By definition these will be considerably less efficient than the usual ones. The greater the difference in temperature between collector, the less efficient the thing will be.

Tony, things have moved on a bit with the new refrigerants, heat pumps are now very efficient above 55deg+. IE CoP is routinely well above 3, for which you used to require UFH temperature but can now use radiators.

Several models can give better CoP at 70-80degC than the older models used to get at much lower temperature, eg 2.5-2.9

As Nigel said, this is aimed at overcoming the barriers for many people who have radiators and can't swap to UFH.

Other candidates include
Daikin Altherma 3H HT
Vailant Arotherm Plus

The use of R290 refrigerant also avoids the GWP in case of refrigerant leaks, which was a problem with the older R410A heat pumps.

Obviously the 2nd Law still applies, so the new models give even better CoP (over 4) if you do have UFH, or for heating lower-grade DHW.

Just got some quotes and the new models were on long delivery times due to supply chain etc, so the installers were keen to quote for the older models.

Rob I have been trying to disentangle this and I think you are correct - they don't include loads for controls and extra pumps and standby.

The CoP is : heat output divided by electric input, at a specific outdoor temperature, and a specific CH water temperature

The SCoP is an average over the year for all the different daily outdoor temperatures in a specific climate zone such as West Europe, and at a fixed CH water temperature. This is the one to look for on the data sheet and is certified in the MCS register.

The SPF is an average over a year, over the different outdoors temperatures each day, and also accounting that
your weather compensation will run the CH at a lower (better) temperature on mild days and higher (worse) temperature only on really frosty days. This is specific to your house, and should be better than the SCoP.

We rarely see CoPs above 3.5 with 30C indoors and 10C outdoors

I would love to see heatpumps working well and widespread but concerned about over egging

Posted By: Ed DaviesTangentially, John Cantor has some interesting thoughts on heat pumps for DHW:
https://heatpumps.co.uk/2021/08/07/heat-pumps-and-domestic-hot-water/

Thanks for the link, Ed. Interesting article and its suggestion of Ecoforest - I'd never heard of them before but they seem interesting. The concept of desuperheaters in heat pumps is new to me.

Ed Davies 1 hour ago quote
Tangentially, John Cantor has some interesting thoughts on heat pumps for DHW:

https://heatpumps.co.uk/2021/08/07/heat-pumps-and-domestic-hot-water/

I agree with djh & revor; a good article.
I particularly concur with his comment regarding space heating only HPs. coupled with point of use DHW. It seems a pity that cheaper A/A HPs have been omitted from the latest Boiler Upgrade Scheme in favour of complex A/W systems. There is too much emphasis IMO, put on DHW which can be easily supplied from other sources.
I do wonder if these over complex, expensive dual purpose systems are favoured more to please the plumbing/heating industry and the manufacturers; who simply want to sell more stuff, rather than thinking of the buying public.

Posted By: owlmanIt seems a pity that cheaper A/A HPs have been omitted from the latest Boiler Upgrade Scheme in favour of complex A/W systems.

If it is a boiler replacement scheme I suspect that A/A HPs are omitted because if you are replacing a boiler that presumes there will be a radiator or UFH CH system so a A/W HP would be a (more or less) direct replacement whereas an A/A HP would require extensive rework of removing rads. and installing air ducts.

Peter_in_Hungary 2 hours ago quote
If it is a boiler replacement scheme I suspect that A/A HPs are omitted because if you are replacing a boiler that presumes there will be a radiator or UFH CH system so a A/W HP would be a (more or less) direct replacement whereas an A/A HP would require extensive rework of removing rads. and installing air ducts.


No Peter: for new builds perhaps, but in existing homes all that is required is some of the many variants of wall or ceiling hung indoor units.
I agree that is probably what is behind SOME of the flawed thinking. However, to attach a state of the art hot water distribution device, i.e. HP, onto what may be dubious ageing pipework with most likely inadequate insulation seems crass stupidity.

Posted By: Peter_in_Hungary

Posted By: owlmanIt seems a pity that cheaper A/A HPs have been omitted from the latest Boiler Upgrade Scheme in favour of complex A/W systems.

If it is a boiler replacement scheme I suspect that A/A HPs are omitted because if you are replacing a boiler that presumes there will be a radiator or UFH CH system so a A/W HP would be a (more or less) direct replacement whereas an A/A HP would require extensive rework of removing rads. and installing air ducts.

My suspicion is that A/A HPs are excluded because they're typically sold/marketed as aircon with heating, rather than just a heater and the government probably wouldn't want to be seen to be subsidising air conditioning systems. How they'll deal with A/W HPs that also provide cooling I suppose is a question to be left dangling...

And here is the towering absurdity of current policy.

I could have installed a multi-split air conditioning system for about a third of the cost of an A2W heat pump. Yes it won't do my DHW, but that's less than a third or so of my gas usage, so we're addressing the main source of consumption.

That air conditioner would perform significantly better than (i.e. reduce my space heating emissions and costs by more than) an A2W system. Installation would be less disruptive than an A2W, particularly if the latter would require underfloor heating, and especially because installing water tanks is one of the main PITA.

But that option receives no government support, presumably because they worry I'd use it for cooling.

Now, I'm in Scotland. The number of days I'd want cooling is neglible. And even if I were in the south of England, the number of days it would be used to cool is small, and the performance of the conditioners is so good, that the electricity usage for cooling would be much smaller than the saving on heating related energy usage. We're a pretty cold country on average.

And, if cooling is a problem, how hard can it be to ask manufacturers to sell air conditioning systems with the cooling functions removed from the control units? Sure owners could buy the 'full' control units, but I bet hardly any would bother. If that were a worry, it wouldn't be -that- difficult for manufacturers to modify the units slightly so that the cooling functions were permanently disabled.

Rant over.

Posted By: owlman+1
Absurd is the right word

Seems to be the appropriate description for pretty much any time government touches buildings. I may be prejudiced by just having read the latest weekly Grenfell summary :( :( and having seen an item about people whose flats have been covered by scaffolding and plastic film for six months. :(

Posted By: Ed Davies

Posted By: gravelldI like the concept of a HP as a 'pre warmer' to a low temperature, … Would need periodic legionella cycles though.

Only if the it's the actual DWW (domestic warm water) that's stored though. If the incoming cold goes through a heat exchanger of some sort (internal large-area coil or external plate heat exchanger) then the volume exposed to intermediate temperatures is small and completely changed on every use so the legionella risk (already small) is pretty much eliminated.

And that would include UVCs right? Given these appear to be the most commonly specced storage unit now, makes you wonder why the legionella cycles are still advised (or maybe I have misread).

Oh... I thought the reason UVCs ran at mains pressure was that the mains passes through the energy storage (water) in a coil? A bit like a TS, only unvented? Sorry, I need to do some more research.

Posted By: GarethCAnd here is the towering absurdity of current policy.

In fact, come to think of it, it's even worse than just excluding A/A heat pumps from subsidy schemes, isn't it?

Say I installed a top notch A++ rated air conditioning multi split system, thereby reducing my heating related emissions significantly. Am I right that, due to the (almost certainly unused) ability to cool, I wouldn't even get an uplift to my home's EPC?

In which case, the current system actually actively discourages A/A. Is that right?

Posted By: gravelldApologies, think I get it now - the entire tank is under pressure from an incoming mains feed.

These cylinders are often referred to as Megaflow akin to calling a vacuum cleaner a Hoover.