One year with an 8kW Dakin Altherma 3

Hardware Heatpump
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So, I have had it for a year.

Do I like it, not much, but maybe I have been harsh.

It has had some issues and focussing purely on efficiency, it could have been better.

I had to wait some time for a firmware update to allow me to run it how I wanted to and it has had a few occasions where it has used more electricity than it should have done due to some random inbuilt fault.

However, we have been warm enough, averaging about 20c upstairs and 22c/23c downstairs.

No failures.

It has been a colder winter than normal and for a while it felt like we were living in a cloud.

It has used 3,061kWh of electricity and produced 14,931kWh of heat at an SCOP/SPF of 4.88

The efficiency is pretty good.

We live in a four bedroom detached house and heat an all glass conservatory so not really ideal and is the root cause of many of my issues.

The heating system isn’t particularly great, installed by a clueless diyer with a fair amount of plastic pipe.

All I do have is massive radiators.

And that is all it takes, big emitters, the heat pump is bargain basement and the pipework is rubbish. But the heat pump is oversized and our heat loss is low.

The conservatory makes up about 40% of the heat loss of the whole building, so about 2kW out of a total of 4.5kw to 5kW.

I run it in the most basic form as that is what works best, fixed lwt with no room temperature control and no wdc.

The heat pump has been 100% reliable and is virtually silent in operation at all times.

In conclusion, despite my whinging, it works, it has been installed well, and it is efficient.

My actual electricity cost for one year is 214.27 at 7p per kWh on Octopus Intelligent Go.

I have sufficient battery storage to use that at all times and if I allow 20% for battery losses my costs would be ÂŁ267.84

That is for space heating and DHW.

If I were on a standard tariff at 25p per kWh then my total costs would be ÂŁ765.25

A gas boiler would have been ÂŁ995.40 at 90% efficiency and 6p per kWh plus ÂŁ100 or so for the gas standing charge.

So, well done Octopus, well done Daikin, it could have been better but pretty good really.

Sorry for the whinging :slight_smile:

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It seems very good to me, scop of 4,88 is not bad.
Please can you tell me your square space and flow temp. Also your insulation?
I am planning similar instalation here in Croatia and every data is valuable for me.

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I must agree with you Matt.

We like chasing the best, and there is always room for improvement. However, I am also very happy with my 16kW Altherma bibloc. I think it is well built, has millions of controls for us to geek over and modulates down quite well.

It is still oversize, full LWT control is not possible so Madoka needs to switch it off when it reaches 22.5ÂșC during the day or 20.5ÂșC at night.

Minimum LWT is set at 30ÂșC, with weather compensation and a -5ÂșC offset at night.

Over the last 12 months it has supplied 4953kWh of hot water (SCOP 3.5, tank at 50ÂșC), 14856kWh of heating (SCOP 4.91) and 8436kWh of cooling (SCOP 4.99).

I consider above values to be extremely good, and hardly worth the effort of trying to do better. It has saved us almost 2400 euro vs our old oil boiler over the last 12 months, plus given us cooling in the summer months. Granted, the installation was very expensive, we heavily overpaid, but hopefully it will save us money in the long run.

Hope it has a long life!

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Thanks for the update @matt-drummer.
We’re still in conversation with Octopus about possibly having our 9kW swapped for an 8kW. A few cold days where we hit the outdoor design temps rather reinforced that the 9kW is somewhat oversized as the house stayed at temp with a peak of about 5.5-6kW heat output, despite -2.6ÂșC outside. Seems a long way away from “9kW heat loss” :smile:

Currently waiting for a decision although getting O to review submitted data and accept that there’s a huge difference between real-world performance and what the calculations claim is an uphill battle.

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They are good figures!
I guess you have warmer or shorter winters than we do in the UK?
Also gets hotter hence you switching to AC / coolingđŸ„”

Do you have the hot water on Comfort/ 50C setting all the time?

When I had Comfort HW it worked fine with Madoka.
When I tried ECO HW it got overridden every time by the heating.
Going LWT / Madoka out of the loop it solved that.

Must be a bug that ECO HW can’t override heating even once you’ve set it to!
Wonder if anyone has raised it as such with Daikin?

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Hey,

I would say we have shorter and warmer winters than the UK, yes. We also usually have a bigger difference between day and night, which allows a bit of tinkering:

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Above is average data these past years.

I have the HW in re-heat mode, at 50ÂșC and with a hysteresis of 20 degrees. It does HW twice or 3 times a day, depending. I played at the start with schedules etc but it is too much of a hassle.

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Hi Matt,
I’ve been really interested to read your journey through the oversized 9kW Daikin and then onto the 8kW as I’m now in a similar boat.
I’ve had the 9kW for just over a year. It’s giving a tolerable SCOP of 3.36 and kept us at a cosy, constant temperature during the really cold weather in January BUT the rest of the year it’s driving me mad by overheating the house and then shutting off and not coming on again until it’s got too cold.
We are at home all day and want a constant, comfortable temperature throughout. I’m fed up with playing around with settings to find what works best; I just want it to do what it says on the packet and run ‘low & slow’ all the time without me having to pamper to it.
Is my understanding correct that heat loss = heat produced per hour?
If so, our actual heat loss averaged 3kW in January and 5.72kW on the only 3 days that the outside temperature dropped to -3 degrees so a long way off Octopus’s heat loss calculation of 7.98kW.

To help me decide whether to embark on a long and possibly fruitless battle with Octopus, can you confirm whether you’re pleased you had yours changed? You’ve said the 8kW has used 3061kWh of electric and produced 14931kWh of heat but how does this compare to the 9kW you originally had? Is it using less electricity and saving you much money?

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I’m obviously not Matt but it sounds like you’ve got the system configured for thermostat-based operation at the moment? In this mode you’re at the mercy of the system waiting for the house to cool once the cut off temperature is reached before heating again.

One solution to this is to switch to LWT mode with a well tuned weather compensation curve. If this curve is set appropriately, it will keep your house at a constant temperature. The downside on a 9kW unit is that it will cycle while doing this but, the big advantage is that it won’t wait for the thermostat to show temperature dropping before starting again.

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The downside on a 9kW unit is that it will cycle while doing this but , the big advantage is that it won’t wait for the thermostat to show temperature dropping before starting again.

Daikin heat pumps do not work like this.

They do not wait until everything has cooled down, they start heating again immediately and do this over and over.

This is not an approach that works, it’s not a solution.

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Hi Matt, I think you may have read my post backwards.

The problem the user is having is an oversized heat pump operating (I believe) in thermostat mode. In thermostat mode, there is a hysteresis that operates when the heat pump reaches temperature and cuts off heating - there is a hardcoded wait until the temperature has dropped 1-2 degrees (I think?) before heating is allowed to resume.

The solution I proposed if replacing with an 8kW unit is not an option is to switch to LWT mode, as this has no wait thermostat-based waiting period before resuming heating when it cuts off thanks to leaving and return temperature equalising.

I agree this means lots of cycling, that this is bad, and the better solution is moving to an 8kW unit. But, purely as a solution to ‘my house gets cold before heating comes back’ - this would work.

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Hi Ben,

I have not missunderstood.

That 9kW unit will just keep heat in lwt mode.

It will turn off for a couple of minutes and then go again full pelt.

And it will just keep doing that.

It creates even more heat and uses even more electricity than just trying to keep it running.

Nothing works, the Madoka is no good with the big hysteresis and lwt will just get you constant heat in loads of eally small cycles.

It won’t stop until you turn it off.

Mine worked much better with big radiators as I could run lower flow temperatures, but only down to 35c, any lower and they are not happy and use no less electricity.

This is the problem with that heat pump, the minimum electrical input is too high as is the minimum heat output a around 3.5kW.

I do agree with no t using the Madoka, it’s uncomfortable with that heat pump, but the lwt mode wont really improves matters appreciably.

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Hi all and thanks for your helpful suggestions BUT I’ve spent a year tweaking this, changing that, trying something else etc and am sick of trying. I was sooo excited to get a heat pump and have been totally flattened by the experience; it should be ‘plug & play’, not ‘spend the rest of your life making adjustments’.

I’m poised and ready to go into all out battle with Octopus, but I’d just like to know whether anyone who has successfully had a 9kW changed for a 8kW is pleased with the result. Has the change solved most of the problems? Does it cost less to run? Does it keep a more consistent temperature in the house?

In short, is it worth the effort of battle or should I just roll over and accept that the tax payer has just given Octopus £7500 to install a heating system that doesn’t do what it says on the packet?

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Hi Caron,

I didn’t really reply to your original question, sorry.

It’s not that straight forward.

The 9kW Daikin does do what it says, it heat your home and your hot water at an acceptable SCOP, that is acceptable by MCS standards.

I don’t think any of these heat pumps are particularly plug and play, they all need tweaking and monitoring.

In my view, the 9kW Daikin is of higher quality than the 8kW.

Increasing my radiator sizes (by quite a lot!) made the 9kW easier to live with.

I think some owners have found an issue with tape heaters that has reduced the minimum electricity input by quite a bit since I had mine.

If somebody brought my 9kW back I wouldn’t be that unhappy.

The 8kW uses less electricity when running at it’s minimum output which is good for me as I run on batteries as much as possible.

Whether it uses less electricity overall, probably yes, as the SCOP is better, but enough to worry about, for me probably not.

You still have the Madoka and it’s flaws with the 8kW, I don’t use the Madoka.

Keeping a constant temperature is only easier with the 8kW when it is warmer outside by virtue of the lower minimum heat output.

But it’s not really that much less, the 9kW can go down reasonably close to the 8kW although the COP obviously suffers.

Initially it was all very exciting and the COP mattered to me more than it does now.

You can look at all the data from other Daikin heat pumps and compare to yours.

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Is the LWT hysteresis fixed?, on some makes, I believe you can set the cut out at say SP + 1 degC and the cut in at say SP - 6C which may extend the cycle time, What vol of water is circulating?, If you had only say even 5C between cutout/cutin then assuming water contents at 10L and assuming that the HP runs (worse case) flat out at 9.0kW then the HP off timewill be ~ 3.5minutes and ontime ~ 0.5minutes, cycle time 4 minutes, to give a average heat output of ~ 1.1kW

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Have you thought about subscribing to Homely or Havenwise? They do all the adjusting for you.

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The Madoka is next to useless, unless you have the right size heat pump. I also do not, I have the 11kw (basically the same as your 9kw) and our heat loss is more like 6kw. The winter months, it’s ok and the weather curve keeps things about right, with a few tweaks to the offset (modulation in Madoka speak). Even then, the unit is running towards the bottom of its output.

The Madoka’s hysteresis is fixed at 2c, so if it goes off (perhaps some baking heats up the ground floor more than usual), it won’t come back on again until 2c lower. Which is pretty cold. I had no choice but to use LWT mode.

The LWT suggestion is workable only if you have an external control, in my case, Home Assistant. For the spring and autumn months, it adds a little heat and controls the heat pump to keep the house within ~1c - which is much more tolerable. Requires internet access, of course, and hardware to run Home Assistant.

An oversized Daikin Altherma with Madoka is basically unfit for purpose. I have tried to get Octopus to switch out mine for an 8kw unit as they have for others, but after many requests for help, they have ghosted me. Thankfully, I found this all out before paying the final bill so I’m not out of pocket. I thought that would motivate them to resolve the issue but they have failed to do so. I’m very angry with them and I doubt I’ll ever use them again for heat pumps. They really haven’t got a clue. Utterly incompetent. Good luck if you fight them, some have succeeded.

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Thank you everybody for your replies & suggestions.

I don’t have the spare money or the inclination to invest in any form of monitoring or additional controls for my heat pump and, more importantly, I don’t believe it should be necessary.

I have been keeping a note of the daily energy input for heating as per the ONECTA App and have now collated this and extrapolated the actual heat loss and hourly input. Assuming I haven’t made a fundamental mistake in my calculations (which is very possible as I’m not a heating engineer), I believe this shows clearly that my actual heat loss is 6 degrees C at -3. It also shows that the hourly energy input only exceeded 900W on 37 days out of the 212 days monitored. So, for the remaining 175 days it was unable to modulate down sufficiently and had to control the temperature by cycling on & off.

This is all way outside my comfort zone, but I think it explains why my home was comfortable in January & February but up & down like a yo-yo for the milder months. Octopus have been unable to offer any other explanation or solution so I’ve sent them the data and asked for a correctly sized heat pump. I suspect that they’ll decline, but I still have confidence in them as a company so we’ll see.

I do wonder how many other victims of oversized heat pumps there are and whether there are enough of us to warrant some sort of group action? If over-sizing is a big problem, surely it would indicate that there’s a fundamental problem not necessarily with Octopus but possibly with MCS, Daikin & others.

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I find it surprising that the (if this is your meaning) house temperature is up and down with a cycling HP. Obviously a different “heat pump” but my (non modulating) 20kW oil fired boiler cycles continuously and madly when my house demand is down around 2kW or so but the house temperature is still maintained perfectly well.
One would think that a 50L buffer (a miny heat store) with a temperature thermostat with a hysteresis of say 10C that switches the ASHP on and off should give pretty good control, at your very low demand of 900watts, 0.9kW, the ASHP will run (on) for ~ 5 minutes and almost 39 minutes off but the buffer should still maintain a steady output temperature, at a infrequent demand of say 7.5kW, the ASHP will run (on) for 23 minutes and off for almost 5 minutes. Obviously, this is not a really acceptable method once the heat demand is > than the minimum output of the ASHP as it should then run continuously with no cycling but I’m pretty sure there are relatively easy switching methods to achieve this. I never see any mention of this form of buffer in any of these forums. There must still be plenty of non modulating ASHPs about working fine even if the do have relatively poor COPs?.
I agree that you shouldn’t have to do anything, your HP should just be plug and play, period.

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The theory is great, and if that was the control system in use then it probably would work great, exactly as you say.

Unfortunately that isn’t how Daikin implement their control system. As RWT rises above target the heat pump compressor modulates lower and lower, eventually when it can’t module any lower and RWT still rises then the heat pump compressor cuts off, so far so good. It then waits for the RWT to drop a few degrees, but nowhere near as many as 10 (and I think a minimum fixed time of 4-5 mins). Then, and here’s the problem, it decides that the RWT is now too cold and needs to be heated up. But instead of coming back on at minimum modulation (after all it only cut out a few mins ago because it couldn’t modulate low enough) instead it decides that the water temp is too low, needs heating, and sets about doing it as quickly as possible, heading towards maximum compressor power within the first minute or two of operation. This obviously massively overshoots the desired temperature, the compressor cuts out, and the cycle repeats.

What you end up with is the ASHP running for a couple of mins, at high power, followed by a few minutes off. It can easily cycle 6 or 7 times an hour. During this time all control over average LWT is lost and you end up with a different average heating output to what it was just before it dropped below minimum continuous running, alongside the efficiency loss of rapid cycling. This happens when outside temperature is relatively high, therefore house heat loss relatively low. A fairly small absolute variance in the heat being delivered to the house can now have quite a big effect on internal temperature.

Changing to use Madoka modulation (and ignoring the target LWT modulation this brings) fundamentally changes the compressor control algorithm. The compressor comes back on more gently than full power in a cycling scenario, but it still ramps towards around 50% power rather than the minimum power that would be far more appropriate under the circumstances.

I know that there are many more variables in the control algorithm we don’t have visibility of and running a compressor probably isn’t as simple as just turning back on at minimum power but the Daikin control seems woefully simplistic once it enters into required cycling.

Edit: As pointed our by Chris, this post applies to the 4-8kW Dakin and not the 9-16kW model.

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I have ours in LWT mode and it does cycle because it’s oversized massively. But, it doesn’t come on full pelt after the compressor stops for a short while. Here’s an example day from Feb this year:

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After a defrost, yes it goes a bit nuts, but that’s a whole other issue.

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