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Measuring your COP

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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

Does anyone track the COP on their system?

I've been doing mine manually since it was installed but I need something better. I'm thinking maybe a raspberry pi with a CT sensor. 

Right now the hot water is getting cop of 4 @50° with outside temp at 16°

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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JulianC
(@julianc)
Prominent Member Member
1138 kWhs
Joined: 4 years ago
Posts: 313
 

It’s a good Q @batalto. I can press a few buttons on my Daikin and it shows the heat output & and energy consumption. So I could calculate COP. But when I look at the separate consumption meter installed with the ASHP, it is showing a far higher number. So hmmmm

Currently my COP must be v high as the ASHP is off 😂. Hot water heater by solar PV. 

I think my plan is to compare monthly consumption to the MCS estimate. Compared to how warm the house is. And the actual electric spend. 

I still have the quandary of using the hall Nest thermostat compared to Daikin weather compensation curve. I think it will be trial & error first year. 

Daikin Altherma 3H HT 12kWh ASHP with Mixergy h/w cylinder; 4kW solar PV with Solic 200 electric diverter; Honda e and new Hyundai Ioniq 5 N electric vehicles with Myenergi Zappi mk1 charger


   
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(@batalto)
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3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

@julianc why wouldn't you use the ASHP in the day to heat up the tank? It's going to be far more efficient than the immersion? Mines currently on constant with the solic over heating until I get to grips with how it works.

Once I move to octopus I'll be heating the tank on the 5p time as the cop and cost will be so advantageous

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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JulianC
(@julianc)
Prominent Member Member
1138 kWhs
Joined: 4 years ago
Posts: 313
 

Using Solic and solar PV is free when the sun shines. And it works dynamically, so stops heating if I turn on the kettle. Whilst the ASHP would provide a COP multiplier, it would still have a cost associated. And increase my CO2 generation. It generates enough hot water for our three shower needs 👍

Daikin Altherma 3H HT 12kWh ASHP with Mixergy h/w cylinder; 4kW solar PV with Solic 200 electric diverter; Honda e and new Hyundai Ioniq 5 N electric vehicles with Myenergi Zappi mk1 charger


   
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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

@julianc I guess my PV battery does the dynamic bit for me. The solic only kicks on once the batteries are totally full

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

I got these figures from Midea for the 12kw unit

    Water Temp COP
    30 35 40 45 50 55
Outdoor air temp
-25 2.29 1.79 1.51 1.3    
-20 2.7 2.3 1.97 1.77 1.56 1.4
-15 2.88 2.62 2.32 1.93 1.75 1.48
-10 2.92 2.66 2.32 2.11 2 1.85
-7 3.2 3 2.63 2.44 2.33 2.1
-5 3.38 3.13 2.78 2.52 2.36 2.14
0 4.09 3.74 3.3 3 2.37 2.24
5 4.94 4.5 4.08 3.51 3.03 2.88
7 5.5 5.11 4.56 3.93 3.31 3.13
10 5.99 5.51 4.81 3.99 3.44 3.13
15 7.32 5.97 5.24 4.52 3.79 3.2
20 8.45 7.18 6.04 5.16 4.32 3.61
25 9.15 8.15 7.79 5.93 4.93 4.09
30 9.66 8.55 8.15 5.88 5.24 4.49
35 10.21 8.78 7.49 6.17 5.58 4.86
40 10.86 9.37 7.99 6.71    

 

Working through and dragging out my Nest thermostat data I was able to determine exactly how many hours of heating I used each month and I used the average temperature to estimate the COP. This is a little pessimistic as the average temperature takes the night lows (when the majority of heating wont be used) and also assumes zero weather compensation which my unit will automatically do. I used the 50 degree hot water COP and worked off 2020 heat data.

below is for each month starting Jan

Avg Temp 6 6.5 8 10 13.5 15.5 17.5 17.5 15.5 13 9 6.5
COP 3.25 3.29 3.41 3.56 3.83 3.99 4.14 4.14 3.99 3.79 3.48 3.29
Hours of heat needed 183 215 218 69 26 0 0 0 18 157 232 304
estimated power kw 675 784 768 232 81 0 0 0 54 497 799 1108

 

This also ignores hot water, but gives me a good starting point to start optimising my needs and assessing my COP

 

1422 hours of heat used
4998
total kw of heating need

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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(@heacol)
Noble Member Contributor
2314 kWhs
Expert
Joined: 4 years ago
Posts: 370
 

@batalto, Unfortunately you will find your actual COP (or SCOP) will be very different and significantly lower than your predicted level, there are 2 reasons for this, firstly, because you run a Hive thermostat, your heat pump will be operating at full capacity 100% of the time, always trying to catch up. Inverter heat pump performance level (COP) readings are taken at the best performance position on the curve to make the units look better, this is usually approximately at 60% capacity or compressor speed, at 100% compressor speed, I have seen performance drop by over 50%.

Secondly, the data you see, do not include any de-frost data. Between 0 and 5 Degrees, it is possible for units to be in defrost mode for 30-40% of the operating time, most units remove heat from inside the property to melt the ice on the evaporator, therefore significantly increasing the load and running cost of the system.

If a system is running at full capacity, 100% of the time, this is the perfect storm and the reason why 90% of high energy costs occur, this is the same as if you were driving your car down the motorway at 70 miles per hour, at the maximum engine  RPM. No-one can reasonably expect any form of efficiency or reliability if you do this, so why do you expect it from your heat pump? They are both machines.

The best way to run a heat pump is on either full weather compensation or a combination of load (internal temperature) and whether compensation and run the system 24-7, do not zone your common areas of the property (remove TRV's on radiators or thermostats on underfloor) remove any blending system on underfloor manifolds, or system separation and only control the bedrooms.

This reasoning is contrary to all advice you will have seen or read, but, you must remember that a heat pump is NOT a boiler and cannot be treated in the same way. By operating it like this, the unit modulates and operates in a more efficient zone, like cruse control on your car. 

Your Midia unit's programmer will work as an internal thermostat, which will modulate the unit and achieve the best possible performance. If a unit is modulating then  the flow temperature will vary from 25-50 degrees depending on the external temperature and internal temperature, 50 Deg will only be supplied at -3 +, therefore at higher temperatures the unit will be putting less load on the evaporator (external unit), this will reduce icing and defrost frequency, therefore significant increasing the performance of your unit.

I hope this helps

Technical Director Ultimate Renewables Director at Heacol & Head of Domestic Heat Pump Design Net Zero British Gas


   
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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

@heacol the table had a min, mean and max COP. I took the mean as my number. It will be interesting to see the outcome, especially as the system has weather compensation

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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(@heacol)
Noble Member Contributor
2314 kWhs
Expert
Joined: 4 years ago
Posts: 370
 

@batalto, You are mistaken, if you are using a Hive thermostat, you do not have modulating weather compensation, you may have weather compensation enabled but it will be at a much higher level than it should be. The Hive thermostat is a dumb on-off device, just like a light switch, you are overriding a very sophisticated controller that the manufacturers have spent millions of dollars developing to suit their unit, with a light switch. You cannot expect the heat pump to supply optimum performance if a dumb device is controlling it. If you want optimum performance and comfort, you need to remove it and let the heat pump do its job.

Do you maintain the speed of your car with the key? Probably not, I presume you switch cruse control on and let it do it's job.  If you let the heat pump do it's job without interference, you may, depending on the design of your heating system, come close to the published figures. We have installed many systems (including ones in old solid stone, single glazed leaky buildings)with annual average COP levels of between 4 and 5.

Performance of a heat pump is predominantly determined by the flow temperature, the higher the flow temperature the worse the performance, clearly indicated in the data above. As a rule of thumb, every 1 degree, you raise the flow temperature above the source temperature, you add 2.5% to your electricity bill. This is not a straight line curve, it is exponential, therefore the higher up the temperature scale the more effect a 1 degree rise in flow temperature will have on the electricity bill.

The only way to get a true indication of COP is with a independent heat meter and electricity meter. The inbuilt systems on most manufacturers units are calculated figures using gas temperatures and pressures and are a rough estimate (mostly overstated) at best.

Technical Director Ultimate Renewables Director at Heacol & Head of Domestic Heat Pump Design Net Zero British Gas


   
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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

@heacol the weather compensation is directly on the heat pump which is connected to the Nest so it preadjusts the water temperature before the thermostat calls it. The nest has no control over the water temperature. For instance, at the moment the heating water temperature would be 38° if the thermostat came on. This was how freedom heat pumps recommends the system is setup. I can't see any other way of running it other than basic scheduling, which is possible. However the controller for the heat pump isn't a Thermostat (as far as I am aware)

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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(@heacol)
Noble Member Contributor
2314 kWhs
Expert
Joined: 4 years ago
Posts: 370
 

@batalto Exactly, the nest has no control over the water temperature and there lies the problem. It is like the jester controlling the kingdom. 38 degree at this time is 18 degrees higher than it should be, which will equate to a running cost of approximately 3 times higher than if the flow temperature was 20 deg C.

I have installed the Midia unit and know it well, the controller has 3 modes, fixed temperature, weather compensation which can either be a pre-determined curve or a programmed curve, or and internal thermostat. If I remember correctly and am not confusing manufacturers, you can also have an additional temperature probe that will measure the internal temperature. This will modulate the unit intelligently to maintain the correct internal temperature. If you have solid stone walls and or thick under floor, use whether compensation only, if you are in a low thermal mass, new build use load compensation (internal temperature) to control the temperature in the property.

I am not sure if you realize but when the nest is satisfies and switches the signal off to the heat pump, the heat pump stops running, and no energy is transferred to your house, however your house does not stop loosing heat. When the Nest switches back on, the heating is now behind and has to catch up, the only way to catch up is to raise the flow temperature which increases the output of the emitters, higher flow temperature on a heat pump means higher electricity bill (a 1 Deg C rise adds 2.5% to your heating bill on an exponential curve, in other words similar to compound interest). If you want a lower heating bill, just replace the lost energy at the time it is lost, do not try to play catchup, but it is your choice.

Technical Director Ultimate Renewables Director at Heacol & Head of Domestic Heat Pump Design Net Zero British Gas


   
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(@batalto)
Famed Member Member
3655 kWhs
Joined: 4 years ago
Posts: 1091
Topic starter  

@heacol the house is pretty well insulated. Our losses are around 30w/m2 with an EPC score of 93. So no idea which mode is best. I don't think we have an internal probe measuring temperature. That said, the controls are in the solar Inverter room, so it's always warm in there anyway and it wouldn't be suitable

12kW Midea ASHP - 8.4kw solar - 29kWh batteries
262m2 house in Hampshire
Current weather compensation: 47@-2 and 31@17
My current performance can be found - HERE
Heat pump calculator spreadsheet - HERE


   
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