Fuelling debate

In the May issue of BSj he levelled some highly charged accusations to this effect at the London Climate Change Agency, which he believes is complicit in allowing organisations to oversell their green credentials. Find out what the agency’s chief executive officer Allan Jones had to say in response..

This is an abridged version of the article by James Thonger, associate director, Arup, which appeared in BSj 05/07. The full version can be read here.

Grid-supplied electricity hasn’t reached its targets: It should be noted that the grid- supplied electricity carbon content has not yet reached the target grid-supplied electricity carbon content of 0.422 kgCO2/kW given in the building regulations. In 2005 it was 0.455 kgCO2/kW, which included 0.363 kgCO2/kW for electricity supplied by gas and 0.873 kgCO2/kW for electricity supplied by coal.

Many projects are overselling their carbon savings: Organisations are selectively misapplying Part L carbon content figures in their calculations to oversell the carbon savings that they are making. Their argument goes like this: provided the electricity is being generated at a carbon intensity that is less than the worst generators, carbon savings are being made. But the calculations adopted mean that the actual carbon emission savings for the schemes are considerably less than claimed.

The old ways were better: In some instances, the carbon usage is actually more than if conventional energy supply methods were adopted.

CHP isn’t all it’s cracked up to be: An example given by the London Climate Change Agency suggested overall carbon saving by changing from grid-supplied electricity to CHP plants is 54%. However, the analysis compares this with a coal-fired power station. Transmission and distribution losses are given in the analysis as 23%, whereas the Department of Trade & Industry’s (DTI) Digest of UK Energy Statistics 2006 gives a total loss of 7.5%. With these calculations it is not surprising very significant carbon savings are being claimed.

Wasted energy isn’t being properly factored in: With only 12% maximum savings possible in an ideal CHP set-up, it is essential that all the heat generated by the system is being used, otherwise the carbon savings will be eroded. In particular, the community heat distribution systems (which are often quoted as having 10% losses) and the electrical distribution systems, which themselves may have distribution losses of 2%, will both need to be carefully analysed to ensure carbon savings are delivered.

Trigeneration isn’t the answer: What most consulting engineers have realised about gas-fired combined cooling and generation plant (trigeneration) is that these natural gas-fired systems consume considerably more carbon than conventional cooling systems using grid-supplied electricity and vapour-compression chillers, because the coefficient of performance of the absorption chillers is so poor.

Building regulations produce a misleading analysis of trigen: The Greater London Authority (GLA) insists engineers use a carbon emissions factor for electricity in their calculations to analyse trigen – taken from the building regulations – called the grid-displaced electricity factor. This factor is 25% higher than the current grid-supplied electricity and 56% higher than the current grid electricity supplied by natural gas.

We are working with distorted results: As a result of these massive distortions in the carbon content of supplied electricity, engineers are able to show in their calculations that there are overall savings in carbon emissions while knowing the reverse to be true. The thinking behind this logic is that it is assumed that local electrical generation will displace the most carbon-intensive grid electrical generating plant. Regrettably, this is not the case because grid supply is primarily based on cost and not carbon intensity.

Allan Jones, chief executive officer, London Climate Change Agency, replies:

Thank you for the coverage of the CIBSE National Conference which I thought was succinct and to the point. However, I noticed your link to another article in the same edition called ‘The Next Generation’ by James Thonger, Associate Director of Arup. Since this article appears to criticise the Mayor of London and the London Climate Change Agency (LCCA) I feel it necessary to comment on the article with some facts, as follows:-

The article states on page 70 that the grid-supplied electricity carbon content has not yet reached the target grid-supplied electricity carbon content of 0.422kgCO2/kWh given in the Building Regulations. I do not know on what contention this is based, particularly as the article on page 72 states that coal fired generation (a high carbon fuel) has increased by 10.5% and gas fired generation (a low carbon fuel) has decreased by 6.4% from 2005 (when it was 0.455kgCO2/kWh) to 2006.

Organisations are not misapplying carbon content figures in their carbon calculations to oversell the carbon savings that they are making. They are simply complying with the Building Regulations and using the carbon factors in the Building Regulations. It might be convenient for some to use the carbon factor for gas fired power stations to justify electric cooling but it would not be correct since gas fired power generation is only part of the grid mix, unless the building concerned was directly connected to a 1000MW gas fired power station via a 400,000 volts private wire network.

A local gas fired generator at a much lower voltage could be used but then it would not make much sense to supply electricity to electric air conditioning whilst at the same time rejecting waste heat which is a natural by-product of thermal electricity generation. Much better to recover the waste heat from electricity generation and use it to supply heat fired absorption cooling so that you are generating electricity from the need for cooling (and heating) rather than just consuming electricity from the need for cooling.

The schematic shown in Figure 1 is claimed to be a LCCA slide. This is in fact an old slide produced under the Government’s Energy Efficiency Best Practice Programme which the LCCA had used some time ago. However, the schematic has been cannibalised by a third party since the original slide had no text, just a schematic and numbers. Whoever cannibalised this schematic cannot calculate percentages since 30 divided by 333 is 9% not 23% so the article criticising the use of 23% as transmission and distribution losses is based on erroneous information. I used the 9% transmission and distribution losses figures in a text slide in my presentation to the CIBSE Conference based on data taken from Ofgem as the slide stated. However, the Energy Minister quoted 2% transmission losses and 7.5% distribution losses as part of his evidence to the Select Committee last year, slightly higher than I stated.

The carbon factors for coal fired power stations vary depending on where the coal comes from. British coal traditionally had one of the highest carbon factors (so the 0.969kgCO2/kWh quoted may well be right) and imported coal has a lower carbon factor, although still high at 0.873kgCO2/kWh as quoted in page 70 of the article. I do not understand the point being made since we all know that the carbon factor of coal is higher than that of gas whether it is 267% (as quoted) or 240% with the 0.873kgCO2/kWh figure.

Figures 2 and 3 are not more realistic since the average annual efficiency of combined cycle gas turbines (CCGT) is 48% (not 55%) as stated by the DTI in DUKES and the efficiency of boilers required to comply with the Building Regulations is 86% for housing and 84% for commercial and as stated before you cannot select CCGT as the grid supply carbon factor. Not only is this incorrect it does not comply with the Building Regulations.

As regards the efficiency of CHP the Government has stated this on many occasions. The carbon savings offered by good quality CHP (cogeneration) is up to 30% as stated in the Government’s CHP Quality Assurance Programme. The point made on the claimed heat distribution losses is a bit of a red herring since the losses would be the same whether the heat network was supplied by a gas boiler or CHP and in any event would be lower than stated for modern heat networks.

Similarly for electrical distribution losses whether buildings are supplied from the grid or CHP. Local CHP would have the effect of reducing losses simply because generation is much closer to the load rather than from remote power stations. For private wire networks the savings are even greater since they can be designed as active networks (usually in the form of a ring) rather than the grid’s passive network design. In Woking, where I developed 80 island energy sites the losses on the private wire networks were negligible and even the electricity traded between these 80 island energy sites across the local distribution public wires network were negligible in that they did not figure at all in the DNO’s line loss tables and distribution losses therefore, were not charged for.

The GLA has been promoting CHP, trigeneration, renewable energy, energy efficiency and other measures to reduce CO2 emissions and for good reason. Trigeneration has been researched and tested by a whole host of bodies, including the International Energy Agency, the European Union, UK Government and other governments. They all show a significant reduction in CO2 emissions against conventional electric air conditioning and refrigeration.

The GLA has been promoting CHP, trigeneration, renewable energy, energy efficiency and other measures to reduce CO2 emissions and for good reason

Coefficient of Performance (COP) figures are quoted by heat pump/electric chiller manufacturers but this is not the same as energy efficiency, otherwise they would be quoting for example, 300% energy efficiency rather than a COP of 3. Peak COP is often quoted but this is not the same as average annual COP. For example, the 500kW electric chillers at Palestra have a quoted COP of 3.8. However, the COP is dependent on ambient conditions with the COP of 3.8 at 25oC, 3.0 at 35oC and 2.33 at 45oC. In other words, the COP reduces as the ambient temperature increases.

The International Energy Agency carried out an exhaustive study into trigeneration in comparison with electric cooling (known as Annex 24) and determined that the correct determination of energy efficiency should be based on the Primary Energy Ratio (PER) not COP since this takes into account the efficiency of the primary energy supplying the chiller. In the case of electric chillers in the UK the efficiency of the electricity supply (from the grid) to the chiller is a little over one third whereas the efficiency of the waste heat to the heat fired absorption chiller was approaching 100%. The carbon factor for waste heat supplying trigeneration at 0.018kgCO2/kWh is very low as stated in the Building Regulations. In addition and as stated before, trigeneration generates electricity from the need for cooling (and heating) rather than just consuming electricity from the need for cooling, thereby conserving the UK’s non renewable energy resources.

Also, electric cooling systems (particularly, the higher COP chillers) use very powerful greenhouse gas refrigerants, typically HFC’s. For example, the electric chillers used at Palestra use HFC 134a as a refrigerant which has a Global Warming Potential of 3,400. In other words, 1 tonne of HFC 134a is equivalent to 3,400 tonnes of CO2. Each chiller contains 59kg of HFC 134a refrigerant. HFC’s are one of the 6 greenhouse gases covered under the Kyoto Protocol and EU Emissions Trading Scheme. In comparison, trigeneration heat fired absorption cooling refrigerants are both zero Ozone Depletion Potential and zero Global Warming Potential.

With regard to the Building Regulations carbon factor credit for displaced electricity of 0.568kgCO2/kWh from on site of local CHP and renewable energy it should be noted that not all grid power generation (eg., nuclear and renewable energy) can be switched off or modulated in response to half hourly grid electricity consumption fluctuations in the same way that fossil fuel power generation, in particular coal, can. Cost will come after the technical ability to perform in response to the half hourly market. It just so happens that both nuclear and renewable energy are low or zero carbon technologies in operation.

Contrary to what is stated in the article trigeneration is being pursued on a number of projects in London. For example, trigeneration is being tendered for on such projects as Elephant & Castle, Kings Cross, New Wembley, London 2012 Olympics/Stratford City to name but a few. Trigeneration has also been recently installed at the Natural History Museum, quite apart from the trigeneration schemes at Southampton and Woking. Abroad, New York has perhaps the largest community trigeneration scheme with their 800MWe CHP system for Manhattan where they have already displaced 385MW of electric cooling with their trigeneration system.

The single biggest barrier to reducing London’s CO2 emissions is the way in which energy supplied to buildings is produced and distributed. Centralised electricity generation, whether through coal (36% efficient), gas (48% efficient) or nuclear (38% efficient) power stations, is inherently inefficient – wasting two thirds of primary energy input in the form of waste heat rejected into the atmosphere with further losses in the transmission and distribution networks. The challenge facing London, the UK and indeed the rest of the world is to tackle climate change whilst affording security of supply at the same time. The huge primary energy losses from centralised power generation is a sheer waste of energy that impacts on the UK’s security of supply, quite apart from the huge unnecessary greenhouse gas emissions. The Energy White Paper recognises this and indeed sets out proposals for bringing forward a range of measures to support more distributed forms of energy.

The single biggest barrier to reducing London’s carbon emissions is the way in which energy supplied to homes and offices is produced and distributed. London’s electricity and gas consumption causes emissions of 35 million tonnes of CO2 per annum, 75% of London’s emissions. Status quo energy technologies and systems have brought about climate change and climate change will not be tackled by maintaining status quo energy technologies and systems. This may be an inconvenient truth for some but a truth it is.

James Thonger, associate director, Arup:

I have read your response to my article and I am pleased that you have taken time to address this issue. However, it is regrettable that the key point has not been addressed. You acknowledge that you do indeed advocate the use of the grid displaced carbon emissions factor to calculate the carbon savings for CHP and trigeneration schemes, but make no justification for the use of this factor except to say that this is what is allowed by the building regulations.

In writing my article, I was aiming to show that the use of the building regulations for the detailed calculations required to analyse carbon usage was no longer valid, given that the benchmark used is not representative of the current carbon content of grid-supplied electricity.

It seems to me that we should all be asking a simple question: “Are we, or are we not, saving carbon with these particular schemes?” If we use a factor in our calculations that is 25% higher than the average factor currently given by the DTI, we are misleading ourselves about the magnitude of carbon savings that are being made, and we may be using more carbon – not less.

As stated in my article, this is not to say that some CHP schemes cannot be designed to offer real carbon savings, particularly in mixed-use developments. However, it is essential that those schemes use the electricity effectively, as in Mr Jones’ private-wire networks in Woking, and use all available heat efficiently to compensate for the reduced electrical conversion efficiency of the CHP installations.

If the UK is to honour its commitments to substantially reduce carbon emissions, we need to set ourselves significantly more challenging targets, not simply a target that is slightly better than the worst. It is incumbent on us all to use all fossil fuels in the most efficient way possible, which is why I am advocating that each fuel type should be benchmarked against specific carbon targets, as detailed in the example calculations.

I believe that it is time that an independent auditor is appointed by the government to advise on the most appropriate factors to use in our calculations, and to verify that the claimed carbon savings are real and achievable.

I am sure that the LCCA would welcome this proposal.

… Allan Jones:

My reply is very brief. I can’t see that you have provided any real evidence to support this contention, but if you want to challenge the government and the building regulations on this, you should challenge the government directly, rather than go through the LCCA.

… James Thonger:

I accept that the LCCA (or indeed any energy service company) will only be following the current guidelines. It is the responsibility of the professional engineering institutions to step up to persuade the government that the time has come to introduce more rigour in the assessment of energy schemes to ensure real carbon savings to the UK as a whole.

CIBSE, the IMechE, the IET and the Engineering Council (UK) should all seek to engage with the DTI to address the immediate issue regarding the calculation discrepancy surrounding the grid displaced carbon emissions factor in the building regulations, and further, to agree revised targets for energy consumption for all fuel types.

Failure to do so will mean that UK carbon emission reductions of 60% by 2050 will not be achieved.