Model beyond compliance to address the ‘performance gap’ and reduce building energy use

We feel strongly that in order to tackle the energy performance gap and ensure that energy efficient design intent is followed through into operation, the role and use of virtual simulation tools in conjunction with an integrated design process needs to be mandated across the industry as a whole; from investors/developers and client occupiers, through to designers, contractors and facilities managers.

The UK construction industry already has these types of simulation tools embedded in the design process through Part L and EPC compliance. But to address the so called ‘performance gap’ between compliance predictions and actual operational building use, the industry needs to start modelling beyond what is required for compliance and undertake true performance analysis across the design-build-operate lifecycle. By doing this it will see significant improvements in energy use, internal comfort, capital spend, and operational costs across new and refurbished buildings.

In April 2018, the Energy Performance of Buildings Directive was revised to encourage a more holistic approach to building performance going beyond energy and incorporating consideration of economic and internal comfort factors.

In 2013, CIBSE produced a standard methodology for ‘Evaluating Operational Energy Performance of Buildings at the Design Stage’ to assist designers in undertaking just this. TM54 outlines a methodology for going beyond compliance modelling by providing an approach for estimating operational energy use at the design stage, accounting for all end uses in the building alongside realistic operating patterns and behaviours.

However, we have found that this comprehensive technical memorandum, has yet to be fully embedded in the industry. We are starting to see TM54 filter through on public projects. But, feedback from our engineering clients has been that a lack of demand from their clients is a major reason for this. We’ve heard many times from them that the client won’t pay for a more advanced model, and so they get a compliance model.

There is clearly more education required on the benefits this approach offers across the whole industry; especially at the investor, developer, client occupier, and contractor levels. But, by using the industry’s existing strengths and technology it is possible to halve energy use in buildings using virtual simulation tools combined with an integrated design process:

Buildings have changed much over recent years, but the way we design, handover and operate them hasn’t. The industry needs to shake off its ‘slow to change’ malaise and catch up with other industries in their use of digital technology and data.

Let’s build better buildings now!

  • UK performance modelling is predominately based on modelling only for compliance
  • Compliance only modelling is a risk that contributes significantly to the Performance Gap in the UK
  • The Performance Gap is often erroneously put down to the difference between how a building is designed and how it’s used by its occupants. This is a factor but it’s not the biggest factor.
  • The Biggest factor is unregulated energy. i.e energy a designer knows the building will use but which doesn’t need to be included in compliance calculations for EPCs and Part L.

  • In fact a CIBSE Carbon Bite on TM54 from the Energy performance Groups states “One of the main reasons for the difference between Part L model results and operational energy use is that the calculation uses standard inputs for variables such as the hours of operation, whilst also excluding numerous energy uses such as small power, external lighting, lifts etc.”
  • In dynamic simulation software it’s very easy to create two different versions of the same model. One that deals with regulated energy for compliance purposes and one that deals with the real building in order to better understand how it will actually perform when built.
  • The industry needs to take responsibility for modelling correctly so that we can focus on and address the other more involved factor of creating a collaborative delivery process. One that ensures integrated performance KPI target setting and tracking right from the start to the end of the process, across design, build, handover, commissioning, and operation via a Soft Landings approach.
  • Accountability for operational performance should ultimately rest with the stakeholder whose interest goes beyond design/construction such as the building owner or operator. At the moment no one ‘owns’ this and as a result building are handed over and then the process of working out how they supposed to operate begins. By employing a separate team or specialist, this is avoidable.
  • Modelling should be done to achieve performance KPIs linked to the real building first and foremost and then a compliance model created from this.
  • Designing just to comply with regulations is bad practice and results in buildings that have ‘unexpected’ post construction issues.
  • For example, we are seeing significant overheating issues as a consequence of a ‘compliance only’ approach. IES recently did a study for Health Facilities Scotland which highlighted that for a hospital bedroom the real world energy consumption and associated heat gains were as much as x6 higher than prescribed within NCM, showing more than 1000 hours of predicted overheating per year as opposed to the zero hours when only undertaking compliance modelling using the NCM.
  • Lack of real building modelling means these issues are missed when they could have been picked up on at design. So really they are not ‘unexpected’ they are ‘avoidable’.
  • NCM data is ok for its intended use in compliance calculations, which is aimed at benchmarking buildings, but it should never be used to inform design decisions.
  • Building performance improves when aspirations are not limited to compliance or, in other words, “going for the ceiling, not the floor” – extract from UKGBC task Group Report Delivering Building Performance May 2016

Over the years, IES has continued to be heavily involved in software development for UK compliance and BREEAM as well as other global rating systems such as LEED. We’ve worked with Green Building Councils all over the world to help create Certification Engines within the IES Virtual Environment (IESVE) that are approved for compliance with relevant rating systems. Our stance, has always been that the role and use of virtual simulation tools beyond compliance, and in conjunction with an integrated design process needs to be more strongly encouraged across the industry as a whole; from investors/developers and client occupiers, through to designers, contractors and facilities managers, with buy in for post-handover operational performance.

Why the contribution is important

There persists in the industry a confusion that needs dispelled; that Part L/EPC Compliance models should somehow suffice for design analysis and in some cases mistakenly be used as a form of operational energy prediction.” The Carbon Trust, ‘Closing the Gap’, report, stated this as a key finding in April 2012.

The compliance model is simply a benchmark exercise and omits key design/energy elements within the building in its calculation. For example, unregulated loads such as plug loads, server rooms, external lighting and so on. This is ultimately why the EPC, currently, won’t align with the DEC, however your Design model could, and a growing number within our industry would say should.

This reliance on Compliance models in lieu of design analysis is contributing not only to un-realistic energy expectations, but also lost energy savings opportunities and also to overheating and other internal comfort issues. Its wastes capex, opex and leads to dissatisfied end users.

We’re currently at a technology cusp. CAD (computer Aided Design) techniques being used at the design phase are the default choice, and being joined by both BIM (Building Information Modelling) and building analyses technologies.

The issue is that buildings do not always operate in real-life the same way as their design intended. This is sometimes called the performance gap, but unregulated energy is a large factor in this. As well as addressing the over reliance on compliance only modelling, its fast being recognised that ensuring design intent is handed over correctly as the building is completed and starts operating is a necessity to bridge this difference between predicted operation and actual operation.

3D models of buildings created purely for geometry, or for performance modelling, or as part of a BIM process are being recognised as a way to gather, store and pass-on important data related to a buildings’ operation.

The ultimate extension of encouraging the industry to undertake true performance analysis at design means that we can also integrate performance into the digital design and construction revolution across the whole building lifecycle. Ultimately, using this technology to align construction and design to the operational use of a building through so called operational BIM or a BIM for FM approach where real operational data rather than design data can be used directly in calibrated energy/simulation models to enable more accurate predictions, optimised operational control and informed decisions on improvement/refurbishment options under consideration.

There is are already much guidance in the industry on this, such as CIBSE TM54 and the UKGBC task Group report, but movement towards this being the norm has been slow. While, there are many compliance based drivers in the industry, the latest Minimum Energy Efficiency Standard (MEES) is based on achieving certain EPC levels, where is the connection to actual operational building energy use?

by EdwinaCramp on June 20, 2018 at 12:28PM

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  • Posted by JAttwoodHarris June 25, 2018 at 12:22

    While i agree for most of the industry there is a real problem with smaller schemes (such as extensions or renovations) where this kind of modelling becomes uneconomic. Renovating existing building stock to avoid sending more waste to landfill must involve in depth surveys if accurate modelling is to take place, putting more cost onto already squeezed budgets. Developers will not take on these costs willingly. These existing buildings (such as the palace of Westminster or Windsor castle) represent a huge amount of the total energy use in buildings, and have much more complicated solutions.
  • Posted by EdwinaCramp July 12, 2018 at 10:43

    Thanks for the comment @JAttwoodHarris. Yes, modelling existing buildings can incur additional upfront costs if an existing EPC model of the buildings doesn't already exist. And as you say developers or others are often unwilling to take on these additional costs when budgets are already squeezed. However, we believe there is an opportunity to encourage the market to accept these smaller additional upfront modelling costs to deliver much more energy efficient buildings because of the savings this approach also delivers in both capital and operational costs. And as you say its the larger buildings that require more comlicated solutions where this technoclogy really comes into its own. The question put was "How can our construction industry use its existing strengths to halve energy use in buildings?" The industry already uses modelling and the UK has a strong history in it, helping address the barrier you highlight and others will enable the industry to step up and start modelling beyond compliance to make a difference. Edwina Cramp
  • Posted by EdwinaCramp July 12, 2018 at 10:50

    This article was added by:

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    Better Buildings: Smarter Cities
    We deliver technology that reduces the carbon emissions of buildings and cities worldwide. Our ultimate aim is to see that technology used by every building of every city to secure a healthy, sustainable and resource-efficient future.

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  • Posted by RTibenham July 18, 2018 at 13:37

    There are currently large holes in the SBEM & DSM modelling methods which prevent healthy innovation from occurring. Some of these are detailed in my own post at:

    In order to realise the levels of energy demand reduction that the government have set out in this challenge, compliance based energy modelling needs to be more detailed. At present, compliance models are unable to regulate ventilation rates based on temperature for example, or include waste water heat recovery systems. The National Calculation Method, with its system of floating 'target emission rates' is confusing to industry participant and consumers and ultimately does not deliver energy efficient buildings.

    It is all too easy for architects and developers to follow a business as usual approach, installing HVAC systems where necessary to deal with poorly conceived architecture, and paying little heed to air tightness, form and shading strategy. This results in designs which are low energy efficiency on the drawing board, never mind in reality.

    The knowledge and systems to do better exist - they just need to be enacted.
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