Why CHP wins out over heat pumps…..or nuclear!

If there’s one thing that puts me off nuclear power it is the attitude of its cheerleaders. There seems to be no limit to what they’ll do to clear the path for their “precious”. Inevitably one of they’re favourite habits is to scaremonger about future energy shortages without nuclear (of course as I point out here such claims are inaccurate and even if they were, as I point out here nuclear won’t be the best solution!) or global warming (I’m not saying its not an issue, far from it! but overblown “climate porn” merely strengthens the hand of the deniers, as discussed recently on “Climatecrocks”). Alternatively they’ll resort to bashing renewables (I go through a few of they’re founding myths here) and try to discredit the benefits of energy efficiency (again a good example of this can be found here).

In this article I will focus on that last of these points (energy efficiency, notably CHP) and demonstrate that all such rhetoric demonstrates is that many nuclear energy supporters do not understand the basics as regards energy consumption. And therefore it is no surprise that the solution that they offer (more reactors) is simply not the panacea that they claim it to be.

What is CHP?

CHP (or Combined Heat and Power) is essentially a way of getting more bangs for our bucks. The energy efficiency of most thermal power stations is around 30-45%, with the remaining 70-55% of energy simply thrown away as “waste” hot water or saturated steam (you’ll find more info on that and CHP here and here). CHP proposes to use this heat for some useful purpose, such as home heating or as an industrial heat load. Many EU countries already utilize CHP heavily so its proven technology, and the choice of fuels is more varied (from biomass to refuse as well as the more traditional coal and natural gas). Using CHP we can raise the effective efficiency of power generation from its present level (33-45%), to between 60-80%. Best of all CHP is scaleable, right the way from multi giga-watt power stations down to the scale of units compact enough to fit a small flat (so called Micro-CHP).

Figure 1, A basic overview of CHP, our goal is to save as much of that 50% of heat losses as possible [Credit: ESRU Strathcylde University]

At present CHP probably represents the easiest and most effective way of reducing carbon emissions (as I discuss here), and reducing fossil fuel consumption. Using so-called Tri-Generation (where a CHP unit is paired with an absorption chiller unit to produce a cooling load paper on this topic here) it is possible to provide a large cooling load as well.

Sustainability, with lots of pro-nuclear hot air

Exhibit A is perhaps David Mc Kay’s so-called “Sustainability without the hot air”. As I’ve previously shown he makes an number of “school boy” errors, both in terms of overestimating the UK’s energy consumption (see here), preposterously suggesting Uranium from seawater as a plausible energy option (debunked by Barti 2010), as well vastly underestimating the true cost of nuclear power (see here) and the fact he failed to account for seasonal and daily variations in energy demand (see here). But the key bone I’ve always had to pick with him is buried in Chapter 21, he tries to claim that CHP is bad from an energy efficiency point of view and that Heat Pumps are better.

Of course the fact he favour nuclear….and more heat pumps means more electricity (which means more reactors on the grid), while CHP would allocate more direct heat generation instead (and provide a large chuck of baseload and seasonal load-following electricity, i.e. less need for reactors) has nothing to do with either his, nor the rest of the nuclear lobby’s, anti-CHP stance! Hardly!

Figure 2, Current and future UK energy consumption, as envisaged by Mc Kay [ Credit: SEWTHA, chapter 27, pg 204]

First of all I would note that Mc Kay drastically overestimates the performance of heat pumps in a UK environment, a point I believe even he has since acknowledged. Worse, heat pumps performance tends to worsen precisely when its coldest, meaning electricity demand will rise just when we don’t want it too. A more spiky level of electricity demand will, as I explain here, mean less nuclear plants not more.

Then there’s also the practical issues we need to address. Well look at the heat side of the equation first.

We need some hot Stuff

The inlet temperature to most UK central heating systems is 60 – 90 °C, while the outlet temperature from a heat pump is typically 20 – 35 °C (its possible to get heat pumps to run at higher temperatures, but only by sacrificing COP’s, which can ultimately result in them becoming a net source of in-efficiency rather than a gain, leading to higher carbon emissions, as I will discuss later).

So in order to use one of these in a typical UK house (or office building) you’d have to gut the place and replace all the radiators with either underfloor or an air-con based heating system. Of course, that would be an enormous logistical undertaking and it would probably make more sense to just retrofit such homes with better insulation (or indeed knock many of them flat and build zero carbon homes!). In practical terms it just does not make sense. With a switch over to CHP we’d only need to change the boiler.

Figure 3, A Domestic Air Source Heat pump unit [Credit: Earth Air Energy UK]

Indeed there is the big question mark whether the number of heat pumps Mc Kay proposes would be up to the job, as there  is a danger of them interfering with each other (again at precisely the times of year when we need them performing at optimum efficiency) as even he discusses here. Certainly, I for one doubt you could use heat pumps alone to heat/cool a major office building or tower block, not unless it was designed with such a task in mind from the ground up (a bore hole underneath for one thing).

And what about the other big source of domestic heating needs – domestic hot water? 20 – 35°C is a little on the chilly side for this (I usually have mine a little higher). Particularly as far as washing clothes or cutlery is concerned (anyone doubting that, wash you’re dishes at that temperature and call me when you’re over the Salmonella!).

Going Industrial

Figure 4, A multi-unit CHP plant at a US oil refinery [Credit: EIG Inc.]

Furthermore the big industrial users of CHP often have very specific heating requirements (the DECC gives a range of case studies here while the CHPA gives a couple more here). Some of the biggest users of CHP are Breweries and Food processors (who typically need heat up to or just above the boiling point of water, i.e. 80 – 120°C), Swimming pools, paper mills, wood processors, chemical works, refineries and smelting plants (the heat requirements for these last few loads varies considerably, but it is generally well outside of the range of temperatures or heat transfer rates a heat pump can supply). It is absurd in the extreme too suggest that such heating loads could be supplied by a heat pump system.

Indeed there are also good practical reasons why CHP is favoured in the applications above. It is often used to dispose of process wastes (which in the case of a refinery for example can represent a serious safety as well as environmental hazard). Also, to take the example of a hospital, while it would appear at face value a good location for a heat pump (i.e. the sort of temperature ranges they work well in). In many cases the whole reason for having a CHP plant on site at a hospital is that it not only saves energy but also acts as the hospital’s standby generator in the event of a power cut (while a heat pump system will increase electricity consumption and leave the hospital even more vulnerable to a sudden power cut).

Electric Dreams

Nuclear energy supporters will often try to extricate themselves here by trying to argue in favour of just using electric powered hot water systems to close the gap. Of course, they fail to mention that such systems tend to be horribly in-efficient (as you’re taking a heat source in a power station at 33-45% efficiency, turning the heat into electricity, loosing 2-5% in transmission then turning it back into heat at 70-85% efficiency). This is why the carbon footprint of gas fired heating systems is 0.203 kg of CO2/kWh while electric water heaters are at 0.527 kg of CO2/kWh  – 2.6 times higher! This would explain why Australia has recently banned electric water heaters on environmental grounds. From time to time, I’ve heard it suggested that the UK should do the same, although the building trade seems to be hostile to the idea (more down to vested interests in terms of ease of installing such systems in high rise flats rather than a desire to save energy – that’s the future tenant’s problem!).

Indeed heat pumps themselves can also increase carbon emissions, if the units are particularly inefficient (i.e. low COP) and connected to a grid with a high number of fossil fuel burning power stations, as this section of the Wikipedia entry on Heat pumps illustrates (based on EU and DOE).

Figure 5, An illustration of the problems effecting heat pumps in domestic settings [Credit: Green Builder Bible (2008)]

On a more fundamental level heat pumps essentially amount to taking a large quantity of high grade energy (electricity) and turning it into a lot low grade heat heat energy. This would explain why a number of advocates of both renewables and nuclear energy I know are extremely hostile towards heat pumps, as they regard them as a quote “…. a false economy” or quote “….the perfect source of hot air for faux-tree huggers”.

Now I’m not saying that heat pumps are a complete waste of time (although, as just stated, there are some people who will tell you they are!). Heat pumps, in my opinion, have their place, but its a fairly narrow remit. Certainly, trying to get the 12 kWh/person/day Mc Kay talks about getting from heat pumps (that would be about 263 billion kWh/yr or the equivalent of 30 GW‘s of installed power output, working over 100% of the time for a year), nevermind the further 12 kWh/p/day of electrical heating he wants to get, is highly improbable. I would estimate the UK market for heat pumps at a fraction of this figure, mostly focused on homes in rural areas that are off the natural gas grid (and one assumes any future hydrogen grid).

As I’ve pointed out before 36.8% of UK energy demand represents heat energy demand. Perhaps the best carbon free way of meeting this demand is directly via renewables sources – biomass, solar thermal water heaters, direct passive heat gain, etc. And yes such systems can work well in the UK, indeed there are some who’ll tell you it works better in northern latitudes than southern Europe (due to the longer days in summer and longer heating season in winter). But ultimately, it’s all about matching energy demand (heat, transport fuel, electricity) to supply, as I discuss here.

Figure 6, A roof mounted solar thermal water heating system [Credit: Solar Thermal Magazine, 2010]

While nuclear can provide heat energy (i.e. by directly tapping into its output of steam) it’s not really practical given the large size of current reactor designs and their location far from cities and industrial centres. Relocating some of these loads to take advantage of this heat would be neither practical nor economic (once you factor in the costs of relocating as well as the radiological protection costs associated with operating next to a nuclear plant). A nuclear energy supporter once quibbed to me that the best place in the UK to build a nuclear plant would  be right bang in the middle of London on the site of Battersea power station. While I can’t disagree with him on a technical level (you could meet most of London’s heat demand with such a plant) something tells me it would never be palatable at a political level!

Power to the Grid

Figure 6, UK monthly electricity consumption over the past few years, note the large “gap” in the middle of the year, that means idle plant for part of the year! [Credit: earth.org.uk]

As far as the electricity side of the equation goes, as I’ve previously pointed out, there are significant seasonal and daily variations in electricity demand, with swings of up to 50%. Meeting these needs through nuclear alone is both technically challenging and uneconomic (as you wind up with some power stations which spend half or more of their working lives off-line as there is no demand for the electricity they supply, drastically cutting back on assumed capacity factors). In the absence of those particular forms of renewable that can undertake intermediate and peaking electricity, or some means of energy storage, some of the world’s future electricity demand will thus have to be sourced from “peaking” thermal power plants.

Figure 7, The load distribution profile for Canada in the 1980’s [Credit: “Energy” by G. J. Aubrecht 2nd edition, based on data supplied  by the Economic council of Canada, 1985]

The above graph, represents the ratio and position of different electricity sources in the Canadian grid (which has a fairly broad balance of renewables, nuclear and fossil fuels). While this figure is a little dated (from the 1980’s), it still is useful in explaining the matter. Note that the “baseload” hydroelectricity would now be occupied by “baseload renewables”.

CHP’s place in the graph would come in two flavours. The first would be heating loads that are on more or less all the time (notably those industrial loads I mentioned earlier). As these CHP plant would be simultaneously generating electricity along with the heat output, they would occupy a wedge between nuclear and baseload renewables (the more renewables on the grid, the more CHP is pushed upwards to eat into nuclear energy’s wedge). The other type of CHP load would be those heat load’s whose demand is largely seasonal (district or building heating systems). They would squeeze in between coal and nuclear (in theory with the right subsidies and setup you could get them to take over a large chunk of the coal wedge). Thus it should be obvious why nuclear energy supporters are so hostile towards CHP. It widespread use could see them becoming “the squeezed middle” between renewables and CHP on both sides.

Energy Consolidation

Ultimately the key argument in favour of CHP is simply practicality – the best way to meet some significant portion of our current and future heat energy needs, is going to involve the burning of some sort of “fuel” (oil, natural gas, hydrogen, rubbish, biomass, whatever available really) too generate heat in sufficient quantity and at the temperatures required. As the major running costs of such a plant is the fuel, shutting it down when the seasonal demand for heat is not present, isn’t a big issue. Indeed, one of the advantages of “Trigeneration” is that it can greatly extend the “heating season” and thus improve the economics of such as system in certain situations.

Figure 8, UK monthly gas consumption over the past few years, again mind the gap! [Credit: earth.org.uk]

Equally, some of the UK (and the wider world’s) electricity load will have to be met by some form of “bunkered” fuel that is burnt in a thermal power station, as and when it is required (particularly at times of peak daily demand, notably during the depths of winter).

Obviously the whole point of CHP is to combine these two tasks with the one power block, leading to an overall cut in carbon emissions. Indeed the quickest way to achieve major cuts in carbon emissions in many countries right now would be via the aggressive roll out of CHP technology. As I have point out before, a modest target for CHP roll out could cut Japan’s energy demand by 12-20% (about what Japan current gets from nuclear!) and it would likely “take out” a large number of gas fired heating units and coal fired power stations, as CHP power units are a good like-for-like replacement with these.

Now of course CHP isn’t perfect, indeed it still emits carbon dioxide unless fueled by a carbon neutral fuel source. But the point is that it is a practical way of getting substantial reductions in carbon emissions right now, while it will take many years or decades to have a similar impact using either renewables or nuclear. In short, it buys us time and also happens to provide backward compatibility with a future renewables heavy energy grid.

Furthermore, there is the political dimension. Many private companies are happy to invest in CHP, as they see it as a big energy saver (and thus a money saver). Convincing more companies to go down the CHP route won’t take much effort (a few tax breaks here and there or the imposition of a modest carbon tax), while getting them to invest in renewables is difficult (at present, although they are increasingly warming to the idea). Getting them to invest in nuclear, as I’ve previously pointed out, is impossible without very a heavy government subsidy in some shape or form. Suggesting that industry should switch too heat pumps or electrical heating (as Mc Kay seems to believe) is just plain silly.

Nuclear Underpants Gnomes

But as I mentioned, it is easy to understand why nuclear energy supporters are so hostile towards CHP (and energy efficiency in general). It does not fit into their whole “too cheap too meter, thousand year nuclear Reich” fantasy. Indeed, given that CHP plants tend to sit in the very part of the gird where Nuclear does (baseload and some of the seasonal load-following electricity) CHP is often nuclear power’s direct competitor. So they’ve lobbied hard against it (and renewables), indeed its difficult to believe that the UK has only recently brought in subsidies to support Renewable Heat (and thus to a less degree mirco-CHP) relatively recently.

But ultimately all that nuclear energy supporters succeed in demonstrating is they’re own ignorance to the problems that they propose nuclear power to be the solution too. Like the Underpants Gnomes the plan for nuclear cheerleaders seems to be:

1) build lots of nuclear plants
2) ?????????
3) Too cheap to meter

Now I’m not suggesting there is no role that nuclear energy can fulfill in the future energy grid. But it is important too realize what nuclear energy can do and what it can’t do, and the costs involved. Trying to ram a square nuclear peg (or a triangular heat pump peg) into the round hole of heat demand isn’t going to work.

About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
This entry was posted in clean energy, climate change, efficiency, energy, fossil fuels, future, Global warming denial, nuclear, peak oil, politics, power, renewables, sustainability, sustainable. Bookmark the permalink.

19 Responses to Why CHP wins out over heat pumps…..or nuclear!

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  8. Fanandala says:

    The article argues as if you grab CHP out of thin air. But it is a secondary product of heat or electricity generation. You can complement any ( thermal ) power station with CHP, and of course if you have a consumer it makes absolute sense. And if the temperature the CHP provides for your application is not high enough, you could probably boost it with a heat pump. Fact is I can use a heat pump anywhere, I can only use CHP if I am connected to a power station. The way I see it, the two technologies do not really compete with one another.

    • daryan12 says:

      “grab CHP out of thin air”
      Then many continential EU countries are grabbing alot out of thin air as CHP represents up to 55% of national power production in some countries! 😉

      You comment suggests a fundmental misunderstanding of how CHP works. CHP can be scaled down (or up) and moved close to the source of heat demand. In many EU countries they used district heat pipes to deliver the heat, and they are installing such networks in one or two UK cities as we speak. Indeed domestic boiler sized CHP plant is commercially available. And in the UK you can even get a subsidy for using it under the RHI.

      In short you seem to be arguing, we can’t move the customer to the plant, when in fact the argument is its easier to move the plant to the customer. It should be noted in the UK that nearly half of the installed capacity is scheduled to retire in the next few decades, so arguing that some of it should be replaced with lots of smaller CHP units closer to heat demand sources, won’t be that difficult to implement.

      “you could probably boost it with a heat pump”
      For the sort of temp’s used in a domestic house CHP operating temps are more than adaquate, some industrial heat loads need a boost, but its vastly more energy efficient to use a boiler for this job than a heat pump. Again you don’t seem to grasp that heat pumps drop in COP as the operating temperature rises (or indeed as the weather gets colder, i.e. when they’ll be working hardest). Within the sorts of temperature ranges we’re talking about (above +50’C) they would be stuggling to produce a sufficiently high COP to counteract the fact that electricity generated by fossil fuel plants operate at an efficiency of 33-40% (i.e. you need a COP of 3-2.5 to break even), meaning the heat pump results in an increase in carbon emissions!

      Remodelling domestic heat demand to support heat pumps would, as I describe be problematic, while with CHP you only need to change the boiler (either with a hook up to district heating or a CHP unit in its place).

      Furthermore there is the issue that much of the country’s heat demand is seasonal. To heat the country with heat pumps, instead of boilers and CHP, you’d need a vast network of power stations (many times more than our current grid) to turn on over the winter, some for maybe only a few hours each day, then turn those plants off completely over the summer (how economic is that going to be!). Whereas CHP units and thermal plants coupled with some form of “bunkered” energy (biofuels, hydrogen, etc.) is a better “fit” to such an energy use profile.

      Heat pumps have their place yes, but along with solar thermal, its likely to be a limited remit.

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  10. Pascal says:

    It would have been nice to have spelled out the acronym “CHP” at least once at the beginning of your article. Then again, I suppose it’s common knowledge to someone who’s reading a blog about energy.

    • daryan12 says:

      Actually, a good point there, in some countries CHP is more commonly known as “co-generation” so I may make a slight edit in future to slip that one in.

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