CIBSE tackles task of operational energy performance of buildings
CIBSE has addressed the task of assessing the operational performance of buildings at the design stage with an ambitious 2-year programme that has culminated in the publication of new technical guidance, TM54.* Hywel Davies, CIBSE’s technical director, explains, ‘There has been a growing awareness for some time that many “low-energy buildings” use more energy than the designers thought they would. The performance of low-energy designs is often little better, and sometimes worse, than that of an older building they have replaced or supplemented.’
The aim of TM54 is to provide building designers and owners with clear guidance on how to evaluate operational energy use more fully and accurately at the design stage. There is also advice on how to make more accurate estimates based on the intended use and operation of the building.
Dave Cheshire of AECOM and one of the principal authors of the report explains that one of the objects of TM54 is to demonstrate that the energy performance of a building depends on how it is used and operated, as well as how it is designed and built.
This issue is highlighted by a graph (Fig. 1) that compares the annual energy consumption predicted by an original Part L model with actual energy consumption being three times higher. Using the approach of TM54 produces an estimate of energy consumption that compares well with the actual figure. A feature of TM54 is to give an range of expected energy use (as indicated in the central bar in Fig. 1).
Anna Menezes, the other principal author of TM54 and a research engineer with AECOM, explains that once basic information about the building such as area, operating hours and occupancy is to hand, the guide provides a set of questions for discussion with the user about how the building will be used after completion.
There is detailed guidance on the evaluation of energy use for a range of purposed such as lighting, small power, server rooms, domestic hot water, space heating, cooling etc.
Since TM54 is concerned with evaluating operational energy performance at the design stage, Anna Menezes suggests that several analyses should be carried out throughout the design process as a way of fine tuning the estimates and improving the performance of the building.
John Snoxall, head of British Land’s business group, says, ‘Buildings, once operated, typically consume between 50 and 150% more energy than original expectations. This highlights that there is a real opportunity in new buildings to align operational performance with design assumptions, which will in time result in delivery of more efficient buildings. This CIBSE TM is therefore very timely and encourages building designers to consider energy at the design stage to improve the understanding of operational energy performance.’
CIBSE president George Adams comments, ‘TM54 is a tremendous milestone moving forward, but we still have a lot to learn and involving architects, clients, contractors and manufacturers is a vital part of the process.’
* TM54 ‘Evaluating operational energy performance of buildings at the design stage’ is available as printed or pdf versions from the CIBSE web site. See link below.
