The Home Energy Model and Future Homes Standard assessment wrapper

[edit] From SAP to HEM

The Home Energy Model, or HEM, is to be introduced in the UK to replace the Standard Assessment Procedure (SAP), which is currently used to demonstrate that new homes comply with Part L of the Building Regulations and to produce EPC's. HEM is still under development and is intended to be implemented alongside the Future Homes Standard in 2025. Alongside this the government is consulting on changes to the requirements for EPCs and DECs (see Brief notes on proposed changes to EPCs)

[edit] Why and how is HEM being developed?

In 2021, the government appointed a consortium of experts led by the BRE to carry out a multi-year project to develop a replacement for SAP, which was first published in 1993. SAP was introduced into the Building Regulations to assess the energy performance of dwellings and has been updated periodically in 1998, 2001, 2005, 2009, 2012, and 2022. In recent years, the accuracy of EPC's has received much criticism, summarised in the article Are Energy Performance Certificates Accurate?

The replacement of SAP and the introduction of HEM is a significant change that will impact a wide variety of areas concerning the estimation, demonstration of compliance, and, to some extent, the assessment of energy use in buildings. Given the importance and timeframe for the development of HEM, the government appointed a consortium led by Etude to quality-assure the work being undertaken. This QA process aims to ensure that issues with the current SAP methodologies are identified and clearly defined, evidence for suggested improvements is thorough, validation processes are robust, the decision-making process is clear, robust, and documented, and project governance is working effectively with the government, key user groups, and technical experts associated with key decisions.

[edit] How will HEM differ from SAP?

Where SAP is effectively the calculated or estimated potential energy consumption on a monthly basis, the HEM has the potential to calculate or estimate this on a half-hourly basis. As such, in order to model the energy buildings might use at this level, more detailed data points or inputs are likely to be required.

[edit] What are assessment wrappers?

To manage these broad range of data points or inputs, it is likely that the model will have the possibility to use a number of assumptions rather than inputting individual data for each project. These assumptions may range in relation to the purpose of the assessment, the occupancy patterns, localised weather patterns, links to other building standards, white goods, air tightness, ventilation, and so on. They may also expand with time. The model is intended to be flexible enough to account for and allow for adjustments based on specific buildings while being simple enough to be workable.

[edit] How does HEM relate to the Future Homes Standard?

The Home Energy Model: Future Homes Standard assessment is a methodology designed to assess compliance with the 2025 Future Homes Standard (“FHS”). The Home Energy Model and FHS assessment wrapper together make up the Home Energy Model: FHS assessment; both are still under development and will be implemented alongside the FHS in 2025. All elements of the topic are under development and, as such, are also at the consultation stage, enabling the industry to participate in their development process.

The consultation will close at 11:59pm on 6 March 2024, for further information about HEM, the Future Homes Standard and the consultation visit the government web page here.

[edit] Related articles on Designing buildings

• Air permeability testing.
• Air tightness.
• Applying Fabric First principles: Complying with UK energy efficiency requirements FB 80.
• Approved building energy calculation software.
• Approved documents.
• Building Regulations.
• Building Research Establishment.
• Changes in SAP 10.
• Co-heating test.
• Conventions for U-value calculations (2006 edition) BR 443.
• Dynamic Simulation Model.
• Emission rates.
• Energy efficiency of traditional buildings.
• Energy Performance Certificates.
• Energy Performance of Buildings Directive.
• IHBC responds to Energy Company Obligation ECO4 and PAS 2035.
• National Calculation Method.
• Passivhaus vs SAP.
• Standard Assessment Procedure SAP.
• Simplified Building Energy Model.
• Target fabric energy efficiency rate.
• Thermal dynamic analysis.
• U-value conventions in practice: Worked examples using BR 443.

[edit] External links

• https://www.gov.uk/government/consultations/the-future-homes-and-buildings-standards-2023-consultation/the-future-homes-and-buildings-standards-2023-consultation#legislative-changes-to-the-energy-efficiency-requirements
• https://www.gov.uk/government/consultations/home-energy-model-replacement-for-the-standard-assessment-procedure-sap
• https://assets.publishing.service.gov.uk/media/65783c77254aaa0010050ae3/hem-tp-02-general-summary-of-wrappers.pdf
• https://assets.publishing.service.gov.uk/media/65788b8f0467eb001355f66a/home-energy-model-and-future-homes-standard-assessment-wrapper-evaluation.pdf
• https://www.gov.uk/guidance/standard-assessment-procedure