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I have installed a 9kw solar system earlier this year.

I’m looking to move away from gas and replace my home boiler with something more efficient. My boiler is over 20 years old.

I heard about some government grant recently to fit a heat pump.

Can anyone give any advice on what I should have installed.

I live in between Hull and York.
 

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Do you want to keep your radiators? Are you happy to replace with low temperature radiators, or keen to get rid of them altogether?
 

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The issue with keeping existing radiators is that heat pumps inherently become less efficient the higher the temperature they have to operate at. If your existing radiators were sized to work at a temperature of 70C, they won't be very effective at 40C. And for best efficiency you might even want to try and get that down to 35C or so. Bear in mind that whether ground, water or air source the source temperature is unlikely to be much above 8-12C, 16C at best on a spring or autumn day with an air source heat pump when you want just a wee bit of heating.

So in summary heat pumps work most efficiently with "low temperature" heat emmiters - either specialised low temperature radiators or underfloor heating (or perhaps "thermaskirt").

Personally I looked at various alternative options that might qualify for the RHI, but ended up installing Air-to-air heat pumps instead, even though they don't qualify for the incentives. They're more efficient and (much) cheaper to install, especially as a replacement for the storage heaters we used to have. And it means I don't have to have radiators taking up wall space. They don't do anything to provide hot water though, so that stays as an immerser heated tank, for now, but with a "solar diverter".

Is your 9kW system single phase, or three phase? Mine unfortunately is three phase, which makes finding a diverter that will make best use of the generation a bit of a pain, since they're inevitably single phase, so we don't get the best use out of it.
 

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Have done it, if you want grant you need a registered installer. Get an energy assessment who will confirm if you need any insulation before being eligible. Look at fitting underfloor insulation to suspended floors, you will probably have to have cavity wall insulation fitted. We have solid walls and I added 50mm cellotex to many of the walls internally.

We had new radiators throughout, a huge 250l hot water tank, 100l buffer tank and a Stiebel Eltron WPL 25A heat pump, from a 40 year cast iron boiler.
WPL 25 A Air | water heat pumps of STIEBEL ELTRON

Used about 25,000kWh of gas last, year now about 6,000KWh of leccy up from 2,500kWh but with some for the car and supply from a 3.6kW solar system. Works brilliantly. Hard work, takes up loads of space but I would not go back.

More info if you want it.
 

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Cost us about £18k, much cheaper than moving as an option and we get RHI payments over 7 years of £10,600, so the system will then have cost about £7k.

Be cautious of systems and how they cope with cold weather, we have a system that has adequate reserves, it does not need to use resistive heating for water nor for de-icing, all of our heat has been from the heat pump element. This heat pump is also very quiet. It is set up to heat up water at midday rather than during the night so that the air temperature is highest then and our solar is generating maximum power.

Installer Search - Microgeneration Certification

Installers here.
 

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I’m single phase.

Thanks for the reply.

I have a 4 bed detached house. Would I need to get new heaters in each room. Sounds expensive.
One (cheaper) possibility if your boiler is still in decent nick would be to keep it but add an Air-to-air heat pump or two to provide background heat and so reduce how often you need to run the GCH.
 

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40 year old boiler just means it was a decent solid cast iron job with minimal electronics. Will probably last forever with minimal TLC and replacement of a few minor items like thermostats.

Suggestion to supplement with air to air heating really is very sensible way forward and will give much better COP than trying to heat water and use old radiators.
 

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40 year old boiler just means it was a decent solid cast iron job with minimal electronics. Will probably last forever with minimal TLC and replacement of a few minor items like thermos
I agreed with this for a long time, but the pilot flame kept running and we used more gas than others. Our insulation has helped but moving to ASHP has been very successful.
 

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My "40 year old boiler" is only fired up about 10 times per year. So the pilot supervision thermostat has an off switch with a good clean snap action, toggle switch, silver contacts. I turn it back on and relight the pilot for the very rare occasion its needed.
 

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Suggestion to supplement with air to air heating really is very sensible way forward and will give much better COP than trying to heat water and use old radiators.
COP, from ASHP

DHW - this year we have generated 2.045MW of hot water for 0.445MW of power
CH - 12.419MW of heating for 1.925MW of power

Total power used is 3.644MW from meter includes pumps, controls etc.

Not sure how you get a better COP?

During the summer the ASHP heats the water at midday, on sunny days the solar panels have plenty of power initially and only need a top up for the final heat pump at 50c. During the winter, wind is the power source via BULB.

Gas is gas, how much longer do you want to burn gas, I have given up with it.
 

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I think i could put this in the lounge and some of the heat would go upstairs as well. I'm assuming it needs to be on an extenal wall? Maybe switch off the GCH radiators in the lounge and move the themostat to a bedroom upstairs?
 

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How much is installation an can i diy install?
No to that one. Installation should be around £600-800 (probably +VAT). If you have it downstairs in the lounge or hall and keep doors open to allow the heat to "spread" you can switch off your heating a bit earlier in the spring and on later in the autumn, and even in winter it should reduce how much gas you use. If it's particularly cold outside you can switch back to just gas (although CoP is probably still worthwhile even then). As you say, you'd have to turn down the lounge radiators and probably relocate the thermostat - and/or switch to something like individual "smart" TRVs (something like the Evohome or Tado), which are probably worthwhile anyway..
 

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COP, from ASHP

DHW - this year we have generated 2.045MW of hot water for 0.445MW of power
CH - 12.419MW of heating for 1.925MW of power

Total power used is 3.644MW from meter includes pumps, controls etc.

Not sure how you get a better COP?

During the summer the ASHP heats the water at midday, on sunny days the solar panels have plenty of power initially and only need a top up for the final heat pump at 50c. During the winter, wind is the power source via BULB.

Gas is gas, how much longer do you want to burn gas, I have given up with it.
Something odd about those COP you imply based on the raw numbers. Care to give some more details of how you measure thermal output to water, eg instruments for measuring flowrate if water and delta TS. What temperature do you set the DHW storage to.

Could you provide a sample instantaneous calculation for say a 5 degree C 85%RH winter day.
 

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COP coefficient of performance,
1kW of power gives 5kW of heat so COP is 5, does not include peripherals like circulating pumps and control panels.

You are now getting different opinions and you need to work out what is best for yourself. If you have space in a garage or utility room for DWH tank and a buffer tank - great.

If you just want a partial solution too top up Air to air may work, if you want DHW cheaply ( we get 2kW of hot water for 0.5kW of power and much of this is solar) then a ASHP is best.

Some ASHP require resistive heating (1kW for 1kW) to defrost and for some DWH. If the heat pump is not larger enough, some people have use incorporated resistive heating to top up. We have never used this except when an engineer switched it on, I changed back quickly.

" Doing so will be challenging, said the Committee on Climate Change, meaning the end of petrol and diesel cars and gas boilers, " yes, gas boilers should be history. Personally I eliminated petrol and gas last year.
 
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