Building performance benchmarks

For various reasons however, organisations do not place energy consumption high on their list of priorities. Generally speaking, facilities managers concentrate on those issues which directly affect the commercial side of the business, such as ensuring a healthy and comfortable indoor environment for occupants and keeping any equipment running effectively.

Energy efficiency is often a lower profile activity. The big issue is convincing others to release the funds or set aside the time to implement even fairly obvious improvements.

This is where energy benchmarks can make a difference. By being able to compare a building's energy performance against others of the similar type, managers can identify opportunities for improvement, and make a case for implementing them.

Although unconvinced by a simple demonstration that a particular improvement could be cost effective, a board may be better convinced by demonstrating that competitors are doing better in their use of energy, and thus have a commercial advantage. They may be uncertain of the viability of seeking particular specific improvements in energy use, but may be happier with a mission statement which aims to place the organisation among the top 25% of their sector in the efficient use of energy.

Applying energy benchmarks

An indication of the commonly used benchmarks – typical and good practice – can refer to in most cases. Here the distribution covers the electricity consumed per unit area of a sample of buildings used for the same commercial activity.

A building's required energy performance could be set at the median point in the sample, in other words where 50% of buildings in the sample consume more energy. However, a good practice level is often set near the upper 25% of buildings.

That said, comparing a building's performance with published benchmarks is often a fairly coarse measure. The information on which the sample is based may not allow a detailed breakdown into individual end uses of energy, nor contain a detailed description of the activities within the buildings.

Hence guidelines for the hours of use of the services, or of the equipment installed to provide the required level of service, are increasingly useful. These factors might even be used on their own to make comparison with benchmarks if they are the only known or measurable factors.

For example, the factors that work together to determine the size of a ventilation fan can, either individually or in combination, produce useful design guidelines, such as: M the installed fan capacity expressed in W/litre/s of supply air; M the installed fan capacity per unit area treated (which forms a part of the Energy Performance Index Method, or EPIM, being developed by BRE).

Access to benchmarking techniques is now easier than it has ever been. The recent publication of the CIBSE Technical Memorandum TM22:1999 "Energy Assessment and Reporting Methodology: Office Assessment Method" provides ready access to a fully developed method of assessing office energy use, complete with worksheets and comparisons with benchmarks which are probably the most detailed yet to be published.

TM 22 will soon be supplemented by the publication of an annex containing similarly detailed methods of assessing banks and agencies, hotels and mixed-use buildings. These have incorporated benchmarks previously published in the DETR Energy Consumption Guides and the introduction to energy efficiency series of publications.

The future for benchmarks

To understand the energy consumption of buildings it is important to understand what is a consequence of its design, its commercial function and level of servicing, or its occupancy and management, and what reflects its location and the local microclimate.

Without such knowledge, operational targets would necessarily be relatively loosely defined. However, within an individual organisation, where many of the factors can be investigated and understood in detail, it should be possible to develop detailed, realistic and achievable energy targets.