I am lost and confused with my Daikin heat pump

Hardware Heatpump
21

This behaviour is not what I expected from a heat pump. I really want to be able to run the heat pump for shorter periods but stuff like this stops me doing it. I don’t think this is how a heat pump should behave.

It was working fine from 13.57 to 18.08 when I turned down the flow from 36c to 35c which stopped it.

It started back up at 18.12 and went through the same strange prolonged heating process until 18.52 where, just as it is about to settle down it decides to defrost even though it is 8c outside and no sign of ice on the heat pump.

Then it goes through the whole heating process again with the `Daikin Dip’ as I am now calling it!

Is this really how it should be, is it me, am I expecting too much?

I have changed nothing for days, it runs really well at times and at other times I think it is not right.

My DHW doesn’t seem right, and the DHW cycle seems to mess things up, it was fine yesterday morning and then the problems started after the DHW run yesterday, the heat pump didn’t resume heating like it was in the morning and it was worse this morning than it has been for the last few days.

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22

This is well documented, but at the same time very annoying even the big companies with decades of history here haven’t nailed this still.

In mild weather like today, mine defrosts every 5-6 hours even with no frost buildup almost like there is a timer countdown.

This is a good read on it:

My dads Panasonic whole house Etherea Air to Air multi-split (1 outdoor unit and 4 indoor “heads”) had a few issues last winter where his unit (I also monitor) was (and still is) more reluctant than our Daikins to defrost. He can sometimes go through the night with maybe one defrost, where our units won’t last more the 30 mins.

This led to a couple of days where conditions led to a cascade effect and death spiral where each defrost did not fully defrost the unit, leading to a thick ice buildup, power use going up and up and heat output dropping……I had to force a manual defrost for him by putting the unit into cooling mode for 20 mins as he complained it was getting cold, yet I could see power ramping ever higher and well outside “normal” range.

The installer has been out, as have Panasonic and spent a whole day on it, to find no problem at all. (That said, he hasn’t had the issue so far this winter which is the 2nd with it)

Most of the time though, his unit barely defrosts, so efficiency is great relative to ours.

My point is: get the algorithm wrong, and it’s bad news and possibly physical damage through ice buildup.

My guess is Daikin err on the side of caution with defrosts for this reason.

23

Afraid not!

Daikin should be best placed to explain the detail of how the product behaves here. The only contact I had there (Darren Manley) jumped ship to quantum earlier in the year though.

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24

Possibly lack of demand?

It’s still relatively rare to use heat pumps for heating; and air to water units whose performance one could actually hope to measure (and complain about) are rarer still.

It’s also not really picked up on the efficiency tests so no incentive to do too much (quite dry air); and with UK not in EU that continental winter test standard head even less reason to change?

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25

Regarding the varying flow rates - the heat pump modulates them to try to maintain the delta t. Faster flow rates mean less time for the emitters to shed the heat so the return temperature will be higher and vice versa.

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26

My heat pump is running much better now I have got my head around things. I am still having a couple of issues though, probably me as usual but I have to ask.

My DHW production doesn’t seem right most of the time, the heat output just doesn’t seem as high as others.

Also my heating doesn’t always resume particularly well after a DHW cycle, it struggles to get going at times.

I am running a fixed LWT but the heat pump is struggling to achieve it at times and if I ask for an increase it’s reluctant to do it, it often fails to raise the LWT

Finally I am seeing my flow temperature decay over time, not all the time, but quite often and that is when I try and raise the flow temperature with little to no response.

My requested LWT is 36c but it will not sit at that and steadily decays. The app and the MMI show the LWT at similar to my heat meter, ie requested is 36c but I am only getting 35c or less.

My overshoot is set at 4c

DHW is not great

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Decaying flow temperature

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The flow temperature is reducing, the electrical input has increased, the heat output and COP are falling. It feels like it is struggling to produce heat, like something is holding it back. The radiators cooled noticeably.

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Maybe @marko has an idea what is going on?

27

I don’t think this is a problem. The drop is only by 0.5° and the return is dropping by the same amount. This just means that the heat pump is trying to match the heat loss, but hasn’t quite managed to lock it in perfectly, so output is a bit less. Around 22:00 it notices, and ups the heat output a little to compensate. COP is a steady 4.0 between changes in input.

This looks to be working as it should, within the capabilities of the controller. If you want the flow to be exactly 36°C, you may need to increase the target by a degree.

It’s not looking great, no, but your experiment from cold showed that good performance was possible.

28

Hi Tim,

Thanks for looking at it.

The drop in flow temperature is more than 0.5c, the requested flow is 36.0c and it had dropped to 34.7c. It is 1.3c below target and continues to fall unless I take action.

This is not in a short space of time, it happens over two hours or so.

I would have thought the heat pump would not take more than two hours to notice the flow temperature is not as requested.

It does have quite an impact though, I know the return is dropping too but so is the dT between the flow and room temperatures and therefore my potential heat output is impacted.

I try to raise the flow temperature but the heat pump doesn’t respond, I don’t expect it to be instant but I would have thought if the requested flow is 36.0c and the actual is 35.0c or less and I ask for 37.0c I would have thought to see some increase in 30 minutes or so.

In respect of the DHW, it does work better at times, probably related to tank temperature.

What I don’t get is why I am not seeing a higher heat output than 6kW or so during the DHW cycle?

29

Does it drop below R1T sensor (you know the one…)?

What if there is faulty logic here with Daikin somehow? I know it’s unlikely, but worth tracking your issue with regards to allowing flow temp to drop, and seeing if it correlates to the higher temperature of R1T.

1 Like
30

Hi Stephen,

My water coming into the house is the temperature as measured by the heat meter so that is that.

My temperature measured by the heat meter decays but it is roughly what is reported by R2T (I can only see round numbers on the MMI and app) and so is the same in the MMI and the app, but they are both below the requested.

As R1T is always higher than R2T then my flow temperature is always below R1T.

All I know is that R2T is reporting lower than my requested flow temp, my requested flow temp isn’t what is asked for and that my flow temp slowly decays over a couple of hours to at least 1.3c below what is requested.

I see this whether I use radiators with a fixed dT of 8c or fan coils with a lower dT.

I thought it might be because it cannot get to the dT of 8c at that flow temperature and rate but it behaves the same at times when I have a lower dT set.

At other times the flow temp just increases as the overshoot allows.

I don’t understand why it decays and fails to respond to requests to increase flow temperature.

I don’t have any leaks as I don’t have to add any water to the system.

I do notice the radiators lose their heat as it is struggling to raise the flow temperature, it is quite pronounced, you can really feel the heat disappear, like it has been sucked out of the house.

I also believe my DHW cycle isn’t producing the heat it should.

I remember in the early days it was suggested that it could be lacking refrigerant.

I don’t know that it is but what would be the symptoms of a lack of refrigerant, how critical is it?

31

Hi @matt-drummer

Worked example from my point above.

Target flow temp: 36C

R1T flow temp: 36.5C (we know somethings not right with this sensor where BUH exists)

R2T flow temp: 35.5C (you’ve said this closely matches your heat meter)

Your heat meter: 35.5C (what your heat meter is recording so we know it is very accurate)

In this example, the unit will allow (if minimum output allows) the flow temperature to drop if for some silly reason it’s using R1T (and not saying it is, just does the behaviour correlate to the sensor or not)

Have I misunderstood your numbers? (Quite possibly!)

32

Hi Stephen,

I don’t know or think that anything is wrong with the sensors in my heat pump, I think R1T and R2T are fine in respect of reporting the correct temperatures. I am not even really interested in R1T personally because it is not the LWT from the heat pump.

When I am requesting 36.0c I am getting 34.7c or less after a couple of hours, the sensors are reporting this as is my heat meter.

I wouldn’t mind if they were wrong, I could just turn the flow up to get what I want, but that doesn’t work.

So, when R2T reports 36.0c so does my MMI, my app and my heat meter, when it reports 35.0c so does everything else too.

My problem is that this flow temperature decays over time, and it actually does decay as reported by my heat meter.

I also don’t get the heat in DHW I expect and the DHW cycle disrupts the heating, maybe the higher flow temperature of the DHW cycle does something to the refrigerant that takes time to recover from.

I don’t bet but if I did I would bet my heat pump has the wrong amount of refrigerant in it.

It’s just my gut feeling though.

33

@matt-drummer Did you fit the internal insulation on the exposed pipes after the BUH?

I have also contacted Daikin, but yet to hear anything useful - the Level2 support guy told me to contact the Bristol service centre, which I have now done, using my non-GMail email address, so it won’t end up in their spam.

34

Hi John,

I haven’t touched my heat pump as it is not staying, I thought it best not to mess with it.

35

At the weekend, I put a bit of leftover pipe insulation on a 6 inch segment of the uninsulated pipe between the heat exchanger and the BUH.

I reckon it might have dropped the R1T-R2T delta by 0.1C, from an (awful) 1.8C, to 1.7C, perhaps 1.6C. But it’s hard to be confident about such small changes. (I’ve just realised the sensor is misnamed, with R1T and R2T swapped)

I’m inclined to stick some temperature probes on the pipes while the pump is running, to see if the difference is real or measurement error.

I thought I’d made progress with my heat pump yesterday, by switching to a dT of 4C. It seemed to be running more within it‘s parameters, with the flow rate not stuck at the minimum. But today has been pretty awful. Just a few C colder outside. :neutral_face:

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36

PS: the BUH itself looks pretty well insulated. I find it hard to believe it is causing a near 2C temp drop in my pump.

The R1T and R2T probes also looked like they were under a suitable amount of insulation. The one just after the heat exchanger is probably better insulated, and closer to a heat source.

With the cover off, the pipe work looked just like the picture posted by @Stephen_Crown before. So I’d say they are built to spec, and not just missing insulation ad-hoc. Unless we were both unlucky :smile:

1 Like
37

Maybe R1T is faulty/badly calibrated and reading too high?

The temperature at R1T is not what goes to your house whether it is correct or not.

R2T is the thermistor closest to the water outlet and is the only one that matters.

The only way to be sure is to measure the temperature at the water outlet when the heat pump is running.

If the thermistors are so bad, there isn’t even a guarantee that the discrepancy seen at 10c or 15c is the same as it is at 35c or 40c, they may have been calibrated to be correct at these sort of temperatures and are not accurate at extremes. None of us know with absolute certainty I suspect.

To properly assess the heat pump performance you need to know the temperature of the water entering and leaving the home, how much of it there is and how much electricity is being consumed.

If these are not measured accurately then it is all little more than informed guesswork.

My values from the MMI are the same as my heat meter.

What R1T is, who cares, it is not what leaves the heat pump. My experience of this heat pump is that it uses no more electricity heating to 37c than it does heating to 33c or lower, if R1T and R2T were closer I suspect it makes little difference, R2T is still the leaving water temperature and you may or may not use less electricity but I suspect very little if any.

When I had 9kW at dT 30c of radiators I needed to heat the water to 42c/43c to get a reasonable COP, any lower was terrible. If anybody has less than 9kW of radiators at dT 30c then you won’t get a COP of much over 3 at lower flow temperatures and probably less.

You have to be able to consume around 4kW of heat to get a COP of 4 because the electrical input bottoms out around 900w.

If you cannot get this your COP will be whatever heat the radiators can deliver at the given flow temperature divided by 900w, it is the best you can do. If you can only get 3kW of heat out of the radiators at 35c flow then the COP will be a little over 3 at best.

If a 9kW owner has 15.5kW of radiators at dT 50c that is 7.9kW at dT30c

If they run their heat pump at a mean flow temperature of 35c with a room temperature of 20c the most the radiators will output is 3.25kW of heat

Assuming this can be done at around 900w electrical input then that is a maximum COP of 3.61

That is the maximum the owner could ever get and in reality it will be lower as it is not possible to always get that flow temperature at only 900w.

I would predict a SCOP of less than 3.

This heat pump needs big radiators to get a respectable COP/SCOP

This is from Jonathan’s data, radiators with around 15.5kW output at dT50c running at a mean flow temperature of about 35c and heat output of about 3.4kW. This is entirely consistent with what we would calculate. There is nothing wrong with this data and as it comes from the heat pump there is nothing wrong with the thermistors at these temperatures. Those radiators could never put out more heat at 35c with the house at 20c

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2 Likes
38

Hi Matt,
Here is a time window from Sunday with approx 10% higher heat output and COP. Inside temperature was very similar.

At this point, the heat pump was pushing above the target temperature.

I think it’s probably because the outside temperature was a few C higher, making the pump more efficient.

I’m not expecting epic COP values from my system, but would like to understand the differences between days. If I can consistently get another 10% performance, that’s worth it.

I’ve currently got a weather curve what’s targeting around 37-39C. Do you think I need that a bit higher with my radiator sizes?

I’ve been reducing the flow temp to try and avoid lots of defrosts.

https://emoncms.org/app?readkey=0e9ab50e73d8ae59d9e6dcc70e5dd5f7&mode=power&start=1706511240&end=1706522040#myelectric

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39

Hi Jonathan,

I find exactly the same with my heat pump.

I get more heat at the same flow temperatures when it is warmer outside, not really what I want! It does also seem to be in the order of about 10% extra heat.

@ColinS helped me with this when I was running in a similar configuration to you. Go back through the `Thank you’ thread.

WDC and Madoka won’t help, they only work when you aren’t already running at the minimum output.

You need to find the flow temperature that gives you about 4 to 4.5kW of heat.

This heat pump should be at a COP of 5 at 7c outside and a flow temperature of 35c. As we know the minimum electricity is around 900w then we know we are aiming for 4,500w of heat.

Your radiators won’t be able to do that at 35c, I would expect you to need around 43c to get that heat output. I had to run at 42c fixed lwt with about 10% more radiator output than you have.

Your radiators should put out about 4,650w at a dT of 20c between mean flow temperature and room temperature. How much electricity this takes will depend on weather conditions in the main.

I would forget the wdc fttb and just run a fixed lwt and adjust to find what works best. Once you have done that it’s what you need to run at.

I have always found radiators to give better results than fan coils. That has been the same whatever radiators I have. The heat pumps aims for a dT of 8c but I rarely get it.

The heat pump is limited to a minimum flow rate of 10lpm, not low enough for me, but the biggest dT possible seems to give the best results in terms of efficiency.

I can’t explain how it works but it feels like the heat pump is always optimising itself to fit with the house and the radiators by striving for the widest dT but with no or very little penalty in electricity consumption.

Defrosting is certainly reduced at lower flow temperatures in my experience so that is a good idea.

It’s a difficult heat pump to get good efficiency from. They are installed in modest sized houses with small heat losses that are unlikely to have large enough emitters to cope with the lowest output that is the same as a 16kW heat pump.

Designing to run at 50c with this heat pump and sizing radiators for this is a mistake and the cause of most of the problems we all encounter with this heat pump.

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40

Thanks Matt. I’ll make time to read the Thank You thread top to bottom!

I’ve stopped using the Madoka for control, and have Home Assistant acting as a software thermostat to turn the heat pump on and off when certain temperature thresholds are met in different rooms.

The heat pump is currently using a very shallow weather curve, but will experiment with a fixed flow temp instead.