Building regulations - new non-domestic buildings - modelling of proposed energy improvements: research report

Conclusions

201. The aim of this project was to assess and identify potential improvements in energy and emissions performance for new domestic and non-domestic buildings constructed in Scotland set via Standard 6.1 (carbon dioxide emissions). This was to inform the setting of targets within the next set of energy standards, programmed for implementation in 2021. This report focuses on the project findings for new non-domestic buildings.

202. Improvements to the current notional building were identified based on an analysis of where construction in Scotland is already going beyond the current notional building specifications, and relevant literature including Part L consultation options in England and in Wales. These improved measures were assessed based on various criteria including their relative cost-effectiveness and feasibility. Based on this, three new alternative standards (low, medium and high) were proposed and their benefits and costs were assessed at an individual building and national level.

203. The fabric standard of the low option is aligned to the better of the two fabric standards used under the current Section 6 2015 standard. Further fabric improvements are included in the medium and high options. All three options include improvements in the efficiency of most elements of building services over the 2015 standards, some of these remain constant across all three options (e.g. boiler and lighting efficiencies) whilst cooling and ASHP efficiencies improve from one option to the next. The size of PV array under the 2015 standard is limited to the lesser of 4.5% of the GIA and 50% of the roof area; the three improved options adopt a similar approach but raise the percentage of GIA whilst keeping the 50% of roof area limit.

204. The intention was, if practical, to base the notional building on a single fuel/heating system type. This would simplify the current approach where the fuel in the notional building depends on that included in the actual building. It could also help encourage the transition to lower carbon fuels. For all options, it is proposed that the notional building is based on gas heating + PV, with an increase in the array size compared to the current notional building. An exception is proposed if a heat pump is used in the actual building, where an air source heat pump (ASHP) is included and the PV element removed in the notional building. This is to help address the concern that using a heat pump in practice could significantly over-comply if compared to a gas-heated notional building with potentially an opportunity for a significant relaxation in fabric energy efficiency even with an improvement in the backstop values.

205. It is noted that the Scottish Government has indicated that for the next (2024) revision of Building Standards, the intention is to move to renewable or low carbon heating systems in new buildings. One method to delivering this would be to build from the proposed approach for notional buildings to be based on an ‘ASHP only’ specification whatever the fuel in the actual building; this would result in a demanding target that would make it difficult for fossil fuel-based heating to comply.

206. The low, medium and high options are estimated to reduce carbon emissions by 8%, 16% and 25% respectively across the build mix. This was evaluated using SBEM v5.6a and the proposed new carbon emission factors, across 12 buildings selected to represent common non-domestic building and fuel types in Scotland. This compares to a recommendation in the 2007 Sullivan Report to achieve aggregate emission reductions equating to at least 37% on 2015 standards. Hence none of these options would meet this recommendation. A move away from the use of mains gas would be needed to achieve this.

207. It is estimated that the capital cost of adopting a gas heating + PV compliant solution is typically between 1% and 3% higher than the current standard depending on the building type and the optional improved standard (for some building types the capital cost is slightly lower than the counterfactual). Adopting an ASHP compliant solution is estimated to always be more expensive than the equivalent gas heating + PV solution, with the capital cost ranging between 1% and 7% above the current standard. In some cases, the difference in capital cost between Gas+PV and ASHP is very small.

208. The national cost benefit analysis shows that the low, medium and high options result in a net cost of £6m, £23m and £107m respectively.

209. In response to a 2018 amendment of the Energy Performance of Buildings Directive. the Scottish Government proposes that primary energy becomes the main target metric for building regulations compliance. Sensitivity analysis based on LPG, oil and gas CHP district heating, (all higher carbon options than individual gas boilers), suggests that if the carbon emission target is retained as a secondary metric it will help encourage lower carbon fuels.

• The sensitivity analysis was undertaken on a naturally ventilated primary school as it was identified as best representative of the building types to most commonly use these alternative heat sources. It was modelled with LPG, Oil and CHP-lead district heating.
• If the new standard was to be based on the medium Gas+PV option then LPG could achieve compliance if combined with PV and adopting the specifications of the high standard. Oil may be able to comply if adopting the specifications of the high standard and an increased area of PV. District heating with gas-CHP is only able to comply with the primary energy metric when combined with the specifications of the high standard and increased PV areas, and did not comply with the CO₂ metric in any of the scenarios considered in the report.
• In all cases, the carbon target was the most stringent of the two targets and dictated the compliant solution.

The Scottish Government does need to consider the results for gas CHP within its broader strategic goal to encourage district heating.

210. The analysis also considered where the notional building target setting methodology may not reward energy efficient design. In particular, the analysis focussed on the lack of incentive for improved efficiency through adjustments to built form and shape as the notional building dimensions used for target setting are defined as being the same as the actual building dimensions. Our view is that to introduce an incentive for built form would be complicated to implement successfully and would be likely to have unintended consequences. Significant further research would be necessary to assess and develop such an approach in a robust and fair way across a wide range of non-domestic building types and avoiding unintended consequences or loop-holes.