The construction of new buildings requires the use of a substantial amount of materials, which have an associated embodied energy for manufacturing, transport, construction and end-of-life disposal. A number of inventories have been developed to collate the typical embodied energy or carbon emissions associated with different building materials and activities, and these can be used to quantify the environmental impacts of different construction methods. However, uncertainty exists in the estimation of embodied CO2-e emissions and other environmental impact results, due to i) inconsistencies in typical embodied carbon emissions values in inventories; ii) errors in estimations of material quantities; iii) assumptions regarding building lifetimes, and iv) errors in estimations of transport distances. This current study quantified the uncertainties associated with the calculation of lifetime CO2-e emissions in a case study net-zero, in terms of operational energy, educational building. This study examined the lifetime impacts of building materials for the building based on a detailed Life Cycle Assessment (LCA) that had been previously undertaken for this site. The study considered the 19 building materials which most heavily influenced the total, transport and recurring embodied carbon footprint of the building and a probability distribution was generated to represent the variability for each of the following uncertain parameters: Lifetime, Embodied CO2-e and transport distance over the building's life. Random sampling was used to generate input variables (1000 samples) based on a probability distribution of each uncertain parameter relative to the building materials. Through the use of a Monte Carlo simulation, the environmental impact for each construction material for a 50-year building lifetime was predicted. Unlike the conventional LCA approach, which provides a single deterministic value, cumulative Monte Carlo distribution curves were used to provide a range of embodied CO2-e emissions for each construction material, and the whole building, through the lifetime of the building. The obtained results revealed a distribution of the total embodied CO2-e of a building which ranged from 2951 tCO2-e to 5254 tCO2-e. This variation in the life cycle carbon emissions highlights the importance of considering an uncertainty analysis in the LCA analysis.
Available for download on Saturday, April 03, 2021