Figure 1 shows the distribution of the 28,259 assessments against the A to G scale. At the time the DEC system was introduced it was considered that the average for public sector buildings would sit at around the D rating, which has proved to be the case. The average DEC operational rating is 113, which is just above the typical rating of 100 - the 'normal' consumption for a specific building type. One can infer from this that the typical building figure is optimistic.
Approximately 98 per cent of the buildings surveyed and assessed for DECs fall in the 0-200 range, which is also good news. This leaves around two per cent of buildings with operational ratings between 201 to 4,574. Of these, 661 are between 201 and 500. The latter indicates a high number of buildings without effective energy management.
Only 24 buildings appear to have an operational rating greater than 500, four of which have operational ratings in excess of 1,000 (two are over 4,000). At the far end of the scale there is a DEC rating of 4,574. This immediately highlights the quality of the data being made available or gathered for the assessment. Moreover, dig deeper, and one often finds that such high figures are for a modest building such as a community school.
Another figure that is interesting from the analysis is that 3001 buildings have been given an operational rating of 200, which is the software default score for buildings with insufficient energy data to enable a score to be calculated. It is not possible to establish how many of them are actual scores of 200 rather than defaults without sight of each assessment. There is also a possibility of misunderstanding the guidance which could result in new public buildings being awarded default ratings when an asset only DEC should have been awarded.
These high value results are highly questionable. The precise cause of the extreme data in those specific assessments clearly requires further investigation.
At the other end of the spectrum, there are 55 buildings with DEC ratings of 0. Are these buildings powered and heated? Are they not in use, or was there no available energy data? Maybe it is an error of data entry.
Another possibility is that assessors do not understand the CLG guidance documents. This has led to some new public buildings being awarded zero ratings as opposed to asset-only DEC's. An asset-only DEC is provided for a newly constructed public building that will not have 12 months energy consumption data. The data set made available does not list the numbers of asset-only DECs.
While the CLG's process is not likely to be at fault, these examples at each end of the spectrum may be symptomatic of a deeper malaise - the competency of the assessors conducting the surveys, and their level of knowledge, training and experience.
It is also a concern that the 3001 buildings with an operational rating of 200 simply do not have sufficient energy data, or the systems in place to monitor energy consumption. This is especially worrying when energy efficiency and cost savings should be a high priority for all public buildings.
While CLG is to be applauded for bringing in a system that reveals this energy management gap, the trick now is to close it. As the BRE has said: "Display Energy Certificates fail to provide evidence of real energy efficiency improvements and carbon emission reductions in public sector buildings".
It could be argued that there are problems throughout the entire data set. Without the means of validating all the data, it is very misleading to aggregate the consumption data into something meaningful - it simply has too many distortions within it.
To its credit the CLG has recognised the shortcomings and is working with accreditation providers to identify the problems and to devise solutions. It is vital that the quality delivered by the various assessment schemes is continuously improved to meet the requirements of the Energy Performance of Buildings Directive. So what are the pressure points?
One area that the DEC scheme does not account for is process energy, which is discounted during a DEC assessment if it can be separated out. However, this energy is still being consumed and needs to be accounted for - after all, its use may not be efficient. The requirement for separable energy to have been reviewed for energy efficiency in the past two years is a bit vague.
As of 2010, while certain DEC benchmark categories (such as offices) take into account extended hours of operation, the calculation does not take into account occupancy levels and whether they have risen or fallen between annual DEC assessments. An organisation that runs a building with low occupation densities could easily earn a C-rated DEC, but they could well be consuming more energy and generating more carbon dioxide emissions per person than another organisation with high levels of occupancy in, say, an E or F-rated building.
DECs don't take into account building age, so it's not possible to examine and compare buildings by age. This is a shame as it would be good to separate buildings built in the last few years from the older building stock for the purposes of comparison.
Ultimately there is still a lot of work to do with improving building energy performance and efficiency. For instance, if newer buildings could be drawn out of the data it would be possible to monitor the success or attempts to deliver zero carbon schools by 2016 and other public buildings by 2019. The Government's aim must be to establish if the performance curve of energy use in buildings moves away from the current average and closer to the A-rated zone.
What the introduction of DECs has done though, is bring to attention of industry to energy consumption in buildings. They have also provided a foundation of data (in access of 30 000 sets) that is increasing all the time. Before DECs there was no standard form of collecting and analysing this data. Fortunately something is now being done and the process improved over time.
Identifying and correcting data collection errors will serve to rectify the problem of poor data; it could potentially generate a skills set of professionals that are equipped to gather important energy consumption and building data.
The fact that DECs are renewed on annual basis can provide building occupiers, owners and operators with a simple visual guide for a year on year comparison of performance. This should encourage pro-active energy management decisions to be implemented in a bid to achieve energy performance improvements.
The data shows that improving the management of energy use is still very much work in progress. However, over the next few years, with the annual renewal assessments being conducted, a trend of improvement should emerge, reflected in the curve in the graph shifting left as energy efficiency improves.
An improved data distribution would not only indicate a positive response to Display Energy Certificates, an increased awareness of building energy consumption and an improvement in management, but might also indicate better overall building performance. After all, only the best buildings deserve to survive in the long term.
Richard Hillyard was with BSRIA and is now an environmental and sustainability manager with Norland Managed Services. Andrew Geens is Professor of Building Services Engineering at the University of Glamorgan.
BSRIA has accredited DEC assessors and provides independent consultancy to improve energy efficiency in buildings. For more information contact BSRIA:
T: 01344 465600