Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

Hardware Heatpump
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The 7kW in Weston Super Mare goes way lower than that, 300 watts. I am using four times that at the moment to produce double the heat I need.

The house in WSM is about the same size as mine and has around the same annual heat requirement as me based on the EPC and the Octopus survey. They told me the only reason I got the 9kW was because my heat loss was 7.3kW, if it had been 7kW I would have got a 7kW heat pump.

There is a massive difference in these heat pumps, my 9kW is a monster in comparison, it’s not just a little bit bigger, it’s twice the size, weighs more than double, has a massive water pump and consumes more than three times the electricity at the minimum level. It is not the small step up in size it appears. Surely installers like Octopus know this?

I am using 1.2kW to heat my house to 23.5c and rising. It’s the least amount of electricity I can use at 42c flow.

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It takes me 2 and a half hours at a COP of less than 3 before it settles down to something almost acceptable. It is just wasting electricity.

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It looks like the Daikin EDLA08E3V3 would be a straight swap for my 9kW.

It uses the Madoka nad the MMI.

I can’t see any issues.

Anybody know an installer near Ipswich that would do it?

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This an MCS requirement, and installers are not allowed to go against that.

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335

Hi Tim,

I know.

My house has an EPC rating of B/89, an EPC annual heat demand of 9,931kWh and Octopus assessed it at 9,137 kWh

None of that is consistent with a heat loss of 7.3 kW an hour

A heat loss of that much for a house of this size is not consistent with such a high EPC.

I know they got it wrong.

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I have sent a formal complaint now referencing the Renewable Energy Consumer Code.

Well see what happens.

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337

Octopus messed up my initial survey saying we needed the 11kW Heat Pump.

Knowing better having done:

  1. Two different heat loss calcs that came to ~9kW +/- 10%
  2. Running our boiler range rated down to a max CH heat kW output of ~8.5kW @ ~45-50C flow temp and ~90% efficiency for two winters
  3. Signing up to Carbon Coop Powershaper.io service - Gas meter 30 minute interval on highest use day (140kWh for just space heating) over two winters showed maximum gas units used for a 30 minute interval was ~4.6kWh (so double to ~9.2kW input gas power over an hour @ ~90% efficiency to get back to the ~8.5kW heat output) - see below photos

They then proceeded to try and get me top upgrade to 3-phase (!!! WTF), as the test I was asked to do “run everything full pelt please” electrical load test came back as ~96amps - and I had already upgraded to a 100amp (max) fuse…computer said no, I had been given no context, and I was not asked to provide context of what I switched on (and what would not be switched on in reality together or when the heat pump was installed).

I convinced them through back and forth email they needed to re-survey, and sure enough it came back around 9kW unit (interestingly they have never divulged actual heat loss calcs ( :thinking:)…has anyone else? (They have a radiator schedule that lists rads - but in my case UFH was not on there - and they also refernce the EPC(!) yearly demand, but thats it)

At the same re-survey, they also re-ran the “run everything full pelt” electrical load test (in which I didn’t run either of the 3kW immersions for example)…it came in at more like 60-70amps :ok_hand:

The 9kW Daikin unit was then listed on my MCS paperwork prior to signing.

They then delivered and installed the 11kW version ( :man_facepalming:), and didn’t tell me (I only realised when I went to register the warranty with Daikin as I wasn’t getting anywhere with it on the Octopus side, and made that outstanding discovery…

That said I did some research, called Daikin who said “don’t worry, not alot of difference” (they were right) and decided to keep it quiet as everything pointed to the minimum output (and input) being identical, and that was alway my worry to be fair.

It would appear I did the right thing I guess as CoP when I’m not driving it really hard on purpose during free or off-peak periods is pretty good. :man_shrugging:

Given all of this, we were in a similar position to @matt-drummer in that no-one local heating engineer would go near a heat pump (the usual “they don’t work”, “house will be cold” etc.), there were no Heat Geeks for over 2 hours away from us so not practical.

I really want Octopus to succeed - we all need them to suceed. What is frustrating is they’re not appearing to learn.

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338

Hi Stephen,

My initial result was a 12kW heat loss as he put in I had no cavity walls!

I had to draw the house plans on his tablet for him and he freely admitted that he got into trouble with every survey, knew nothing about heat pumps and had a heated dressing down over the phone from the office whilst doing my survey.

I understand that he no longer works there.

They completely ignored my gas usage, I have never used more than 110kWh in a day and that includes DHW.

I truly don’t think it matters which one of these heat pumps you get from the range as long as you never need the higher output. The only real difference is the cost, they are virtually identical, just turned down to different levels.

I am just as disappointed in Daikin as I am Octopus. It is clear that no thought has been given to the heat pumps and where they end up other than cost.

I am happy to pay for quality but these companies just focus on profit believing people won’t pay for a decent product. I don’t think that is true, what we don’t like payong for is being fobbed off and deceived into buying something that doesn’t do what it says.

I was not an expert and I am still not but I know a lot more now.

It is not unreasonable to assume that a 9kW heat pump would have a range of operation suitable for the size of home it is intended to fit, just trimming the top end is a crappy bodge in my opinion. You would think each one worked in a window of output in relation to their size, but no.

Or maybe there is a setting(s) that enables the heat pump to run at a lower level? I wish they would call me so I could ask the question.

Couple all of that with a culture of form filling, hard cut offs imposed by a regulator, lack of knowledge and no thought and it is a recipe for unhappy customers if they are interested enough to want to know how efficient their environmentally friendly heating is.

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Why so bad today?

I thought it would be in its element now it is colder and the heat demand is rising, but it seems not.

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They could always avoid fudging up the heat loss calculation with daft assumptions and come up with a heat loss of under 7 kW.

It’s not like MCS has the spine to stand up on it’s own; let alone the capacity / appetite to question the technical assumptions behind your heat loss calcs. :wink:

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Yesterday was as close as we have been to the conditions modelled by the heat loss calculation.

The house started and ended the day at 24c and averaged 23c for the day.

Outside was an average of 6c

If I started at 24c and ended and 24c and never went below 22c then I think it is safe to say that I need about 75kWh to maintain the house at a constant 23c.

The difference between inside and outside was 17c for the day.

That means my heat loss at 23c/6c was 3.125kW an hour

I really cant see how the heat loss can ever be 7.3 kW an hour at 21c/-2c

Am I correct in my train of thought?

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At least it looks stable now and the COP is probably as good as you will get with your set-up and 42c flow

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This works out at 184 W per degree (aka heat loss coefficient), so a 25 degree difference at -2C would be a heat loss of 4,600 W. Which is, as you say, less than 7.3 kW.

9 kW of radiator output (rated at dT 50) would need to be run at a flow of 52 degrees to match that output and room temperature.

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344

….which is oddly close to the 50C design flow temp….that Octopus standardise on it seems

Or is that a happy coincidence?!

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345

Hi Tim,

Thanks.

I don’t want the house to be 23c particularly, I am only doing it now to help match the house to the heat pump so at a 21c difference my heat loss is about 4.2kW an hour.

I have been running at a fixed flow temperature of 42c for a couple of days now.

The house is warm enough so everything is good in that respect.

COP is not great though, which is OK in itself.

But I am using more electricity than I could be, quite a lot more possibly?

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I’ll stand correction this but your ‘net’ heat loss was 3.125kw at 6kw (excuse me for being pedantic but no need to say ‘an hour’ as kw is already a rate, like speed). Your ‘gross’ heat loss from the building to outside would have been higher but it is offset by other energy sources and people and solar gain to get this net figure. This is why, at the probable base temp of 16c, your net heat loss is Zero and you have to extrapolate down from there and not from 23c.

Clearly the heat pump input required is the net figure but as I said in an earlier post, if you need zero at 16 and 3.125 at 6c then at -2 you will need = 5.6kw from the heat pump. Hope I’ve remembered my quadratic equation solution from school.to get this number;

6 a + Constant = 3.125kw
16 a + Constant = 0 kw

Solve for a and the constant then calculate -2 a + Constant = 5.6kw ?? I hope!

347

Indeed, as Michael de Podesta’s explains in “Cold Weather Measurements of Heat Transfer Coefficient”:

So to estimate the actual amount of heat dissipated in the house I should really take the heat pump output and:

  • Add 2.4 kWh/day for each person in the house
  • Add 10 kWh/day for all the electrical items
  • Subtract 3 kWh/day for the hot water lost.
348

Another way of understanding the gross vs net difference is to think of an empty church. Even if the outside sits at -2c for a month the inside of the church will be a few degrees above this. This is due to a) some solar gain and b) the ground underneath is much warmer than -2c which is why ground source heat pumps exist.

So when calculating your Heat Pump energy at -2c you have to factor this ‘hidden’ heat gain into the equation and the base temp assumption is the easiest means to do this.

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When I did this exercise for my house, I calculated a gradient of 270 W/K with a base heat of 600 W from electrical sources, plus 400 W from humans. So, in theory, that’s 1 kW less heat I need from the heat pump.

350

The degreedays calculation method is the standard way to make these adjustments. I admit to have never gone as far as the detailed regression analysis but here it is;

Degree Days.net Baseline Regression Tool
.

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351

OK, it gets a bit more complicated I agree.

I am not sure agree with extrapolating from 16c as I have calculated this at a range of outdoor temperatures and I always come back to a heat loss of about 4kW at 21/-2

We don’t even use 10kWh of electricity a day on other electrical items but even if we did they are always there although it varies from day to day.

However we calculate this my heat loss is never anywhere near 7.3kW and all this has been done whilst heating our conservatory.

Most compelling to me is our previous gas use over two winters. I have never tried to save money and turn the heating down. The most gas we ever used in a day was 110kWh. If that is true I don’t see how my heat loss can be 7.3kW unless my gas boiler was more than 100% efficient!

The conservatory is an issue at it adds a lot of heat loss but isn’t actually a room that should be considered when looking at the worst case.

We would shut the double glazed doors to it and pull the thermally lined curtains, we wouldn’t leave it all open sucking heat out of the house when we were struggling to keep warm with the heating system.

I am going around in circles a bit, I know but I am struggling to find a solution to my unhappiness with what I have got.

Radiators would help with any heat pump I am sure but there’s a limit to how much money I want to throw at this.

The heat pump has a minimum electrical input that is not consistent with my heating requirements.

I am scared that I will replace the radiators and then end up with something that cycles a lot using more electricity and a house we still have to run hot.

Not very technical but I also have a wife who is very understanding and will let me do whatever I want but I feel bad about wasting what is her money too.