Heat Pump Questions

Telegraph_Sam

Likewise I visited an establishment that runs these boilers. I could imagine that the running costs in Central Scotland could be competitive. Against which there is the investment required and the debateable environmental economics. Swings & roundabouts

QrizB

doodling said:

A gas fired (combined cycle) power station is around 60% efficient at best and you can assume a 3% loss on the grid so overall 58% at best.  1kWh (thermal) of gas therefore gives 1.74kWh at the output of a heatpump with a COP of 3. Or 0.95kWh at the output of a gas boiler.

Alternatively, today (with over 50% of the grid's electricity coming from fossil fuels) the carbon intensity of grid electricity is ~250g/kWh (from Drax). With a COP of 3 that's around 83g/kWh.

Burning natural gas produces about 227g/kWh (UK Gov figures).

Reed_Richards

Telegraph_Sam said:

That seems to agree with my conclusion that the arguments in favour of HP's are environmental rather than economic, and that there would be quite a price to pay for switching 

It's wrong to assume that everybody has access to mains gas.  If you do then I agree that switching to a heat pump could not be justified economically at present.  But if you have electric storage heaters you should be able to reduce your heating costs by switching to a heat pump and if you use oil or LPG then I don't think you would be worse off with a heat pump.  Now the cost of installing one is considerable but fortunately this has been heavily subsidised,  After March 2022 that subsidy will be reduced.   

doodling

Hi,

QrizB said:

doodling said:

A gas fired (combined cycle) power station is around 60% efficient at best and you can assume a 3% loss on the grid so overall 58% at best.  1kWh (thermal) of gas therefore gives 1.74kWh at the output of a heatpump with a COP of 3. Or 0.95kWh at the output of a gas boiler.

Alternatively, today (with over 50% of the grid's electricity coming from fossil fuels) the carbon intensity of grid electricity is ~250g/kWh (from Drax). With a COP of 3 that's around 83g/kWh.

Burning natural gas produces about 227g/kWh (UK Gov figures).

T⁰he figure you quote for gas is not from UK gov as the note in your source makes clear. The correct figure for a condensing boiler is around 0.204kg/kWh based on 0.18316kg/kwh from https://www.gov.uk/government/publications/greenhouse-gas-reporting-conversion-factors-2021 and assuming 90% boiler efficiency.

If you want me to use the Drax methodology then the CCGT efficiency needs to drop to 46.7% or if we believe their CO2 figures 394g/kWh (I make it 392g/kWhbased on the gov figures and 46.7% efficiency). Taking into account a COP of 3 then making electricity and using a heat pump, rather than burning gas emits 131g/kWh vs. 204g/kWh. I haven't added a transmission efficiency into that but it won't make a huge difference.

I fully accept that using a heat pump allows you to use wind/solar/nuclear so the average carbon intensity is less, but until we stop using gas for electricity generation then I think a marginal approach based on gas electricity generation is the most valid, simply because that reflects the reality.

Telegraph_Sam

Can these calculations all be condensed into a simple comparison of gas combi boilers as is with ASHPs' and GSHPs' performance from both environmental and economic points of view, or are there just too many assumptions that have to be made and variable factors that have to taken into account for the exercise to be viable?

QrizB

doodling said:

I fully accept that using a heat pump allows you to use wind/solar/nuclear so the average carbon intensity is less, but until we stop using gas for electricity generation then I think a marginal approach based on gas electricity generation is the most valid, simply because that reflects the reality.

I disagree with this point of view, as should be obvious from my previous post.

doodling

Hi,

QrizB said:

doodling said:

I fully accept that using a heat pump allows you to use wind/solar/nuclear so the average carbon intensity is less, but until we stop using gas for electricity generation then I think a marginal approach based on gas electricity generation is the most valid, simply because that reflects the reality.

I disagree with this point of view, as should be obvious from my previous post.

The reality is that if I add a 6kW (electrical) heat pump to my house today then the increase in electricity consumption will be met (in the short to medium term) by burning more gas, not by ramping up unused wind /solar / nuclear capacity (because there is none).

In the longer term then one might hope that an increased demand for electricity might prompt more construction of low carbon generation but that is very much a second (or third) order effect.

I think we will have to agree to disagree. 😀

Reed_Richards

doodling said:

The reality is that if I add a 6kW (electrical) heat pump to my house today then the increase in electricity consumption will be met (in the short to medium term) by burning more gas, not by ramping up unused wind /solar / nuclear capacity (because there is none).

This makes no sense unless you explain what came before the heat pump.  

GunJack

matelodave said:

I'd argue that a heatpump is no more greener than a gas boiler until ALL our leccy comes from renewable sources.

Around 50% or more is still produced by gas and by the time it's fought it's way through the national grid the efficiency must be well below that of burning gas at around 90-95% in a condensing boiler.

IMO if it make you feel all warm and fuzzy to go green then thats OK but dont' imagine that its going to save you money.

I installed a heatpump to replace manky old storage heaters and because I didn't want a big oil or gas tank in the garden as we dont have mains gas., not because I thought it was green. However, that said, we've been pretty lucky until SYMBIO went bust as we've always managed to get quite low priced leccy.

It's now jumped from 12.25 to 21.25p/kwh which will add around £700 to our annual energy costs. Mind you, the heatpump probably only accounts for about 4000kwh or £360 of the increase, the rest is general use domestic consumption. 

4000kWh of leccy would double my annual consumption!!!  My nice, efficient BoilerMate and condensing gas boiler only takes 8,000kWh of gas for all hot water, heating and hob cooking in a 3-storey, 4-bed house with 3-4 adults. A heat pump installation makes no economic sense for me, and my house IS well-insulated (built 2007).

matelodave

GunJack said:

matelodave said:

I'd argue that a heatpump is no more greener than a gas boiler until ALL our leccy comes from renewable sources.

Around 50% or more is still produced by gas and by the time it's fought it's way through the national grid the efficiency must be well below that of burning gas at around 90-95% in a condensing boiler.

IMO if it make you feel all warm and fuzzy to go green then thats OK but dont' imagine that its going to save you money.

I installed a heatpump to replace manky old storage heaters and because I didn't want a big oil or gas tank in the garden as we dont have mains gas., not because I thought it was green. However, that said, we've been pretty lucky until SYMBIO went bust as we've always managed to get quite low priced leccy.

It's now jumped from 12.25 to 21.25p/kwh which will add around £700 to our annual energy costs. Mind you, the heatpump probably only accounts for about 4000kwh or £360 of the increase, the rest is general use domestic consumption. 

4000kWh of leccy would double my annual consumption!!!  My nice, efficient BoilerMate and condensing gas boiler only takes 8,000kWh of gas for all hot water, heating and hob cooking in a 3-storey, 4-bed house with 3-4 adults. A heat pump installation makes no economic sense for me, and my house IS well-insulated (built 2007).

If you use 8000kwh of gas for heating/hotwater (lets ignore cooking) then with a heatpump (SCoP of 3) you could expect to use around 8000/3 = 2600kwh of leccy so you need to compare the cost of 8000kwh of gas with 2,600kwh of leccy.

However no one is suggesting that a heatpump is less expensive to run than mains gas for the same equivalent amount of heat because it's not. The debate has swung around to whether it's greener to use one instead of of a gas boiler and the consensus is that it probably could be and no doubt will be at sometime in the future if we stop using fossil fuels to generate leccy. I've no doubt that there'll be some unintended consequence of going down that road.

Chucking out a perfectly serviceable gas boiler and spending £10-!5k on a heat pump  and hopefully getting £5k back in a grant and then spending a bit more on your energy costs doesn't really make economic sense for most people even if it doesn make you feel greener and more virtuous.

However if leccy came down to 10-15p/kw  (or even 20p/kwh)and gas went up to say 10p/kwh then it could be worth doing the sums although theres would be millions of very unhappy people out there who've got gas boilers, so I cant really see it happening.