Narrowing the performance gap: realising the art of the possible

Author: 22/07/2013

It’s a well-known saying that “in theory, theory and practice are the same - In practice, they aren’t”. The difference between actual and predicted energy use in both new and refurbished buildings is becoming indisputable. The size of this difference? Significant – typically at least 150-200% but often much greater. Yet the reasons for this difference are not widely understood.

The 'performance gap'

Several themes are emerging that help to explain why buildings in use are hard pressed to achieve the energy performance predicted at design. These factors span every stage of the building’s life - design, procurement and construction, installation and commissioning, occupation and maintenance -and in isolation or collectively can severely limit the actual energy performance of a building in use. The National Energy Foundation is committed to improving measurably the use of energy in buildings, and we have worked in a broad range of settings to achieve this. The situation is undoubtedly complex, but the scale of the task needn’t be paralysing – there are a myriad of adjustments open to all in the built environment sector which, if taken, will enable us to narrow the performance gap– at an industry and individual building level. 

Building fabric

The passive features of a building are of course integral to its energy performance. Yet the overall fabric performance of the building may not meet design predictions if ‘buildability’ isn’t considered fully, which introduces subsequent construction difficulties. Excellent schemata may not translate well to the physical space, limiting their performance before the building work is even fully underway. The situation can be further compounded by the services design not being realised accurately in physical installation. I champion involving the end-user where possible in the specification process – being involved at the outset sets the foundation for a holistic approach to building performance evaluation and optimisation and can create a ‘golden thread’ of performance outcomes to guide every step of the design and delivery process.

Commissioning process

The segregation of roles, minimal communication and compressed timescales that so often typify the commissioning process mean the rationale of why the building was designed, or systems configured, in a particular way can easily slip off the radar. When faced with a building with which they have had no previous involvement, an incoming Facility Manager has to rely on previous experience to improve its energy performance, and follow best practice in tailoring the building’s settings and services to best meet the occupants’ needs and activities, then monitor closely and revisit frequently. Benchmarks, like CIBSE TM46, and methodologies like CIBSE TM22 are valuable resources to assist this process. The increased uptake of soft landing methodologies, extended and seasonal commissioning are helping to bridge this knowledge gap – and deliver buildings that work for the occupants all year round.

Management systems and controls

Building management systems are inherently complex and interdependent. There is no “set and forget” panacea, subject to both changing occupant needs and operator error. BMS systems often do not retain historical performance data so ensuring that an accurate record is kept over time of settings, key environmental and performance parameters ensures visibility at least of what has gone before – and is a step towards avoiding performance decay. 

The complexity of controls is also emerging as having a significant impact on a building’s performance – no more so than in building lighting. Whatever the M&E system, “Keep it simple” holds true: Non-intuitive controls, with no feedback to the user to confirm successful operation, impenetrable instruction manuals, or rejecting adequate manual controls in favour of complex, remote control - all risk unnecessary energy use. Tackling this issue goes back to the building design phase – and a call for ‘fit for purpose’ solutions that will impact effective use of controls. Regularly checking optimal control settings, taking the building’s occupancy and use into consideration, and ensuring clear and simple instructions at ‘touch points’ where building users interact with the building through manual or remote controls, can make a very real difference to both energy use and occupant satisfaction.

The deployment of sub-meters is now  not only mandatory in new non-domestic buildings but, if correctly configured and reconciled, provide granularity of building energy usage at both a ‘horizontal’ (by floor or area) and ‘vertical’ (by function) level. Conducting a building energy assessment, using CIBSE’s TM22 framework for example, facilitates comparisons (with similar buildings or in the same building over time) and deepens insight into building energy use, providing a robust basis for action – be it system improvement, re-commissioning, fault rectification or occupant guidance.

Improving building performance is reliant on implementing measurement and monitoring protocols, quantifying and comparing performance, and conducting a root cause analysis, to unpick the reasons prediction and practice are different. Responses need to address the cause, not the symptom. How well these responses are implemented of course shapes their degree of success.

Energy use in context and sharing learning

Once actual energy usage is really understood, it needs to be put in context with other, similar buildings. It is then we can share the genuine learning of what works, and what doesn’t. This will take bravery, but the industry is squaring up to this challenge – as can be seen by recent media campaigns. If we can share what really does and doesn’t work, and why, the prize is considerable for us all - lower costs, reduced energy usage and achieving carbon reduction commitments, as well as buildings where people like to live, work and play.

Closing the performance gap

Through our projects and services, the National Energy Foundation is shaping and witnessing the art of the possible in real-life settings in closing the performance gap. When there is a whole system approach to building delivery – addressing eventual energy use at design, procurement, construction, commissioning, hand-over and operation – we will see the performance gap diminish.