Thank you OpenEnergyMonitor: Octopus Daikin ASHP monitoring

Stephen_Crown · 10 November 2023 12:30

Have you considered asking Octopus to swap out your 9kW (9kW/11kW/14kW/16kW) unit with the 8kW (4kW/6kW/8kW) unit given that may be your best bet given the context?

(you may need to get to design day -3C or so to evidence the oversizing given defrosts unfortunately affect output from ~ -3C to +4/5C - output picks up again or at least flatlines once absolute humidy starts to drop away below those temps)

Bottom of page 13 onwards shows 4/6/8 models have same refrigerant charge and compressor etc, so may as well go for the top end 8kW given likely same minimum output (I seem to remember seeing/.reading someone has one as runs about 4-500W input power at minimum output) across them all, and the 8kW has the faster recharge time for cylinder

EDLA04-EDLA08- technical data book.pdf (7.6 MB)

matt-drummer · 10 November 2023 13:35

Hi Stephen,

Yes, it is an option I am considering.

As yet neither Octopus or Daikin have responded to my concerns, I need to wait for that to happen.

It is also possible for me to replace the heat pump at my cost, it is likely to be little more expensive than the radiator changes and the electricity costs over the lifespan of the heat pump make it a no brainer really.

The most gas I have ever used in a day was 110 kWh.

Yesterday my heat loss was 2.71 kW an hour.

The house was on average 23c (ignore the graph on my data feed as that is not the true temperature here)

Outside was 7c

23c - 7c = 16c

At 21c/-2c my heat loss is 2.71kW x 23/16 = 3.90 kW an hour.

I do the same calculation every day and have the data on a spreadsheet, the heat loss @ 21c/.2c is between 3.20 kW and 3.90 kW an hour

I will never need 9 kW or even 7.5kW if that is all I get on a cold day.

I need a heat pump that provides enough heat on the worst day (and my heat loss includes a conservatory that I don’t need to heat when really, really cold. I can just close the doors and curtains to it) but is able to modulate down to a level that provides enough heat on days like today at a decent level of efficiency.

I cannot work out why anybody would put this heat pump in a 98m2 house with an EPC rating of B/89 that has a historical maximum gas use of 110kWh in a day.

You don’t need to be a heating engineer to quickly conclude that my heat pump and house are not well suited.

ColinS · 10 November 2023 15:55

Matt

I hope you’ll excuse a couple of comments on this. First of all we don’t switch heating on when the outside temp = 21c. Normally it is put on at 16c or below. The 16c base temperature is sort of explained when you look at DegreeDays calculation to work out the SCOP.
Base Temperature (or Balance Point) for Heating & Cooling Degree Days
This base temperature difference is accounted for by internal heat sources (people, cookers and anything that produces heat inside) plus stuff like solar gain.

I’ll stand correction on this but I think that means you extrapolate down from 16 to -2 to match your heat input from 0 to Max.

With this logic the 50% heat input comes half way between 16 and -2 = 7c

So If your heat loss is 2.7kw at 7c then it will be 5.4kw at -2c

From my experience of defrosting a safe assumption would be a 25 % output degradation during foggy cold days vs the Tech data supplied by the manufacturers. So I would suggest a 5.4/0.75 = 7.2kW heat pump.

The main reason you cannot get a good performance at the moment is the radiators and less so a badly cycling heat pump. I am doing a spreadsheet on this which I’ll send you when finished.
Hope this helps

ColinS · 10 November 2023 16:00

Oh and I should also point out that if this 7.2kw is correct at -2 then this is a minimum that assumes 24 hour operation, if you set back for 8 hours at night then you will need more during the 16hrs daytime hours and the house will take a while to get back to the desired temp… I say this from bitter experience!!

Vinny · 10 November 2023 16:20

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matt-drummer · 10 November 2023 16:31

Hi Colin,

There was a post earlier in this thread or in another linking to an article about heat loss. It is a straight line that was found to be offset slightly be other internal heat losses.

You are smarter than me but I am sure that even though the heating may only start at 16c or so it is still just the difference between the inside and outside temperature and the `house’ values that determine the heat loss.

The equation is just

Heat loss = house value x temperature difference.

I call it house value as it is something to do with u values and such that I don’t have time to look at right now.

If I know the heat loss at one temperature difference I can easily determine the house value and plug it into any temperature value.

My `house value’ is something like 0.15, that is the losses out of the walls and the windows etc.

I did compile of spreadsheet of data of heat produced and temperatures that confirms this.

However, I don’t really need to know any of this as I have had two winters here with gas and he most I ever used was 110kWh on a day last December.

I always heated the house the same with gas and so it will have averaged 20c in here for a day when if I remember it was about -5c all day and night.

It was the most gas we have ever used and as the house remained at the same temperature for the whole 24 hours it can only have lost around 4kW an hour at most.

My current radiators are quite capable of heating this house to 22c at a flow temperature of 30c when it is 7c outside. I did it on one day.

The problem is the high minimum output of the heat pump, it’s too much for this house.

I was just looking at the 4 to 8kW range, they are far more suited to a house of this size.

Basically they are 8kW heat pumps that are derated.

My (kW has the same minimum output as mine but your house is twice the size of mine.

How can this heat pump be suitable for both of our houses? It doesn’t make sense to me.

matt-drummer · 10 November 2023 16:43

Am I right in thinking that I would be getting exactly the same performance from an 11, 14 or 16kW version of this heat pump?

I assume all of them would be trying to work at the same lowest level and would be consuming the same amount of electricity to produce the same amount of heat?

This is based on them all having the same compressor and pump with the only real difference being in the available fan speed?

From all that I have read and understood from this I actually have a 16kW heat pump that can’t produce 16kW and is `limited’ to 9kW?

ColinS · 10 November 2023 16:56

Matt
I’ve finished a first pass to look at the optimal Flow temp point for your system. From re reading some of the posts above I can see that @markocoheat has done something similar before but I hope it bears repetition in a slightly different way.

As discussed above - For any given flow and outside temps the maximum output is the lesser of the max rad output or the max HP output. Even when cycling the minimum radiator output should be greater or equal to the Heat Pump output at it’s minimum compressor and fan speeds. If not then some Compressor energy is wasted.

Radiator output goes up with flow temperature.
Heat Pump output goes down with flow temperature (and outside temperature)

From this it is clear that there is a maximum output at a certain flow temperature - the max is not at the lowest flow temperature, nor the highest, so there is a peak/optimum.

The main issue with your current system is that it cannot turn down below 920 watts input. If you had the 7kW Daikin in Weston SuperMare then that seem to go down to half that level. This spreadsheet extract shows the optimum (orange highlight) for both 920w and 400w. For the moment 40c is the minimum temp your system should really run at.

The NA’s in the tables are for when the HP has to go above it’s minimum compressor setting to match the house’s heat loss. It is only in the NA regions that the weather dependent curve should be used.

So you can see that as the outside temp rises above 5c with your present system you have to raise the flow temp to use all the heat produced (an inverse WD line). Below 5c you again have to raise the flow temp as it gets colder (a normal WD line)

So I would suggest setting a WD line as follows 41c for 6c and above, and 43c for minus 2c to give 5.2kW out from the radiators at the lowest temperature. OR set a fixed 42c and tweak it manually when it gets cold!

MD Simulation 1.xlsx (14.9 KB)

Good Luck

matt-drummer · 10 November 2023 17:07

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.

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.

matt-drummer · 10 November 2023 17:28

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?

Timbones · 10 November 2023 17:29

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

matt-drummer · 10 November 2023 17:43

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.

matt-drummer · 10 November 2023 18:25

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

Well see what happens.

Stephen_Crown · 10 November 2023 18:32

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

Knowing better having done:

Two different heat loss calcs that came to ~9kW +/- 10%
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
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 ( )…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

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

They then delivered and installed the 11kW version ( ), 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.

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.

matt-drummer · 10 November 2023 18:44

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.

matt-drummer · 10 November 2023 20:15

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.

marko · 10 November 2023 20:17

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.

matt-drummer · 11 November 2023 11:23

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?

ColinS · 11 November 2023 13:29

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

Timbones · 11 November 2023 13:36

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.