Robert Cohen Shares his Views on the Definition of Nearly Zero Energy Buildings
When the government abandoned its long-nurtured zero carbon buildings policy soon after the May 2015 election, the EPBD requirement[1] for all new buildings to be Nearly Zero Energy from the end of 2020 was the last remaining hope on the policy horizon for truly low energy standards to be mandated for non-residential new build. Even after the referendum vote for Brexit, I believe they will still be coming to the UK. But if they do, will this policy deliver the intended transformational outcomes? That will all depend on how Nearly Zero Energy (NZE) is defined.
By 2020, it is now expected that the UK will have left the EU. Nevertheless, that does not necessarily mean the UK will no longer be part of the EU Energy Union. From the energy supply perspective, the UK is far from being an island state: there are many existing physical gas and electricity inter-connectors with the ‘Continent’ and Ireland. Furthermore, our juxtaposition with Ireland places the UK squarely between one Member State and all the others. I cannot see the UK or the EU wanting a trade border in the middle of these interconnectors, so the UK remaining within the Energy Union seems the most sensible option for all concerned. The more interesting point for buildings policy is that the Energy Union is a comprehensive package, relying on both supply-side and demand-side initiatives in a consumer-led market. Energy Union membership comes with also signing up to policies which aim to reduce energy demand. I deduce that, come 2020, the UK will still be required to comply with the EPBD and the EED[2] (both about to be recast by the European Commission this autumn) and the EU-ETS[3].
Ensuring all new buildings are NZE should be a totemic, pivotal part of the EU’s moves towards a secure, sustainable and competitive energy system. It will avoid new construction adding to the existing problem. And it will demonstrate pathways for retrofitting existing buildings to NZE levels. Many commentators and policy makers envisage the vast majority of the EU building stock transformed to the NZE level by 2050, as a fitting response to the 2015 Paris Agreement.
I share this vision, but with a massive caveat: NZE buildings must be defined so that they are not only NZE as designed and indeed as constructed, but most importantly they must also be NZE in operation. In other words, the NZE badge should be reserved for buildings whose energy performance is verified to be NZE compliant by measurements over a year of operation with normal occupancy.
That said, I also believe the NZE requirement should focus only on the energy uses under the control of the building developer, typically those needed for heating, ventilation and cooling (HVAC) to provide a comfortable working environment, together with domestic hot water, lifts and lighting in common parts, i.e. excluding the energy used by the activities and lighting of building tenants, because they are usually not under the influence of the building owner or their managing agent. This base building scope has a strong precedent: it is the traditional remit of building energy performance Regulations.
There is a third perspective needed to complete the NZE definition: how close to zero is ‘nearly’. Stakeholders might expect NZE buildings to be approaching zero energy use on a scale that covers the full range of performance for the applicable building type. Australia offers a template, fully-proven for the operational performance of office buildings and critically making allowances for a building’s hours of use. The NABERS[4] scale for rating office ‘base building’ energy performance has eleven points from one to six stars, with half stars between the whole stars. The scale was calibrated in 1999, when 15% of buildings performed poorer than 1 star, average base building performance was 2.5 stars and 4 stars was best practice. Today, the stock average rating is 4.2 stars, while nearly all new offices achieve at least 4.5 stars, most reach 5 stars or better, and a few are beginning to achieve 5.5 or 6 stars. The NABERS 6 stars level is defined as half-way from 5 stars to net zero energy and is a credible contender for an NZE target that genuinely lives up to the name. In energy terms, it translates to about 30 kWh/m2 of electricity per year for all base building services in an all-electric building.
To summarise, a policy that requires all new buildings to be ‘nearly zero energy’ from the end of 2020 must make verified in-use performance the objective. Only this approach can help solve the energy trilemma. The Design for Performance project led by Verco and the BBP[5] is exploring the technical and market mechanisms needed for new buildings in the UK to achieve verified low energy performance.
[1] See Article 9.1(a) of Directive 2010/31/EU of 19 May 2010 on the Energy Performance of Buildings (recast)
[2] Energy Efficiency Directive
[3] Emissions Trading Scheme
[4] NABERS (the National Australian Built Environment Rating System) covers energy, water, indoor environment and waste. The NABERS Energy rating scheme has enjoyed particular success in driving improvement in energy performance of larger prime office base buildings in Australia, for which it is now mandated (on sale or let) by the Building Energy Efficiency Disclosure Act 2010. NABERS is also available, but less widely used, for office tenant ratings, whole office buildings, and for shopping centres, hotels and data centres. NABERS Energy is based on measuring and benchmarking the CO2 emissions arising from the energy use of buildings.
[5] Better Buildings Partnership
Robert Cohen
Robert Cohen, Technical Director at Verco Energy Consultants, managed the PROBE POE studies (1995 to 2002) then led two European projects which paved the way for non-domestic building energy performance certificates to be based on metered energy use. More recently, he helped develop the Low Carbon Workplace Standard for the Carbon Trust, the TM22 Energy Assessment and Reporting Methodology for CIBSE and the Landlord Energy Rating for the Better Buildings Partnership. His ambition is for actual building energy performance to matter.
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