Automating refined on-site construction carbon emissions calculation for prefabricated buildings based on BIM: Model development and validation

Prefabricated construction significantly contributes to low-carbon building efforts, especially during the on-site construction stage. Traditional methods for estimating on-site construction carbon emissions (CE_A5), which multiply machine working time by empirical energy consumption rates, often lack operability and credibility. Hence, this study proposes an approach for calculating CE_A5 based on the construction processes of prefabricated buildings as the functional unit, and it develops a building information model-based tool using ArchiCAD, Rhino, and Grasshopper. This tool enables the extraction of the construction process activity data list from building engineering plans and then integrates it with a pre-established database of construction process carbon emission factors to calculate the carbon emissions of each construction process and accumulate the total CE_A5. Validation through on-site measurements at a multistory steel structure in northern China demonstrated the approach's feasibility. The developed method successfully extracted data from building design, structural calculations, and component production from the ArchiCAD model. For major subprojects generating 98.3 % of total CE_A5, the exported process activity data was consistent with manual calculations, with 1.7 % requiring manual adjustments. The approach provides refined calculation results that are specific to the construction subprojects and subprocesses. The on-site measured CE factors for the construction processes contribute to a more realistic parameter database. It can be used in the early stages of a project to quickly calculate CE_A5 as well as to accurately present the proportion of carbon emissions generated by each construction process, which allows for identification of the main sources of CE_A5, facilitates comparisons between different processes, and enables the low-carbon optimization of construction plans.