@cathoderay 

I think your calculation works but the major flaw is that you are pinning everything everything on the house heat loss and that is very difficult to calculate accurately.  If you built your house yourself and know exactly what it was made of you might have a chance of getting a reasonably accurate figure.  With a house where you're guessing what it's made of and with how much you have no chance.  The only way to get a really accurate heat loss figure is to measure it using a know heat source but even then you'd have to be careful to make sure you took account of solar gain, wind and rain on the day(s) you measured. This would be a long, expensive process, which is why it's rarely, if ever, done.  

The figures installers come up with are good enough for their estimating purpose but not for calculating an accurate COP. I would hope that a good surveyor would get to 10 or 20 percent accuracy but I doubt all do. 

As Derek has said, you need a decent power meter setup to measure COP properly.  The ones used for MMSP aren't that expensive - a few hundred pounds.  Using these will be a lot more accurate than relying on a heat loss estimate.  You need a flow/heat meter and integrator to measure and record energy delivered, an energy meter for energy consumed and few more bits and pieces to pull it all together.  Google 'Sontex 531' to get an idea of the sort of stuff needed.  This isn't true industrial grade equipment but probably more accurate than your plumber's guess at the house heat loss.  😉 

@kev-m - I do know what the house is built of, old solid sandstone walls of various but known thickness, plus an extension I added with cavity walls etc, some oak framed and some galvanised and even some latticed cast iron framed windows etc, but I do agree, know what the U value is for the stone walls (which are by far the biggest route for heat loss) is far from straight forward. And then there are the cast iron window frames - what is their U value? The same applies for draughts - how to account for a draughty window (the cast iron ones are very leaky) and how to then recalculate the heat loss after reducing the draughts mainly by the use of secondary glazing - and wind/rain effects, which are not trivial, the back of the house is exposed to the prevailing winds. I think the best that can be said about my idea of working back from building heat loss to heat pump output is that perhaps it was an interesting idea to explore, but in practice would not deliver.

Likewise, I remain unconvinced by the output from the Midea controller. Unless we know that the Midea unit has "a decent power meter setup to measure COP properly" then I can't see how we can be sure the figures it reports are accurate. The temptation on manufacturers to tweak reported output in their favour must be enormous. I mentioned VAG and dieselgate earlier - if a 'reputable' European car manufacturer can go to such lengths, then surely it is also possible that a Chinese firm may also decide that their European customers should as they say live in interesting times.

I will look further into MMSP meters. From what I have read so far, it all seems very complicated, and I think I am right in saying it can only be done properly with an inline flow meter, which involves draining down the system to fit it, not to mention where to fit it, as space is tight, and the meter itself can I believe introduce its own resistance, and there may be other considerations eg whether the presence of glycol in the system can be accounted for. 

It might be simpler to go for a drastically less complex assessment, and simply compare energy use now (in kWh) with energy use when I used oil (again, in kWh). If the rooms are at design temps using both systems, and the kWh use has not gone through the roof, then I can at least say that I have not been disadvantaged by going from oil to an ASHP (which is my underlying concern). If that is the case, then maybe I don't need to know the COP...    

@batalto - I have finally bit the bullet and installed the Midea MSmarthome app on my mobile and connected to the Midea controller. I am sure it is connected, because the settings that appear on the phone are exactly the same as those on the Midea controller eg if I check the schedule on the phone, it is the same as on the controller, one schedule, DHW on every day between 1300 and 1400. No Chinese dragons have yet emerged from my wifi but I guess it is only a matter of time. I'm planning only to run the app for a while to get some data, then probably turn it off/disconnect/redo passwords etc.

I can't however for the life of me find any way to access the historical data you managed to screen grab so well. I have turned on the 'Active electric consumption function' and still there is no place where I can see any way to access historical data (which I expect won't be very much yet, until it has had time to accumulate). On the Home page I have a 'button' labelled ASHP (the name I gave it) and next to that it says 'online'. If I tap on the button, I get the controls for heating and DHW with the current settings shown eg DHW shows 50 degrees (target temp) and 42 degrees (tank current temp). Towards the bottom I have Schedule/Silent/Holiday/Eco and only Scedule is active, and it shows the correct schedula as noted above. On the heating screen, the is a Heating 'button', and that appears to set the mode (heating or cooling or auto, mine is obvs on heating) and a Curve 'button' which calls up a box with 'Zone1' in it and an on/off slider (currently on), but that's it, nothing else at all.

I have searched google hard for an MSmarthome manual, and can't find anything. Can you please give me any pointers you can about how to access the data you managed to screen grab? Any help very much appreciated.

@cathoderay Just follow the images below

Posted by: @batalto

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Just follow the images below

Got it, thanks so much. The Electric Consumption was greyed out before, but when I entered some price data (including 0 for gas as we don't have mains gas...), the Electric Consumption panel became active. Initially blank, but a short while later it had some data for 1300 hours on the chart, so I think it is up and running. Great!

Posted by: @cathoderay

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It might be simpler to go for a drastically less complex assessment, and simply compare energy use now (in kWh) with energy use when I used oil (again, in kWh). If the rooms are at design temps using both systems, and the kWh use has not gone through the roof, then I can at least say that I have not been disadvantaged by going from oil to an ASHP (which is my underlying concern). If that is the case, then maybe I don't need to know the COP...    

That would be a fair analysis. Also (and I think this is as important) are you as warm and comfortable as you were with oil?  Or maybe it's better; my ASHP is much better than my storage heaters were, as well as using a lot less energy and £.   I think where the Midea calculated numbers might be useful to you is to compare COP when you make changes to your system. But even then, what matters is energy use and comfort. When I did a lot of tweaking last year that's what I was looking at, not the COP. 

@cathoderay

I have been giving your idea some thought and believe that it may be possible to have a simple spreadsheet calculation, that provides a very rough estimate of the daily COP value. This could then be developed to produce weekly, monthly and even annual estimates.

Such a method would require a reasonably accurate estimate of the actual 'standard' heat loss, and the need to assume that the heat loss varies linearly with change in the ambient air temperature, though I am starting to suspect that the latter requirement may not be correct, and that heat loss follows a more exponential relationship. The estimation would also need to ignore any effect of solar gain, wind chill, rain cooling and human activity. Allowance for production of DHW would also need to be made.

If the 'standard' heat loss value of 12.4kW is estimated with an indoor temperature of 21C and an outdoor temperature of -2C, then this would give a change in heat loss 0.539kW for each 1C of DeltaT between indoor and outdoor temperature.

If the average ambient temperature can be calculated or obtained, and the average indoor temperature can be assessed, the average DeltaT can be obtained, and the average hourly heat loss can be calculated as shown below.

If the Average Indoor Temp. = 20C, and the Average Ambient Temp. = 10C, then the Average Hourly Heat Loss would be :-

20 - 10 x 0.539 = 5.39kW

Over a 24 hour period this would equate to approximately 129.4kWh of heat energy.

If the electrical input energy is obtained from the power meter for that particular day, and came in at say 25kWh, then the COP value for would be:-

129.4 / 25 = 5.17

By recording these values over a period of time it should be possible to carry out a comparison of the calculated data with that provided by the controller. It should also demonstrate the wide variation of energy used, and COP, with variation of ambient air temperature.

It would be interesting to see what results, if any, can be obtained by this method.

Posted by: @kev-m

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But even then, what matters is energy use and comfort. When I did a lot of tweaking last year that's what I was looking at, not the COP. 

I agree, in health service research they talk about structure (how many beds theatres etc), process (how many hip operations done) and outcomes (how many are pain free after their operation) and it is outcomes that are by far the most important. COP is a process variable, feeling warm is an outcome! I do agree though that it might well have a use for comparing the effects of changing parameters.

The two biggest things I have noticed so far comparing the ASHP with the last three winters when I used mains electricity and Argos type heaters are firstly I feel warmer, and don't have the irritations of chilblains and numb hands and feet etc, and secondly, the house is noticeably less damp. It used to feel positively clammy, bedding and upholstery felt damp etc. Compared to oil, I think they are probably about the same, perhaps less damp with the ASHP as it is on all the time, whereas the oil was very definitely timed, and condensation could and did occur when it was off eg overnight.

I have yet to see how the ASHP does when it gets colder outside. It has managed to keep up so far this autumn, but we haven't really had a spell of 5 degrees and below weather, which is when the dreaded defrost cycles kick in. I already have the monitoring in place for this, access to the open source temp data for hourly ambients, and a data logger in the kitchen that records the room temp every hour. I expect in due course I will post some charts here on how the system manages.

@derek-m - thanks very much for looking into the possibilities further, your suggestions are very much what I had in mind. All of the data is available, but with a time lag for the ambients from the weather station. The indoor temp in a core room, the kitchen, is as indicated above, already available, not just as an average, but as hourly data, and it is probably a good enough average for the whole house, as some rooms are a bit warmer, and some a bit cooler. That means I can in theory do a simple spreadsheet with:

Hour/day             Ambient temp     Inside temp      Heat loss for the hour

1800 21/11/22            9                      19             (19-9) x 0.539 = 5.39kW

etc etc and then sum for 24 hour periods, and then divide by the kWh use (input) either from the external kWh meter or the app (it will be interesting to compare the two) over the 24 hours to get the COP.

[accidentally hit Save while typing this, that's why an incomplete version may have appeared]

@cathoderay can't you just use the mass flow rate? You know temp in and out. You know the flow rate, you know power consumed. that's all you should need to calculate COP as you can see heat delivered.

@cathoderay

Sounds like a plan.

@batalto - I now also have historical data showing up, all seems to be working. The app claims that so far today I have put 10kWh in, and got 40kWh of heating and 2kWh of DHW out, giving me a COP of over 4. That's enough to give one a warm feeling inside, but I am not sure I believe it! It will be interesting to see how the app data compares with the calculations suggested above. If they happen to be close, that will go some way to suggesting they aren't far out, as the data sources are totally independent of each other.

Posted by: @batalto

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can't you just use the mass flow rate?

The problem I think is recording the data, which is only on the controller Operation Parameters pages, not in the app. Yes I could sit in front of the Controller with a notepad and pencil, and note the readings avery 6 minutes, but friends might remark I need to get out more often. It might be practical and possible to do it for just an hour, and then see how a COP calculated that way compares with ones derived from the other methods.

Mustn't forget the paramountcy of outcomes, a warm house at acceptable kWh input is a pass, whatever the COP. Likewise, a cool house and/or unacceptably high kWh input is a fail, whatever the COP.