Comparisons between the UK Standard Assessment Procedure (SAP) and Home Energy Model (HEM) for a zero-carbon ready home

Zhang, Xinyi; Henshaw, Grant; Fitton, Richard; Sitmalidis, Anestis

Abstract

The decarbonisation of the building sector, a significant sources of carbon emissions, is critical for achieving the UK's net-zero ambitions. To improve the accuracy of residential energy assessments, alongside the anticipated Future Homes Standard (FHS) 2025, the Home Energy Model (HEM) will be proposed to replace the Standard Assessment Procedure (SAP). This paper compares the SAP 10.2 and the HEM using a zero-carbon ready (ZCR) home as a case study. SAP, a steady-state model, is contrasted with HEM, which incorporates more detailed and dynamic modelling of energy flows. The study reveals that HEM predicted 23.92% higher annual space heating demand and 19.22% lower hot water heating demand compared to SAP. These differences are attributed to HEM's ability to account for short-term variations in occupancy, weather, and system performance. Additionally, HEM demonstrates a more detailed representation of photovoltaic generation and consumption dynamics, highlighting its potential to capture the interaction between on-site energy production and household energy use. These findings underscore the limitations of SAP and highlight the importance of adopting more advanced modelling approaches like HEM to support the proposed FHS 2025 and net zero goals.

• Presentation Conference Type: Conference Paper (unpublished)
• Conference Name: CIBSE IBPSA-England Technical Symposium 2025
• Start Date: Apr 24, 2025
• End Date: Apr 25, 2025
• Acceptance Date: Sep 9, 2024
• Online Publication Date: Apr 30, 2025
• Publication Date: Apr 30, 2025
• Deposit Date: Jun 9, 2025
• Peer Reviewed: Peer Reviewed
• Additional Information: Currently, full text is only available to conference attendees via private link. However, based on previous years’ practice, the proceedings are expected to become open access on the CIBSE IBPSA-England website later.