DISPLAY ENERGY CERTIFICATES BENCHMARKS
part of the carbon footprint shown on the DEC. This very low figure probably indicates a lack of sub-metering installed, but perhaps also insufficient awareness of this provision in the methodology. It also suggests that some buildings which currently have poorer ratings would benefit from measurement of separables. There is also a strong case in a number of categories to allow more major electrical equipment as a separable in order to make the DEC Rating more representative. Commentators have
The analysis found that DEC benchmarking worked well for buildings such as schools
argued for DECs to include allowances for high occupancy density. While obviously important, this was considered when TM46 was developed, but was rejected because of a lack of robust, low-cost methods for collecting accurate density information – without which there would be considerable potential for abuse.
Conclusions The initial DEC benchmarks and categories were created from data from many sources, which were variable in their date, quality, accuracy and representation of the stock as a whole. Some building types had very little data at all to inform their allocation – for example, crown courts were put in the ‘general office’ category, and prisons in ‘long-term residential’. It was anticipated that some building types
would turn out to be in the wrong category, or might require new ones. In the event, only 10 of the 237 building types appear to be significantly outside their category or benchmark and would benefit from adjustments or re-allocation, representing only 6.2% of the DECs reviewed. There appears to be a strong case to
extend the definition of separables to electrical ‘process’ equipment in a range of benchmark categories. The prospect
Percentage grade distribution within benchmarks Filtered data – 29,320 Ratings count>80 (decv04 15/8/10)
General office
Schools and seasonal public building
Clinics
Hospital – clinical and research
0 10 Grade A 20 30 B C D 40 E 50 F G 60 70 80 90 100
A number of commentators have argued for DECs to include allowances for high occupancy density
of a better DEC rating is likely to drive building owners and occupiers to meter more separables, and the requirement for a report will help them to understand how to improve the performance of technical equipment often outside the understanding of DEC assessors. To define what should or should not be eligible will require more work and industry consultation. It can reasonably be argued that more densely-occupied buildings should have a larger benchmark, but a serious constraint is how to verify the intensity of occupancy over a year. However, in the same way that separables are allowed if properly metered, buildings with good occupant counting systems might potentially be permitted to make allowances. Metrics for intensity of use need to be agreed for each benchmark
category – for example, perhaps the number of pupils on roll might be suitable for schools, or person-hours per year for offices with robust information from security access systems. The data could potentially be used to adjust the DEC benchmark, to enable a comparable allowance for intensity of use as is currently available for hours of use. This or a similar process might also enable better account to be taken of unoccupied space. Following this initial review, the CIBSE
benchmarking group is now considering appropriate ways to address the 10 building types and four categories that require adjustment of the benchmarks in some way. CIBSE will be consulting on these once proposals are ready. CIBSE is also in discussion with several sectors about the current benchmarks, and how to collect data to assess the appropriateness of the benchmarks for extending DECs to cover private sector buildings.
l The full report and table on the study can be found alongside the digital version of the article at
www.cibsejournal.com The benchmarks for operational ratings are published in CIBSE TM46: Building Energy Benchmarks, available at:
www.cibse.org/bookshop
l Bill Bordass of Usable Buildings Trust, Harry BruHns of UCL Energy Institute, roBert CoHen of Camco, and PHil Jones of Building Energy Solutions, were engaged through the CIBSE Research Fund to carry out the DEC review.
30
CIBSE Journal May 2011
www.cibsejournal.com
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