Opinion

Using BIM to close the performance gap

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Over the last 12 months we’ve seen an encouraging shift in the understanding of BIM in the UK. The true value of BIM is becoming clearer, in that the ultimate outcome is not 3D CAD and coordinated services design, it’s the creation, capture, analysis and sharing of information throughout design, construction and operation of an asset.

Embodied Carbon and Capital Cost are highlighted within the BIM Task Group mission statement to reduce waste in the construction and operation of our built environment. The introduction of BIM level 2 will enable this goal to be achieved and it is widely perceived that this will be the start of savings and increased efficiency within the industry. As a result, a clear definition of a client’s aspirations in terms of performance are crucial for a project and ultimately a buildings success.

At the recent BRE/BuildingSMART BIM prospects event, AECOMs David Philp – a leading light in the implementation of the UK Governments BIM strategy suggested that the Soft Landings framework coupled with the Government BIM strategy is a ‘golden thread’ linking data created during design with the operational phase of buildings. In order to better manage buildings with a view to reducing cost and carbon, we need to better understand their design intent and how they are being operated in reality. It is estimated that 80% of cost lies beyond the construction team involvement.

Energy Management using BIM
So, how do we look at energy management using our Building Information Model? The first step is to set up an Employers Information Requirements report (EIR) before any design is carried out. Performance against those requirements can be checked and evidenced as design progresses.Typically performance metrics will focus on cost, carbon, and comfort, there may also be specific goals such as BREEAM Excellent and/or a particular EPC rating.

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Historically it’s been challenging to validate how buildings perform in real-terms, and to compare that with the expectation that may exist at the design stage. A very simple example of this is when we compare a buildings Energy Performance Certificate (EPC) against its energy bills and Display Energy Certificate (DEC). This has resulted in what many refer to as a Performance Gap, but in fact the EPC would never reflect the real building energy consumption as it doesn’t take into account unregulated energy end uses, out-of-hours operation, or special functions within the building.

CIBSE Technical Memorandum 54 published in August 2013 provides a methodology for more accurate energy prediction at design stage. The document advocates the use of Dynamic Simulation Software and creation of a ‘Design’ model alongside the ‘Compliance’ model which utilises best estimates for loads, occupancy and lighting patterns etc.

The BIM Process
The EIR is set out at the Strategy stage of a project. Plain language questions relate to strategies for providing electricity, gas and water. Even before a model has been created,the designers can respond to questions related to availability of resources on the site and climate considerations.

Moving through to Briefing and Concept Design stages, a basic building model will be developed and the performance with respect to Energy/carbon, daylighting, comfort, water consumption, LZCT, materials environmental impact, capital and running cost is evaluated. We might choose to produce preliminary Part L Compliance and EPC certificates at these early stages to ensure that the design is on track.

As design progresses, the layout of the building will change on a regular basis.Construction elements might also change and regular tweaking and re-evaluation of performance is carried out. The Final EPC, BREEAM, and Part L certificates are produced during the Design phase.

In the Build and Commission phase, a Construction model is developed and the construction process is underway. Again there may be a need to re-visit the performance metrics if changes are made to the design – different windows, an alternative cladding system. Once the building and systems are assembled we can carry out Enhanced Commissioning, we can pull metered data from the building back into the simulation software to compare the Design with the As Built scenario.

In line with the Governments Soft Landings framework at Handover evidence with respect to energy/carbon, cost, visual and thermal comfort, controls strategy is created and captured. During

Operation and Maintenance we can create a feedback loop, capturing metered data, comparing with the design scenario and feeding information into subsequent designs. At a future date when there is a change of use or proposed refurbishment of the building an assessment can be made based on the data gathered over time as to what the most cost effective improvement measures would be.

BIM is mind-set and process, not just technology
Model Level of Detail (LOD) appropriate to the design stage is critical. The technology for this has been around for some time now and is continually evolving.However technology on its own does not provide a BIM solution. Process and the mind-set of people involved in the process needs to change in order to fully exploit a BIM enabled workflow. This is starting to happen more and more as the industry moves along the adoption curve.


At IES our experience is that customers who get the process right see the technology fit together much better. This was evident at our recent BIM faculty event where we had guest speakers from the industry speak about their experiences of a BIM enabled workflow and successful BIM Interoperability. To view these examples visit http://www.iesve.com/discoveries/tag/bim/.

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