The London Energy Transformation Initiative (LETI) released an opinion piece in February 2023 which looks to challenge the current methodology of calculating the carbon impacts of operational energy, whereby they are largely conducted solely in reaching compliance. Currently embodied carbon and operational energy assessments are looked at separately, whereby the operational energy figure (kWh) is multiplied by a carbon factor (kgCO2e/kWh). This figure would then be used in addition to the embodied carbon (kgCO2e) figure to create the Whole Life Carbon (WLC) value. However, both are highly related and LETI have investigated methods in which they both can be considered in conjunction to inform design decisions.
As part of this study, LETI investigated the following methodologies:
- An annual total approach – utilising either a single carbon factor applied to energy consumption or an average of annual figures over the 60-year lifecycle as the grid decarbonises.
- An hourly approach – different carbon factors are applied for each hour of the day, depending on the carbon intensity of the grid.
- A split grid carbon intensity – two carbon factors with the higher carbon factor applied to energy use above the LETI Energy Use Intensity (EUI).
- Renewable procurement – varying carbon factors are applied based on whether renewables are implemented in the development.
- Embodied carbon of energy infrastructure – includes embodied carbon of the energy infrastructure.
- Modelling uncertainties – investigating the uncertainties around WLC modelling and ways to acknowledge this.
- Don’t bring operational energy and embodied carbon together – keeping the methods separate.
- Other ideas considered – other ideas were explored.
An investigation of all these methods was undertaken, applying them all to 6 separate case studies across homes, offices and schools use cases. Through an internal voting process, it was determined the most suitable method to better understand the trade-offs between operational energy and embodied carbon was ‘A split grid carbon intensity’ in conjunction with ‘Embodied carbon of energy infrastructure’.
The split carbon method looks to support those buildings which take advantage of the decarbonising grid. This applies a decarbonised carbon factor to the first portion of the operational energy (representing the first 20 years of a developments lifespan) up to LETIs EUI target (a target set for buildings in order to reach the UK’s climate change targets and achieve net zero operational carbon), then a non-carbonised factor to any remaining energy above this (representing years 20-60), as shown below.
Figure: Split carbon factor conversion methodology (Source: LETI)
Due to the large uncertainty in how quickly and how much of the grid will decarbonise, this method must present two scenarios, known as ‘uncertainty bookends’. This shows two opposing scenarios of no decarbonisation and full decarbonisation of the grid as shown below. This method also includes the carbon impact of energy infrastructure including generation and distribution, which can be obtained within software such as GaBi or the ecoinvent database.
LETI highlight that the next steps are to understand the widespread thoughts on this proposition and look to further establish the methodology, consulting with RICS, UKGBC and others.
Moving forward with WLC analysis the proposed method is extremely viable and certainly the most accurate, providing advantage to those developments which do choose to reduce their emissions in line with the UK’s climate targets and would encourage all developments to do so to reach these operational energy targets. This method certainly shows promise in pushing the industry into taking advantage of the decarbonising grid and with further input from established boards this will hopefully be implemented as a recognised methodology for calculating Operational Carbon.
Written by Ajjay Dhesi