@alan22 Dont despair Alan, your premise is sound. Be sure of your heater output (is it 3 kW) and use two if necessary. The experimental evidence will be the most accurate measurement of heat loss. Obviously a larger volume will take longer to reach a stable temperature.

@heacol Brendon, I dont want to get into a disagreement with you and I have no problem with you looking for work on the forum but what you are suggesting isnt possible without ultra low flow temperatures requiring a large amount of radiator area and or expensive triple/fan assisted radiators. These arent possible/cost effective in most retrofit homes.

I just happen to have the COPs for two Acond HPs to hand, they arent bad heat pumps but even with 35C flow, at -3C OAT the best only just gets to a COP of 4, and thats before any losses in the circuits. The only heat pumps that get anywhere near a SCOP of 5 on heatpumpmonitor.org run at about 30C. If you insist you can do better then get some of your installations monitored on there and prove it, Im sure that would drum up a lot of business.

@bontwoody mmmm theory is a wonderful thing, but rarely follows through in to practice. You are only looking at a very small piece of the puzzle. Unlike high temperature heating, low temperature heating is far more complex than lines on a graph produced in a laboratory.

By the way, all heat pumps using the same gas have near identical theoretical performance, any difference is a manipulation of figures. The difference comes with the system design and control. With the same heat pump, get it wrong, and your SCOP will be below 2, get it right, and it can be above 6 at exactly the same installation cost, maybe even lower.

I am not looking for work, I have more than I can handle. There are over 150,000 badly installed heat pumps out there and more are being added to the list every day.

Remember folks, don’t let striving for the best get in the way of accepting the good….

@heacol actually Acond use R290 instead of R32 but I don’t think that materially changes the point I am making. 

I am a scientist and so trust empirical not anecdotal evidence. 

Posted by: @heacol

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@bontwoody it is easy to get SPF's above 5 in ANY house, including old draughty solid stone buildings, I have hundreds to prove it. Get the design and operation right, and it will work. Get it wrong, like most, and it will not. Simple.

If you follow the manufacturer's recommendations, you are 99% guaranteed to get it wrong.

So how does this work? can I hire a system designer then get my plumber to fit? or am I tied in to a company to do all? at the minute it seems a bit like witchcraft just to figure out what and how to install. 

Posted by: @alan22

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Posted by: @hughf

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Posted by: @bontwoody

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@hughf I guess you just have to think of them as under floor heating on the wall! 😉

good luck convincing anyone that their radiators will never be warm to the touch... That's why I stick with 38.5 as the hot end of my WC curve - it's just easier that way. Also, my fan coils switch off below 37 ish degrees, flow temperature switch inside.

 

It's a fair point, I'm used to coming in from work and lighting a multi fuel burner and feeling skin burn, the idea of tepid radiators is not exactly appealing but.....I have a friend with underfloor heating, when you go into his house it;s the same temperature all the time, never gets hot exactly but it never feels particularly cold, it's a different sort of environment, one I'm only starting to understand, how you turn that up a bit when it's cold though...

 

As I said, you don’t need to design for 30 degree flow if you don’t want to. I designed for 47@-5 but ended up running them a bit warmer as my wife wanted it 22.5 in the house.

As long as you don’t do something daft like design for 55 flow all the time, if you want warm radiators, have warm radiators….

We’ve ended up with a larger house, heated to a more comfortable temperature, whilst spending a bit less per day than we did before on gas. As a bonus we no longer burn 18MWh of gas per year and don’t have a boiler in the house taking up space. Win-win all round….

And no, I couldn’t tell you what my COP is…. But it works, and it isn’t bankrupting me.

Posted by: @alan22

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So how does this work? can I hire a system designer then get my plumber to fit? or am I tied in to a company to do all? at the minute it seems a bit like witchcraft just to figure out what and how to install. 

the best thing I can suggest is to hire heacol (but says he is vastly overworked and there is only 1 of him after all)

the next best thing is to find someone from the HeatGeek qualified list and talk to them.

if you want a BUS grant, you are tied to a contract with an MCS company to do the whole thing. If you don't want a BUS grant there are other ways.. where are you on that?

I don't know what a BUS grant is, I don't qualify for grants as far as I know.

@alan22 if you’re replacing a fossil fuel boiler you qualify: https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus

Posted by: @editor

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@alan22 if you’re replacing a fossil fuel boiler you qualify: https://www.ofgem.gov.uk/environmental-and-social-schemes/boiler-upgrade-scheme-bus/p >

I'm in Scotland, not aware of a similar grant scheme here. 

For a moment there I thought I was getting free public transport 😀 

@alan22 🤣 

Here’s the Scottish scheme: https://www.homeenergyscotland.org/heat-pumps/grants-and-funding/