Hi Ivailo,
My dT is set at 8c and is currently 6c with a flow of 35.7c
My COP for the last 30 minutes is 4.38, it’s OK for me.
I will experiment with different dTs over the coming days to see what I can do.
My radiators are massive though, they can handle this.
Maybe a lower dT will give me a better COP, we’ll see.
Thank you for the advice and guidance.
Hi Matt
I think the other factor to consider with the comparison between heat pumps (another one I know), is the primary pipework. If you reduce the dT, you need more flow or bigger pipework to carry the same heat. At least I think that’s correct, our systems will all have a different pipe layout which is either good or (as in my case) less able to deliver the required heat. Just thinking back to the radiator balancing discussion from a few weeks ago:
And on the temperature measurement position. I might not have the same monobloc as you lot, (reminder mine is the older Daikin 11kw) but I have occasionally noted down readings of the leaving water temp in monobloc, the backup heater which is separate to the monobloc being in the house (and now very much disabled) and on the Sontex heat meter and I also seem the same pattern of losses through the backup heater.
I’ve run some stats on the energy produced for 2022 which might be useful to show the difference between the in-built sensors and a certified meter.
Just thought that would be interesting for the discussion above. I don’t know whether ESPAltherma can be used with my heat pump, and I wouldn’t know where to start if it could. In my case BEIS/OVO provided the meters to enable me to track performance. And now I’ve managed to grab the data feed off them I have improved the SCOP, and it’s looking more like 3.4 rather than the 2.8 of last year.
Hi Sam,
i am pleased yours is working better, mine is too.
To mean anything and be comparable, COP has to be a measure of the heat delivered to the home in relation to the energy used to produce the heat.
The heat going to the home is a product of the difference between the temperature of the water going into the home and leaving the home and how much water that is over a given time period.
Measuring the incoming water at a place inside the heat pump where the temperature is always higher than the that of the water actually leaving the heat pump is always going to overstate the heat delivered to the house.
It is obvious, basic common sense.
For that reason I will ignore any non MID monitored installations in future for comparison purposes as I have no way to verify the accuracy of the data, they could be taking measurements anywhere and I would never know.
I have learnt my lesson.
The R1T on my non BUH equipped model (smaller size mono) is in the same place as R2T on the bigger unit with BUH going by the 3D Model posted above, its in a sleeve on the pipe right before it goes into the circulation pump.
Completely understand not using non-MID sensors for comparisons but I’m hoping to get good results as your R2T compares well to your heat meter.
Hi Jordan,
That is very interesting, thank you.
I think you’ll be fine with your monitoring, the data seems fine as long as you pick it up from the correct place.
Your R1T is giving the same information as the R2T on the 9kW+ BUH equipped models, I suspect the R1T on the non BUH 9kW+ models does exactly the same.
I am sure the LWT is reported correctly from R1T without BUH and from R2T with BUH.
I am going to discount non MID monitored systems unless I know where the data is being collected for obvious reasons.
If I know the data comes from the correct places then it is OK to look at them and compare but it is pointless unless I know, and an absolute waste of time when I know the data is not correctly gathered.
Hi Stephen @Stephen_Crown
Did you delete that post with the pic of the exposed pipes, and a guesstimate of the heat loss in the outdoor unit? I’ve had the email notification but it doesn’t seem to be in the topic here.
If we assume my R1T and R2T are not lying/faulty, then there is always a 2C loss in the BUH and associated large bore piping in the unit. At 30l/min, that’s approximately 2 x 30 x 4.2 / 60 kW or 4.2kw. More importantly, 10l/min is 1.4kW, which is a huge chunk of the output.
The simple graph above, plotting R1T temp (before), R2T temp (after), and R4T (return), shows how 2C makes all the difference to the numbers! R1T never goes below R4T, but R2T drops quickly below until the HP compressor cuts in again. Basically, the HP/BUH/pipes are sucking heat out of the radiators, which has to be restored before the Target Flow Temp can be reached. This doesn’t affect the house temp, because the R2T is still above the indoor temperature, but the transfer of heat to the outside and the required extra energy to warm everything back up is hammering the COP.
I’m probably going to remove the panels and check the insulation, or lack of, on the BUH and piping. It’s got to be going somewhere! I’m quite impressed that it can lose that much heat in such a small area/volume, but then the ambient-flow dT is 20+C.
Could some kind of radiant heat from the heat exchanger be providing an inaccurate reading of actual water temperature? Rather than the water actually losing heat in that short space which seems unlikely.
Hi John,
This is the truth.
What goes into your house is all that matters in terms of efficiency and ultimately cost.
What is lost in the heat pump to the outside world is lost, unfortunately, it is not heating our homes!
R2T for us with BUHs is what goes to the home, looking at what comes out of the heat exchanger at R1T is not what is sent to the home, we might like it to be, but it isn’t.
The BUH is losing heat, how much compared to those without the BUH I don’t know as I don’t know exactly where R1T is placed in non BUH models, but even if we did know, there’s still probably some heat loss between the heat exchanger and the outlet from the heat pump.
I’m not sure how much it matters, the heat pump is capable of a COP of 4.5 to 5+ based on LWT at R2T.
Maybe it could be better.
What I do know though, the COP does not improve by calculating heat loss using R1T with a BUH and R2T, that is just delusional and false.
Getting R2T closer to R1T is the answer.
I wonder if R2T thermistor is faulty, or incorrectly fitted to the pipework, as I can’t see how it can possibly be that much lower than the return pipe while the heat pump is inactive.
Maybe but I’m not sure it matters in this context although there may not be the actual apparent heat loss so you may well be correct. I have discounted it fttb, the water coming out of the heat pump is at a certain temperature, in my case what is reported by R2T. If I want it to be closer to R1T then I need to mess about inside the heat pump, probably not something I want to do at this stage.
So you could be correct but all I have to work with in the house is water coming out of the heat pump at a certain temperature and my heat meter, my really good billing grade heat meter, confirms that it is the same as reported by R2T just before it enters the circulation pump and leaves the heat pump headed toward my house and about 1c less than reported by R1T as the water leaves the heat exchanger. To use the temperature reported by R1T and ignore R2T and my heat meter would increase my heat production and COP by 15%, but it wouldn’t be true.
With a BUH R2T is the temperature of the water leaving the heat pump. It is reported in the MMI and my heat meter confirms it as do my three thermometers,
There is nothing wrong with using R2T as the source for heat production calculation, it is correct.
Using R1T with a BUH fitted is not the correct temperature to use as that is not what goes to the home.
The fact that R1T in a BUH equipped heat pump is higher than R2T is a separate issue, they are not connected with calculating heat production.
R2T is THE leaving water temperature in BUH equipped heat pumps, it’s a fact. R1T is not THE leaving water temperature in BUH equipped heat pumps, also a fact.
Discontent with the temperature loss between R1T and R2T is something else, it doesn’t mean it’s OK to use R1T as the basis for heat production just because it gives a better result.
Whilst the heat pump is inactive these are just pockets of water that are not moving.
Aren’t the readings irrelevant?
Isn’t that why the heat pump samples, to move the water around and get a true reading?
One part of the heat pump could be warmer than another, especially water around the BUH which seems to be a bit more lossy than we might desire?
Hi Tim @Timbones
Thanks for the input, really appreciated. I’m trying to think my way through this. Maybe Daikin will have some idea - I’ve asked them about it. Where would the heat come from to keep R1T higher? Maybe the residual heat in the heat exchanger? Which is then lost in the BUH? I note that @Stephen_Crown has only a 0.8C loss R1T-R2T, so my thinking is indeed a problem of some kind with the R2T thermistor. There remains the question of the loss in the BUH and associated pipework, but at least that’s lower.
The “pockets of water” are moving when the sampling occurs - the graph below shows that pump activity drops R2T below R4T, and they remain relatively static when it’s not.
When the compressor turns off, we would expect the flow temperature to drop down to the return temp. Not below return.
This data shows 380 Wh of cooling, which is more than half the energy transfer as was used for heating. This says to me bogus measurements.
Also curious that (other) flow and return temps rise when water stops flowing, and drop when it flows again. But let’s tackle one thing at a time…
It will be instructive to look at @Stephen_Crown 's 11kW Daikin, which is also monitored by ESPAltherma reading the HP’s internal sensors. He reports a smaller R1T/R2T drop, 0.8C, but apparently his measured FlowT does drop below FlowReturn to some extent - I haven’t looked at that yet.
You’re asking the OEM a technical question that is within their capacity and interests to answer. And you’re doing it in writing. Should be fine. 
That’s less curious
Heat will soak.
When water flow rate drops the deltaT across plates etc will fall (so water gets hotter)
Lots of reasons this can be the case
I have been thinking about the water temperature loss between R1T and R2T
What I am seeing is an LWT at R2T of 35.0c and water coming into my house at 35.0c, the same temperature so my heat produced is based on this.
The water temperature at R1T is 36c so what would I gain if I eliminated this temperature loss?
My LWT at R2T would still be 35.0c as requested and the heat delivered to my house would be the same.
What I might potentially gain by getting R1T and R2T practically the same temperature is reduced electricity consumption in achieving my LWT at R2T of 35.0c because the rest of the heat production process wouldn’t be working so hard.
I wouldn’t actually see any more heat produced, I may, potentially, see an increase in COP because I used less electricity to do it.
I wonder whether it is worth insulating more of the pipework and/or if it is advisable?
What could go wrong?
@matt-drummer that’s my plan.
Check out all of those large diameter pipes that are not insulated:
Photo from Octopus 
Energy installation.
