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Problems with Daikin 18 kW High Temp ASHP

Bramshot · 2022-11-29T12:38:25Z

Firstly, the description, it turns out that it is not an 18 kW heat pump at all, but more like 12 kW with a 6 kW so called ‘ backup heater’. So feel cheated by that to start with. DHW, claims it can produce leaving water at up to 70 C, so DHW at say 60 should not be a problem, right? No, it cuts out at DHW 55. OK , not the end of the world and 55 is more than adequate but if you can set 60 ( you can set higher) it should be able to do it! No apparent reason for it to shut down. Disinfection cycle uses immersion ( ‘booster ‘ in Daikin speak) to get it up over 60. Despite this, in general, it has been working well until the colder weather came along. I now find that when ambient drops to 2 or 3 it starts to freeze up on the evaporator, and has to do a defrost cycle once an hour. This takes around 15 min, so it’s on for an hour , off for 15 min. It never reaches its set leaving water temp, so heating the house is suffering. And we haven’t had any really cold weather yet. I am sure it would be ok, it it could only last longer than an hour between defrost cycles. Are these things designed for our relatively humid winters as opposed to cold dry continental winters. Have I been sold a ‘pup’? Has anyone else had experience of these units?

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Air Source Heat Pumps (ASHPs)

Last Post by Bramshot 2 years ago

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Terry Nolan

(@haggistrap)

Active Member Member

Joined: 2 years ago

Posts: 15

07/03/2024 12:04 am

@derek-m thanks again!

we agree! The outside temp hasn’t got above 5c, hence why I have set it to the absolute lowest min flow temp at 55c over winter. If WC were on the HP would operate at over 55c.

ideally I need 60c plus at around 0c outside temp. But I have reduced this to try any enable the HP to work less hard.

Any idea on why the HP can’t maintain the flow temp as indicated by the graphs? I don’t really understand what it’s doing, it appears to stop heating water even when it should be capable of doing so?

thanks

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Bramshot

(@bramshot)

Active Member Member

Joined: 3 years ago

Posts: 17

Topic starter 07/03/2024 1:12 am

@haggistrap Terry, our HP do not run at 70C. 55 is about the max. It will run cooler . Mine is weather dependent and runs between 35 and 50 normally for mild to cold weather. Will go up to 55 when sub zero. It will never do 70. I have seen mine get up to 60 when heating domestic hot water to 55. For the disinfection cycle it has to run the immersion heater as well, so 60 out of the heat pump is about the maximum. One of the misconceptions I had and mentioned in our PMs was that it would work at temperatures comparable to a gas boiler. It doesn’t. Nor do I recall seeing anywhere that it was claimed to get that hot, though I was expecting it to be able to heat DHW to 60 without using the heater as well. I spent a long time trying to make it do it, to see if it could, though 55 is a perfectly acceptable temp for DHW.
My house heats perfectly well with low flow temps at moderate outdoor temps, it surprised me how low it could go and still heat the house. (For others reading this , we both have the same system installed).

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Derek M

(@derek-m)

Illustrious Member Member

Joined: 5 years ago

Posts: 4425

07/03/2024 1:19 am

Posted by: @haggistrap

↑

@derek-m thanks again!

we agree! The outside temp hasn’t got above 5c, hence why I have set it to the absolute lowest min flow temp at 55c over winter. If WC were on the HP would operate at over 55c.

ideally I need 60c plus at around 0c outside temp. But I have reduced this to try any enable the HP to work less hard.

Any idea on why the HP can’t maintain the flow temp as indicated by the graphs? I don’t really understand what it’s doing, it appears to stop heating water even when it should be capable of doing so?

thanks

T

The WC settings need to be adjusted to match the heat loss of your home. Do you have a copy of the heat loss calculations?

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HughF

(@hughf)

Honorable Member Member

Joined: 4 years ago

Posts: 489

07/03/2024 9:15 am

Radiator upgrades really are something that people should do… a 600x1200 type22 is about £75 from Screwfix, comes with fresh new white paint, no sludge inside, looks nice and clean on the wall. You can heat most rooms in most houses with a rad that size.

Heck, even if all you do is swap to type 22s for all the rads in your house and keep the sizes identical, it’s worth doing.

Hopefully we will see the end of type 11 and type 21 rads as we move to low temperature heating.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Terry Nolan

(@haggistrap)

Active Member Member

Joined: 2 years ago

Posts: 15

07/03/2024 9:29 am

@bramshot

thanks for the reply and PM

my HT can operate up to 70c for LWT, according to the below manufacturer info. In the real world, in Scotland is a different story but that’s how it was sold to me!

DAIKIN.CO.UK "https://www.daikin.co.uk/content/dam/dauk/document-library/Brochures/Heating/Heating+Installer+brochures/Daikin+Altherma+3+H+HT_767.pdf"

Features and benefits
› Ideal for boiler replacement, due to its high leaving water temperature (LWT) › LWT of 70°C down to -15°C with heat pump operation only
› Operation range down to -28°C
› Updated software for better performance

https://www.daikin.co.uk/content/dam/dauk/document-library/Brochures/Heating/Heating%20Installer%20brochures/Daikin%20Altherma%203%20H%20HT_767.pdf

and more the info that states it’s for older homes, like line and it’s ok for old radiators too.

Air-to-water high-temperature heat pump designed to be the perfect heating system replacement in older homes

With no gas dependency, the Daikin Altherma 3 H HT F can connect to older emitters like radiators and provide heating, cooling and hot water with one unit, with no need for additional building works

https://www.daikin.co.uk/en_gb/residential/products-and-advice/product-categories/heat-pumps/air-to-water-heat-pumps/daikin-altherma-3-h-ht-f.html

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Terry Nolan

(@haggistrap)

Active Member Member

Joined: 2 years ago

Posts: 15

07/03/2024 9:33 am

@hughf totally agree and I’m likely to do this in the summer.

however, Daikin installer and Daikin specs of my HP tell me this is not required for their high temp heat pump!

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Bramshot

(@bramshot)

Active Member Member

Joined: 3 years ago

Posts: 17

Topic starter 07/03/2024 11:00 am

@haggistrap Those are porky pies. It will not give those outlet temps. I will look through the data sheets I have but I am petty sure they say different and say ‘with heaters ‘too.

of course it may be dependent upon the loading of the HP and if ours are underrated as we suspect it will not then be able to reach its maximum.

i did think I had PM d you by replying to your last but apparently it is not done that way.

It didn’t need to be private so I copy the text here.

Hi, there was a major problem with Hive TRVs. By the way, Hive do not recommend use with HPs.

When you use Heat on Demand, it calls a 30 min boost to turn on the heating. If the need for HoD goes away, the boost is cancelled. If HoD is still required after the boost is ended it starts another boost. However, the problem is that it does actually turn off the heat demand for 2 min before the next 30 min boost. You would not notice this with a gas boiler, but it is no good for a heat pump which has to go through a lengthy restart process each time it is turned off. I found that when HoD was active, the HP would turn off every 30 min and then have to work its way up again. So was only actually producing heat for about half the time, ( all this in addition to any frosting issues, which were actually less likely!)

I have obtained an off delay relay which is connected to the Hive heat demand output. The HP is then connected to the relay output. The relay provides the same functionality as the delay timer for a bathroom fan to stay on when the light is switched off.

I have set my delay to 8 min. So the relay will close so heating comes on when Hive brings on heating, but will remain on for 8 min after Hive turns heating off. If the Hive output turns on again within that period the output remains on and the timer resets, to time 8 min again next time the output turns off. Thus the HP can ‘ride through’ any hive off period shorter than 8 min and effectively ignores the 2 min off period.

But you may ask “What happens if Hive turns off for 8 min and 2 sec? Another short off period.” That would not matter as much as it was intended for the heating to be off then anyway, but in fact it tends not to happen because the delay adds some much needed hysteresis to Hive, ( it basically has zero hysteresis). As the heating is, in effect held on for an additional 8 min whenever Hive turns it off ( even when it is not a spurious short off period), the rooms heat up that little bit more, so it will take that much longer for the room to cool back to the turn on point. So the off period will be slightly longer than it would have been.

Anyway it works a treat for me and has eliminated this issue. Could some of what you are assuming are defrost events actually be this Hive ‘ artifact’ arising from using Heat on Demand with your TRVs?

I also have a solar and battery system and can follow the house power demand using that, so can see when the HP is turning on and off.

My house sounds similar size and insulation to yours, also radiator heating, all were assessed as being sufficiently large without needing a change.

The HP has no problem reaching its target output temp when well below zero outside. But I am using the backup heaters below 2 deg. That in itself was a disappointment, I thought I was getting an 18 kW unit but it is actually a 12 kW HP with 6 kW of electric heaters! Or is it booster, or is that the hot water, always get confused between them!

My HP output temp is linked to outside temp, so lower as temp rises. Goes up to 55 or higher below zero, and gets there in each heating ‘ session ‘ between defrosts.

My total electricity consumption is astronomical in winter, I can get through £1000 a month in Dec / Jan, but that does also include 2 EVs and the rest of the domestic load but is on Octopus Go cheap night rate, which helps. At present the heating is using about 30 kWh / day. On average, looking at my power usage graphs from the solar system it is running at an average of about 4 kW in the worst weather, smoothing out the defrost cycle ‘ bumps’, so could be as high as 100 kWh / day. However I barely use any grid power in the summer and monthly bill averages about £330 / month. Still less than with Gas. Just checked the Daikin app and it claims usage Dec and Jan for heating was about 1500 kWh and for water was about 180 / 135 ( but a lot of visitors in Dec!).

Will be interested to hear what the engineer says.

My installers were suggested by Daikin, they bent over backwards to help my issues ( which were largely due to my over expectations) but I did get the feeling they didn’t really understand the system or how it should be set up, let alone actually read the instruction manuals! I was putting them straight some times, like they did not set up the hot water / heating change over valve correctly. Although the system was installed and operating in days it took months to iron out the bugs. The defrost issue is one bug that seems intractable!

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HughF

(@hughf)

Honorable Member Member

Joined: 4 years ago

Posts: 489

07/03/2024 6:56 pm

Every Daikin data sheet I’ve seen says 60 max…. And Daikin are keen to use their built in backup heater at every opportunity, so we see quite a lot of them starting on the backup heater, totally unnecessary imho.

And as for using Hive to control a hp, I couldn’t think of a worse thermostat to use to control any heat source. If you set your weather comp properly then you don’t even need a thermostat. I jumpered mine out back in October and have just left the heat pump on since then.

Off grid on the isle of purbeck
2.4kW solar, 15kWh Seplos Mason, Outback power systems 3kW inverter/charger, solid fuel heating with air/air for shoulder months, 10 acres of heathland/woods.

My wife’s house: 1946 3 bed end of terrace in Somerset, ASHP with rads + UFH, triple glazed, retrofit IWI in troublesome rooms, small rear extension.

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Toodles

(@toodles)

Famed Member Contributor

Joined: 4 years ago

Posts: 2734

08/03/2024 11:57 am

@hughf When I was researching what, which, where, how and why for fitting an ASHP and ridding ourselves of a starting to fail gas boiler, I asked potential installers about utilising my existing Hive boiler interface, controls and TRV’s. They said ‘No’ not at all suitable for this. I have still used one of the Hive TRV’s on the bedroom radiator as I wish to have a programmed change in temperature at night. There may be better TRV’s around perhaps but I already had this one and it serves for this purpose. The installers supplied a NeoStat controller which is as crude as they come ON-OFF! I now have the smart control by a Homely controller - much better! Regards, Toodles

Toodles, heats his home with cold draughts and cooks food with magnets.

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Bramshot

(@bramshot)

Active Member Member

Joined: 3 years ago

Posts: 17

Topic starter 08/03/2024 2:08 pm

@toodles Hive is working fine for me after the mods I did. However, I agree it would have been useless without it. Hive do not actually recommend its use with HPs.

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Terry Nolan

(@haggistrap)

Active Member Member

Joined: 2 years ago

Posts: 15

10/04/2024 2:48 pm

Update on my Daikin HP.

so, apparently a number of these Daikin HT ASHPs were sent to the UK with insufficient refrigerant gas. Today, My Daikin engineer took all the gas out, weighted it and it was significantly low on gas. He and the Tech specialist think this is why my unit hasn’t been performing as it should.

The unit is now heating back up, took around 4 hours to complete the weigh gas and refill.

I had noticed even in warm temps I.e. 8 to 12c my unit will still run defrost cycles, so I’m hoping not to see that behaviour over the next few days. Though next winter may be the test in reality to confirm if the correct gas level will sort it out.

anyway a bit of optimism now 😀

👍

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