Ecodan - are these COP figures correct?

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  • matelodave
    matelodave Posts: 8,571
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    edited 2 August 2022 at 2:44PM
    This is the graph of the energy consumption for my 11kw Daikin for 21st July. I know its not an Ecodan but it gives you some idea of what might be going on.

    I switched the heatpump on to heat hot water at just after 0800 but forgot to shut if off until about 13.30. You can see that the run time is around an hour and it used 0.9kwh it then settled down to a standby of around 120watts until I remembered to switch it off. Todays graph is very similar but I only had it switched on for an hour and it ran for about 55 minutes and again used 0.9kwh.

     If I leave it on for 24 hours but with the heating and hot water off then it will use approx 120 x 24 = 2.88kwh./day If I leave the hot water on then it will boost it around every eight hours using about 0.3 to 0.4kwh which indicates that it's better to run it once a day (or in my case once every two days at this time of the year)

    BTW this is an Efergy  Engage clamp on monitor which logs the consumption every six seconds and I can download the six second, minute, hour or daily data to an Excel (or in my case Libre Office) spreadsheet. Maplins were flogging them off for £25 before they went bust - 
    https://www.bing.com/videos/search?q=efergy+engage+hub&docid=608027254819392592&mid=830C9536E986A39E9D98830C9536E986A39E9D98&view=detail&FORM=VIRE
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  • dllive
    dllive Posts: 1,205
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    I suspect that Mitsubishi engineers had a "blind spot" about how large their standby load is, or can be.  Because my heat pump was installed towards the end of the RHI scheme it was obliged to have its own electricity meter which monitors the power it draws.  That means I can be pretty sure about what mine is doing.  I'm also "Reed-Richards" on that other forum so you can read my comments.(nothing profound).  
    Perhaps thats what Ive got. Ive got two additional displays they added to my consumer unit: 1 showing the usage of the immersion heater; the other showing the heat pump. (The immersion heater number is always static because its never used [Ive disabled the legionaries setting])
  • dllive
    dllive Posts: 1,205
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    Im not sure if this adds anything to this thread, but its nice to see a video: https://www.youtube.com/watch?v=aYDIrBObFLc

    I pay 28p per kWh. So if my Ecodan is using 67kWh each month just to heat up some water for 30 minutes every 2 days, thats costing me nearly £18pm!

    So thats not the same as a really efficient/small fridge is it?
  • matelodave
    matelodave Posts: 8,571
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    edited 2 August 2022 at 3:51PM
    That's why I actually shut mine right off - the standby power to keep the compressor warm is around 90kwk/mo or nearly 1000kwh/year =  £290. (It wasnt too much of a problem when I was getting leccy at less than 10p/kwh although £100 a year did seem a bit steep).

     I don't do it when the temp is below around 18- 20 degrees just in case it causes problems with the compressor although I have noticed that if the compressor gets too cold, it wont start and the heatpump tries to activate the boost heater to bring the temperature up

    I'm guessing that the compressor heating is supressed when its running - I'd suggest that the way Ecodan do it, by measuring the compressor temp and only heating when required is a bit more sophisticated and energy efficient than my 12 year old Daikin which just seems to cook it continuously.

    I reckon thats why the performance of the heating system is determined by it SCOP which is a seasonal average rather than COP which is measured at a defined temperature difference rather than over a period of time.

    TBH I think you are getting a bit hung up on trying to determine the COP rather than looking at the performance of the system over a longer period of time and it's not easy to do without using a proper test set up. I dont know how accurate the built in heat meter is compared to a properly calibrated unit which should integrate input and output temperatures against the water water flow. 

    There's lots of stuff on t'interweb - have a cogitate upon this -  https://heatpumps.co.uk/2021/08/07/heat-pumps-and-domestic-hot-water/
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  • Rodders53
    Rodders53 Posts: 2,084
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    edited 2 August 2022 at 3:58PM
    According to Misubishi, your system consumes 22 Watts in "non active" or off/standby modes.
    https://erp.mitsubishielectric.eu/files/library/files/erpdocs/lot1/w112xx_001_002_d.pdf
    Nor does it have a crankcase heater.

    Neither of those things explain your numbers, though.  (Although 22 W is 16 kWh per month approx).

    I'd be looking to accurately measure the electrical input to the heatpump with a meter rather than the gubbins inside the Ecodan/controller/display?  Does that metering device in your consumer unit do that?  Have you got dated recordings of that meter's numbers?
  • dllive
    dllive Posts: 1,205
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    Hi guys,

    I thought a few photos may help show what Im working with....

    This is my consumer unit. The heat pump has its own fuse, and theres 2 displays; 1 for the heat pump and the other is the heat pump's immersion heater.

    (There is another display not in this photo that shows the meter reading for the house. This is the reading I give to the energy company when requested.)


    This is the Ecodan default screen. It shows the DHW is scheduled (to come on once every 48 hours at 3pm); and the Heating is turned off.




    This screen shows monthly breakdown of energy consumed:



    This screen shows monthly breakdown of energy delivered:




    This shows the energy consumed so far this month. (interesting to see DHW is showing 0. DHW is scheduled to come on every 48 hours. So that would have happened since the 1st Aug. Heating is showing 4kWh even though all heating is turned off)


    This shows the energy delivered so far this month



    Each month I keep logs. For example, the past 2 months logs are:

    1 July 2022
    Consumed: 92 (DHW 28; Heating 64); Delivered: 79 (DHW 79; Heating 0)
    Immersion: ""
    Heat pump: 13689

    DHW COP: 2.8
    Heating COP: 0
    Overall COP = 0.8

    Meter reading: 49003
    KWh used in past FOUR weeks: 135
    _________________________


    1 August 2022
    Consumed: 83 (DHW 15; Heating 67); Delivered: 45 (DHW 45; Heating 0)
    Immersion: ""
    Heat pump: 13719

    DHW COP: 3
    Heating COP: 0
    Overall COP = 0.8

    Meter reading: 49118
    KWh used in past FOUR weeks: 115


    ============================================

    While Ive been writing this post, an oddity has occurred to me. If I subtract the Heat pump meter reading for 1 Jul from the 1 Aug heat pump meter reading (13719 - 13689) it equals 30kWh. How can that be less than the Consumed figure!?

    Ive just been out there listening to a hum or anything to suggest something is running. But its completely silent. (which is not to say something isnt running!).

    Perhaps I should just turn the damn thing off, and only turn it on whenever I need a bit of hot water? I dont even know how to turn it off (theres a big red button behind the unit itself) or what the potential ramifications are for turning it off.

    As ever - any comments/guidance is gratefully received. :)


  • Patrol
    Patrol Posts: 134
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    My GSHP has a circulation pump on the "hot side" which runs either 24/7, or with the compressor (if an accumulator tank is present according to a download I found but not in my GSHP manual). Switching from 24/7 to compressor reduced my electricity consumption (I have switched it back as previously thought compressor was ok with a bypass valve). Is it possible your Ecodan has something similar.
  • dllive
    dllive Posts: 1,205
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    Hi guys,

    I sent an email to Mistubishi and got a swift reply.

    He said "The data displayed on the main controller is estimated and may not be exact. The system is likely to be consuming less in standby consumption than what is displayed on your main controller. I have attached a guide which should explain the standby consumption." and attached the below pdf.

    Although the table doesnt list my model (PUHZ-W112VAA), the 21 [degC] < Ta column shows that it probably uses about 100W in standby mode (which it currently is) IF using a clamp meter (which Im not!)

    He says to the data on the Ecodan is estimated, and the pdf says that using a clamp controller will give a much higher figure. Im not much the wiser tbh. :|







  • shinytop
    shinytop Posts: 2,088
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    Hi @dllive, it looks like you found all the info there is on the Ecodan ! I've seen this discussion before on the forum@Reed_Richards mentioned and have monitored mine (it's a 14kW monobloc).  It consistently uses 24W on standby; that's when it's running and in stop mode, or in standby via the control panel.  That's measured using the separate meter provided with the MMSP monitoring, which gives per minute readings.  This is the ASHP unit, the FTC and the 3 pumps in my system (these pumps have a small but present standby consumption).  I think if you have a monobloc Ecodan yours will be similar.   

    As to the COP, unless you have MMSP or similar, COP is an estimate and will not be that accurate, especially at low consumption.  To measure COP you need to measure heat produced by the ASHP and that's not easy.  You need to measure how much water is being heated up and by how much and to do that you need accurate temperature sensors for flow and return and a proper flow meter.  A standard Ecodan doesn't have these.  I don't know how the Ecodan estimates energy produced for its own COP estimates.  It will either use its own estimate of flow and its standard  temperature sensors and calculate it or it will just use the output flow temp, ambient temp and a lookup table.  What I'm saying is take the absolute COP number from the Ecodan controller with a big pinch of salt.  It's much more useful used as a relative number to compare on your system when you make changes. BTW I don't think other brands are any different although I don't know.  IMO comparing COPs estimated by different ASHPs in different houses is a bit pointless.    

    You may well be better off using an immersion heater if you're only using the ASHP to heat your water every 2 days. t's a bit like buying a big expensive car to go away for the weekend once a month.  You'd be better off hiring one. But if your COP is 0.8 overall it's not going to save you a lot.  

      

               
  • dllive
    dllive Posts: 1,205
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    Thanks for that @shinytop . I think what I have is a mononbloc Ecodan. (Ive just trawled through my emails with the installers and they mention it being a 'monobloc').

    You say that yours only uses 24W on standby, whereas mine is 4x that at 100W! Unless theres another setting somewhere that I have to turn off? I dont think there is becuase - as you can see from my photo - the heating is in 'prohibitive' mode?
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