Heat and Energy Efficiency Technical Suitability Assessment: consultation analysis

Q4 Methodologies needed to meet Requirements of a HEETSA

66 respondents provided answers, many making multiple comments. This includes details of methodologies that exist and potentially could be used for HEETSA and gaps where additional methodologies are needed.

Existing Methodologies

Respondents recommended a diverse set of existing tools and standards to assess different aspects of retrofit. The responses have been grouped into 10 categories of methodologies that are currently used for retrofit. It is anticipated that multiple methodologies will be required for each HEETSA building assessment. They are ordered from the most frequent to least frequent recommended categories.

• Frameworks: The British Standards Institution (BSI) Retrofit Standards Framework (Publicly Available Specification (PAS) 2035, PAS 2030 and PAS 2038) was the most frequently mentioned as a quality assured framework and retrofit process. Reference to the Scottish Government’s Net Zero Public Sector Buildings Standard (NZPSB) is also included within this group.
• British & international standards: (British Standard (BS), European Standard (EN) and International Organisation for Standardisation (ISO) were strongly represented covering a wide range of topics. These included moisture control, historic building conservation, building performance evaluation and testing, electrical safety and the new BS 40104 - Assessment of Dwellings for Retrofit.
• Energy whole building modelling tools: Steady state energy models (e.g. Reduced Data Standard Assessment Procedure (rdSAP), Standard Assessment Procedure (SAP), Simplified Building Energy Model (SBEM) and Passivhaus House Planning Package (PHPP)), semi-dynamic models (e.g. Home Energy Model (HEM)) as well as dynamic simulation modelling tools (e.g. Thermal Analysis Software (Environmental Designs Solutions Ltd Thermal Analysis Software (EDSL Tas), Integrated Environmental Solutions (IES), EnergyPlus and DesignBuilder).
• Performance standards: Performance standards backed by quality assurance and certification, such as Passivhaus Enerphit (using PHPP) and the Association of Environment Conscious Building (AECB) CarbonLite Retrofit Standard.
• Technical and industry guidance: Technical guidance for retrofit generally and for Heritage Buildings particularly. This included guidance from various bodies including Historic Environment Scotland (HES), The Chartered Institute of Building (CIOB), Historic England, the Sustainable Traditional Building Alliance (STBA), The Royal Institution of Chartered Surveyors (RICS), the London Energy Transformation Initiative (LETI) and People Powered Retrofit. The Chartered Institution of Building Services Engineers (CIBSE) guidance such as TM54, TM59 and the Domestic Heating System Guide were also noted as useful sources of information.
• Energy & environmental modelling tools for building elements: Suggestions included Wärme und Feuchte instationär (WUFI), thermal bridging modelling, U-value calculations, condensation risk analysis, heat loss calculations and systems efficiency modelling. This highlighted a range of specialist methodologies addressing distinct technical issues.
• On-site investigation methods: Various investigative methods were proposed for surveys, more intrusive fabric inspections and practical testing. For example, in-situ U-value testing, air permeability testing, mould surveys, thermal imaging, ventilation assessment and heritage impact assessments.
• Regulatory, policy and government initiatives: These included Building Standards and Approved Documents requirements. Additionally, the upcoming Scottish Passivhaus Equivalent Standard and the Scottish Government Retrofit Assessment Policy Report. A key consideration was policy alignment in retrofit practice. There was also reference to reports from government funded research: (i) Review of retrofit assessment in Scotland for improving home energy efficiency: technical report^[1] and (ii) Defining and identifying complex-to-decarbonise homes: research report^[2].
• Certification & accreditation schemes: Examples suggested included the Microgeneration Certification Scheme (MCS), Trustmark, the British Board of Agrement (BBA), the National quality infrastructure and UKAS.
• Whole life carbon and costing tools: Embodied carbon, whole life carbon, and Lifecycle Cost Analysis tools to take account of both cost and carbon impacts of retrofit measures over a building’s lifetime.

The gaps identified comprise both methodologies that should be used more frequently and robustly, and a need for new or updated methodologies. Some respondents specifically preferred improving existing methodologies rather than developing new ones.

The following gaps were noted, commencing with the most frequent comments:

• Occupancy assessment: To adequately assess the current occupancy situation, involve the occupants in the assessment process and ensure the retrofit strategy suits the occupants as far as practicable.
• Verified upon completion: Outcomes should be verified upon completion. For example, this could be through post-occupancy evaluation and in-use performance measurement.
• Strengthening data gathering: There were calls for increased in-use performance measurement and more accurate energy modelling generally. A few specifically suggested modelling aligned with CIBSE TM54 to more accurately predict carbon reduction and financial forecasting related to fuel poverty. Lifecycle Cost Analysis and Whole Life Carbon Assessment were recommended to take account of cost and carbon impacts over the lifetime of a building.
• Existing condition & context: Some respondents highlighted the need for the inclusion of information on the building condition and maintenance, with three also highlighting the need to add relevant context.
• Traditional & hard-to-treat buildings: There is a need for more and improved guidance on evaluation methods for traditional buildings and non-standard construction types. The scope of such methodologies might extend beyond those applied to simpler buildings within HEETSA.
• Property specific: A property specific approach was advocated. Respondents warned against using predictive data from software such as RdSAP and against reliance on prescriptive solutions that may not suit individual buildings e.g. defaulting to heat pumps. Respondents also emphasised the need for coordinated planning so that improvements to building fabric, heating and ventilation work together effectively.
• Flexibility: A standardised yet flexible methodology was proposed recognising that different buildings and retrofit scenarios require different approaches.
• Cost of assessments: There were concerns about the cost of the HEETSA assessments.
• Costs of measures: There should be a standard methodology to identify the most cost-effective balance between energy efficiency measures and clean heating technologies. This should account for both upfront and ongoing costs, as well as payback periods.
• BSI framework: PAS 2035 and PAS 2038 have limitations, such as standardised methodologies for assessing outcomes. HEETSA should go beyond the current assessment requirements of these standards.
• Communal and mixed tenure buildings: There is a need for methodologies more suitable for tenements and mixed-tenure properties. For example, greater consideration of communal solutions and addressing multiple owners and tenants.
• Expert assessments: HEETSA should allow the assessment to be based on the expertise of qualified professionals. It should also avoid default lists that cannot be over-written.
• Standardisation: There is merit in the whole industry using the same calculation methods, integration with existing tools and aligning with the upcoming Scottish Passivhaus Equivalent Standard.
• Unsuitability of RdSAP: RdSAP is not suitable for retrofit as it was not designed for this purpose. It contains limited data collection, simplified default values and standardised construction. The resultant level of energy modelling lacks detail and provides poor prediction of both heat loss and financial savings. The list of recommendations is often taken as being technically appropriate for the building when it may not be.