Life Cycle Assessment
On this Project:
LCAs performed on standard buildings showed that the use phase dominated the impacts over the course of a building’s lifespan. Consequently, building energy efficiency was the target of reduction measures and high-performing buildings began to emerge. The design of living buildings followed, which are buildings that are defined as being net-positive energy and water. In these energy efficient buildings the significance of the use phase diminishes, shifting the focus to other life cycle stages.
This research includes a whole-building LCA of a living building (the Frick Environmental Center) that focuses on the impacts from green building materials, a decentralized water system, a net-positive use phase, and the disposal of structural materials. The material processes used in this LCA were modified by removing the use of highly toxic chemicals per the product submittals; results showed carcinogenic impacts were decreased by up to 96%. The septic system, which is not aerated, used for wastewater treatment contributes to 37% of the global warming potential (GWP, kg CO2eq) for the whole building’s lifespan due to methane emissions. The solar panels on-site generate more electricity than the site demands, allowing for 44,000kWh of green energy to be returned to the grid. Lastly, a scenario analysis was performed on multiple waste streams for materials of two structural models (lumber or steel) with a concrete foundation. Results showed that based on the frame and waste stream selected, the end of life GWP impacts could vary from +14,000kg CO2eq to -10,500 kg CO2eq for the as-built structure. This whole-building LCA aims to identify and mitigate hotspots of the case study building, and to reduce life cycle impacts of living buildings moving forward.
After a whole-building life cycle assessment was performed on a living building, results showed that this building is not net-zero carbon. Building designers and operators worked hard to ensure the energy profile of the building was net-zero, which they achieved by a large margin. However, once all the material replacement impacts, not to mention the emissions from the water system, were added it became clear that the total embodied carbon was much higher than the amount offset by electricity fed back into the grid. This brings up an emerging conversation about embodied impacts of high-performance buildings. Because the use phases are so low, or in the FEC’s case negative, the embodied carbon in the materials quickly dominate the life cycle impacts. This illustrates a shift from reducing the energy loads to figuring out next steps to further reduce the embodied impacts of buildings. These impacts are significantly affected by material selection, sourcing, and product lifespans; this supports the need for an improved material database in order to accurately assess their impacts to get a true picture of a green building’s embodied impacts. It is therefore critical that building designers take all of these factors in when creating a new structure since these impacts carry more weight in living buildings.
This also introduces the potential for a conversation about regular energy offsets. Similar to that of modeling the energy and water profiles on an annual basis, perhaps embodied carbon should be modeled on a 5- or 10-year timescale to account for regular material replacements. This way, embodied impacts could be tracked in order to calculate what quantity of offsets should be purchased, allowing the building to truly achieve net-zero carbon over its lifetime. Alternatively, adjusting the required amount of electricity generated on-site could be a way to achieve net-zero carbon as well; if the electricity of the building is modeled as being artificially higher than it is in order to account for embodied material impacts, the required electricity generated will automatically offset the impacts from material pre-use and use. The Living Building Challenge requires these offsets are tracked for the building pre-use (construction) but has no requirements for continuous offsets. The main objective now is to account for life cycle embodied impacts so the best option can be evaluated a case-by-case basis whether that is purchasing offsets, increasing the electricity generated on-site, or any other effective offsetting option.