0.2 CarbonLite Retrofit Energy Targets

Footnotes:

1. Water standards: https://www.aecb.net/publications/aecb-water-standards/
2. Hot water use: http://www.aecb.net/publications/the-importance-of-hot-water-system-design-in-the-passivhaus/

3. Conclusions arising from the work that led to the CLR guidelines.

The AECB has analysed a large number of existing retrofits and carried out detailed modelling of the UK’s most common house types.

• The AECB would expect energy efficiency and comfort standards for new and existing buildings to be demonstrably consistent with the UK’s Climate Change targets. Broadly speaking, this might be Passivhaus, AECB Building Standard for new buildings, AECB Retrofit Standards and other ‘subsidiary’ standards covering water, daylighting and whole life carbon such as this suite of  other AECB standards.

The research behind the CLR guidelines and suggestions arising from them:

• As a result of the modelling work undertaken as part of the CarbonLite programme, the AECB has adopted a working assumption that a minimum 50% reduction in the energy used for space heating across the UK dwelling stock is required – but that due to range in dwelling types, condition and context a standard that allows flexibility is required (see above).
• The CLR is based on the principle that different types of domestic buildings represent different challenges to retrofitters and defining targets (and ultimately standards) should be approached realistically, pragmatically and with an eye on encouraging a level financial playing field for assessment across different ownership patterns as far as possible.
• The CR targets are set out in three categories, based on three ‘archetypal’ UK house types (alternatively these categories can be more flexibly used to identify an appropriate CLR target based on the shape – or ‘form factor’ – of a building).
• The targets are further differentiated into two sub categories, ‘predominantly external wall insulation (EWI) used’ and ‘predominantly internal wall insulation (IWI) used’ – to allow for variations in context for example architectural character, planning, conservation and other financially insurmountable project specific limiting factors.
• The benchmark for judging the percentage heat reduction is based on the modelled energy consumption of the three CLR ‘non-retrofitted’ house types. Therefore CLR offers a set of space heat consumption benchmarks, one based on each ‘unimproved’  house type. The modelled space heat demand has been cross checked with other national modelling results as well as official government measured consumption data. The data has been sense checked against the authors’ own measurements and that of other AECB experts. This provides consistency and a degree of confidence that the benchmarks are realistic and meaningful. This work underpins the new AECB Retrofit Standard.
• With options for EWI or IWI retrofits across three house types this currently results in six CLR targets ranging from around 70% to almost 90% reduction in space heating, depending on the house type.
• The space heat demand figures have been produced using both PHPP and (full) SAP in order to give users of both software packages a familiarity with the discrepancies arising between the two. A full report on this exercise is available here, and is currently being updated and PHPP modelling matched to EPC bands, as part of collaborative working with thePassivhaus Trust and Elmhurst Energy.
• CLR also has also modelled the financial performance of a fairly large number of whole house retrofit scenarios based on the categories above and assumes that a range of measures need to be accommodated. For example, options including: retaining good quality doubled glazing and frames; renewing only the glazed units of windows; using perimeter insulation to reduce heat losses to floor edges rather than disruptively renewing solid floors; different formats for whole house ventilation such as mechanical ventilation systems with or without heat recovery and so on.
• CLR accepts retrofitters will be balancing the cost against performance on each individual project – the energy targets set are called ‘CO₂ prioritised’ in the course material. A second set of backstop SSHD numbers – notionally called ‘Cost Prioritised’ are used to illustrate solutions for each house type around the minimum 50% reduction mark.
• Meanwhile, developments in electrical efficiency, controls, insulation, ventilation and glazing technologies continues apace. CLR has focused on relatively simple, proven technologies that can be implemented now, but is also responsive to successful new approaches and products via the various feedback mechanisms built into the programme: the LEBD and CLR case studies are a good examples of the virtuous feedback loop.