Planning for an ASHP installation in South East England
Hi all. I am considering converting from a mains gas boiler to an ASHP, and long term cost is obviously important. I understand that the cost of electricity has shot up compared to oil, which can certainly pose a dilemma for those with oil tanks. For me using a gas boiler, the rising cost of gas seems to make the proposition to move to an ASHP no worse that before. Wholesale gas prices are rising, and it is the cost of gas that is pushing up electricity. I got a quote from British Gas for gas or electricity only tarrifs in the South East:
8.06p per kWh gas
31.8p per kWh electricity
I think with with a COP of ~3.95, the prices are the same. I am considering the Ecodan R32 Ultra Quiet PUZ Monobloc Air Source Heat Pump (11.2kw), and indications are that my property might be fine with 40oC flow temperature, so I hope the annual average COP of 4 would be achievable. The South East is fairly warm on average, so ASHP vs GSHP is a tough call for efficiency, ignoring the installation price.
Obviously I am ignoring the large outlay cost of the ASHP, but I am putting this down to “doing the right thing”, going green and understanding that I am paying a premium to be a relatively early adopter. Indications are that the tax system might help reduce the taxation on electricity and move to emitting fuels. I don't want to put a long term cost burnden on my bills though, or reduce the value of the property.
Regarding CO2 emissions, I am working on:
0.184kg of CO2e per kWh Natural Gas (ignoring boiler efficiency)
0.0582kg of CO2e per kWh of electricity (2020) with heat pump COP of 4.0
0.038kg of CO2e per kWh of electricity (2023) with heat pump COP of 4.0 https://www.icax.co.uk/Grid_Carbon_Factors.html
It seems like in 2023 my heating will be 20% the emissions of my current gas boiler.
Does all this sound reasonable, or am I missing some unknown factor that detaches my cost and emissions estimates from reality? I guess the average COP is the main unknown.
Also is the Ultra Quiet really 42db at 1 metre under significant load? E.g. heating up the hot water? My heat pump will be about 5 metres from the nearest bedroom window, I would like that in the summer when the hot water is heating up at night, that the pump isn't audible in bedrooms with windows open for me or my neighbour. Are there any better ASHP around 12KW than the Ecodan?
I would value your input.
Hi @ollie and welcome to the forum.
I think the prices you have are fixed rates, which are a lot more than the current cap, especially for gas. The current cap is roughly 20p/4p electricity/gas, so about a 5:1 ratio. I'm not sure that will be a lot different after April.
You may be able to achieve a SCOP of 4, but that's definitely at the upper end of what most people get. Living in the SE will help though.
In terms of C02, some people say you should calculate the C02 reduction based on 100% of your ASHP electricity being generated by gas. This is because gas is used at the margins to flex production up and down and your extra few kWh will, in reality, be generated by gas. I don't agree with this approach but it's quite a common one amongst heat pump and EV 'hesitant' folks.
The ultra quiet Ecodan will be just that. Unless you live in an extremely remote place with no traffic, wind or any other outside noise and you don't have a fridge, freezer or any bathroom fans you will hardly notice the ASHP noise unless you really try. You can also time your HW to come on when you want. And when heating water in the summer, the ASHP isn't working particularly hard.
I think unless the gas/electricity price differential changes a lot then you will struggle to beat gas for price. But it's good fun trying and however you work it out, you'll be emitting less C02.
Good luck and please ask more quesions.
@kev-m thanks for the reply. Regarding the pricing of energy, the rates I looked up were British Gas single fuel. The two tarrifs offered were "The Green One v9" (which seems like green washing on a gas tariff) and "The Fixed One v9", both of which are 8.06p per kWh. I did a search on www.moneysupermarket.com and found on the cheapest tariff that the electricity is about 5.4 times that of gas. This compares with 3.95 ratio for British Gas. I also learnt that British Gas are a rip-off (although I knew that already).
The property it is going into is a 1960s house with retrofitted cavity wall insulation, good loft insulation and double glazing. I am planning to have an extension done and that part will be very high spec insulation, UFH, maybe triple glazed. The older parts of the house will be radiators. I am running an experiment right now with dropping the heating flow temperature to 45C for a few days, and we hit -1C outside and all rooms maintained temperature. There is a couple of rooms that were very slow to reach temperature, so have little margin, but those are a bedroom with a small single panel radiator and a bathroom towel radiator. Both will be easy to upgrade.
Regarding the CO2, I can see the thinking behind considering that extra load will be gas based, although I think this short term view doesn't really reflect ongoing changes to the energy mix. The carbon ratio of the energy keeps dropping and as extra capacity is added to meet the new demand of EVs and heating, much of this will cleaner. Certainly with an extra 30GW of wind coming on by 2030, there could be times in the summer that CCGT would be off entirely, much the same as coal is now. Here is hoping. I found
Some really interesting info in that attachment.
That's good that your heating works at 45C at -1C outside. A couple of new radiators will be an easy upgrade.
I think it will be hard to beat gas for price with an ASHP in the foreseeable future, although it may get a little less hard.
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