Posted by: @bontwoody

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I would be very interested to know what COP you were getting from your heat pump if you are able to measure it accurately.

Thanks for the clarification. I think my (S)COP is between 3.0 and 3.5. I have two ways of getting the COP: via the Midea app/LAN (midea_ac_lan), which has running totals for total energy in and out, meaning I can calculate energy in/out over a period, and then the COP for that period (can be any interval I want), and over modbus using amps/volts in and flow rate/LWT/RWT out to calculate the COP. I refer to the former method as the LAN COP and the latter as the calculated COP. Both give similar results, the calculated COP tends to be about 10% higher than the LAN COP.

All of this is Midea data, and it is possible that in the spirit of dieselgate, heat pump manufacturers have their very own compressorgate software running in the background. However, I do have a dedicated external third party kWh meter supplying the heat pump, and overall the Midea energy in data is within about 5% or less of the external kWh meter readings. I also have an inline analogue flow meter, and it generally shows the flow rate to be about what the Midea data shows (Midea heat pumps don't vary the flow rate very much, so relatively easy to compare the analogue value with the Midea value). Crude (IR thermometer on black insulating tape on the pipework) LWT/RWT temperature measurements also suggest the Midea values aren't that far out.

Bottom line is that I think my COP values are tolerably accurate. They also show a sensible (expected) pattern eg colder weather => higher LWT => lower COP, which also improves credibility a bit.

Here's a chart of the minute by minute modbus data for the 3rd of April this year (a day with useful temperature variation). There's quite a lot going on - stable running, defrost cycles, short cycling, etc but you can also see all the data needed to calculate the COP is there (assuming volts in is 240V):

Hello! 

Owner of a 5-22 kW EcoForest GSHP here. Located in East Manchester. Just snuck into the domestic RHI scheme with commissioning date of 29 March 2022 

Posted by: @amanda1

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I am not a housing association tenant. I am an owner occupier.

Mea culpa. I had extrapolated too far into your comment about the scheme offering heat pumps to both tenants and owner occupiers.

I am also taking note of what you say about your neighbours' experiences. Although you are sharing information around your Highlands community, I wonder how much you've learned which you would've preferred to have known in advance.

Operating a heat pump effectively can be a steep learning curve.
I was intrigued that one neighbour defrosted the external unit using a kettle.
Most ASHPs have an anti-frost feature which occasionally circulates warm water back to the compressor unit to prevent it icing up.

This is indicative of a lack of training and documentation from the installers.
It needs raising with Home Energy Scotland.

If you are unable to obtain a satisfactory response, then take it up with your MP.
There's little point in the Government telling us that they are 'strengthening the requirements of the Building Regulations on the matter of energy' if Part-L wasn't being implemented in the first place.

Posted by: @amanda1

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everybody in these forums seems to have huge houses and have their system on timed with underfloor heating and indoors temps of 21C

You're right to call out that point.

And it's contrary to what's required for the UK to reach Net Zero by 2050.

The households which are more likely to take energy efficiency measures are those in fuel-poverty and with pre-payment meters.
Targeting those would have a greater impact.

Posted by: @amanda1

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I came across this set of instructions for some Housing Association tenants in the Hebrides:

Have you noted that the newly-appointed Chair of the House of Commons Committee on Energy & Climate Change is Angus Brendan MacNeil MP of Outer Hebrides.
That will bring a refreshingly different viewpoint to the corridors of Westminster!

@transparent interesting your point about the Outer Hebrides MP. My MP is Douglas Ross - I have contacted him in the past about energy tariffs and have had some success. [Redacted for reason given below]

Re What would I have liked to know that I didn’t - nothing really, because I did do a lot of research online (not vox pop research!) before deciding that this was my best option. I am still trawling the internet and youtube on a daily basis to add to my knowledge. I have found Heat Geek very useful for example.

Re:Freeze Stat - the Ecodan has a Freeze Stat setting whereby it defrosts itself. This Freeze Stat setting has parameters of 3C -20C with a minimum setting of 3 degrees available. The default is 5 degrees ie when the outside temperature hits 5 degrees the Freeze Stat kicks in. If you want to set it lower than 3 degrees you can, but effectively you are deactivating it and then you are reliant upon the glycol in the system to prevent freezing.  The 5 degrees default and 3 degrees minimum is all very jolly in leafy Surbiton but you might note from the temperature stats I attached in my last reply, here in Tomintoul the average temperature last December was 0 degrees. Ergo, the Freeze Stat set at 3 degrees would mean that the anti-freeze cycle would be permanently on =£££££££££££. My neighbour (she of the hot water) initially had hers set up with a default of 5 and her Ecodan was consuming £400 a week until she had them re-set it. The Mitsubishi manual says that you can set it at ** which is effectively deactivated, but that then there is a RISK of the primary water  freezing. In an article on this forum someone writes at length about glycol and they make the point that the fluid in the system freezing up is not as big a hazard as you might think. 

They have had ASHPs in Canada and Scandinavia for decades. I have found some useful info about COP in very cold climates in Norway, but very very little in the UK. This is one of the reasons I joined this forum, to pick people’s brains about the Freeze Stat setting (before winter strikes). But nobody on this forum seems to live in the arctic climate we have here….so I have not found much so far! I also have a snow situation that I have to tackle before winter - I need to put snow guards on the roof to stop tons of snow falling on top of the ASHP…..

@amanda1 I'll preface this by saying I have done no research on this whatsoever, and living in leafy close-enough-to-Surbiton have very little experience with prolonged sub-zero temperatures, but my vague understanding is that if the system is on and running then it probably won't freeze. Post a thread on it, I'm sure you'll get lots of interest as it's not a topic that I've seen on here before!

@amanda - we don't allow political commentary on this forum.
We're ok with you mentioning Douglas Ross, however.

When us citizens need to draw attention to deficiencies in national regulation of heat-pump installations, then your MP is the correct route of course.

I believe Douglas has decided not to stand again at the next election. That's a good position to be in if you want to make some waves.

I have good communication on energy issues with my own MP, and received a written response from a Government Minister via him earlier today.

When things aren't working as they should, then it's important that MPs are informed.
How else can we expect matters to be put right?!

@scrchngwsl thanks. I started googling again just after I posted that reply, and I have found out quite a bit more on this forum that I hadn’t come across before, and online, in the last half hour or so. It appears that provided there is a sufficient concentration of glycol in the system, it is protected against freezing even with the Freeze stat function deactivated. I am now in the process of ascertaining what concentration of glycol is in my ASHP. It needs to be at 30% for this location, according to one Mitsubishi manual.

@scrchngwsl thanks. I started googling again just after I posted that reply, and I have found out quite a bit more on this forum that I hadn’t come across before, and online, in the last half hour or so. It appears that provided there is a sufficient concentration of glycol in the system, it is protected against freezing even with the Freeze stat function deactivated. I am now in the process of ascertaining what concentration of glycol is in my ASHP. It needs to be at 30% for this location, according to one Mitsubishi manual.

The percentage of glycol also depends on the pressure (Charles' Law).

At atmospheric pressure, the proportion required can be obtained from this graph:

But glycol has a lower thermal capacity than water.
It carries less heat energy.
The higher the proportion in your circulating fluid, the greater the volume which must be pumped to transfer that heat.

@amanda1  in general, the purpose of the anti-freeze protection function of the HP is usually for the "AND" situation: "outside air temperature below X AND water temperature in HP system below Y"

If both are true then run something to stop it freezing up. Note, the second part of the AND can only become true if the heating hasn't been running for quite some time, long enough for the HP's water to cool right down. So if the HP is running to keep the house warm, then you wouldn't expect this condition to occur. so your neighbours experience puzzles me. however, I caveat this with I don't know exactly how the mitsubishi does things under these conditions, someone on here will be along shortly no doubt who does know.

@iancalderbank thank you for that. The occasion in question was after a night when the temperature had dropped to -15. The pump wasn’t able to get her hot water up to temperature and it had been running all day, and I am not sure what part of the unit she poured (she said, trickled, actually) the water on, but it sounds like a high risk strategy to me 😂…..I was thinking more along the lines of hair driers….I know that her hot water is on a timed setting and I don’t know what the target temperature of her water is. It’s possible that because of the timings there was a big differential between the temperature of the DHW and the temperature it needed to reach. This is something I hope to avoid on the principal that if your DHW is kept at 50 with a 10 degree margin, and not on a timed setting, it shouldn’t take so long to get up to temperature from 40 to 50, and although the pump will have to kick in to heat it more frequently than in higher ambient temperatures, it will not have to be on for long periods to do so. That’s my theory anyway…..I am not a physicist…..There may have been snow lying for some days at that point. We do get power cuts here but there wasn’t one last winter.

@cathoderay Thanks for the data. I have uploaded some of my own for a period of similar outside temperature. The first thing i notice is that your flow temperature is higher than mine and so you would expect a lower COP, which is the case.

I went back and looked at my consumption data pre and post fitting the heat pump. Very roughly on an average April day I was using about 1 cubic metre of gas (approx 10kWh) and about 3kWh of electricity when my heat pump was doing an equivalent job. Not massively scientific but ball park enough to see the HP was doing as expected.

Barring breaking any laws of thermodynamics and that your readings are accurate, you must be putting the heat into your house that the COP figures suggest, so the conundrum is, where is this heat going?

My first port of call would be to address the thermal insulation levels in your house as I think you said that they werent great. I suppose that if the rate of heat loss were very large that the heat pump might struggle to put energy quickly enough the overcome it. Its a pure guess and Im not sure of the logic of such a situation, but heat in must eventually equal heat out. Sorry I dont have any better ideas.