This guidance provides a simplified approach for what should be included in a Decarbonisation Options Assessment and has been developed in alignment with industry standards and methodologies such as PAS 2038: 2021 (Retrofitting Non-Domestic Buildings for Improved Energy Efficiency), BS EN 16247-1:2012 (Energy Audits Part 2: Buildings) and ISO 50002 (Energy Audits Requirements with Guidance for Use) - please see Appendix 4 for the relevant links.
A Decarbonisation Options Assessment may require baseline information to be collected relating to:
1. Context and setting - the building(s) architectural, cultural and historic context, and its physical setting, including aspect and exposure, access, planning constraints.
2. Condition - the building's structural condition, and its construction, services and controls, the presence of defects and the need for repairs or maintenance.
3. Occupancy - the number of occupants and their pattern of use of the building, including set-points and operational limits of indoor environmental conditions (such as temperatures, air flows, illuminance, noise) and any seasonal variations.
4. Energy performance - how much energy the building uses, broken down by uses and fuel type(s), and how its energy performance relates to typical and/or good practice benchmarks - (see section 7.19).
This preliminary information should be collected in advance of site-based assessments to support the identification and prioritisation of suitable decarbonisation options. During a site-based assessment a competent assessor should then evaluate decarbonisation options. For information on sampling and extrapolation options see figure 4 below.
Figure 4 Sampling and extrapolation for similar assets: Where similar assets are within the estate, then consideration can be given to whether assets can be grouped into archetypes (i.e. similar types of buildings, where similar decarbonisation options would be applicable). This would enable a sampling of a subset of these buildings to establish relevant decarbonisation options, costs and installation options. These results can then be extrapolated back up to understand what the requirements would look like for the whole estate. |
Whilst Decarbonisation Options will be specific to individual buildings, there are likely to be some common interventions and technologies which are required across an estate. Prior to the development of an evaluated shortlist of Decarbonisation Options for each site, an initial longlist of potential solutions should be researched to fully understand their potential, and to understand which scope of emissions the different solutions address. Appendix 2 includes a template Decarbonisation Technology Long List to assist the identification of an initial longlist of potential solutions.
This should not exclude any particular activity and include technology groups from energy reduction technologies (e.g. LED lighting, BMS, and fabric improvements) to low carbon technologies (e.g. heat pumps) and zero carbon technologies (e.g. Solar PV), as well as any other innovative measures.
Many Decarbonisation Options need to be considered within a system of interventions and metering/monitoring systems, this offers the optimum to drive decarbonisation both from a technical and cost perspective. This is referred to as a Whole Building Approach (see figure 5 below for further information).
Figure 5 Whole Building Approach Preference should be given to taking a Whole Building Approach to decarbonising a building, particularly with reference to decarbonisation of heating systems. A whole building approach is where all possible carbon reduction opportunities (technologies/solutions) across a building, and their relative interactions, are carefully evaluated to identify the maximum decarbonisation potential for the building through the best selection and prioritisation of carbon reduction opportunities. A Whole Building Approach is important to ensure that carbon reduction opportunities are designed to match the required future energy demand, and are not under/over specified, resulting in excess carbon emissions. For example, it is important that building fabric is optimised to reduce heat losses before a heat pump is installed. This ensures that the installed heat pump size and cost is minimised, and that the ongoing costs of and emissions (prior to Grid Decarbonisation) from operating are reduced. If a heat pump was installed before the building fabric had been optimised, then in time the heat pump would providing excess heating, resulting in excess carbon emissions and potentially other issues such as poor thermal comfort for building users. |
In addition to the Whole Building Approach, consideration should be given to how energy is supplied to different technology options, particularly with regard to Grid Decarbonisation (see figure 6 below for further information).
Figure 6 Grid Decarbonisation Decarbonising the National Grid means reducing its carbon emissions, as in, decreasing the emissions per unit of electricity generated. Renewable energy generation is on the rise, with more renewable generation such as wind and solar farms being connected to the National Grid. Ultimately this means that the carbon emissions associated with electricity consumption will reduce per unit of electricity consumed over time. It is important that the impact of grid decarbonisation is modelled into decarbonisation options when assessing the carbon savings of electricity projects. Continuous grid decarbonisation means that all- electric options are likely to be the way forward in many cases. This is likely to put additional burden onto the local electricity network which may mean that electrifying a building(s) will require grid reinforcement and an additional cost burden. The UK Government have published a trajectory of carbon emissions factors for grid electricity which users can utilise in their evaluation of carbon impacts. Please see Appendix 4 for the relevant link. |
When conducting a Decarbonisation Options Assessment, the following Decarbonisation Options should be considered to optimise the decarbonisation potential. Also, consideration should be given to sequencing that also considers age of an asset and likely replacement timeline.
Whole Building Approach
Fabric First | > Insulation details and airtightness provided for thermal envelope, reducing heat losses |
| > Internal/external wall, cavity, floor and roof insulation to ensure appropriate thermal performance |
| > Use of high-performance glazing to reduce unwanted solar gain and minimise heat loss whilst optimising natural daylight |
Passive Heating, Ventilation and Cooling (HVAC) Systems | > Natural ventilation > Any proposed changes to airflows and/or air handling equipment should be risk assessed to decide which appropriate actions to take. Authorities would need to carry out an appropriate COVID-19 risk assessment, just as you would for other health and safety related hazards recognising current guidance and good industry practice |
Heat and Energy Networks | > Options for joining a heat/energy sharing network should be properly considered and where appropriate prioritised, and where possible this should be served by low or zero carbon technology or at least there should be some longer-term strategy for decarbonisation of any heat network heat raising plant |
Building Level Systems - Heating, Cooling and Hot Water | > Heating, cooling and hot water systems should be served by low or zero carbon technology local heating systems such as heat pump technologies assessing various heat sources (air, water, ground) |
| > Efficient zoning of heating, ventilation and air conditioning systems and controls should be adopted to enhance energy performance |
| > Options for enhanced or newly added heat recovery |
Building Level System - Ventilation and Cooling Strategies and Systems | > Where mechanical ventilation or cooling systems are required, low fan powers, variable speed drives and energy recovery should be implemented to enhance energy performance |
| > Efficient zoning of heating, ventilation and air conditioning systems and controls should be adopted to enhance energy performance |
| > Any proposed changes to airflows and/or air handling equipment should be risk assessed to decide which appropriate actions to take. Authorities would need to carry out an appropriate COVID-19 risk assessment, just as you would for other health and safety related hazards recognising current guidance and good industry practice |
| > Options for enhanced or newly added heat recovery |
Lighting | > Low energy lighting (LEDs) should be implemented alongside optimisation of daylighting and daylighting controls, automated/sensor controls, time scheduling and dimming functions |
Building Energy Management Systems (BEMS) and Controls | > BEMS to enable manageable optimisation of control set points and time schedules centrally. Integration of BEMS with energy metering and sub-meters to enhance energy efficiency and allow identification and implementation of improvements |
Specialist Equipment, Lifts and Small Power | > Specialist Equipment, Lifts and Small Power should be reviewed for energy efficient alternatives |
Low and Zero Carbon Technology | > Low and zero carbon technology options should be reviewed to support options outlined above (such as heating, cooling, hot water), and also to support additional onsite renewables generation (e.g. Solar PV, Wind) Energy storage solutions can be considered alongside low and zero carbon technology |
For some sites it may be that multiple decarbonisation options are equally suitable and provide similar results (e.g. Solar PV and Wind generation), and a choice of technology should therefore be made based on a wide range of metrics such as installation cost, ease of installation, lifetime, operational maintenance costs, cash flow.
In addition to the above, consideration should be given to bespoke and innovative technologies. Gaps in existing technologies are likely to occur where innovative and new technologies are evolving, this currently includes areas such as heat and battery storage, demand side management and artificial intelligence. These should be considered and monitored but may not currently be suitable for a significant contribution to decarbonisation. Furthermore, consideration should also be given to the embodied carbon and overall environmental performance of energy related equipment (see figure 7 below for further information).
Figure 7 Embodied Carbon and Overall Environmental Performance of Energy Related Equipment When purchasing new energy related equipment for a building, selection should be based on the 'overall' environmental performance and specifically the associated embodied carbon of the product. The embodied carbon represents the carbon emissions already associated with the product/service associated with the upstream and downstream processes relating to the product, installation, ongoing maintenance and disposal. This guidance has principally been developed to encourage and enable collaboration around NZ strategies for Operational Energy, but some principles for evaluating embodied carbon are outlined below: Upstream Embodied Carbon: is attributed to the emissions associated with the extraction, transport and manufacturing of the raw materials used in the product/materials before it is supplied to the customer. The Environmental Product Declaration should be requested to draw a direct comparison with market alternatives (more information in ISO 14025: 2006). An EPD is a transparent and objective report which reflects what a product is made from and how it impacts the environment across its entire life cycle. Downstream Embodied Carbon: is attributed to the emissions arising from the ongoing maintenance and servicing of a technology and how the service is provided and the supply of spare parts. Prioritisation should be given to technologies serviceable within the local area first, before wider geographies, and parts that can be sourced within first the UK, then EU before the Rest of World. |