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COMMENT
Methodologies such as predicted energy use from SBEM Part L or EPC ratings are based on standard assumptions that are not in line with how the building will be operated in real life Shikha Bhardwaj, Hawkins\Brown
adapted to the UK, under the management of the BRE. The scheme currently focuses on the commercial sector and aims to address the issue of the energy performance gap between the EPC rating and the actual in-use energy consumption of office buildings. This can be achieved by the two product offerings, including Design for Performance (DfP) and Energy for Offices.
Design for Performance / Energy for Offices Design for Performance (DfP) is a more rigorous process as it starts early, and involves developers committing to design, build and commission a new office or major refurbishment project to achieve a specific rating. However, as it is more process-led, you could follow the approach without acquiring the actual NABERS rating certification. On the other hand, Energy for Offices is used to measure the energy efficiency (of an operational office building), based on metered data and then to rate its performance. Overall, building performance is measured via a six star rating system with a recommended minimum rating of four stars. This is in order to extract the most benefit from the scheme, as it takes a large amount of work and commitment to achieve a good rating. The target is set by the developer/client body, and is then used by designers as the minimum design target for the building. DfP only begins with signing the agreement with BRE that includes the nominated target energy rating. It is a very contractual and commissioning-based approach that ensures steps are taken in a certain way, and recorded, modelled, and monitored to get the desired outcome. The process requires detailed energy modelling at specific RIBA stages that includes all proposed MEP systems and expected plug-in loads. Third-party evaluations in the form of Independent Design Reviews (IDR) ensure the desired rating can be achieved once the building is in operation. The final certificate is issued 12 months after full operation, based on actual energy data. The certificate is renewed yearly to ensure the building is being operated as designed.
The scheme measures and rates areas that generally fall under the
landlord’s responsibility; the Base Building, mainly including HVAC, lifts, domestic hot water, common area lighting, and small power. This is a small proportion of the final scheme, and most landlords don’t operate their own space. The final rating can be highly influenced by tenant fit-out and management processes. Therefore, it is essential to ensure tenants are aware of their obligations.
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Guidance and processes should be in place for clarity – including fit-out guides with detailed design requirements. Tenancy design can be reviewed and modelled to gauge how it affects the performance of the building as a whole, which obviously reduces their flexibility. That might be seen as a disadvantage, but high flexibility doesn’t necessarily create a highly sustainable, low-energy building.
Consider all costs Lastly, the summary would be incomplete without the mention of costs, given it is a highly detailed process and involves specialists, design reviews, registration, and metering – there are many fees associated with the scheme which does make it more costly with potential impacts on the design programme. So, it’s important to get a breakdown of the associated fee and how modelling affects the design decisions to get it covered in the cost plan and overall design programme. Additionally, while the NABERS UK scheme is only applicable to offices, we have had clients request it be applied to lab-enabled offices. This might complicate the process without necessarily providing the benefit of a lower energy outcome or good rating, because the method is only tailored to standard workspace design. For certain scenarios where NABERS UK is not considered the most fruitful and viable, the CIBSE TM54 methodology could be adopted instead. The key is to identify and commit to the detailed processes in spite of the complexity instead of relying on the compliance tools. The benefit of using such a scheme covers designing a building with a more accurate energy prediction, thereby closing the energy performance gap. This is a critical step in setting the right targets and KPIs to help reach net zero 2050.
Shikha Bhardwaj is lead sustainability designer at Hawkins\Brown ADF SEPTEMBER 2023
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