23/08/2017

The practicality of the Simplified Building Energy Model – the most common method used to determine Energy Performance Certificates – is increasingly being questioned as MEES legislation approaches.


With Minimum Energy Efficiency Standards (MEES) legislation coming into force next year, the issue of building energy performance – and how it is measured – has come sharply into focus.

As of April 2018, MEES will bring in a new legal standard for minimum energy efficiency that applies to rented commercial buildings, posing both obstacles and opportunities for landlords, developers, lenders and investors.

Currently, commercial buildings have an energy efficiency rating that ranges from A to G, with F and G being the worst performing. Under the new law however, a minimum Energy Performance Certificate (EPC) rating of E will be enforced, meaning buildings will be barred from being let to new tenants unless they can make the grade.

According to the EPC register, 18 per cent of commercial buildings in the UK with a certificate are rated F or G. The number of overall properties that fall into that band is likely to be even higher considering those that have remained unsold or unrented since before 2008 (when non-domestic EPCs were first introduced) may not have been assessed at all.

While this has resulted in some owners hastening to execute major energy efficiency improvements on their properties in order to meet MEES requirements – which is something generally to be welcomed from an environmental perspective – there remain certain controversies concerning the way in which the majority of EPC ratings are determined. That is through the Simplified Building Energy Model, or SBEM.

The problems with SBEM

The SBEM, which supports the National Calculation Methodology (NCM), the Energy Performance of Buildings Directive (EPBD) and the Green Deal, is used to generate EPCs for non-domestic buildings on construction and at the point of sale or rent.

As one major case study for the international journal, Buildings and Energy, summarises: “Simplified models are a quick tool for energy assessment, and that is the main reason for many countries to adopt this approach in their building energy regulations. However, simplified models may also have a considerable uncertainty in their results, which may compromise the building energy labelling process.”

One of the major reasons for a SBEM’s unreliability is that it’s possible to evaluate energy performance based only on the basic information immediately available to the assessor, either via visual observation or data supplied by clients. Where data is not available, simple assumptions relating to the building’s thermal insulation, energy system design and equipment parameters are made. While this makes the process quicker to produce, each assumption will be based on default figures rather than actual ‘as built’ data.

The consequence of this method is that various systems are often graded at a lower efficiency level, leading to the whole building asset being certified as less efficient. In terms of MEES this can be very significant, with the EPC grade able to be pushed over the threshold (i.e. from D down to F). The reverse outcome is also possible, whereby a building can be passed as meeting the required energy efficiency standard, when in reality it falls below.

The problems associated with SBEM don’t end there.

In the UK, SBEM can be carried out by assessors with little to no experience or qualifications in implementing energy efficiency projects, creating a “race to the bottom” scenario whereby landlords looking for a quick EPC fix often opt for the lowest priced offering.
This has further compounded the situation explains SMS Plc’s Head of Energy Efficiency, Sean Keating.

“By mandating the use of a modelling tool you pre-suppose some standard results. But the results are highly dependent on the competency of the energy assessor, the time allocated to the job, the quality of the data collected and input relating to energy and fabric systems,” he says.

“An EPC in the market is considered as binary – either one is produced or it isn’t. In practice this leads to the focus being on getting one quickly and cheaply. In contrast to this, a proper energy assessment requires a good level of skill, good availability of information and an appropriate amount of time to undertake the study. There is conflict between these two requirements.”

As a result of all this, landlords are being left with EPC ratings that can be far from accurate. Many buildings, therefore, end up with a certificate of F or lower when a more thorough assessment of the site might well find it is actually above the MEES minimum (E or higher).

In these circumstances, the property owner would be quickly mandated to make a marginal improvement in energy efficiency based on false information. Wouldn’t it be better for owners to be aided in order to plan and execute more substantial refurbishments that improve energy efficiency and improve rental value?

Dynamic Modelling not the answer, either

A further issue concerning SBEM in relation to MEES is that rather than just being used to calculate energy regulation compliance, it is now being used in the actual design of new buildings with the aim of ensuring that they achieve these compliance minimums. Besides being a purpose for which SBEM was never intended, this can create yet more problems, says Keating.

“For property management organisations with a reactive mentality, there is certainly a risk of using SBEM as part of a design approach – essentially designing energy conservation measures based on the need to get across an EPC grade boundary.”

Rather than genuinely focussing on improving energy efficiency for both maximum financial and environmental benefit, Keating stresses the use of models in this way exposes “the backward engineering of building energy efficiency measures to meet the constraints of the grading methodology.”

This not only goes for SBEM, he says, but also for Dynamic Simulation Modelling (DSM), which is considered a more robust, sophisticated, and accurate methodology of calculating and designing a building’s energy performance.

Though DSM has significant advantages over standard assessment tools like SBEM – largely owing to greater emphasis on more complex external factors such as solar gain, as well as more accurate occupancy and activity profiles – it is still reliant on some unrealistic models of behaviour.

Despite its benefits, for this reason DSM is not the ultimate answer if realising greater overall energy efficiency is at the heart of property owners’ intentions, rather than just compliance.

More scrutiny of EPC assessments needed

So what might this mean for future of building energy performance, the models that measure it, and how both can be improved in order to achieve better overall energy efficiency?

“Investment in DSM should not be the first priority; it is the processes around the modelling which are more important,” says Keating.

“From my experience the insufficiency of energy modelling is not clearly understood by most property management agents. A reason for this may be that the group are shielded from the impact of the inaccurate assessments; by not holding responsibility for the operation of buildings and the associated energy budget.”

However, with EPC grades now increasing in importance due to the introduction of MEES, this is set to have a bigger influence on property valuation and rent reviews, meaning the property management industry should start to wake up to pitfalls of poorly scrutinised EPC assessments.

“These organisations will need to start by challenging the assumptions input into their EPCs,” Keating recommends. “Good energy consultants will be able to scrutinise these and advise on accuracy as a first step towards planning to improve asset efficiency, as well as associated EPC ratings.”

The more frequently and more thoroughly EPC assessments are inspected and questioned, says Keating, the better the modelling processes will become. This in turn will result in the reality of buildings’ energy performance being reflected more accurately and help highlight optimal design options for more precise and cost-effective energy efficiency modifications.

The future: BMS integration

Despite their glaring drawbacks, SBEM and other calculation methodologies are unlikely to go away as a mechanism for evaluating the ‘asset efficiency’ of buildings. While models may be refined down the line as a greater number of EPC assessments are challenged by more enlightened property owners, Keating believes the grandest gains are to be made through the integration of smart technology in building management and design.

“Models will be relevant in the future,” he assures, “but increasingly I would expect these to become calibrated by linking up with building management systems, sub-metering, weather data and Internet of Things (IoT) devices to create more intelligent and useful pieces of management technology.”


For more information on how we can help your property realise better energy efficiency, get in touch. Contact our Energy Management team on 02920 739 540 or email us we’ll get back to you. 

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