large side. Gosh. Whoād have thought?
On the ESPAltherma, Iāve looked at the technical docs for the EDLA09D3V3, and there doesnāt appear to be an X10A serial port area on any of the boards. Maybe if I opened it up Iād see one. Since it does basic MQTT to talk to HA, and I already use MQTT for lots of monitoring etc., I could avoid HA, which is deeply horrible. I also asked Octopus if they fitted OEM gear, but no. Mad, as itās a business opportunity, and would actually allow them to monitor remotely and make AI/ML-supported suggestions on better configuration.
I had a post install check up after 3 weeks and asked the `engineerā about OEM. I was told I didnāt need it and I was wasting my money and that I should just get on and use it like everybody else does.
I have a 9kW Daikin installed by Octopus last April and I am attempting to configure it for comfort and economy. I am confused by the āLeaving temperature setpointā on the home display. I had assumed that it would equate to the flow temperature when the unit had been running long enough to attain a steady state which is confirmed by my temperature sensor on the flow pipe. Am I missunderstanding something or do I have a fault?
This isnāt unique to Octopus - quite a lot of heat pumps are oversized for their property, partly due to inaccurate heat loss and air change calculations, but also MCS sizing rules. Generally speaking, with the right configuration, they can still perform reasonably well.
I have a 11 kW Mitsubishi in a house that needs just 6 kW.
I havenāt researched it enough to make the bold claim I am about to make but Iām doing it anyway.
I think the problem with Octopus is the choice of heat pump, particularly the more modest homes with the 9kW version of the Daikin.
It just cannot run at a low enough output for the heat requirement of a house like ours whilst other heat pumps seem more capable of this.
Obviously I am no expert in heat pump design but I donāt see the point of the range of Altherma 3ās from 9 to 16kW when they are all essentially the same heat pump.
Even the Octopus engineer says that all of them are exactly the same.
The range of heat output is just too small to work in a house that needs heating with external temperatures of between -5c and +18c.
I get the impression that the range of heat pumps from other manufacturers are better suited to the intended use.
Getting my heat loss wrong by a factor of 2 is hard to deal with coupled with what to me appears to be a limited heat pump.
It works, but not that efficiently compared to others.
They are at the bottom of the performance table for a reason.
This is my weather dependant curve. With an outside temperature of 9C then the indicated target flow temperature of 29C looks about right but the flow temperatur rise to 34C then drifts up to 35C at which point the compressor switches off but the pump continues to run. Does this suggest I have a fault as the flow temperature is about 5C higher than the target? Maybe my heat pump is actually targeting the return temperature which is close to 29C?
My house is a 174 square metre bungalow/ The heat loss calculation was 8457W at -2.2C. 13 of my 14 radiators were replaced. I have a few features that are not recognised by the MCS calculations - MVHR, external wall cladding insulation as well as a mix of insulated cavity walls and timber frame walls, multifoil and PIR under rafter warm roof insulation. I had previous quotes from other installers for 14kW and 11kW heat pumps. My guestimate based on stats from my old combi boiler was about 7kW so I was pleased that Octopus were at least in the right ball park,
I donāt have a heat meter yet, I am only monitoring temperatures and power consumption. I have solar pv and a 9.6kWh battery and I am on the Cosy tarif. So far comfort and running costs are looking good compared to last Autumn with my gas combi.
I will look at my MMI display when the heat pump is running later and see what my home display shows compared to the actual data from my OEM monitoring system.
Iām not sure what the 29c next to the radiator symbol is actually meant to represent.
Do you have any overshoot or modulation set?
Have you any offset from your WD curve? Check on the Onecta app or the Madoka controller.
We have worked out that this heat pump has a minimum electrical input of 920w and at a COP of 5 as tested when 7c outside the minimum heat output is 4,600w at a flow temperature of 35c.
That needs a lot of heat loss and radiators to cope with it.
Your WD curve does look like the flow should be about 29-30c at 9c outside.
I wonder what they replaced your radiators with?
Do you have the schedule that Octopus produced showing their output?
They will have to be huge to run at 30c flow temperature.
If your bungalow is at 20c indoors and the flow is 30c then you will need something like 35 to 40kWh of radiator output at delta t of 50 or about 20kWh at a delta of 30 which is what Octopus did my radiator schedule at. These are rough calculations that I have done quickly in my head.
I have learnt/been reminded of this earlier in this thread.
I can heat my house at 30c flow and 7c outside but efficiency is bad as my radiators are about 60% of the size they need to be to handle the heat produced by the heat pump. My solution at the moment is to run a higher flow temperature until I replace the radiators.
I am having to run at about 43c on a day like today and aim to go down to 35c. I donāt think this heat pump is very happy below this. Theses are our findings so far.
None of it stops your heat pump working and heating the house, its just not very efficient.
Your MMI should be able to tell you the approximate heat production for heating, DHW and total.l
