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Measuring your COP

batalto · 2021-08-02T19:32:27Z

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°

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Air Source Heat Pumps (ASHPs)

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batalto

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Topic starter 01/09/2021 10:12 am

As a note to everyone I've adjusted the weather compensation downwards as it was a collective opinion it was too high. We shall see how it fares with the wife.

Another point is that we have completed the first full month with the ASHP and I have data.

August last year we used 33 cuft of gas, or 1,045kw of gas to heat our hot water - given nothing else would have been running in August. Taking into account the crappy boiler efficiency of 58% that means effective gas was 606kw. This August the ASHP used 140kw which means (assuming we use the same amount of hot water) that the COP is around 4.33.

In August we bought a total of 64kw from the grid, and used 771kw total. The power share of the ASHP was 18% of total power, so the ASHP share of power bought was 11.6kw and our unit tariff 17.14p (according to our bill) - total bill for the month (excluding standing charges) was £1.99

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
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Mars

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01/09/2021 2:53 pm

I've also been playing around with our settings, and I hope to do a blog update as it is relatively interesting.

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Kev M

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03/09/2021 7:28 pm

@batalto, what have you changed it to (and from)? Ours is still as installed but I might change it.

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batalto

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Topic starter 03/09/2021 8:05 pm

@kev-m just the flow temperatures. I lowered the temperature at higher ambient to 25° when it's above 15° outside and then it increases down to 55 at -2°. We'll see how well that works when the heating actually comes on and I'll have to tweak from there

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Mars

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03/09/2021 8:30 pm

Further to Derek's assistance with our heat pump, our weather compensation has had zero effect on our efficiency.

For the past 10 or so days, I've lowered our flow rate to 35C (from 45C) and there has been a positive improvement, but it's not as significant as I would have hoped for. I'm in the process of putting together a blog piece as stated, and hope to have it published in the next couple of days.

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batalto

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Topic starter 03/09/2021 9:40 pm

@editor has your heating been on?

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Derek M

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03/09/2021 10:31 pm

@editor Hi Mars,

I suspect that you will not see a vast change at the moment, since the heat demand is still quite low.

Please explain what you describe as a 'positive improvement' and how you are measuring efficiency.

To actually calculate the COP for an ASHP, it is necessary to not only measure the electrical power input, but also the heat energy output. Whilst measuring the electrical energy with reasonable accuracy is fairly simple, measuring heat energy with any degree of accuracy requires temperature and flow measurements of the water circuit and then calculation of the resulting value.

I would expect that, at the moment, your ASHP is frequently starting and stopping. From observations of my A2A ASHP, when it first starts up the electric power used is quite high, even before it starts outputting any heat, then as the temperature starts to increase the electrical power reduces to approximately half the initial level. Like a car accelerating up to a speed and then maintaining that speed.

You could try lowering the water flow temperature to 30C and monitor how often your ASHP starts and stops.

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Derek M

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04/09/2021 9:14 am

@editor Hi Mars,

When you say that you lowered the water flow temperature from 45C to 35C, did you just lower the setting, or did you enable weather compensation as we discussed?

This post was modified 4 years ago by Derek M

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Mars

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04/09/2021 1:34 pm

@derek-m, I simply lowered the flow rate as the weather compensation didn't appear to be doing anything.

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Mars

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04/09/2021 1:47 pm

Derek, I don't my message was clear - the flow rate has been dropped to 35C with the heat curve option selected (not CH set point).

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Morgan

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09/09/2021 10:47 am

Posted by: @heacol

@morgan As I have stated, Mitsubishi's own wireless internal thermostat. I am not surprised at the thermostat they have recommended, we see them all the time (and put them in the bin). It appears that they are boiler installers, not purely heat pump installers, Boilers and heat pump are completely different, like cars and motorcycles.

@heacol

Having spoken to the installer he states he can install the Mitsubishi controller rather than the Neostat but it will only control one zone. I pointed out to him the radiators he intends up and downstairs will be a single zone.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
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Brendon Uys

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09/09/2021 12:13 pm

@morgan That will work well, tell them you only want TRV valves on the bedroom radiators, and just lock shields on the rest. Tell them also you do not want system separation as it adds 20-50% to your heating bill as it removes the connection between the heat pump controller and the heating system.

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