OPINION Your views from across the built environment
CONFUSION FACTOR
Uncertainty over carbon emissions factors for the national grid is undermining consultants’ ability to make the correct technology choices for buildings, argue Phil Jones and David Shaw
So, what’s it to be: 0.591, 0.568, 0.543, or maybe even 0.517?
Which of these emission-factor levels should we, as professionals, apply? These figures all seek to represent the carbon intensity of the electricity delivered by Britain’s national grid (the amount of kilograms of CO2 produced per kWh of electricity). All the factors quoted have been disseminated by government departments at one time or another to ‘help’ engineers calculate the CO2 emissions arising from the energy used in and by buildings. It’s true that emissions factors have
to take account of an ever-changing mix of energy sources being used to generate the UK’s power. At present, nuclear accounts for around 20% of the total grid mix, but our ageing nuclear plant is being decommissioned, pushing up the fossil fuel share – which means the emissions factor is rising steadily. Consulting engineers need accuracy
in order to make the right choice of solution for each project in hand. Emissions figures are used to find technical solutions that replace grid- supplied electricity, in order to meet statutory carbon reduction targets in, for example, planning applications. So, if there are so many possible factors to choose from, how can engineers be sure of getting the right result? It has to be tempting for a designer,
who favours one particular technology over another, to use the emissions factor that makes the most persuasive case for their preferred solution. There is terrible confusion around this issue and it is vital that we get some clarity and commonality. Without this, there is potential for all sorts of unintended
12 CIBSE Journal August 2011
we can probably learn from the energy markets and their use of ‘spot’ prices. Government departments need to work with some common ‘agreed’ factors. Then we could offer the industry an ‘historic’ figure based on last year’s values; and a ‘future’ figure based on predictions from the energy markets. This would make it easier for consultants to explain their technology choices to clients. One government department should take responsibility and publish these agreed factors each year to minimise confusion. In addition, some experts, such as
consequences. In worst-case scenarios, buildings will meet their statutory obligations but miss their carbon targets because of inappropriate system selection based on the wrong carbon factor. For example, if you select combined
heat and power (CHP), you have to take into account the primary fuel you are using to drive the process. If you assume all the electricity produced on site by the CHP is displacing grid electricity from a coal-fired power station, then your figure will be highly persuasive. But it is less impressive compared with purely gas-fired power generation. The emissions factor can also materially change the size – and even the number – of the CHP engines that are specified: the higher the factor, the more carbon that can be saved using fewer or smaller units. So we need to streamline the method
for calculating the emissions factor, to help designers make more informed choices. However, the government will struggle to select just one figure. The collision of different influences on the mix of grid electricity means the picture is changing all the time. Despite the difficulties of establishing a single emissions factor,
There is terrible confusion around this issue and it is vital that we get some clarity and commonality
Robert Cohen of Camco, have called for harmonisation of emissions factors. For example, given that most Display Energy Certificates are part of a Carbon Reduction Commitment footprint, it makes sense, and would save administrative cost, if both policies were to use identical factors. Using different factors for design calculations and greenhouse gas reporting (DECs, CRC and so on) only adds to the confusion, plays havoc with any ‘as designed’ versus ‘actual’ performance assessment, and is difficult to justify given the current huge uncertainties about the future grid mix. It’s true that, once smart meters have
been rolled out, we may be able to take account of day and seasonal variations in grid factors, and use a ‘marginal’ value. But in the meantime, an annual average is the best available option. The lack of precision, although apparently small, makes all the difference to an engineer’s calculations and can impact on statutory reporting. Getting the equation wrong undermines everything the industry is trying to achieve in reducing the carbon impact of buildings.
l Phil Jones (above left) is chairman of the CIBSE Energy Peformance and CHP groups, and DaviD shaw is business manager of Baxi-SenerTec UK
www.cibsejournal.com
Steve McWilliam/Shuuterstock
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