Is all of the tank at 34c to start?
The temperature sensor is near the bottom of the tank and I would assume the water is hotter at the top?
But I would expect the heat pump to have to produce more heat than the heat actually required to raise the temperature of the water in the tank, there will be losses along the way.
I have been talking with Zak from Farnborough quite a lot this week.
He has the same 9kW heat pump installed in a similar size house to mine and I think he is about as radiator limited as I am at the moment.
We are running very similar flow temperatures and the weather seems similar.
I have been watching his pump for a few days and his and mine seem to be getting very similar performance.
I have not looked too closely but nothing instantly jumps out as being different between his pumps performance and mine.
Probably not, but we have no way of knowing.
Yes, though the coil is taking a considerable portion of cylinder, and we can only see (from your charts) the temperature of the water coming out of that coil. We might be able to say it’s 34C at the middle of the tank, depending on it’s exact geometry.
Indeed, the two systems look to be running very similarly, comparing Zak’s Farnborough (blue)
to your Ipswich (red)
This is what your DHW cycle should look like though, putting 5.9 kWh of heat into the cylinder.
(Calulator says 5.8 kWh to heat 200 ltr from 20C to 45C)
Look at how even and smooth all the feeds are, with a pretty constant gradient and ΔT.
(Still got that funny bit of electricity at the beginning - must be a Daikin thing)
Similar here, Daikin Altherma 3m 9kw, in a property that only needs 5.5kw @ -2, I have ESPaltherma running, just got it into Emoncms yesterday, Data is public can be found here: https://emoncms.org/feed/list.json?userid=%2048352 I can’t get the ESPaltherma visualized into the app yet, app here: Emoncms - app view dashboard
Maybe @Timbones has identified a big reason for my problems, or perceived problems with my heat pump.
I have been looking back over different days and I see the same potential issue.
I have never understood why I don’t get the same heat earlier in a heating run that I do after 90 minutes or so.
This has been making want to keep the heat pump running longer and has been putting me off running in shorter bursts to keep the house temperature under control.
But maybe my heat production is being consistently under reported for some reason?
Under reported during the early to middle stages of any heating cycle.
It certainly looks that way for DHW and the heating shows a similar pattern that I was just attributing to radiators.
I have avoided asking/arguing about what is going on with the heating as I don’t know everything there is to know about thermodynamics and how water behaves when it is heated.
But I have always been puzzled by what appears to be my radiators being able to put out more heat later in the heating cycle when the house is warmer and the delta t between the radiators and house temperature has reduced.
Could I have a faulty heat meter or sensor?
How can I accurately test for that?
Maybe I should just buy another heat meter, the cost is a drop in the ocean in relation to what I have already spent.
At least then I can eliminate that as an issue.
That’s a ΔT of 3.1 vs. 3.2, which is pretty close. Which part of the cycle was this in? Maybe collect some more measurements, swapping the clamps over periodically.
Does the heat pump itself report any numbers you can look at? It would be interesting to see what it thinks the flow temperature is (or more specifically, the ΔT).
I assume that the flow rate shown on your charts is read from the heat meter? That looks to be pretty solid, so no concerns there.
Hi Tim,
The flow rate is from the Sontex heat meter and is solid as you say, I don’t think I have any installation issues there. I made sure it was in a clean unobstructed part of the pipe at least 30cm from any bends.
The heat meter is correctly orientated for flow direction and angled correctly for a horizontal installation as per the instructions.
The flow temperature sensor is installed just before the three port valve but I can’t see any issues here.
The temperatures I took last night were at rest. I will try and monitor them in use when I get home later for the DHW cycle.
I have two of these thermometers, I added two to basket on Amazon by mistake. I may even have a third one from a different manufacturer as I am sure I bought two types just to make sure I had a way of checking results when radiator balancing. Belt and braces and all that!
I am just reading the Sontex instructions to make sure I haven’t missed anything. It talks about commissioning but I have never pressed any buttons on the heat meter itself, it just worked. Maybe I was supposed to do something?
I am now convinced that something must be wrong with my monitoring, the DHW cycle cannot be correctly reported, I can’t see any other explanation?
I have gone back and applied the Carnot line to the graphs on different days and that shows what I would have expected to get but I don’t really know how to interpret that.
I have just been reading about the Carnot cycle and it being a theoretical maximum COP that is not achievable and can never be exceeded.
But I am exceeding it at the moment, is that possible?
I could be wrong, and the sensors are fine. I noted on October 25th that you did get a good DHW run, so it is possible to get good performance and/or good data.
Edit: more specifically, the first reheat of that day was good, but the other two were poor: link to time period - maybe it’s affected by the temperature of the tank?
I think this is what the heatpump factor is for, typically around 0.45. There’s a button on the app to work it out for you - tick “Show as % of carnot COP” to get the magic number for the current window, then untick it to show the simulated heat output. It will vary quite a bit as you move around, so try to set it on a “good” bit of system running.
Thanks Tim.
Looking at my DHW water yesterday something must be wrong.
No other Daikin heat pump I look at does what you highlighted yesterday.
What possible explanations are there for this?
Could it be cause by the heat pump?
The heat production should be a relatively straight flat line all the way through the DHW cycle, my heat production is too low at the beginning and builds and the reported heat produced is some way off what would actually be required to raise the temperature of my 200 litres of water by 16c
This is the key point for me. If your heat pump has successfully raised the temperature of (all) 200 litres by a number of degrees, then it must have produced a certain amount of energy (kWh). If the heat pump was not performing as expected, it would not manage to raise the temperature.
The uncertainty here though is how hot is the water in the tank before it starts.
Hi Tim,
I have spoken to @TrystanLea this morning.
We are about to run a test by emptying the tank completely, measuring the starting water temperature and then running a DHW heating cycle to 50c
I will measure the water again.
The we will know how much energy was consumed and produced to heat a known volume from a known temperature and we can compare that to what it should have taken.
Edited to add, great idea from Tristan.
OK, the test is ready to start.
I drained the hot water tank until the temperature from the hot tap matched that from the cold tap so I know the tank is completely full of cold water.
The starting temperature is 12.4c and the Daikin app shows the tank at 12.0c.
The tank is a Joule Cyclone CY205L Indirect Hi Gain.
The tank capacity is 205 litres and the heat exchanger rated volume is 11.8 litres.
We will see what is reported as being used to heat from 12.4c to 50.0c
It should take about 9kW of heat to raise the temperature of 205kg of water by 37.6c if my calculations are correct?
Results are in!
An unfortunate defrost at the start, not sure what difference it makes?
Water is 50c and took a bit less heat than I predicted to heat the tank.
Heat production looks more like we would expect.
Thanks @matt-drummer
It’s strange I cant specifically see the 205L variant with the high gain coil? I can see a 200L version, which has an actual water volume of 194L Joule Cyclone High Gain Indirect - Joule
37.6K x 4150 kJ/kg.K x 194L = 8.4 kWh
With the immersion heater positioned below the coil there is probably some cold water pooled there at the bottom which reduces the water volume a bit more, perhaps 10-15% by the looks of it? lets say 170L (12.5% under the coil):
37.6K x 4150 kJ/kg.K x 170L = 7.4 kWh
There will also be some energy required to heat the water in the primary pipework which would have cooled down a bit since the early space heating finishing at 11:30. I wonder what the primary pipework volume is?
What was that little wobble towards the start at 12:40?
I think we can see the heat that went to heating up the primary pipework dissipate into the radiator circuit around 13:42, looks like it’s about 0.5 kWh, suggesting all in all 8.4-0.5 = 7.9 kWh went into the tank, suggesting perhaps 182L of the volume was heated? leaving ~12L in the cold part below the coil?
You mentioned that the tank temperature sensor is quite low down? is it in pocket F? My guess is that the poor performance you see is when the stratification layer is just above pocket F and ~50% of the coil is sitting in water at 45-50C whilst 50% of the coil is in cold water around 12C.
Id be tempted to move the temperature sensor to pocket J at the top, you will run out of hot water quite quickly after the temperature drops at position J so you might need to tune your schedule to suit.
Ah ok, dont think that’s a big issue.
Just noting that the deep-linking to heat pump data with a time window is absolutely marvellous to see in action in this thread.
Note to self, I should try this!! 
Today’s 2.98 COP DHW full reheat vs a 1.8 COP partial reheat yesterday. What a difference!
Can a cold vs. warm tank really explain the issue we’ve been seeing, or were we just lucky today? The subsequent heating cycle this afternoon still shows the same problem, where output is below expected for the first ~90 minutes.
[heatpump factor = 0.5]
