@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

@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).

Posted by: @haggistrap

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@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? 

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.

@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!

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

@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!

@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.

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.

@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 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.

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 😀

@haggistrap at least they've found the potential source of the issue. Fingers crossed that this will solve the issue. Keep us posted and updated.