The shift towards a net-zero future is pushing the boundaries of how we understand and manage energy consumption in UK homes. At the forefront of this transformation is the Home Energy Model (HEM), a new methodology set to replace the long-standing Standard Assessment Procedure (SAP). To gain a deeper insight into this development, I sat down with Emma Hart, a Senior Energy Analyst at the Building Research Establishment (BRE), who has been closely involved in the project.
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A New Dawn in Energy Modelling
Meeting Emma at the BRE offices, I was struck by her enthusiasm for the HEM project. “The Home Energy Model is set to revolutionise how we assess and improve energy efficiency in domestic properties,” she began. “It’s not just an upgrade from SAP; it’s a complete overhaul designed to meet the demands of a net-zero future.”
SAP, which has been the backbone of Energy Performance Certificates (EPCs) since 1993, has seen only incremental updates, the last being in 2012. This outdated methodology has become a bottleneck in accurately modelling energy use, especially as we push towards ambitious decarbonisation goals. Emma emphasised, “SAP was great for its time, but the landscape of energy consumption and technology has changed dramatically. We need a model that reflects current realities and future possibilities.”
The Mechanics of HEM
The Home Energy Model is designed with two core components: a centralised calculation engine and flexible ‘wrapper’ components. These wrappers add standardised assumptions, primary energy factors, and emission calculations tailored to different policy needs. Emma explained, “This dual structure allows HEM to be versatile and accurate across various applications, from new builds to existing homes.”
One of the standout features of HEM is its open-source methodology. “Transparency is key,” Emma noted. “By making the code publicly available, we ensure that everyone understands the calculations, which fosters trust and consistency across the industry.” This approach addresses one of SAP’s significant flaws—its decentralised application, which often led to inconsistencies.
Addressing Technological Advances
A significant criticism of SAP has been its failure to keep pace with technological advancements. “The last decade has seen a surge in new energy-efficient technologies,” Emma said. “HEM will incorporate these advancements right from the start, and updates will be more frequent and systematic.” This is crucial for accurately assessing the energy performance of homes equipped with modern appliances and renewable energy systems.
The HEM methodology also boasts a half-hourly time resolution, a leap from SAP’s monthly assessments. This granular approach allows for more precise modelling of energy consumption and the benefits of renewable technologies and energy storage solutions. “It’s about understanding the real-time dynamics of energy use,” Emma added.
The Path to Implementation
The rollout of HEM is planned in stages, beginning with its application to new builds in 2025 under the Future Homes Standard (FHS). This standard aims to ensure that all new buildings are ‘zero carbon ready.’ Emma highlighted, “FHS is essentially a new version of Part L of the Building Regulations, focusing on energy efficiency and the phasing out of fossil fuel systems in new buildings.”
The transition to HEM for existing homes, particularly for generating EPCs, is still under consultation. “We expect consultations to begin later this year, with implementations following thereafter,” Emma informed. The timeline may be uncertain, but the direction is clear—HEM is the future.
The Challenges Ahead
Despite the promise of HEM, there are challenges ahead. The transition from SAP to HEM for existing homes raises several questions. “What happens to homes already assessed under SAP? Will they need new EPCs under HEM? These are critical issues that need addressing,” Emma acknowledged.
The consultation process will be vital in ironing out these details. “We are committed to engaging with stakeholders across the industry to ensure a smooth transition,” Emma assured. The goal is to have a methodology that is not only accurate but also practical and implementable at scale.
Conclusion
The Home Energy Model represents a significant leap forward in how we understand and manage domestic energy use. By addressing the shortcomings of SAP and incorporating modern technologies and more granular data, HEM is poised to drive the UK towards its net-zero targets more effectively.
As Emma Hart succinctly put it, “Our aim is to create a model that is fit for a net-zero future. HEM is not just a tool; it’s a foundation for sustainable energy management in UK homes.”
The journey to implementation may be complex, but with experts like Emma and the dedicated team at BRE, the future of domestic energy efficiency looks brighter than ever.
Tobiasz Karcz
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