When setting a low-carbon objective for a building, it is important to clarify how design decisions relate to that objective. A useful emissions assessment helps an investor understand why an option is preferred. Its purpose, data and included sources should therefore be defined together. Energy modelling can form an important part of the assessment; how results will inform project decisions should also be discussed at the outset.
Start by defining the purpose
Comparing design options, assessing an occupied building and preparing an organisation’s emissions inventory serve different purposes. A corporate inventory considers the organisation’s reporting boundaries and activities. A building energy analysis does not replace that entire inventory. A corporate inventory groups emissions as direct (Scope 1), from purchased energy (Scope 2), and other indirect emissions (Scope 3). GHG Protocol — Corporate emissions accounting.
The initial decision is which question needs answering. For example, a system selection discussion may examine options’ expected energy use and associated emissions. An operational assessment may instead prioritise understanding actual consumption. Identifying who will use the result and for which decision provides a useful starting point for discussing the information needed and the report’s contents.
Consumption, cost and emissions are different indicators
Energy consumption describes the quantity of energy used, while cost describes its financial value. Energy-related emissions accounting links consumption data with emission factors for the relevant energy source. A factor’s source and the period it represents affect how the result should be interpreted. GHG Protocol — Calculation tools and emission factors.
It is therefore useful to view energy, cost and emissions results separately when assessing an investment. When comparing options that use different energy sources, a change in one indicator should not be assumed to occur in the same proportion in another. Energy modelling can also help examine design options in terms of energy use and operating cost. US Department of Energy — Energy modelling for design decisions.
Which decisions can energy modelling support?
An energy model calculates building energy behaviour using geometry, construction characteristics, systems, operating conditions and climate data. This approach supports the examination of design and system options. Results depend on the conditions defined in the model. US Department of Energy — Building energy modelling.
When moving to an emissions assessment, the compatibility of energy results and the emission data to be used needs to be reviewed. Seeing options compared under the same operating assumptions helps explain the reasons for a design decision. For an occupied building, measurements and operational information provide a separate data source; design predictions and actual performance should be clearly distinguished in the report.
Recognising a building’s other emissions sources
Material production, transport and other life-cycle processes are also associated with emissions. The boundary for assessing materials’ embodied carbon should be defined separately from energy-related emissions. European Commission — Buildings’ life-cycle carbon impact.
The release of some refrigerants into the atmosphere also has a climate impact. US Environmental Protection Agency — HFCs and climate impact.
These topics make it important to discuss which sources will be included at the outset. A discussion that begins with energy analysis can separately establish whether a broader emissions assessment is needed. Keeping each result’s included sources clear makes the assessment understandable to the decision-maker.
What is useful to see in a results report?
Decision-makers should be able to see the starting conditions for a comparison alongside the period and operating assumptions used. Clearly stating the assumptions under which an option was assessed makes it easier to apply results to design decisions. The same framework can show which information has changed in a later revision.
A design comparison, an organisation’s emissions inventory and accounting for an emissions reduction project serve different purposes. GHG Protocol also treats corporate accounting and project-level reduction accounting separately. The method should be selected according to the study’s purpose. GHG Protocol — Project-level emissions accounting.
Initial preparation and AECO’s contribution
The project stage, building use and options to assess can be shared at an initial discussion. Architectural and mechanical information supports preparation for design analysis; existing consumption and operating information supports an operational assessment. Identifying the teams providing the information and any gaps helps clarify the scope.
AECO’s building energy modelling service focuses on connecting energy performance with design and system decisions. If the work is to inform an emissions assessment, the method and data needs can also be discussed when defining the scope. Share the decision you would like to support in your project to discuss the analyses and preparation information needed.
Sources
- GHG Protocol — Corporate emissions accounting
- GHG Protocol — Calculation tools and emission factors
- US Department of Energy — Energy modelling for design decisions
- US Department of Energy — Building energy modelling
- European Commission — Buildings’ life-cycle carbon impact
- US Environmental Protection Agency — HFCs and climate impact
- GHG Protocol — Project-level emissions accounting