The new SAP has a revised carbon intensity for grid electricity (set in the consultation at 0.591 kgCO2/kWh, up from 0.422). This has a big impact on the resulting carbon emissions from heat pumps, in most cases making them higher than emissions from the worst boiler you can legally install. This goes for both air source and ground source.
You can see from the graph above that at a grid carbon intensity of 0.591 even a GSHP with a COP of 4 is struggling to outperform an 86% efficient gas boiler. The real world COPs seen at Barratt’s Chorley scheme (2.6 for GSHP) and recent field trials by Mitsubishi (3.0 – 3.4 for ASHP according to a letter from Mitsubishi in the latest CIBSE mag) mean that heat pumps would emit significantly more carbon than the boiler.
And yet in the low carbon transition strategy, DECC state that heat pumps will be eligible for the Renewable Heat Incentive (pdf – see para 1.22), rewarding them for being a renewable energy source! What the hell are they thinking?
Here’s how I did the numbers:
Here’s the baseline using an 86% efficient gas boiler:
Primary energy | Assumed efficiency | Useful energy | CO2 kg/kWh | kgCO2/yr | |
Space heating | 3663 | 86% | 3150 | 0.206 | 755 |
Water heating | 3256 | 86% | 2800 | 0.206 | 671 |
Electricity | 2800 | 100% | 2800 | 0.591 | 1655 |
Total kgCO2 | 3080 |
For the heat pump scenarios I’ve assumed that all space heating comes from the heat pump, along with 60% of the domestic hot water load. The remainder of the DHW load is met from an immersion coil. Here are the numbers for a COP of 4:
GSHP | Backup systems | ||||||||
Useful energydemand (kWh) | Demand met (kWh) | Primary energy | CO2 kg/kWh | kgCO2/yr | Demand met (kWh) | Primary energy | CO2 kg/kWh | kgCO2/yr | |
Space heating | 3150 | 3150 | 787.5 | 0.591 | 465 | 0 | 0 | 0.591 | 0 |
Water heating | 2800 | 1680 | 420 | 0.591 | 248 | 1120 | 1120 | 0.591 | 662 |
Electricity | 2800 | 0 | 0 | 0.591 | 0 | 2800 | 2800 | 0.591 | 1655 |
Subtotal HP CO2 | 714 | Subtotal backup CO2 | 2317 | ||||||
Total kgCO2 | 3030 | ||||||||
Saving | 1.6% |
Electric heating is getting a lot of attention, particularly off the back of David MacKay’s book. But until the grid is significantly decarbonised (a long way off) we shouldn’t be putting any incentives in place for heat pumps.
Note that my numbers assume a heat pump is only being used for heating (which is typical of domestic installations). If you use a GSHP for heating and cooling the picture changes and you can save significant carbon depending on the site.
What about off gas grid?
It depends on the alternative fuel. If it’s delivered gas, the picture changes a bit, but not drastically. For a COP of 3.2 against delivered LPG, you get a carbon savings of about 5% for example. For oil, it’s better at 11%. See this post for more about comparing with heating oil.
But the point I was really trying to make is that heat pumps should not qualify for any incentives as a renewable energy until the carbon intensity of the grid comes down. As soon as that happens, great, let’s put in as many heat pumps as the grid will bear. But until then, they should be treated like any other fossil fuel derived heating.
From what you say, it sounds like GSHP could be a viable alternative off gas grid, and so should at least receive support in this case (in practice, I doubt many people would install a GSHP where grid gas is available).
However I also agree with Robert below – that it would be short-sighted to use the current CO2 intensity of the power grid in assessing a technology that could last for decades (especially when estimates of the grid intensity are as volatile as oil prices).
Interesting article and I can see youve got your sums right. I have been involved in the SAP consultation and everyone thinks it is ridiculous to use this new figure for the future carbon emissions of a heat pump.
All the electricity providers are legally bound to reduce the electricity emissions in 2020 by 30-40%. Targets beyond this are even more stringent.
An average heat pump supplied by us is expected to run for 25years and so using the spot carbon emissions right now is nonsensical for the whole life emissions.
A heat pump installed in 2010 should be expected to have an average carbon emissions over its life of 35% or so less than the new figure.
Incentivising equipment which will have a big impact in future is more sensible than other technologies which will have a diminishing effect. for Example fossil fuel CHP will fill a gap but will never be useful for the 80% reductions required by 2050. Heat pumps have the potential to be heating the majority of buildings in 2050 and incentivising their uptake now will build the infrastructure and delivery as well as provide funds for R&D to improve the performance.
So in summary I would dissagree with your conclusions but agree with your calcs.
Feel free to respond by email if you want to pursue this.
Hi Robert. Thanks for the comment. I think it’s extremely hard to predict future carbon intensity of the grid.
You and I would both agree that we have to fight to keep government moving towards its obligations for reducing carbon. But we’re staring down the barrel of a serious energy crunch, with around 30% of the UK’s energy generation due to switch off before 2015 either because of the LCPD or simply because the plant is at the end of its life. There’s a real risk that grid carbon intensity will rise through the middle of the next decade as a blundering government, taken in by promises of CCS-readiness, try to fill the short term gap with new coal.
Because of this huge uncertainty, we must wait until the carbon intensity of grid electricity is sufficiently low (and continuing downwards) before looking to install heat pumps on the wide scale. I’m in favour of using heat pumps! But not yet.
Like gas CHP, I think heat pumps are a mature technology and they have the potential to save carbon where low carbon electricity is available or the alternative is something like heating oil. In my view gas CHP should not receive the RHI either.
Have you run the numbers for the impact of change in carbon factors for CHP?
Not yet but I suspect the numbers will be about the same as CHP with gas at 0.192 and offset grid electricity at 0.568. So about the same as before.
Interesting article Casey!
Personally, I do believe that heat pumps have a role to play now: in hard-to-treat properties that are off the gas grid. When replacing coal, oil and LPG, they make far more sense in terms of carbon savings and fuel bill savings.
When the consultations begin on the Renewable Heat Obligation, we should aim to get this restriction applied.
[Additionally, I believe that the RHO should preferentially go to the fuel poor hard-to-treat homes, most exposed to the energy price rises that are inevitable as a result of our (vital) climate change policies – the cost of which are passed through to the consumer).
Darryl,
I’m interested in your confidence in heat pumps for hard to treat homes off the gas grid. I live in rural West Dorset. Our local authority has a bunch of monies from EDF for these types of projects. However, in my experience, the older rural hard to treat homes tend to be very poorly insulated, single glazed and leaky.
Even including replacement windows and roof insulation, I question the potential to install a heat pump. specifically, the need to oversize heat emitters to deal with the lower operating temperatures.
I’d really be interested to know if you have dealt with these issues.
Hi Nick
You are quite right – many rural homes are poorly insulated, and crossing your fingers whilst throwing a heat pump in won’t quite cut it.
Of course, solid walled homes require a full package of energy efficiency measures: replacement windows and roof insulation as you suggest, but also solid wall insulation. Once that is done, I do believe it makes sense to consider a heat pump. I’m no technical expert so will happily defer to those who are, but it does seem to me that in this scenario they would make sense. And whilst this scenario may seem unrealistic, I would argue that for Government to even get close to their climate change targets, especially the one for 2020, there needs to be a real focus on upgrading hard to treat homes and real assistance for the more expensive measures that this entails.
The 2006 English House Condition Survey suggests that 12% of those in fuel poverty live in homes that have no gas supply. These households need support to improve the thermal envelope, but also improve the efficiency of their heating system, for social as well as environmental reasons.
Further to the comment above, I refer you to the newly announced Energy Assistance Package in Scotland (an amalgam of the Central Heating and Warm Deal programmes)
http://www.scotland.gov.uk/Topics/Built-Environment/Housing/access/FP/eap
The programme will offer packages including solid wall insulation and air source heat pumps to vulnerable households living in rural off-gas properties.
Heat pumps will be supported under the RHI because they qualify as renewable energy under the EU Renewable Energy Directive, and therefore contribute to the UK’s binding target of 15% renewable energy by 2020. I doubt this will change your opinion, and indeed one might question what the point of a renewable energy target is if not to reduce CO2 emissions.
The proposed SAP emissions factor is higher than the Defra rolling average (about 0.54 kgCO2/kWh). I’m not sure why they are different but think we should be using a consistent set of emissions factors.
If the grid does not decarbonise we are in real trouble anyway regardless of whether some heat pumps have been installed or not. We just have to make that happen.
I don’t think the RHI can realistically differentiate between counterfactual fuels and different distribution systems – it would quickly bocome a nightmare to administer.
Finally there is the interaction with the EU ETS. Since there is a cap on emissions from the power sector, bringing more demand for heat or transport from the non traded sector to the traded sector should not lead to any extra emissions due to the cap. It is still possible to see a rise or less than the required fall in any one country’s grid emissions because those emissions should have been reduced elsewhere – this is the nature of carbon trading. Now I don’t think the ETS is tight enough until the caps are set by climate science and I also question the use of the safety valve Kyoto offsets. Nevertheless, as with the point about grid decarbonisation above, carbon trading is going to be a key tool that Government’s use to meet climate change objectives, and it just has to be made to work.
The point Rufus makes in his final paragraph is especially interesting – that increasing electricity consumption (through heat pumps) will not increase overall CO2 because of the EU ETS cap.
Exactly the same logic is being used by some to argue against the need for energy conservation and energy efficiency in electricity end use. The argument goes that any carbon saved by a householder fitting an energy efficient lightbulb in the UK simply allows that emission allocation to be bought and the carbon emitted elsewhere in the EU.
The EU ETS is thought of as a cap, but in actual fact it sets the minimum as well as maximum amount of CO2 that can be emitted. It should prevent heat-pumps increasing CO2 emissions but also prevents energy efficiency measures that affect electricity demand from reducing CO2. Of course the caveat to all of this is whether the cap is robust enough…
It’s important to note however, that whilst electricity demand reduction may not make sense in carbon terms, it does make sense in financial, ‘security’, and productivity. It also enables the EU ETS to be delivered at a lower cost, reducing costs for consumers who ultimately pay for it in their electricity bills.
Stumbled across this looking for numbers to feed a friend speaking at the RIBA debate on Zero C next Tuesday (http://bit.ly/RzXYY).
Re the grid getting decarbonised over time being a justification for HPs now I am also sceptical. Using electricity for heat, even via a HP, increases electricity demand which increases the amount of renewables needed to keep the CO2/kWh down.
Nicely set out argument, only question would be your definition of primary energy which I would see as the primary energy, eg for electricity about 3 x the delivered energy.
Nick
I couldn’t find any data from Barratt’s Chorley Wood development, I assume it’s not in the public domain. I did find these notes though from Dr Tony Sung of the University of Manchester at the “Construct IT Spring 2008 Members’ Meeting” regarding the project.
(http://www.construct-it.org.uk/pages/events/members_meetings/May_2008/Members'%20Meeting%20Spring%202008%20Summary_2.htm)
“Three [GSHP] systems have been tested and although performing at only a coefficient of 2.6 – which appears quite low, in mitigation they were set to produce an output of 55°C. If set to a more realistic 35°C then they would reduce CO² emissions by around 62% and has a payback period of around 15 years using today’s electricity prices.”
The Barratt Investor Relations website confuses the 55°C results and the 35°C projections, wrongly saying the COP 2.6 system reduces CO² emissions by 62%, doesn’t say what it’s comparing it with, and blah blah blah et cetera.
55° is a waste of time (and energy, as the saying goes), and you wonder why Barratt wasted all that cash telling themselves something they could have read in a book. But having worked for a housebuilder once…
For a successful use of GSHP in a social housing off-gas refurb, try http://www.harrogate.gov.uk/immediacy-2660.
Also interesting is an empirical study of CO² savings of at least 35% from 1100 GSHP systems by Blum et al, “CO² savings of ground source heat pump systems – a regional analysis”, Renewable Energy / Sciencedirect.com.
Anthony
All valid points but I do think the inclusion of only 60% of the DHW water being taken care of by the heat pump is a little skeptical especially with modern heat pump technology. It might be the technology that will drive the industry forward as it is efficient and reliable, would it be viewed in the same light if we were all using heat pumps and suddenly gas boilers entered the scene with the resources that are available today I doubt the same enthusiasm would be there as it is for ASHPs and GSHPs. My own experience of heat pumps is they are the future proof boiler when installed correctly and its the gradual but sure acceptance by the heating contractors that will make or break any technology. From a domestic scale biomass is unrealistic from a fuel supply perspective and GSHP is not really a mass market product due to the installation. The only real mass market solution is ASHP’s and with the RHI it I don’t think there is much to rival it for a number of years to come.
Interesting series of posts. Going back to Casey’s original article, my immediate question is why the SAP figure is 591 gCO2/kWh when actual UK grid carbon intensity figures are typically in the low 400s (delivered)? I wasn’t involved in the SAP consultation so I cannot answer this question – but my company did run (one of) the first GSHP demo project for BRE 13 years ago and we’ve done quite a lot of analysis of carbon performance.
As previous posters have noted, GSHPs really deliver benefits in off-gas-grid locations, where they can typically displace oil-fired and direct-electric systems, whatever figure one uses for grid carbon intensity. The benefit is obviously greater for space heating (condensing temperature around 35C, high COP) than for water heating.
More interestingly, the heat storage value of GSHP driving underfloor heating is often overlooked. We examined the potential for high-thermal-inertia GSHP systems to absorb intermittent over-supply by generators (using so-called smart grids). This may become more important as offshore wind installed capacity increases. Of course, this would be true of any system offering thermal storage, but it does provide some rationale for converting high-grade energy (electricity) into lower grade heat: heat is simply much easier/cheaper to store.
Some very valid points raised here, especially regarding how the ‘application’ of heatpumps significantly effects the CoP – in carbon terms it’s plain stupid to connect a heatpump to a distribution system that needs permanently high water temperatures.
One very important point that has been missed here however is that the carbon intensity of mains gas is not fixed at 0.206, it is going up, quite rapidly and it is happening now. As North Sea gas dwindles, we are importing more and more gas as LNG, the gas liquification process is highly energy intensive. The transportation of the LNG then further. This is not yet reflected in SAP.
So looking at the medium term, the total emissions from burning gas are going up, the emissions from generating electricity have to come down (by law), so the future for well applied GSHP’s looks secure to me, but for RHI to be credible it needs to fully take the application into account.
The valid points raised here, especially regarding how the ‘application’ of heatpumps significantly effects the CoP – in carbon terms it’s plain stupid to connect a heatpump to a distribution system that needs permanently high water temperatures.
I have a question @GuyCashmore is it possible to raise the above temperature by using the above application.
[…] a very interesting article at http://carbonlimited.org/2009/08/11/heat-pumps-emit-more-carbon-than-gas-boilers-so-why-will-they-ge…. Basically it says that because electricity from the grid is partly generated by fossil fuel power […]
Belatedly, a comment – why on earth would anyyone install electric resistance water heating with active solar, when they cxould continue to use an LPG or gas condensing boiler, the latter both costing less to install and emitting less CO2?
It seems quite mad.
In time maybe ground source heat pumps will be available that can actually heat the water – like gas, LPG, oil or district heating from CHP can do.