My heat pump is too big, what should I do?

John · 2024-03-08T17:54:51.949Z

Thanks @matt-drummer @KnightPhoenix You only need to look at my EmonCMS.org entry for 18 Jan - avg ambient -1.6C, 118kWh generated for 4.9kW avg over 24 hours, room temp at 23C, to see that Octopus’ heat loss figure of 8.3kW at -2.2C is a bit unlikely. Even I’m pretty amazed by that!

matt-drummer · 2024-03-08T18:08:27.206Z

Then that is all you need.

But you don’t need to convince me or Zak, you need to convince Octopus.

KnightPhoenix · 2024-03-09T01:08:23.383Z

John,

I am just here to tell people how I flagged my issue and the proof I provided up front.

I have worked for 15 years in customers facing software/ IT support and a year in an R&D role.

If you go to a company and say ‘i think it’s broke’ they may investigate but may also say ‘you don’t know about this we are the experts, it’s all ok’.

If you go to a company with two heat loss survey’s (or even just heatpunk calculations), evidence of your actual heating usage (over a long extended cooler period) and system data, then provide a solution showing exactly what needs to be changed they are a lot more likely to listen to you and hear you out (trust me this works in most industries).

I not only specified the heat pump change but due to the specific circumstances I also specified 5 radiator changes including a new K3 500 *2400.

Not only was I listened to but as I had done all the background work it was easy to get both the senior engineer and one of the directors on board and get the system designed to work as I wanted (40°c flow rate made possible by the smaller pump and radiator changes).

I am glad you have identified this issue and I really want anyone with one of these beasts to be able to get it swapped and have a SCOP in the high 4’s too but as Matt has said, it is Octopus you need to convince and while a one off calc works for me it may take a bit more proving to get the right people in after sales to budge.

If you don’t want to do the above you can try and call up and tell them it is running inefficiency and you believe the heat loss is wrong and ask them to check it, however unless you know what sizes the windows and doors were listed at and how much loft insulation the original surveyor specified you may not get too far.

The other point to be aware of is that octopus usually only specify a cop of 3.6 for the big unit and if you are getting this (even if it is not optiomal) they can say it is as designed.

If you then want to argue it is not operating efficiently as it should be due to being oversized contrary to part L of the building regulations (part L volume 1 section 5.8(b) " b. A sizing methodology that takes account of the properties of the dwelling, such as the
Chartered Institute of Plumbing and Heating Engineering’s Plumbing Engineering Services
Design Guide.
Systems should not be significantly oversized.") you would need to show that it is in fact significantly oversized.

Sorry if the above is a bit long and dull in places and I am not here to bash anyone, just want to see a few more people climbing up the SCOPs and start showing everyone these things can actually work if you size end install correctly.

Robert.Wall · 2024-03-09T11:31:00.360Z

To that I would add: be professional, polite but firm. State the facts, not guesses, and don’t exaggerate.

scanfer · 2024-03-09T11:32:09.198Z

Thanks for that. We still have the “9”.
My data shows a sub 4kW heat loss on recent cold days, hadn’t thought of that approach. Back to Octopus with that data!

Timbones · 2024-03-13T17:22:19.797Z

matt-drummer:

My heat pump was replaced today.

Comparing with itself, can very clearly see the improved performance (blue = before, red = after).
(Jan 1st to Feb 20th vs. Feb 21st to Mar 13th)

Screenshot from 2024-03-13 13-40-221041×683 83.6 KB

KnightPhoenix:

Octopus replaced my EDLA09DA3V3 with the EDLA08E2V3 on the 10th of January.

Here’s the same analysis for Zak’s heat pump (Nov 1st to Jan 10th vs. Jan 11th to Mar 13th)

Screenshot from 2024-03-13 13-46-321041×687 105 KB

matt-drummer · 2024-03-13T17:45:19.222Z

Thanks Tim,

It is very clear that we both had the wrong heat pump.

In some ways, Zak more than me, I was able to make the 9kW work better in my house, but I did go to extreme lengths to get the best out of it.

Timbones · 2024-03-20T14:10:02.392Z

8 posts were split to a new topic: Can oversized Ecodan be swapped for a smaller unit?

Rob-G · 2024-10-18T19:47:16.958Z

Hi guys just a bit of an update on my situation.

Octopus performed another survey, and the heat loss report came back at 6.5kW not the nearly 8kW from the original.

They informed me they would replace the 9kW heat pump with an 8kW. They installed the new heat pump last week.

Last October I saw a COP of about 2.5 with a 9kW unit. With the 8kW unit, I am seeing 4.2 so far. I am still seeing some cycling as 15 degrees is borderline for needing heating in my house. It will be interesting to see what happens when it gets a bit colder.

I’m sure there’s further room for improvement but I’m happy to leave it as is for now and get a baseline unless I get bored later in the winter .

My thanks to everyone on here, you have all kept me sane.

To be fair to Octopus they have corrected the problem, I don’t know what went wrong with the original calculations whether it was s/w or user error. They seem to have sorted it out either way so hopefully we won’t have any more stories about oversized 9kW units.

meatballs · 2024-10-18T20:55:28.140Z

15.5C was the standard temp where houses were thought to generally maintained their internal temps without any additional heating required so that would be expected.

TrystanLea · 2024-10-19T17:51:06.999Z

@Rob-G are you monitoring your heat pump with an emoncms heatpump dashboard? or are your COP values form the unit itself? just interested regarding the conversation here Is an oversized Daikin really a problem? - #13 by TrystanLea

Rob-G · 2024-10-19T18:53:56.794Z

Just the MMI and a CT clamp that provides power usage to my Home Assitant via my Zappi.

tims24 · 2024-10-22T12:59:42.807Z

Hey Rob-G,
How quickly did Octopus move it all forward with yours?

Just found this thread today… reached out to Octopus mid-last week as I also suspect our 9kW is oversized - was a fairly early install with a surveyor on his first job both as surveyor and team lead (!); spends the majority of its running time at minimum output and it looks like they’d double counted some of our rooms in the original heat loss survey…
Surprised to have Octopus get back to me within 24h to arrange another survey (booked for tomorrow) without so much as a question. Will be interesting to see what happens but they certainly seem willing to listen to concerns, which is probably good.

Appreciate the info’s probably elsewhere but when was your 9kW installed out of interest?
Cheers!

Rob-G · 2024-10-22T13:43:20.177Z

Mine was installed in October 2022.
I first questioned the performance with them in December 2022 so it has been more of a marathon than a sprint.
I suspect you will get action much quicker as a few of us have proved there was a problem either with their surveyors or the software they were using.
I gave them my own heat loss calculations using Heatpunk and provided graphs of the power use to show the cycling there was a lot of too and froing with checking config etc.
I think it was May this year they originally agreed to replace the heat pump.
I imagine they would have changed it quicker if I had pushed them a bit.
I wasn’t in any particular hurry as long as it was done before the weather turned.
Even with the initial poor COP the running cost were about the same as a boiler due to my solar, battery storage, and being on Intelligent Octopus but my running costs are probably about to half.

tims24 · 2024-10-22T14:02:36.202Z

Thanks, that’s all good to know. Will see what comes out of tomorrow’s survey & go from there.

Ours went in during August 2022. Curious now if most of the “problematic” installs all happened before the 8kW’s became widely available perhaps?

Had a few conversations with O since install about efficiency and reducing flow temps, and we’d obviously noticed the 900w floor on power consumption. Still costs less than running our oil heating though especially throwing in solar, batteries & intelligent; so all good… just could be better without the 900w idle!

squarepeg77 · 2024-10-22T14:18:41.362Z

We had a 9kW Daikin installed by Octopus at the end of May 2023. We were told we were borderline between needing 8kW and 9kW and a chimney that was missed on the first survey tipped us over to needing 9kW unit.

9kW is probably too big for our house and I’m sure we’d get much better performance from an 8kW unit, as we are regularly running near minimum power. But I personally can’t face pushing for a replacement. We just have the heating go off for a while once the temperature is reached… not perfect, but we’re used to it from having a gas boiler. We’ll wait for next heat pump for 24/7 modulated running.

However, I’ll keep torturing myself by watching this thread

Rob-G · 2024-10-22T17:18:15.306Z

If you think it’s oversized contact Octopus. They will do another survey and let you know.

It was important to me to get it sorted because I advocate for renewables and low-carbon tech, I wanted to recommend heat pumps and Octopus to colleagues, friends, and family with the heat pump I had I could not.

KnightPhoenix · 2024-10-23T00:24:41.807Z

Happy to discuss the process further if any of you need a y assistance with this.

If you go to Octopus and give them a survey by an independent party (or heatpunk) and show them the day from the heat demand page on open energy monitor it should show your heating needs.

If this is under 7.3kW then you should have the smaller unit. If it is borderline you really should try additional insulation first.

Remember you only need the full power for around 10 days a year so for the rest of the time it is oversized. Personally I would rather have a jumper day or two or use a fan heater occasionally (I have never needed to).

squarepeg77 · 2024-10-23T06:04:36.351Z

Let’s restate what I think is the key point: the real problem is not that that the 9-16kW Daikins are “too big”, it’s that they have a minimum useful/efficient output of around 3.6kW (900W minimum input power * COP). And almost any property will find that too much heat output for many hours of many days.

So we don’t really want a smaller peak output unit, we want a unit that modulates down to a more typically useful range.

Thanks for the offers of help, but I’m going to keep my 9kW (for a useful working lifespan).

Good luck to others seeking a replacement.

matt-drummer · 2024-10-23T06:13:09.692Z

I completely agree Jonathan.

It is not that the 9kW is too big.

Even houses with a heat loss that requires this size heat pump will struggle with it.

I said it before, I can’t think of any house that it suits, it’s just a poor design.

I would have much preferred to have kept my 9kW tto.