Calculation of Carbon Footprint

 Emission factors (EF), are key metrics used to quantify greenhouse gas emissions produced per unit of energy consumed. They represent the amount of carbon dioxide equivalent (CO2e) emissions associated with specific energy sources like coal, natural gas, or electricity. Typically expressed in kilograms or metric tons of CO2e per unit of energy output (e.g., kWh for electricity), these factors are vital for evaluating the environmental impact of energy consumption, assessing carbon footprints, and guiding policy decisions to reduce emissions and transition to cleaner energy sources.

Emission factors enable a conversion from the input measure of an emission source to the resulting amount of relevant GHG emissions. The accuracy of carbon footprints hinges on these factors. For instance, one can determine the emissions from electricity usage or distance traveled by multiplying it by an appropriate emission conversion factor. These factors are derived from Global Warming Potential (GWP) assessments outlined in reports from the International Panel for Climate Change (IPCC).

 The total embodied carbon stemming from the cradle-to-site cycle can be represented by the following equation (2-1) below (Moncaster and Symons, 2013):

 For Stages A1 to A3, BS EN 15804:2012+A2:2019 treats them as a unified module. Carbon emissions for each construction material are determined using specific carbon emission factors. According to the IPCC, these factors indicate the potential of waste or wastewater to produce particular gases, with higher values indicating greater emissions. Essentially, emission factors serve as conversion tools to estimate CO2 emissions from activity data provided for Stages A1 to A3.

As per the standard BS EN 15804:2012+A2:2019, Stage A4 is designated as the construction process stage within the life cycle assessment. This stage encompasses both direct and indirect emissions. Direct emissions refer to the carbon emissions that arise from the combustion of fuels utilized for transportation purposes. Indirect emissions, on the other hand, encompass carbon emissions resulting from the electricity consumed during construction activities, as well as emissions associated with the extraction and transportation of primary fuels.During Stage A4, the embodied carbon of each material is evaluated using an emission factor that is specific to the transportation mode employed for transporting the material over a unit distance. The emission factor is expressed as kgCO2 per metric ton-kilometer (kgCO2/t-km), representing the amount of carbon dioxide equivalent emitted per unit distance travelled by a metric ton of material from the manufacturer to the construction site.

 The above figure illustrates the process of computing the carbon footprint for stages A1 to A3, which involves consolidating product stage emission factors (expressed in kg CO2e/kg material). These factors encompass both energy-related and non-energy-related emissions. Subsequently, for stage A4, the carbon footprint calculation entails utilizing the transport emission factor (expressed in kg CO2e/kg material), determined by multiplying the distance traveled by the transport mode factor. Once the emission factors for stages A1 to A3 and A4 are determined and combined, the resulting factor is multiplied by the activity data to derive the carbon footprint for stages A1 to A4. These equations are integral to the functionality of the provided calculator.