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Home Energy Model: Revolutionising energy efficiency assessments
As part of the drive to improve the efficiency standards of homes, the government has released an additional consultation alongside the Future Homes Standard. This is the “Home Energy Model: Replacement for the Standard Assessment Procedure (SAP)” (December 2023). The current plan will see the HEM go live in 2025 alongside the Future Homes Standard.
Liam Seamer, Senior Consultant – Energy and Sustainability, takes a look at what we can expect from the Home Energy Model and how this will impact how we assess energy efficiency in the UK going forward.
What's wrong with SAP?
The Standard Assessment Procedure (SAP) has been the government’s approved software since 1993. It was originally designed to be a very simple calculation that could be completed using pen and paper by an assessor on site. It evolved over time to its current desk-based assessment, but the core calculation remains the same as the original 1993 methodology. The ability of SAP to accurately model modern dwellings and the technologies they use is limited, often highlighted by the performance gap. In order to robustly deliver a net zero future, a new methodology is needed.
What is the HEM?
The Home Energy Model seeks to shake up the energy efficiency market by introducing a new methodology to assess the performance of a dwelling. The Home Energy Model is the result of a significant development process which has sought to align with modern international energy modelling standards and the best available technical evidence. The HEM represents a change in direction of methodology compared to SAP, with key changes including:
· Increasing the time resolution – HEM uses a 30-minute time interval compared to SAP’s monthly analysis, offering greater accuracy and granularity in results.
· Modelling energy flexibility and smart technologies.
Additional benefits of a new assessment procedure include being in-line with international standards, BS EN ISO 52016-1:2017, and more efficient updates thanks to a new modular software design.
Key takeaways
- SAP is outdated and is known to have limitations.
- HEM is a more detailed analysis of the building, offering 30-minute simulations compared to monthly.
- It is enhanced with smart technologies.
- The timeframe to be able to complete a HEM is likely to increase compared to SAP, therefore costs to developers are likely to increase.
- Energy Performance Certificates (EPCs) are still intended to be an output document of the HEM for use as a point of reference regarding a building’s efficiency. However, the government will be releasing another consultation later in the year regarding EPC reform and how this will be influenced by the new HEM methodology and subsequent EPC results that are generated.
- Dwellings will be more accurately assessed thanks to a more detailed energy tool with greater flexibility to account for different modelling parameters.
What's next?
The consultation has recently ended and the government's response will be published within 2024 with the intent of going live in 2025.
The Building Research Establishment (BRE) has created a draft software giving a very early indication of what the HEM tools may look like, providing the opportunity to interact with the methodology to increase understanding of how the HEM may work.
We will be monitoring the evolution of the HEM to ensure we are equipped to help our clients with any questions and will offer HEM assessments as soon as required.
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