Comparison of the greenhouse gas emissions of a high-rise residential building assessed with different national LCA approaches – IEA EBC Annex 72

Abstract

Introduction: The international research project IEA EBC Annex 72 investigates the life cycle related environmental impacts caused by buildings. The project aims inter alia to harmonise LCA approaches on buildings. Methods: To identify major commonalities and discrepancies among national LCA approaches, reference buildings were defined to present and compare the national approaches. A residential high-rise building located in Tianjin, China, was selected as one of the reference buildings. The main construction elements are reinforced concrete shear walls, beams and floor slabs. The building has an energy reference area of 4566 m2 and an operational heating energy demand of 250 MJ/m2a. An expert team provided information on the quantities of building materials and elements required for the construction, established a BIM model and quantified the operational energy demand. Results: The greenhouse gas emissions and environmental impacts of the building were quantified using 17 country-specific national assessment methods and LCA databases. Comparisons of the results are shown on the level of building elements as well as the complete life cycle of the building. Conclusions: The results of these assessments show that the main differences lie in the LCA background data used, the scope of the assessment and the reference study period applied. Despite the variability in the greenhouse gas emissions determined with the 17 national methods, the individual results are relevant in the respective national context of the method, data, tool and benchmark used. It is important that environmental benchmarks correspond to the particular LCA approach and database of a country in which the benchmark is applied. Furthermore, the results imply to include building technologies as their contribution to the overall environmental impacts is not negligible. Grant support: The authors thank the IEA for its organizational support and the funding organizations in the participating countries for their financial support.

Overview and Main Findings for the Austrian Case Study

“…Finally, it should be pointed out that, although the investigated building is well insulated (good low energy standard in Austria), equipped with an efficient heat pump, and powered with the relatively clean Austrian grid mix (large share of hydro power), the environmental impact of the operational energy use (B6) of the building is about seven times higher than the impact of the building materials over the whole life cycle. However, the outcome of 19.44 kgCO 2 -eq per m 2 per year for B6 seems to be in line with findings in [13], for example, where the variation the national assessment results varied between 7.9 and 45 kg. As the main reason for the differences can be found in the GHG emissions of the electricity mixes used in the different counties, according to [13], the relatively low carbon mix in Austria, despite the fact that the whole energy consumption of the building was considered, leads to a result near the lower threshold.…”

“…However, the outcome of 19.44 kgCO 2 -eq per m 2 per year for B6 seems to be in line with findings in [13], for example, where the variation the national assessment results varied between 7.9 and 45 kg. As the main reason for the differences can be found in the GHG emissions of the electricity mixes used in the different counties, according to [13], the relatively low carbon mix in Austria, despite the fact that the whole energy consumption of the building was considered, leads to a result near the lower threshold. Another important aspect to explain the large differences between construction related emissions (A, B4, and C) and emissions from the energy supply (B6), is the chosen methodologic approach to include only building components, which are affected by the change in the load bearing material and not the whole building.…”

“…Another important aspect to explain the large differences between construction related emissions (A, B4, and C) and emissions from the energy supply (B6), is the chosen methodologic approach to include only building components, which are affected by the change in the load bearing material and not the whole building. This methodological decision also explains the relatively low GHG results for both buildings (concrete 362.74 and CLT 300.61 kgCO 2 -eq per m 2 ) compared to national results in [13]. Another reason is the specific kind of concrete used, which allows extra slim concrete building elements (with related lower GHG emissions) and, of course, the CLT with lower GHG emissions during production stage in general.…”

“…A good overview on methodological issues is presented by Gustavsson in [12], with emphasis on the material properties of concrete and timber. A different approach to tackle methodological issues is carried out by Frischknecht in [13], with kind of a round robin test of national approaches of building assessments with the goal to identify national discrepancies as a basis for harmonization. Results in [13] show huge deviations between the national approaches, which mainly result from the background data used, the scope of the assessment and the reference study period applied.…”

How Can Existing Buildings with Historic Values Contribute to Achieving Emission Reduction Ambitions?

“…Life cycle-based national GHG emission benchmarks or reference values are receiving more attention in different countries, and there are on-going discussions on the possibility of legal bindings [34]. The lack of harmonized background data and methodology choices used in different studies is considered as a major challenge in the utilization of LCA studies to establish benchmarks [34][35][36]. Most existing benchmarks also provide aggregated values for both new and existing buildings, mainly due to a lack of LCA studies from existing buildings and heritage buildings.…”