Tuning performance of Dakin 8kw Altherma 3

Hardware Heatpump
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Bumping this thread - I’ve had an 8kw Altherma 3 installed by Octopus last August, and have had/am having some issues, many down to the installation which wasn’t great (D2 pump firing at 3am due to the tank thermometer not being connected…among others), but some are just me trying to figure this all out.

Firstly, the pump speed was set to “low” so was getting ~2.6kw heat output - not great for a house with 5kw heat loss! Fixed that and now getting more like ~6.3kw output with a pretty good flow rate. dT is 5c.

However, the MMI is set to Room Thermostat with a Madoka downstairs. After correcting the offset so that it actually reports the correct room temp, the heat pump works fine down to about -3 outdoor temp, but seems to struggle with anything below that. Being up in the Peak District hills we get some pretty cold weather!

We’re also finding that the unit will just run and run, regardless of set temperature until the time of day setting kicks in (ie. when we leave for work in the morning). We have it set to 19c but it’ll get up to 20c without switching off.

I have a schedule set with a 4 degree setback in the daytime 8am - 5pm and 3 degrees at night 10pm - 3.30am. I’m seeing a pretty poor COP of 2.8 vs Octopus’ expected 3.48. I suspect this may be because I have the WD slope set to 50c at -3c outdoors, and 20c at +20c external.

However, I am told that changing this to LWT may help. The thing is - does running this 24/7 actually work? What does it do to the unit, our elec bills and stuff? At present it feels like we’re trying to use this like a boiler which cannot be right or efficient…

We have a battery which helps the running costs a lot but find it runs out by 7pm most days, and so have 3 hrs of peak rate power to run it.

That was a ramble, so apologies for that, but I am hoping someone can help as my wife isn’t best pleased. I’ve yet to buy some OpenEnergyMon kit, but I’ve known/met Glyn for a long time via our EV club meet ups etc over the years.

Cheers
Ed

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Yes. Have a read/watch of Should Your Heating be Left on All the Time or Not? - HeatGeek

Peak period ends at 7pm, so battery should be fine? Consider switching to a tariff like Cosy Octopus that gives another cheap period in the afternoon.

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Ah, we’re on Intelligent Go, so 23:30 to 05:30 is our off-peak period. With 2 EVs and an all electric household…we use quite a lot of electricity! Cosy is only half the day rate at “cheap” periods, but is still double our night rate.

Thanks for the Heat Geeks link. I think I’ll give LWT a try. If it could maintain a constant ~500w during the day that’d be great, but at present it never dips under about 1.5kw even when the temp is >= target (19c).

Are there any other settings I need to watch out for when changing to LWT? Mainly so I can make a note and restore them in future if need be…

Thanks again

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Hi Ed,

There are a lot of threads that have gone through the limitations of the Daikin Altherma on this forum. Rather than retread them in this thread I’d highly recommend you search for topics with “Daikin”, “Altherma”, “EDLA” in the title and read through the threads, there’s a wealth of experience and information for you to glean, which I think you will find help you to understand your heat pump and how it performs.

One thing I can definitely suggest is that you don’t want your WDC down to 20C LWT, these units are not happy running below 30C and it will be causing short cycling. Also your slope is extremely steep, that’s something like 1.5C change of LWT for every 1C of outdoor temperature change. I’d be pretty sure this will be leading to short cycling (and therefore reduced COP) as well. With default settings the Daikin heat pump will stop running if the flow temperature is >1C above the target which will be happening regularly as the target LWT jumps around much quicker than the unit is able to adjust.

I think the heart of the question you are asking is “is it economical to run a heat pump all the time?”. The philosphy you’ll see is that you want to run your heat pump “low & slow”, essentially this means that you need to balance the heat lost from the property with the output from the heat pump and as a result maintain the indoor temperature that you find comfortable. At this balance point, your system should be running at its most efficient, even though it is running all the time.

To achieve this you need to dial in the most efficient WDC that you can for your system in your house. This takes a bit of experimenting with changes to the system and the WDC (and why having some sort of monitoring of the system is key, so that you can understand performance and how this changes relative to the settings that you change).

Finally, another tip I have is to go to heatpumpmonitor.org and find systems that are similar to your own (same heatpump, similar property profile) and infer their settings from the output you can see in the dashboard (you can filter for “daikin” and find more systems by reducing the number of days of data required, to 90 or 30 days from the default 365).

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Hi Sam

That’s amazing - thanks for taking the time to write all that. Whilst I’m a tech guy by trade, I am a total novice at heat pumps. I have and continue to research the forums for my unit and any info, and I do find it quite overwhelming. Lord knows how a non-tech person is supposed to make this stuff work - I guess proper surveys and damn good installers make all the difference there.

Good shout on finding similar systems, and getting some proper monitoring system installed. I do use HomeAssistant with the Daikin Onecta integration, but obviously the data is nowhere near as good as with the ESPAltherma kit.

Thanks again !

Ed

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@ebyard Have a look at Homely as you tell it the temperature you want while you are at home and it automatically works out the cheapest way to operate your heatpump to give them. It collects data from your system so can calculate your homes heatlose and thermal mass etc.

I believe your setbacks are too high, but not totally convinced the clasic “low and slow” with a fixed waether compensation curve is best when out all day.

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Good luck with that and a Daikin heat pump!

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That’s a large setback, causing the heatpump to work hard to get the house warm again each time. The low-and-slow approach would keep the heating steady throughout the day, using lower flow temperatures to minimise power consumption. This also improves performance (COP) of the heatpump, meaning more heat produced per unit of electricity.

You could increase the room temperature during the time of cheap electricity, aka load shifting. This would allow you to treat the house like a heat battery, reducing the heating needed during the rest of the day.

If the house is always empty during the day, then maybe drop the heating by 1° at most.

To really optimise the heating, it’s essential to collect data throughout the day, plot some charts, and check the behaviour is sensible.

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Firstly you don’t need to change it to LWT to make improvements.

The running all day when set to 19C is because the Madoka hysteresis is +1.5/-0.5 so it will keep heating to 20.5C until it stops calling for heat. The Madoka is also prone to overreading so reducing the brightness may help.

If you have modulation enabled the Madoka will attempt to reduce the flow temp when it starts to overshoot, but it’s better to reduce your weather curve so it doesn’t have to adjust so much. Tweak and lower your curve until the HP sticks around 19C naturally (might help to disable modulation whilst you get this dialled in).

With your setbacks if modulation is enabled the Madoka may cause the HP to work excessively hard to reheat. Would suggest you either reduce the setbacks, or disable modulation so that the HP will reheat, but will track your set weather curve. If you are setting back then you won’t be able to get your weather curve as low as if you have it constant, or with a minimal setback.

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Yeah I amended the offset in the MMI to reduce the Madoka reading by 1c, and the temps are now accurate to a co-located Tapo thermometer, so I’m happy it is now accurate enough.

Ah ha - yes modulation is enabled, which explains why I am seeing LWT=55c even when it is 6c outside, and the HP is pulling 3.6kw…! I’ll reduce the setbacks and disable modulation. Thank you! :slight_smile:

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Interesting - today, for instance, the house went from 17.2c at 3am up to 19.7c at 8am. By 9am it had dropped 1c already, and then a further ~0.3c every hour until 5pm…and that’s with an external temp of 3c or so.

So if I set it down 1c, it’d be kicking every 3 hrs I suppose. I’ll give it a try.
I could overheat the house but we find it hard to sleep when its warm, so that probably isn’t going to fly with my other half…!

But yes, data, data and more data. I’ll see what I can get sorted.

Cheers

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But he does not want heat all day, and is happy with the temperature the property recovers too by the time he gets up. Leaving home by 8am, will result in nearly all this reheat being on cheaprate.

The issue is the heatpump will then need a much higher flow temperature to recover, this could easily incease the electricity used per kwh of heat by 50% while reheating the property. But you got a little lower heatlose from having the lower daytime temperature.

Find the best daytime setback 1st, as the evening recover is using battery and full priced electricity unlike the 3:30am recovery.

Or just tell a system like Homely what you require rather then trying to tell the heatpump how to do it.

To keep bedroom temperatures low overnight a single smart TRV could be used to limit bedroom temperature from say 8pm to 3am. (With bedroom door closed.)

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I’ve switched to LWT control, and find it very natural - trying to use temperature to control things felt very indirect. One trick I discovered on here… When you’re in LWT mode, heating schedule is in the form of adjustments to LWT. You can configure these and then even if you switch back to thermostat control, it will still honour the lwt adjustments. So overnight setback can be in the form of dropping LWT by a degree, for example.

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I’d suggest leaving modulation enabled. It allows Madoka to override the flow target temperature based on the indoor temperature. A value of 10 corresponds to roughly 3c rise or fall in flow target. See this post for more details.

The first and best thing you can do is dial in the weather curve. The best times to do it are when its around freezing for a couple of days, to set the lower end, and then again when it’s milder, say 14c. But as a starting point, try 42c at design temp (usually -2 or so) and 28c at 13c. You’re aiming to find the point the house stays roughly at the same temperature on cloudy days without too many other indoor heat sources (cooking etc).

You should find a few things happen:

  1. The compressor works much less hard now it’s target flow temp is lower. It should do the low and slow you’re expecting.
  2. The indoor temp should stop increasing and shooting past your desired setpoint. Modulation will help govern this and compensate for sunny days, cooking/human activities etc.
  3. Running costs and COP will be much better.

There’s no real difference between using Madoka for control versus LWT mode in this regard since the goal is to produce just enough heat to compensate for the heat loss only. The Madoka is just there to guide the flow target temperature. There are other Madoka quirks you might find over time but for now, getting your WD setting right is top priority, IMO.

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I found it terribly crude - it adjusts in huge steps. AFAIK room temp has to shift by 0.5 degrees before it will do anything. Would seem much better if it added a degree to the flow temp after a drop of 0.2 degrees, rather than waiting for a drop of 0.5 degrees then adding 2.5 degrees to the flow temp.

But agree that it provides a bit of feedback while tuning weather curve, but once you’ve got the latter in place, room temp should be fairly stable and the modulation is rarely called upon.

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I completely agree - it is far too crude, which is why I use LWT and Home Assistant to make flow target adjustments. Of course you can choose a lower modulation value which reduces the step change. Since we all know that getting the WD is key, Daikin really should give us at least the option to narrow the hysteresis. If they gave us a 1c hysteresis option with the boundaries as percentages, that would give 0.25c adjustment points in the modulation algorithm. Cut back in at 0.25c below setpoint. But since Daikin won’t be reading this, we can only dream… I bet those LEDs giving off heat is another reason they designed it as they did.

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While tuning the weather curve, you can make temporary adjustments through the MMI main zone dial. That’s less hassle than editing the curve since that requires installer mode / reboot. Once you’ve observed how the LWT affects room temp you can go on to edit the weather curve to lock the changes in.

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Thanks all - much appreciated. I’ve started playing with it and will see how it goes - we just need some more cold weather now :grin:

A bit OT but for HPs to be mass-adopted, this stuff just needs to work - install it, switch it on, config it, job done. The HavenWise app type thing, but inbuilt in the unit. It all reminds me of EVs circa 2016/7…

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Agree… it should be a case of choosing between fixed flow temp or WD modes and if using WD mode, the readings from outside and inside temperature sensors work out the required flow temp keeping indoors within +/- 0.5c of the setpoint. I mean… how hard can it be?

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Agreed, I think the likes are Homely mentioned by @Ringi or Havenwise are going to be required unless the heat pump manufacturers have a “Tesla” moment, where someone comes along and properly uses software to make their unit “just work” by automatically optimising the system for the install, it actually shouldn’t be that difficult (which is why Homely and Havenwise already exist!), but that’s the inertia of incumbancy for you.

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