DISPLAY ENERGY CERTIFICATES BENCHMARKS
RIGHT LEVEL I
The ‘benchmarks’ in Display Energy Certificates have recently undergone a major review, resulting in a number of recommendations for change, write Bill Bordass, Harry Bruhns, Robert Cohen and Phil Jones
n 2008, a milestone for identifying energy use in buildings was reached in England and Wales: buildings over 1,000 m sq which are frequently visited
by the public were required to display an energy certificate showing actual, measured energy use. (This requirement applied only to buildings frequently visited by the public, and it did not apply in Scotland.) The ‘A’ to ‘G’ energy ratings shown on these Display Energy Certificates (DECs) have now become widely recognised as important indicators of building performance. The DEC grade is based on an operational
rating which compares actual building energy use to a benchmark. This rating is a linear scale from 0 (true zero-carbon) to 100, the benchmark value giving the CO2 emissions for typical stock median performance levels) and beyond. The DEC benchmarks cover 29 building
categories and are derived from various sources. But there has been some debate about the accuracy of the benchmark figures. To address this, CIBSE set up a group to review the DEC data, in particular the Operational Ratings and to compare actual ratings with the TM46 benchmarks in order to assess their applicability. CIBSE was given access to the 45,000 DECs lodged on the Landmark national register between October 2008 and mid-February 2010. The review has now produced some concusions and recommendations for revisions – outlined below – for consideration by the Department for Communities and Local Government.
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DEC analysis The DEC benchmarks are based on a rationalisation and considerable simplification of values taken from many sources. A total of 237 different building ‘types’ are identifed in the benchmarks – with each type assigned to one of 29 ‘categories’. Benchmarks are set at the median level for each category (as far as these were known) for annual use of electricity, fuel and heat, assuming standard hours of use. The DEC methodology allows bigger
benchmarks to be earned where buildings are used for longer, but not just for the presence of technical features such as air- conditioning. Mixed-use benchmarks – for example, for a school with a swimming pool – can be built up using the specific component benchmarks and their respective areas. After excluding a number of DECs from the sample because of factors such as implausible floor areas or ratings, the group ended up with 29,310 DEC records, or 65% of the total. Overall, the analysis found that the
benchmarking system works well for those categories most commonly found in the database where the median of the DEC grade distribution was within 2% of the benchmark – for example, for schools, which made up 52% of our sample, or 15,335 buildings. The system also seems to work well
with the median almost exactly at the D/E boundary – for offices 11% of the sample, or
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CIBSE Journal May 2011
www.cibsejournal.com
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