Arup Thoughts: Measure energy to cut carbon
Have you ever considered that the route to a low-carbon future may not be through measuring carbon at all? Trying to appraise a building’s operational performance by its carbon emissions can be complex and confusing. However, energy consumption is a much clearer metric.
As engineers and building designers, we’re used to dealing with energy in units of kilowatt-hours. So we can design buildings to use less energy. We can also monitor and measure that energy consumption through utility bills – usually the electricity and gas a building uses.
However, as the world tackles climate change, the focus has shifted towards carbon. So we must convert our figures for energy consumption into carbon emissions. The idea is to try and achieve the lowest possible carbon emissions – because different forms of energy produce different amounts of carbon.
In other words, carbon is being used very much like a common currency. This introduces complexity because the exchange rates used to convert different forms of energy into carbon changes frequently. For example, if more renewable or nuclear power generation comes on-stream then the carbon content of electricity from the national grid would be reduced. Similarly, as the proportion of gas imported to the UK increases, so does the carbon intensity of gas fired plant equipment. This can radically alter the choice of systems and solutions put forward by design teams.
For a building designer, this means the rules keep changing – sometimes even during the life of a project. The carbon factors used to determine Building Regulations compliance and Energy Performance Certificates in the UK are updated with each new revision, typically every three or four years. As a result, it is possible for completed buildings to be labelled with a very different energy rating than expected during design, potentially leading to premature obsolescence.
When the 2006 Building Regulations were published, the ratio of carbon content per kilowatt-hour between electricity and gas was just under 2.2. In 2010, this ratio had risen to more than 2.6, an increase of 20%, and it continues to change over time. This makes it hard to confidently predict future building performance compared to an identical building served by a different energy source. That building may use the same amount of energy as when it was designed, but perform less well on carbon emissions because the exchange rate has changed.
So what can we do about this situation? Governments and their advisers should take a more long-term view of the carbon content of fuels, especially grid supplied electricity, when they revise Building Regulations. Using 15-year averages would be better than using three-year averages and would help to stabilize the market.
But I think this misses the point. Energy efficiency should focus on reduction of consumption in the first instance, before considering the carbon content of how that demand is met. Energy consumption is readily measured and managed through direct metering, without the need for currency conversion. The introduction of a cap on energy required to meet the base building loads (such as the Fabric Energy Efficiency Standard developed for domestic buildings) would be a sensible step for the non-domestic sector.
Thinking of a low-energy future instead of a low-carbon future also puts the numbers in terms people can more readily understand. Too much emphasis is placed on the comparative difference between carbon emissions from buildings still in design and calculated benchmarks. A return to absolute energy demand figures would be more intuitive and transparent for all involved in the property industry.
We don’t need such complexity to tackle climate change; simply focusing on reducing energy consumption would still lower carbon emissions and also be likely to motivate building users through tangible reductions in their energy bills.
Roy James is an associate director at Arup with more than 14 years of experience as a building engineer, particularly on commercial office developments. His blog originally appeared on ARUP's Thoughts Blog. Edited by Jessica DuBois-Maahs, associate content manager, CFE Media, jdmaahs(at)cfemedia.com.