Posted by: @wintergreen

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I will need a device that can output 55 degrees at a market-leading COP.

You could add additional emitters to that area so that a lower flow temperature would work. 

Phil

@Wintergreen,

apologies if others have covered...

is your total heat loss really 43kW?  That's huge; the biggest domestic ASHP I've seen is 16kW. 

55 degrees is high for any ASHP; most will do it but the COP isn't going to be a lot better than 2, even with the ones touted as HT.  I think (don't know for sure) that while these units can do high temperatures, the COP is not necessarily better than 'normal' units.  My ASHP (14kW Ecodan) will output 55 degrees all day at -2 but the COP will be around 2.  One thing you rightly pointed out is to be careful with defrosts, which will lose you at least 10-15% of capacity below 2-3 degrees ambient. Also be careful with the rated outputs; they are often lower than the badged value at low ambients. 

Remember an ASHP can only output at one LWT at a time. If the upstairs doesn't need 55 degrees LWT then you might be better with one for the downstairs and another for everything else.  If your heat loss really is 43kW you're going to need multiple (or commercial grade) ASHPs anyway. 

Finally, I don't know much about ufh but you do have to make sure it can emit enough heat at the flow rates an ASHP needs, which are normally higher than gas/oil systems. 

Hi – I have a 16kW Daikin HT ASHP – system details below – which we’ve been running since August 2020. We have a combination of UFH and radiators. The system we have can only be used with a basic Daikin controller which gives no information on consumption or COP. I’ve managed by a process of elimination to work out consumption data and to date the heating consumption (not incl. DHW) is as below. Heating has been off since the start of April, and I’ve used this past winter’s figures for this next winter:

During 2021 and early 2022 we were using the system as if it was a gas boiler, doing everything wrong – room stats and zoning, running at high temperatures (there’s a blending valve on the UFH), no weather comp. It coped and was happy producing LWTs up to 70 or so for the radiators (!) but was obviously very thirsty in terms of consumption. This past winter with the help of the folks on this forum I’ve corrected these errors and obviously seen a big difference in consumption. I’m not actually running the HT capabilities of the system now but the house is quite comfortable; we possibly didn’t need a HT system but that’s what was recommended and we are just trying to run it as efficiently as possible.

I realise this doesn’t help much with the topic specifically but just wanted to add some insight into my Daikin HT journey particularly in respect of consumption. I’m more than happy to answer any queries about our experiences with the Daikin HT system.

System details:

• An outside unit - Daikin ERRQ016AAV1
• An inside unit - Daikin EKHBRD016ADV17
• A 500L thermal store - Daikin EKHWP500PB (no immersion heater installed)
• A very basic Daikin controller EKRUAHTB
• Manufacturer stated COP’s are 2.11 at -7, 3.01 at 2, 4.26 at 7, and 4.67 at 12C
• We have a 6.1kWp PV installation with 20 SW-facing panels and a SolarEdge SE6000H 6kw inverter, which produces around 8MWh pa, 3MWh of which goes back to the grid

Many thanks for the helpful responses. 

@marzipan71 I'm still struggling to get figures out of Daikan. It's mystifying to me that suppliers aren't more transparant as to the key performance parameters of their products. Do you know what the LWT is for those COP figures?

@kev-m apologies - that heat loss figure was not quite right. The total heat loss in the rooms we use (!) is 18,000. But 5 of those are bedrooms, which are in practice scarcely heated, and even then only for a short time in the morning and evening.

For anyone interested, this is the result of my researches to date:

I am slightly surprised that there isn't a closer relationship between these COPs and the MCS SCOP figures, but of course they only cover a small part of the device characterisitics.

My current plan (it changes daily) is to go with a pair of Arotherm Plus 7kW pumps - one dedicated to the UFH and the other for rads around the house. I will post separately about my slightly eccentric DHW plans, because it would be great to get some input on those.  

@wintergreen here's what I have - apologies if it's too small to read. I was left two sheets by the installers - with completely different COP figures for the same pieces of kit! First file has the figures I quoted above. Agree about difficulty getting data - I have no way of monitoring COP via my controller as other users are able to do with their kit.

...also this set of figures - same kit!