Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

Hardware Heatpump
123

Reaching the target flow temperature.

[quote=“matt-drummer, post:122, topic:24589”]
With more electricity and flow rate it could have carried on producing 9kW of heat from what I can see?[/quote]

No.

Your radiators are incapable of dissipating more than ~5 kW with a flow temperature of 47C and a return temperature of ~40C.

They might be big enough to do this on paper. In practice they have not been balanced (most of the water is shortcutting around one or more radiators and leaving the rest starved) and the system is incapable of utilising the full capability of the emitters.

Output capability also drops as the internal temperature increases. Octopus rated your system at 18-20C ambient temperatures internally; not the 21-23C that it is operating at. The closer the room temperature to the radiator temperature the less heat they are able to dissipate.

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124

Those DHW runs; assuming the tank were at similar starting conditions and the settings were the same; are suspect.

If heat output keeps on falling for a given set of operating conditions it does lend weight to looking at the unit. Very unusual for them not to do what they say on the box though - hence the initial suspicion on the metering!

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125

If it kept producing 9kW of heat, then the flow temperature would have kept on rising. Think of the whole heating system as a closed circuit (which it is):

  • The heat pump recieves water from the house, adds heat to it and sends it back:
    return temp + dT => flow temp
  • Water flows around the radiators, which emit some heat, cooling it down:
    flow temp - dT => return temp

So when the HP reduces power to keep the flow temperature stable, which means the radiators are emitting that same amout of energy. If the HP puts more more heat into the circuit than the radiators can emit, then the flow temperature rises.

See this chart for my system, which shows heat producded vs. the calculated output of my radiators. It only settles into long runs when the radiators can emit all the produced heat.

image
image1012×514 47 KB

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126

Before I had my heat loss survey carried out I calculated my required radiator sizes. The output is around 180% of that I have now. If I put a radiator in my office then the radiator output will be double that installed now.

Presumably that will improve my situation were I to install those radiators?

All of my radiators were equally hot to the touch yesterday, not very scientific I know, that must mean that water was flowing through them?

127

Hi Marko, the tank was 2c warmer today at the start of the run. It was 35c yesterday and 37c today.

The settings are all the same.

128

“Yes but…”

If one were 47/46C supply/return and the others were 47/37 supply/return then way more water would be flowing though the one that was 47/46C supply/return and the temperature at the heat pump would be more like 47/45C instead of the 47/37C that most of radiators were at.

This “over flow” or “bypassed flow” dilutes the return temperature from the system and leads to it running at elevated temperatures at the heat pump end for a given mean water temperature in (most of) the radiators; effectively reducing how much they kick out for a given supply/return vs what they should.

There was zero information in the handover pack as to how Octopus had ensured the radiators were balanced. No calcs for what the flow through each one should be. No notes to say how it had been achieved etc. Most likely hasn’t been done. That is unsurprising. MCS are all about the heat pump (the easy bit) not the system (the hard bit). Most boiler bashers don’t have a clue how to balance systems either. Set the pump to 3; have the water hammering around through shortcuts/bypasses; call it good.

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129

Thanks again Marko.

It all makes sense

Balancing radiators sounds like a complicated job and probably quite difficult in a retrofit.

And therefore beyond the capability of most installers and expensive I guess.

I can promise that Octopus have not balanced my radiators, they heat loss surveyor couldn’t even draw my house the right way up without my assistance.

How long does it typically take to balance radiators?

Presumably it requires changes to pipework in most instances?

Now I am reading about radiator balancing and I will watch some videos.

I will see how it goes.

130

Depends entirely on what valves you have available for balancing / how unbalanced the pipework is naturally.

If you look at the spreadsheet shared earlier, you’ll see that every radiator had a design flowrate, and there were a selection of “pre-settable TRVs” on the next page that would allow you to twiddle the pre-setter under the TRV head to set the Kv value (resistance) then essentially walk away.

If you don’t have this kind of thing you do it the hard way with lockshields.

Some are accurate and ddesigned so that you wind them closed then wind them open X turns to get the Kv which gives you the flowrate that you want.

Others are from B&Q. Good luck. Best I’ve found for those is to let the radiators go cold, grab an infra-red camera attachment for a phone, then whack it on and watch the radiators “fill” with heat. Open up valves on those that fill too fast. Close down valves on those that fill too slow. Let it go cold again. Repeat.

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131

Did you get the ModBus interface set up at all?

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What is the ModBus interface?

133

What is happening here?

Screenshot 2023-10-29 at 14.26.04
Screenshot 2023-10-29 at 14.26.041718×912 138 KB

Beginning of the DHW cycle. 3 minutes of ramping up to 1.8 kW electrical input with zero flow.

That doesn’t feel plausible to me. What is this electricity meter measuring?

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134

I have no idea what it is doing Marko.

I have three meters, one for the heat pump itself, one for the immersion heater and one on the back up heater inside the heat pump.

That electricity consumption is all from the heat pump, no immersion or back up.

There’s so much strange behaviour from this heat pump that I don’t understand.

Some is certainly my own ignorance and lack of knowledge.

I don’t feel comfortable keep commenting here about it.

I appreciate all the help and advice I have been given.

Any changes I have made to the settings and the way I have operated the heat pump have had minimal impact, nothing makes it significantly better or worse.

That in itself leads me to believe something deeper is wrong, I can’t get it to perform terribly compared to now and neither can I improve it.

There is also a lot of inconsistency, same weather, same settings, same house temperature but the performance is not consistent.

And then I look at the way the heat is produced, it’s erratic.

What I do seem to notice is that the COP is better with higher electricity input, whether that is always the case I don’t know but it’s my feeling.

I am pretty sure that my radiators are too small, they are not balanced, set up is probably not optimum and the heat pump is too big when it’s relatively warm.

I think the performance will be better when it is warmer with bigger radiators and operated more like a gas boiler chucking in less frequent slugs of heat.

When it is colder and the heat loss is higher I will probably be able to run it at lower flows for longer.

Bu maybe there is something wrong, maybe too little refigerant as has been suggested once?

135

You’re not the only one at a loss here!

That unaccounted for behaviour is a “boiling a kettle” amount of energy. With no change in temperatures recorded by heat meter and no flowrate/heat output. Something must be chucking out heat for that to exist.

Perhaps ask Octopus (as they’re the ones with budget for a site visit) to verify that all is well with the unit as far as they are concerned? (you don’t have a contract with Daikin unfortunately, so probably can’t ask them to explain the behaviour vs the datahseet)

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136

Yes that electricity heated something, where the heat went I don’t know. Some in the blip at the beginning? The rest outside?

What about the dip in heat output at about 16.07, I have less heat than electricity.

I have a warranty direct with Daikin for seven years.

What that means, I’m not sure.

I can’t imagine that either Octopus or Daikin want to read negative comments about the product.

Of course, until I know what the problem is, I will reserve judgement.

It is clear that it is not working as it should.

I am assuming that the OEM gear is working properly, I think it is overall as the data agrees with my other sources.

137

the same thing happens with the Daikin that give the expected performance, let’s assume it’s warming up the compressor

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138

At this point I think it’s only fair to change the focus from the in house side of things towards the heat pump(Octopus or Daikin).
By not having the expected performance from the DHW as well, it’s clear that even though the radiators don’t seem to be ideally sized, something stops the whole system performing.

  1. If we assume the HP functions properly but for some reason the heat doesn’t get transferred efficiently(air in the top of the heat exchanger) then there’s nothing you can do.

  2. If something is wrong in the heat pump(shortage of gas, elements that control the gas, valves, sensors) that’s clearly nothing you can do, only guessing(enough of that).

3.If everything works well with the HP, whatever it is the issue you will find out from them.

The warranty is there to be used.

Good luck!!

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139

So I just checked my radiator flow and return temperatures.

Every radiator’s flow is about the same and the difference between the flow and the return on each radiator is between 4c and 5c.

Can I conclude that water is flowing relatively well through each radiator?

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140

Blimey. That’s not an insubstantial amount off preheat vs…none by most others in this weather.

Agree. Look a little later though and it’s back to COP3 ISH in DHW mode which suggests something not mechanically terminal?

Those links are an eye opener on a few counts

  1. Perhaps fan coil mode to force a 5C dT instead of an 8C dT is a deliberate efficiency fudge

  2. These things can kill themselves mechanically (burst their plates) if sensors fail. I wonder if R290 units need to have any more interlocks for safety that would make them more robust too

  3. There have been failures that can cause low COP; some of which are electronic so could be intermittent

  4. These units don’t like low flow temperatures. 35C or up. Interesting but not understood. Why do some units love these and others hate them?

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141

Just wanted to drop in and say this is a really interesting thread. I have another Daikin on the Heat Pump monitor list, the Altherma 11.2kw in Farnham, Surrey, so will be experiencing similar outside conditions to the other Hampshire Daikin’s mentioned above. Mine is the other R410a Atherma monobloc.

What has been discussed here over the last few weeks is similar to the journey I’ve been on over the last 2 1/2 years. I was one of the participants in the OVO/BEIS electrification of heat trial. My first installer was eventually kicked off the scheme (and MCS), my system was then nursed back to health by another installer who was parachuted in, but they only had scope to improve some of the pipework.

Over this time for heating, I have removed the fixed-flow rate, tried pure weather compensation (house gets too hot), low LWT with the Daikin controller modulation, higher LWT with Daikin controller modulating. I seem to be settling on a min LWT of 35C at 13C (generally the temp the house needs heating) and a max of 40C at -5C outside. The house was warm enough during the -8C we had last winter, with the heat pump gently ticking over outputting 5kw all day (another sign the pump is over-sized).

I too have similar conclusions, the heat pump is over-sized for my house, the radiators are probably too small in some rooms. And the radiators need further balancing still. I think my pipework is less than ideal, there are several branches and plastic has been used in places, however with a low heat requirement I should be able to make it work. ‘Cheap’ city plumbing TRV and locksheilds were used and I am really struggling to balance the system, if anyone has a recommendation for improving the radiator valves please share. Only one TRV in my bedroom is actually used, so I don’t really need TRV’s.

I don’t want to take over this thread though, so if you have ideas my own chat is here

Thanks again for documenting all this, I’ve found it a really interesting read.

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142

Thanks, any input is useful.

I expect there are lots of us in similar positions. I’m not saying it’s a problem confined to Octopus but they have been installing a relatively large number of Daikin heat pumps.

The sad thing is, I would imagine that most owners are oblivious to what is going on.

I haven’t experienced sub zero temperatures yet but I have read that Daikin heat pumps are not as good at delivering the rated output at these sort of temperatures, but that is just what I have read.

If that is true, then I doubt my heat pump is over sized.

I don’t think my radiators are too small for the house as I have no trouble heating to 23c when it’s 7c outside at 30c flow temperatures.

I too struggle with pure weather compensation, the house gets too hot and the flow temperature is too low for the heat pump.

So far I can only conclude that the heat pump has a narrow window of operation in terms of efficiency and at the moment I can’t seem to get into that window.

Whatever I do has minimal effect on COP, I can’t destroy it with high flow temperatures and I can’t seem to do better than about 3.3 to 3.4 for heating.

It’s all a bit disappointing.

My trvs are all wide open, I see no value in restricting the heat pump by shutting down radiators.

My radiators are well sized for the rooms and the temperature in each room is in proportion to that designed even if I am running a little warmer overall.

I have Drayton trvs fitted.

I looked at fitting Danfos auto balancing trvs. I downloaded their app and tried to configure my radiators, those I have now and what I plan to change to. The minimum flow temperature I could choose was 40c but even at that it said that their valve was not capable of flowing enough water. That was for K3 radiators at 1200mmm x 600mm. It had no chance with my K3 500mm x 2200mm!

Whether they would actually work or not I don’t know. They are not expensive, about £30 each.

I have some plastic pipe but I can’t see any flow problems, my radiators are all roughly the same temperature and all seem to be flowing water with a difference between the flow and return of each one of 4c to 5c.

I should have my thermal imaging camera later and I will be able to check how they fill.

If I can eliminate any problems with my radiators I should be able to concentrate on getting the best out of the heat pump and/or working out what is wrong with it.

If my heat pump really does have such a narrow window of operation then I will start to feel like it has been mis-sold.

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