Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

matt-drummer · 5 November 2023 11:41

Hi David,

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.

I’m 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 don’t 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

Timbones · 5 November 2023 11:55

This sounds like normal heat pump operation in mild weather - it has aimed for 29C but the radiators aren’t able to shed the heat that is produced, so the flow temperature keeps on rising until it exceeds some threshold (i.e. +5C). The pump keeps the water flowing through the radiators to lose some heat and to monitor the temperature. When it’s dropped enough (say -5C) then the compressor will start a new cycle. No fault here as far as I see.

Dave55 · 5 November 2023 12:44

Hi Mathew,

The Daikin operations manual states that it is the “Leaving water temperature setpoint”.

Not sure about overshoot or modulation settings. I could not see these in the menu or manual. The heat pump is modulating. It peaks at about 3kW when heating my hot water to 50C and goes as low as 800W when maintaining the heating in mild weather.

This is my radiator schedule:

hs1

The MMI data for yesterday’s heating is 9kWh electricity for 32kWh of heat so COP of about 3.5. For hot water 3kWh electricity for 8kWh of heat so COP of about 2.7. I am not sure how accurate these figures are as the resolution is 1kWh but they are close to the estimated SCOPs – 3.6 and 2.8.

Dave55 · 5 November 2023 12:59

Hi Tim,

That makes sense. So if I set the heat curve to the Octopus design spec of 50C for an outside temperature of -2C which will result in a higher flow temperature the target and measured temperature should match?

The concern with that approach is that I have already discovered that the Madoka thermostat appears to have large hysteresis so with a target room temperature of 20C I suspect it would continue heating until the room temperature reaches 22C then switch off until it falls to 18C. I could try this but I think I would prefer comfort over efficiency.

I guess the answer is I need larger radiators to achieve both comfort and efficiency.

matt-drummer · 5 November 2023 13:51

Hi David,

Your radiators are better than mine, I only have 8,893w at the same design temperatures I intend to double my output.

Your conclusion is correct though, you would need bigger radiators to run most efficiently with a 30c flow.

But if you are happy with how it is working for you then it is fine.

I wanted to find out why I couldn’t get the quoted COP and whilst radiators are the main issue we found other issues with the heat pump along the way, not so much with it working but the design limitations in my house.

SCOP is the efficiency over a long period and if you look at the whole year there will be colder times when the COP is lower.

Whilst your COP for yesterday was close to the quoted SCOP for heating it is not actually close at all because on a day like yesterday it should have been close to 5. I think it would be if you could run at 35c flow for a long period but like me, you radiators will hold you back.

I would try increasing your flow temperature a few degrees for a day using the offset from your WD curve and see what the result is. Your home should be just as comfortable and you should see longer runs of heating and periods in between.

You need to be in installer settings to change the overshoot and the modulation. I’m not sure your heat pump should be

ColinS gives a good explanation on how these work in post 194 onwards.

Assuming your house started and ended the day a the same internal temperature then your heat loss was around 1.33kW an hour. If it was 20c inside and 9c outside yesterday I would predict your heat loss at 20/-2.2 to be around 2.7kW.

It is hard to believe that your heat loss calculated by Octopus is realistic. Even if I am a bit out with my assumptions based on your heat produced yesterday your heat loss is nowhere near 8.457kW an hour at 20c/-2.2c

One other thing that came out of this was the performance around 0c. By all accounts it is not 9kW but more like 7.5kW due to defrost cycles and DHW production. If your heat loss is correct then you may find your heat pump is slightly undersized, but I doubt that is the case having just roughly calculating your heat loss!

ColinS · 5 November 2023 18:21

A few more thoughts on the DHW programming;

When the heat pump starts the DHW cycle it must first heat itself (in Summer especially) and the pipes to the tank and their insulation. It then has to heat the pumped water up to the tank bottom temperature after which it can start putting useful heat into the tank. So for each DHW cycle there is a fixed ‘loss’ of electricity for the compressor during warm up plus a ‘useful’ energy input to actually raise the DHW temp.
A good working temp for the tank is 43 to 45 c - I couldn’t get into a bath at 45c and just could at 43c.
There are some days when you use more hot water than others and so the temperature drop in the tank can vary between - say 2 or 3 degrees (no usage -perhaps you are away for the day - but there will be static loss) and maybe 10 or 15 degrees. If the temperature drops more than this you probably want to reheat it for your washing up and showers etc…
You have the same fixed loss whether you heat it by 2c or by 15c and the average COP will be better with the 15c heat up due to the lower average temperature.
A SCHEDULE approach will have a variable heat up level - some days more efficient than others. Although a schedule could be set for say 2pm when the outside temp is at it’s max, the COP gain vs the middle of the night will be quite small.
Hence REHEAT with a reheat hysteresis of 10c is much more efficient every time and it also, automatically, caters for those days when you have a very high usage. On Schedule you would have to to a powerful (and wasteful) cycle using the Madoka on such days
It only makes sense to use SCHEDULE if, like me, your system is at it’s design limit in sub zero temps and you would rather it heated the house without interruption during the day and so set the schedule to heat when you are asleep.

Does this make sense?

matt-drummer · 5 November 2023 18:34

Hi Colin,

Yes it makes sense and I agree.

The only problem with reheat is that it is not very intelligent.

It may not happen that often but there was one day in particular I remember where it reheated and then only two or three hours later carried out the scheduled heat at 14.00.

This gave a COP for the scheduled heat of less than 1, it would have been cheaper to just use the immersion heater.

I need to come up with a solution that works for my wife and isn’t too wasteful.

It went against everything I stood for!

ColinS · 5 November 2023 19:15

There re three options with my Daikin;

Reheat only
Schedule only
Schedule plus reheat - which must be what you are on now??

I’m proposing option 1.

Let me know if they have cut out option 1 now as mine is 15 months old.!

ColinS · 5 November 2023 19:20

I should point out that I had mine on schedule only for nearly a year before I found that Trystan had achieved a much better COP, and the the above dawned on me!

matt-drummer · 5 November 2023 20:04

I would love reheat only.

I will check again but I am sure my only options are schedule or schedule + reheat.

Neither are ideal.

ColinS · 5 November 2023 20:31

Field Code 6-0D = 0 = Reheat Only

Page 178 in the installer ref guide

Field Code 6-00 sets the reheat hysteresis in this mode ( I suggest 10c) - page 181

ColinS · 5 November 2023 20:33

Oh and 6-0C = reheat set point - I suggest 45c (also page 178)

marko · 6 November 2023 10:01

There are no issues with the MCS sizing calculations.

The issue is the garbage assumptions that your typical MCS certified company puts into the calculations.

Not all properties are uninsulated tents with the doors open and a blower fan to force ventilate them. Unfortunately those are the default assumptions and that’s what your typical MCS certified company uses.

Even when they have smart meter data available to size the installation more appropriately.

matt-drummer · 6 November 2023 10:08

I completely agree Marko.

Do a calculation using assumptions and guess work.

Come up with an answer and completely ignore the facts staring you in the face, the actual energy consumption!

My heat loss surveyor was shocked when I told him what I thought my heat loss was and he compared it to his assessment.

I explained how I arrived at my figure but I was ignored.

I should have pursued it more but with other, what seemed, bigger issues I messed up.

matt-drummer · 6 November 2023 12:58

Hi Colin,

I do have reheat only.

It is displayed differently to some other menus, when you go into heating mode it only shows two options on the screen, you have to move the left dial upwards and reheat only appears at the top of the list.

ColinS · 6 November 2023 17:55

Good to hear.

I think we’ve covered all the main issues with Daikins above - especially how to get more output from a fixed input.

The two puzzles that remain, at least in my mind, are 1) how to optimize the Daikin when it is cycling - it’s fine when running continuously but other units do much better when cycling - can we learn from how the other units are programmed? and 2) How to optimize output at freezing temps when it starts defrost cycling. (you can see the problem if you look at my unit on February 8th.)

Should we do this on another thread?

matt-drummer · 6 November 2023 18:40

Hi Colin,

I hope you are well.

I’ve had enough of my Daikin heat pump today, so I have started another thread about whether to ditch it or not!

It’s mad that I have essentially the same heat pump as you in a house that is less than half the size.

I struggling today to see how I can make it work, it’s not gone very well the last couple of days.

I have no faith in my installer or the heat pump manufacturer and I am loath to dump another £5,000 plus installation on radiators to make a bad installation a little bit less bad.

I really want a smaller heat pump and not a Daikin!

matt-drummer · 6 November 2023 18:55

It was going ok until I changed the modulation from 10 to 4 and that didn’t work so I put it back up to 10.

But it’s not the same, I don’t know what happened, maybe the days are just different.

I left it running last night at 23c on the Madoka to see if I could extract a decent COP from it.

But all I am really doing is wasting electricity chasing a decent COP which is silly.

So I have turned it down to around 35c flow.

The house is plenty warm enough and doesn’t turn into a sauna as the day progresses.

The COP is relatively terrible but it uses much less electricity which is the point of it.

In the end I sit here with a heat pump that is heating the house ok but I know it is using 50% more electricity to do it than it needs to.

Spending £5,000+ on radiators isn’t going to make it better, it’s just going to be hotter in here than I want for a bit less electricity or I am going to get loads of heat in a compressed period of time with loads of off time in between. in order to keep the house temperature at a sensible level.

None of it is what I was hoping for

matt-drummer · 6 November 2023 21:54

This is a new one!

Can anybody explain what is going on here?

Something has to be wrong with this?

HydroSam · 7 November 2023 07:19

I think this is a combo of immersion being used for DHW tank and the heat pump running for heating.

Have you followed @ColinS suggestion of fixed flow temp for heating and reheat for DHW?

I have and I’ve found random trickles of 3kw, which I’m sure equates to the immersion heater kicking in to maintain 45C, I’m not getting the 10C hysteresis I hoped for on DHW.
My data and DHW settings (not display is old Altherma but settings are same as far as I can tell)