Ever since Without Hot Air first hit the scene in 2008, Professor David MacKay has been the Man of the Moment. If you haven't yet read the book - which is available online as a pdf for free - then you should, because it's a great read. Bright. Cogent. And to the point. And very Cambridge, in the way that Cambridge has become a centre of excellence for the understanding of climate change. You don't find many sceptics in Cambridge - just pointy-heads and loads of nerds clever enough to make out what is going on in our atmosphere. Mackay is a pointy head par excellence but one who has the ability to explain it all to mere mortals who don't happen to inhabit one of Cambridge's rarefied quadrangles.But recently I have begun to hear dark mutterings about Mackay's new found influence with government, and this has now turned up in the comments column on my blog. Now I've no reason to attack MacKay - why he's even written something nice about me on his blog once (as far back as March 9 2008)- and he seems like a pretty good bloke from all I can see and hear (I've never met him). But it seems people are upset that since he took the Queen's Shilling and became Chief Scientific Advisor of the Department of Energy and Climate Change in September 2009, he has used his new found influence to promote air source heat pumps as the answer to our problems.
"While in theory ground-source heat pumps might have better performance than air-source, because the ground temperature is usually closer than the air temperature to the indoor temperature, in practice an air-source heat pump might be the best and simplest choice," he writes in his book.
And yet there a dozens of knowledgeable people out there who are distinctly queasy about air source heat pumps and think they may just make matters worse, especially if people rip out their old boilers and switch to ASHP ASAP. But you have to do the maths in a little more detail than he has done to work out the difference between theoretical and actual performance. Or just listen to David Strong for a few minutes (something I had the pleasure of doing in Cambridge last night).
Yet ASHP has been installed as one of the primary beneficiaries of the Renewable Heat Incentive. Conspiracy theorists detect the hand of David Mackay in designing this incentive - what else would DECC's Chief Scientific Officer do?
So it would be good to know just what has been going on here. MacKay has come a long way very fast — he only completed his book in September 2008 — and it would be unlikely that it didn't contain one or two errors and omissions. The worry is that he's just been a bit too rushed in all this, and that he simply hasn't had time to get up to speed on the critical issues.
For lovers of irony, you can't help but reflect on the title of his book here. The thing about air-souce heat pumps is that, Without Hot Air, they are next to useless!
Mark
ReplyDeleteThanks for you kind comments about my Cambridge lecture last night. If you would like to know more regarding my concerns about air source heat pumps, see my article "Blowing Hot and Cold" on the Inbuilt website at http://www.inbuilt.co.uk/news--events/presentations--articles.aspx
Best wishes
David
And then there are those who are queasy about any kind of heat pump, because of the reliance on electricity and low operating efficiencies in many practical contexts.
ReplyDeleteRipping out a decent gas condensing boiler to put in a new heat pump just doesn't make sense unless the boiler is not working. I am convinced the embodied energy in all this kit we are determined to substitute for existing systems is not insignificant. But I haven't done the arithmetic, yet.
Keep up these interesting posts, Mark. New ones light up my RSS feed.
I'm a real fan of David MacKay's numbers approach and would like to give him the benefit of the doubt on this one. Are we saying he also suggested promotion of liquid biofuel and biomass in boilers? Sorry to repeat myself but surely this is yet another cock up rather than conspiracy.
ReplyDeleteHowever I agree with David Strong's analysis on air source and am even sceptical about compact units in Passivhaus as we discussed at EcoBuild. David Olivier has also been very damming in his criticism of the heat pump analysis in SEWHA.
In the future the numbers might be different. No gas, all buildings renovated to very low heat requirement (or we are all wearing seal fur in winter) and grid decarbonised. At that point even a heat pump with COP of 2 is better than direct electric so might have a role. But instal ASHPs now and carbon emissions will doubtless go up.
David Strong, thank you for the link to your article on ASHP, very interesting.
ReplyDeleteI completely agree with you about the need for independent research - it seems we know very little about the real world use of energy in building and houses in particular when insulation and various bits of 'low-carbon' kit are retrofitted. There is plenty of optomistic save 'up to 80%' with cf bulbs but I find the lack of information on, or interest in, the actual outcomes frankly wierd. It sends my political cynicism into overdrive.
They must care about the outcomes mustn't they? They can't just be promoting this or that 'solution' to bolster their power and positions can they? Hmmm
They do have form in lots of other areas like Defense and NHS. Sorry, I'll go and lie down for a bit.
I also wanted to say that if David MacKay, as Chief Scientific Advisor is managing to make the Department of Energy and Climate Change look at and take notice of the figures then he will have done a fantastic job. I for one would happily overlook a bit of a blind spot on heat pumps if he could nudge them in the direction of reality.
ReplyDeleteHowever, there is another possibility. SEWTHA was an important book, it showed that reason and some straighforward maths could cut through acres of waffle and make-believe and get down to some stark choices. Not everyone liked that. Absorbing your critics is a common way of dealing with them.
In the following case it backfired:
"Professor David Nutt of the University of Bristol was Chair of the Advisory Committee on Misuse of Drugs until being relieved of his post on 30 October 2009 after criticising politicians for "distorting" and "devaluing" research evidence in the debate over illicit drugs" Wikipedia
I do hope I am wrong.
@buildingstoat
ReplyDelete"I completely agree with you about the need for independent research - it seems we know very little about the real world use of energy in building and houses in particular when insulation and various bits of 'low-carbon' kit are retrofitted."
The Welsh School of Architecture at Cardiff University and six other universities are currently engaged in monitoring upgraded housing to see how people create and maintain conditions they consider to be comfortable.
The project will report its initial findings later this year.
"Heat pumps are the future" seems to have been said once a generation, e.g. in the 1950s the ERA did useful research on them. Again around 1980 the government studied the options after North Sea gas, which were by then considered to be heat networks using mainly power station waste heat, or electric heat pumps or synthetic gas. It came down in favour of CHP not heat pumps or synthetic gas and recommended starting heat networks in several cities.
ReplyDeleteThe surprise today is that the UK proceeds as if heat pumps are the future without any published evidence of the real COPs to be expected. Some COPs McKay quoted may be full-load laboratory test figures and the 2.9 limit set by RHI is a notional figure to be met so that the CO2 emissions don't look embarrassingly bad versus a condensing gas boiler.
Most air source systems with backup resistance heaters, or a slight design or installation fault(s), struggle to give a COP of more than 2 (for all heat put together). At COP 2, quite a few other heating systems emit less CO2, making one wonder "why heat pumps?" indeed at COP=2 it could be 2025 before a heat pump emits any less CO2 than a good gas boiler. But isn't the next 10-15 years "the tipping point"?
Re. the last posting, for some years the UK has spent less on relevant buildings and energy research (per capita) than other OECD countries, except perhaps Turkey or Portugal. That means there's no money to do proper measurements of how much energy different buildings consume, or how to make the failures rapidly better. Rather a barrier, that.
Given I have a background in thermodynamics I might feel excited about being able to get stuck into the minutae of COP's and the various impacts on efficiency caused by irreversible processes inside the heat engines we are talking about. However that would be missing the simple question here, which is :- is it better to use electricity to drive a heat pump to warm our houses or to use local fossil fuel burners such as the well established gas boiler? ("Is it better" understood to mean - does it generate less CO2 overall.)
ReplyDeleteWell, it depends where you get your electricity from - if it comes from solar generation (i.e. no CO2) then it is clearly (2-3x ?) more useful to use electricity to pump heat from the air or ground into our houses than to simply generate I^2.R heater in a 3 bar fire.
However if the electricity comes from turbines driven from heat then the argument goes - you can only get 30% of the energy out as electricity so the (2-3 ?) gain of a local heat pump is wiped out and you might as well have burnt the oil/coil/gas right in your own house.
So the mix of where our electricity comes from is important in establishing which of the two interpretations above is dominant.
There is one rider, of course, - by switching local delivery of heat from local fossil fuel burners to electrically driven heat pumps we DO provide the possibility, over time, to improve the mix of renewable energy by adding more renewable capacity to the central grid. If you stick with fossil burning in peoples houses then the renewable component cannot be upped.
In the event of switching local heating to electrically driven heat pumps grid capacity would HAVE to increase, but IF this can be done cost-effectively with renewables then in principle you could eliminate domestic generation of CO2 for heating, and not equivalently increase grid CO2 generation.
Just a tuppence worth - great blog and great book, thanks Mark !
David Strong criticism of ASHP centers on the lack of data on actual performances. Yet he talks about the challenging British climate and the loss of efficiency when defrosting.
ReplyDeleteI believe that there is a self contradiction there. David Critices the hype about ASHP based on lack of test data; that's OK but passing judgment on their efficiency without supporting data is falling into the same trap, isn't it? There are figures as to how much defrosting consumes: 5% of the annual energy (ref: Ross Chillers); that seems reasonable to me.
Yet, we should apply the same critical judgment to GSHP.
Permafrost used to be found mainly in the very north of Europe. Not anymore. So many GSHP are undersized that they operate at below the efficiency of ASHP.
Sure, GSHPs have a greater potential for much higher efficiency when design right, but they deserve criticism too when they achieve COPs of 2.8 as at the National Energy Foundation headquarter, or achieves COPs of 3.2 in a recent projects I reviewed, but in many cases, add the geothermal pump and you end up with a seasonal COP way inferior to a mediocre ASHP. That's the state of many systems built by contractors who won the contract on cost only at the detriment to good companies who loose out for proposing carbon performing systems.
And by-the-way, it is worthwhile taking a minute to plot ASHP efficiencies against external temperature v. mean delivered temperature (COP=a.DT² + b.DT + c) and plot COP hour by hour for a whole year. Of course you shouldn't believe the COPs quoted as a single figures by manufacturers. But I think you should apply the same rigour to both ASHP and GSHP.
At least ASHP come as a packaged product with a predicted efficiency, whereas GSHP efficiencies depend on the competence of the contractor to estimate how much geothermal pipework is required, hence the long list of failed projects in the UK and these temporary diesel boilers standing next to buildings that got it wrong and now sit on a block of ice, way colder than our 'terrible' English weather.
I don't recommend ASHPs in particular, but I expect GSHP to achieve at least 30% better. That is sadly far from reality.
At a lecture at Cambridge earlier this year, an audience member questioned MacKay about moving towards heat pumps as the ghg generated from electricity production greatly outweighs that from gas and suggested this was worse for the environment not better. MacKay countered that his primary agenda is to get the UK off of fossil fuels and that finding better sources for electricity production was critical, after getting rid of all fossil fuel dependency. If you understand this as his primary agenda, then you can better understand his position. Of course, to me the real question then becomes, is the current primary goal to get the UK off fossil fuels or is it something else?
ReplyDeleteRather than MacKay's book being a "great read", I would suggest it is fundamentally flawed and highly misleading.
ReplyDeleteDavid MacKay's "...inflated demand figure of 195 kWh/d is nowhere near our real energy demand, and has mislead people into believing the myth that Britain’s energy demand exceeds its renewable resource, whereas the reverse is true: our renewable resource is much greater than our energy demand." http://www.energynumbers.info/british-energy-demand-and-professor-mackays-estimate-of-it-an-explanation-of-the-differences
It's worth noting how MacKay responds - actually fails to respond - to this criticism: http://www.withouthotair.com/reviews.html#critical
Also worth a read:
1. http://www.justmeans.com/-No-Hot-Air-About-Renewable-Energy-While-Blowing-Smoke-David-Mackay-plays-Brutus-Sun-s-Caesar/27338.html
2. http://thisbluerock.wordpress.com/2011/05/16/david-mackays-sustainable-energy-without-the-hot-air-perhaps-a-little-hot-air-2/
Alan,
ReplyDeleteYou are responding to a very old post - none the worse for that - but Mackay and the 2050 calculator have been touched on several times since.
Surely the problem now with renewables isn't that they can't produce enough — almost no one argues this — but that we don't have sufficient storage in place and we don't seem to have much prospect of building sensible amounts by 2050. Relying on gas fired power stations for back-up isn't going to be acceptable by then.
Put another way, renewable power is no longer the question. It's storage.
No, storage isn't the question either. Storage is a bit of a red herring, really.
ReplyDeleteWhat matters is balancing supply and demand. Storage is only one of many ways to do it. What we use currently is a mix of storage, interconnectors and dispatchable generation. You can have a 100% renewable grid that balances with high energy security, also using a mix of storage, interconnectors and dispatchable generation.
Balancing a 100% renewable grid is a solved problem, just as the scale of the renewable resource, and the rapid expandability of the supply chains, are solved problems.
(sorry to dig up this old thread, but I do get inbound links from it, so people are reading it)
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ReplyDeleteThanks for your comments Alan. I'm not convinced about your point that storage is a solved problem. Interconnectors are all very well but they are passing the storage buck up the line to another country, not solving the fundamental issue, And if what you mean by "dispatchable generation" is water pumping, well that's just another form of storage. Then again, you may be meaning something quite different. In which case elucidate.
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