Daikin 9kW ASHP application discussion

[John (John Gouk)]

@matt-drummer

What is maybe more concerning is how your heat pump is determining flow temperature compared to reality and delta t between flow and return.

Indeed. Since it’s using the possibly dodgy R2T (-2C - ish compared to the others) to determine LWT, presumably the actual LWT will be +2C more than the MMI thinks it is in its displayed LWT value. I’m pretty sure the MMI is using R2T and not R1T, because my readings are so different.

That means that the actual dT is 2C greater than that that the MMI is using - maybe. We can only surmise and try to deduce where the dT calculation gets its numbers from. I did suspect it was R1T rather than R2T because R1T-R4T was around 5, whereas R2T-R4T was about 3C, but maybe my rads can’t support the higher LWT that would make the dT 5C.

But without checking using known good sensors etc. it’s hard to know.

[matt-drummer (Matthew Gregory)]

Hi John,

Don’t the DS18B20s give you a good idea of what your actual dT is?

They may not be entirely accurate in terms of temperature but the difference between them is?

[squarepeg77 (Jonathan)]

I confess I’ve only skimmed this thread, but would like some opinions!

I’m using ESPAltherma to monitor my system (9kW) and the R2T and R4T temperature values for flow and return published emoncms. I haven’t applied any calibration / offsets to either value as I’ve wanted to try and understand what the heat pump is doing.

The heat pump is set to leaving water temperature control, with a target delta T of 5C.

Here’s a graph from Home Assistant showing a decent 2 hour period yesterday between defrost cycles:

It seems likely that “Leaving water temp. before BUH (R1T)” is being used to try and match the set point. Do others agree?

Here’s the difference between R1T and R2T and between R2T and R4T:

So, R1T is typically 1.8C higher than R2T.
Delta T didn’t settle to the requested 5C. (Although R1T minus R4T would be over 6C)

The emoncms chart for the same period is here:
https://emoncms.org/app?readkey=0e9ab50e73d8ae59d9e6dcc70e5dd5f7&mode=power&start=1705237160&end=1705250720#myelectric

I’ve got a cheap 2-probe thermometer and have measured typically 5.5C to 6C delta flow inside my garage. I’ve got a 10m+ pipe run outside to the heat pump, so I figure that the delta T at the heat pump is probably a bit higher. I’ve had a quick attempt at measuring this by poking the probes under the insulation on the flow and return pipes at the heat pump and was seeing a delta T of around 7.5C, but I’m less confident in this measurement.

I might get some DS18B20s to try and get better measurements, with logging.

So, part of my system’s poor COP is probably due to using R2T/R4T values that are under-reporting the real delta T. I can adjust that in heatpumpmonitor, but if they are affecting the delta T and flow temperatures the system is trying to reach, then that doesn’t seem ideal.

If the system thinks the delta T is lower than it really is, I think the flow rate will be artificially low. It may also have higher flow temperatures than necessary?

One more thing: has anyone tried insulating the pipes inside the heat pump that are not insulated?

[matt-drummer (Matthew Gregory)]

Hi Jonathan,

I am going to sound harsh.

On my system which has a heat meter and electricity meters R2T is the leaving water temperature and R4T is the returning water temperature.

You can really do what you want but the only way to know is to fit a heat meter and electricity meters, anything else is just guesswork.

Your COP is about what I would expect with this heat pump and the radiators on your schedule.

It is similar to what I had and the COP is comparable.

The radiators aren’t big enough to run this heat pump at a low enough flow temperature to get a decent COP.

I have three times the radiators you have and there is no way you could ever be close in my opinion.

I have written this to be constructive, you may not like it but if you want real decent performance I think you have to look at your radiators, they’re just not enough.

The heat delivered to your house is calculated using the flow and return at the entry to your house, if you lose some outside then that is not heat delivered to the house.

If your pipework is losing temperature outside then surely it will affect both flow and return, not just one of them. hy would the dT at the exit of the heat pump be more than it is at the entry to the house?

R1T is inside the heat pump before it exits at R2t.

My R1T temperature is higher than R2T but it doesn’t mean the temperature at R1T is what comes in my house.

Your dT on your graphs seems to be 5c as requested, or have I missed something?

I cannot see how your dT can be higher than the 5c you have asked for, I’m not necessarily Daikins biggest fan at the moment but it works on my heat pump, I think they know how to build heat pumps.

The flow rate also matches my heat meter, there is no problem here for me.

There may be some small differences but I truly cannot see the relatively massive errors in temperature readings and flow rates being possible, not enough to make any meaningful difference to the efficiency.

I could be wrong, of course, but that would make me determined to find out for sure.

A proper certified heat meter and electricity meters are worth every penny, they will potentially save you a fortune by enabling you to see what is really going on.

[squarepeg77 (Jonathan)]

Hi Matt,
Yes, I know our radiators are on the small side - but I’m not going to change any.

I want to understand the system and the monitoring. I don’t think a COP of 2-point something is likely. In fact I think it must be inaccurate.

I don’t think we know the variance between units and R1T/R2T. If you had ESPAltherma data to go along with the heat meters, that would be informative.

emoncms calculates our heat energy output today at 68kWh, with an average temperature of 0.2C. Home Assistant doing a Riemann-sum integral gets 74kWh of heat output. And some of this is overcoming the temperature drop overnight - heat pump was off until about 4am.

I’m not sure how to reasonably calculate the heat loss from this. Can it be roughly done as heat input divided by time? That would be 68kWh / 20 hours = 3.4kW, for 25W/m2.

Our house is about 135m2 and has cavity wall insulation and loft insulation, but solid concrete floors and fairly old double glazed windows. 25W/m2 it is not.

Heatpunk estimates our heat loss at about 4600W at 0C, or 44W/m2.

Our house has never been this warm.

With the evidence I have, it’s the COP calculation is wrong, driven by inaccurate flow/return temperatures.

[matt-drummer (Matthew Gregory)]

This is an excerpt from your data today.

You have about 15,500w of radiators at a dT of 50c

At a dT of 20c your maximum heat output should be about 4,600w, it is spot on.

I got a COP of 2 point something with radiators bigger than yours measured with a heat meter.

It is about what I would expect. My house was warm too, it was just the COP was poor.

But I am not telling you what to do, it’s your house and you are there and know best.

Adjust as you see fit based on your measurements, I don’t think anybody can really guide you.

I can only tell you that my MID monitored heat pump that is the same as yours agrees with the data from the heat pump.

R1T is completely irrelevant, it is not the temperature of the water coming out of the heat pump, R2T is.

I discussed this with a Daikin engineer on Friday and they laughed when I told them. R2T is what comes out of this heat pump, they confirmed it. R1T is a temperature inside the heat pump before the water has travelled through all of the other equipment and leaves the heat pump. The leaving water temperature is all that matters and it is what the heat pump is using to set the dT between flow and return. We can see 5c on your data, it must be working and it is what you have asked for?

The data from the MMI matches more or less my heat and electricity meters and I have no reason to doubt it.

I think your data is right and that really is how your heat pump is performing, it all makes sense based on your radiators sizes.

What do you think your COP really is today?

Mine is 3.21 so far

If you want advice on what to adjust and by how much I am sure some of the others will be able to tell you what they have done and how they arrived at it.

But from somebody with a heat meter, I can tell you that my R2T and R4T agree with the heat meter as does my flow rate and that my R1T is 1c to 2c higher than R2T

I can’t and don’t adjust or calibrate my data to match R1T because that is not what is leaving the heat pump.

I haven’t fitted ESPAltherma partly because I have no idea how to set it up and I am hoping to get rid of this heat pump imminently and don’t want to do anything to harm that.

But honestly, if it confirmed what I said, I am sure you would still think yours wasn’t right.

I don’t blame you.

I was just trying to help you see where your problem really is, it truly is the radiators, they’re not just on the small size, they are way under what you need to get what you want out of this heat pump.

No offence intended, I think it is better to be honest than just agree when I don’t.

[Timbones (Tim)]

@squarepeg77

I want to understand the system and the monitoring. I don’t think a COP of 2-point something is likely. In fact I think it must be inaccurate.

I have a very similar property with practically identical heat loss and not enough radiators. My heat pump (different manufacturer) has been running at 40°C for most of the day. We’ve used almost exactly the same amount of electricity today. If your house is warm enough, then it’s likely that the heat output is being under reported.

@squarepeg77

With the evidence I have, it’s the COP calculation is wrong, driven by inaccurate flow/return temperatures.

I concur, especially looking at the DHW cycle. It looks like the backup heater is enabled? That’s going to kill CoP, but even 2 on the rest of the cycle is poor.

[Timbones (Tim)]

This is weird. What’s going on here?

The primary pump is coming on periodically to “sample” the water temperature, and flow is lower than return, resulting in negative heat (cooling). We’ve seen this on someone else’s system when discussing which RT to pull from their heat pump. I would expect to see flow and return being the same at the end of each pump run. You may need to run experiments with longer pump runs to calibrate the sensors.

[squarepeg77 (Jonathan)]

I had left the back up heater enabled, but with the equilibrium temperature set to -5C. Clearly it still decides it is necessary at times, even when it’s not -5C.

I saw the BUH kick in last night, so set it to DHW only, and it came on again this morning, during space heating!

I don’t understand the “Equilibrium” Yes / No setting and the MMI help seems different to the installer manual.

@Stephen_Crown can you please confirm the settings you’ve used to completely disable the backup heater?

I will also flip the breaker, but would like the settings to match so it doesn’t try to use a BUH that isn’t powered.

Thanks for the continued advice everyone!

[Stephen_Crown]

@squarepeg77

@Stephen_Crown can you please confirm the settings you’ve used to completely disable the backup heater?

I will also flip the breaker, but would like the settings to match so it doesn’t try to use a BUH that isn’t powered.

Hi @squarepeg77

Here is the relevant info:

Disable BUH through configuration:

Daikin Controller —> Installer settings —> Backup Heater —> Operation —> “Restricted”

Check running hours here (mine is still 0hrs since September’22)

Daikin controller → Information → Running Hours → BUH

Also as covered in these links, I’ve flipped the switch for the BUH breaker in the consumer unit outside next to the heat pump:

My heat pump is now running at a COP of less than 1.0, help!

Daikin controller → Information → Running Hours → BUH Apologies for rubbish photo: [image] [IMG_7820]

Daikin LWT

Is that 1hr of BUH use? As in the below? (Just double checking the photo) Daikin controller → Information → Running Hours → BUH I would honestly disable its use (log in as “user profile” installer with code: 5678) Then go to: Daikin Controller —> Installer settings —> Backup Heater —> Operation —> “Restricted” Then go back to main menu and “User Profile” —> “Advanced User (code: 1234)

[squarepeg77 (Jonathan)]

Thanks @Stephen_Crown

My BUH has never ran, apparently.
Another bug, I suppose.

[Stephen_Crown]

@squarepeg77 I’m late to this thread, but why do you think the above is a bug?

I am certain mine is accurate as the breaker is off and always has been.

[squarepeg77 (Jonathan)]

I saw the back up heater running yesterday evening and again this morning.

@Timbones noticed it running during a DHW cycle

I’ve only been tracking it in Home Assistant since yesterday evening, but it ran twice this morning

[Stephen_Crown]

OK, thats bizarre…flip the breaker switch!

Also:

Per @Timbones you will want to calibrate flow and return sensors by running the pump continuously without heat (so -10C on the LWT/Weather comp offset), and you’re looking to get the sensors to basically match (e.g. if return/inlet shows “23.6C”, flow should also read “23.6C”) after a long period of time as there is no heat input.

Any delta can be removed in Home Assistant or EmonCMS formula by adding an offset on the sensor.

[Stephen_Crown]

Mine (R2T) is offset by 0.3C, and now my performance is very close to @matt-drummer (tbc still not MID comparable in accuracy, but much closer, and behaviour/patterns from the data are still valuable even without MID compliant sensors)

This excercise came about as a result of learning R1T on our BUH models (EDLA 09/11/14/16) is not of any use.

Absolute values are less important: heat output is more related to the delta between the values the sensors report, so the sensor data matching when the pump is running fast but with no compressor running (no heat input) is key for the mass flow rate formula.

Daikin 9kW ASHP application discussion

I suggested to keep the pump running to ensure that the two readings are as close as possible, as there’s only the heat exchange and BUH heater between return and flow. The chart I showed above wasn’t run as an experiment, just a section I noted during normal operation. The pump was running at the start, which brings the temperatures together at least.

Daikin 9kW ASHP application discussion

Except that while the water is flowing all parts should be reading the same temperature if there’s no heat input. Raising the temperature by 1° requires a not-insignificant amount of power, that won’t be lying around in the heat exchange for long.

[tiger_cook (Neil)]

@Timbones

The primary pump is coming on periodically to “sample” the water temperature, and flow is lower than return, resulting in negative heat (cooling). We’ve seen this on someone else’s system when discussing which RT to pull from their heat pump. I would expect to see flow and return being the same at the end of each pump run. You may need to run experiments with longer pump runs to calibrate the sensors.

This maybe an ESPAltherma & Home Assistant polling/template out-of-sync issue - ESPAltherma every 30 or so seconds from the HP, vs the sub-second power draw values from your external CT clamp when calculating the COP, could you filter out negative values via a template before sending to OpenEnergyMonitor?

Daikin Altherma, ESPAltherma & Home Assistant with OpenEnergyMonitor

I think, I nailed it, it’s a bit crude - I created another template that listens to the original COP sensor template, If the new ‘cop_true’ template value is in between 0 and 8 that listens to the original COP sensor, log value, otherwise log 0 (no negative or uber efficiency values). I hope this makes sense. Thoughts on my cowboy approach welcome - name: "cop_true" unique_id: "cop_true" unit_of_measurement: 'COP' state: > {% set cop_true = (states('sensor.cop_power') | fl…

[MBC (Mark Berryman)]

This is a long thread and I admit to not reading it all through! It seems that folks are unsure of their COP calculation accuracy and I wonder if you are aware of this from John Cantor’s website (though I guess most are using numbers from ESPAltherma rather than a CT clamp):

Note, most of these products with a Current Clamp actually measure the current. They are accurate for normal electric heaters, but there will be a considerable error when used with electric motors. e.g. heat pumps. They can be checked or calibrated by running the heat pump whilst counting pulses of your electric meter over a time period. (use a stop-watch) . Electric meters give ‘pulses/kW’. This is printed on your electricity supply meter. Your actual consumption in kW can be calculated from this.

[squarepeg77 (Jonathan)]

I’ve got a Pi Zero and a pair of DS18B20 temperature sensors that I will setup to measure the flow and return in my garage. I’m interested to see how they compare to R2T - R4T.

I will also try the calibration procedure noted above

[Robert.Wall]

@MBC

I wonder if you are aware of this from John Cantor’s website

John Cantor is clearly referring to the cheap and cheerful off-the-shelf devices that do indeed measure current - and often only current and guess a preset constant voltage - and therefore are only able to calculate (at best, if the display unit is mains-powered) or guess (at worst, if everything uses batteries) apparent power, which is what @johncantor infers by “there will be a considerable error when used with electric motors.” because the power factor of the motor means real power will be significantly less.

All OEM devices, when used with the voltage monitor (emonVs or a.c. adapter) will measure real power, to within the accuracy of their calibration. This can be better than 1% if done carefully.

[johncantor]

Old fixed speed (non inverter, non variable) heat pumps could have quite a bad power factor. This gives a false high power reading. However, inverters have a very good powerfactor, so just measuring current can be good enough for simple analysis, and sometimes you can calibrate the CT, BUT be mindful that part-load powerfactor can be worse than full-load.
I personally like the very frequent readings from a CT clamp, but accuracy is never certain. Accurate pulse-counting from a kWh meter can be used along side a CT. … one for accuracy for COP assessment, the other for good 'resolution.
I really must find time to renew a lot of my website in case things have moved on. some of it is now quite old!