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Home Energy Model - CIBSE Response

Executive Summary of CIBSE Response

The consultation has been problematic for industry to effectively respond to.

The launch of the two HEM consultations coinciding with the Future Homes and Buildings Standards Consultation and the Heat Zoning consultation over an annual holiday period has been problematic for industry. We believe the industry has put their best efforts into responding to the Future Homes and Buildings Consultation but has not had enough time to digest and effectively consult on the Home Energy Model consultations. The 3-week extension was still not sufficient time to co-ordinate any meaningful evidence gathering (which is planned at the start of the consultation process based on the closing date of the consultation period) to support our consultation responses due to the late notice of the extension, and since it was not a simple extension, but a necessary one to re-visit some of the earlier analysis and draft responses.

The consultation period given to respond has also been compromised by the following issues:

  • the three FHS / FBS / HEM consultations had the same time frame for responses, and a similar timeframe to the heat zoning consultation
  • the time frame given was over an annual holiday period,
  • the consultation packages are among the largest and most significant consultation
    packages the industry has received to date, making it difficult to focus efforts on all
    consultations at the same time,
  • the consultation is essentially about a python code that the industry lacks expertise in understanding, thus they are unable to effectively identify issues within the coded
    language. This creates a barrier for industry to effectively contribute and raises concerns around the tool being a ‘black box’; when testing using the pilot online tool they are unable to determine the reason why certain inputs do not provide the desired outputs.
  • the consultation lacked evidence of how it has been tested (e.g., certain equipment has been found not to perform as expected within the FHS wrapper and this has raised questions as to the robustness of the testing specifically with regard to PV diverters and batteries) – this continues to be the case, after the issues acknowledged by DLUHC which led to the extension); we have been provided supporting information and would be happy to share this with DLUHC on request,
  • the consultation documentation lacked important details (e.g., how will the core HEM tool be protected, what safeguards will be put in place to prevent altered versions of HEM being used for compliance, what is the proposed timeframe for implementation and plan for training and upskilling the industry and what is the proposed plan for the PCDB). These large overarching questions make it difficult to ascertain responses on the specifics around the methodologies and smaller questions given in the consultation (e.g., what are your thoughts on the choice of name for the new model?).
  • the consultation package was not complete when launched (i.e., the publication “Domestic Hot Water Use: Observations on hot water use from connected devices” is still awaiting publication by DSNEZ, and BS EN ISO 52016-1:2017 referred to in Q16 of the HEM consultation needs to be purchased in order to review it as part of the consultation), and the online tool had various issues (i.e., it was not available for various periods during the consultation period and was found to have an error approx. 3 weeks before the consultation deadline).
  • the supporting Q&A sessions held by DESNZ did not explain in any detail what was
    included within the consultations and were not best placed to answer the majority of questions relating to the specifics of the consultation, pushing these questions instead to DLUHC (e.g., proposed changes to the PCDB and the cost/testing ramifications on existing products in the PCDB, methodologies that under pin HEM, validation exercises carried out).

As a result of these issues, and despite our great efforts to engage with our members, we have received limited comments and so our response is not as comprehensive and detailed as we think this consultation deserves.

About the Consultation

The Home Energy Model: Future Homes Standard assessment is the methodology which will be used to demonstrate that new dwellings comply with the Future Homes Standard.

It will replace the Standard Assessment Procedure (SAP) version 10.2 for the energy rating of dwellings.

The Home Energy Model: Future Homes Standard assessment is still under development and will be implemented alongside the Future Homes Standard in 2025.

The government consulted on the Model while it was still at a formative stage, so that industry could participate in the development process. This consultation:

  • summarised the development work undertaken to date; and
  • invited feedback to enable further model development in advance of its introduction

It was part of a wider government package of material relating to the Home Energy Model and the Future Homes Standard.

You can see further details and the consultation questions on the consultation platforms.

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