Life Cycle Assessment
Life cycle assessment (LCA) is the necessary underpinning to truly understand and engineer how complex systems, products, or processes use materials, water, and energy resources throughout their lifetime. Life cycle assessment is a useful tool for evaluating the environmental impacts of a system. For example, LCA can be used to quantify greenhouse gases, energy and water usage, and emissions from a building's life cycle phases, and can be a useful tool for greening buildings.
Life cycle assessment as a tool provides a comprehensive and quantitative analysis of the environmental impacts of a product or process throughout its entire life cycle. Established guidelines for performing detailed LCAs are well documented by the Environmental Protection Agency (EPA), Society for Environmental Toxicologists and Chemists (SETAC), the International Organization of Standardization (ISO), and the American National Standards Institute (ANSI). While there are elements of life cycle assessment in all of our research, we also conduct research specifically on method development for LCA.
Dynamic Life Cycle Assessment Approach for Whole Building Evaluation
Life cycle assessment (LCA) can aid in quantifying the environmental impacts of whole buildings by evaluating materials, construction, operation and end of life phases with the goal of identifying areas of potential improvement. Since buildings have long useful lifetimes, and the use phase can have large environmental impacts, variations within the use phase can sometimes be greater than the total impacts of other phases. Additionally, buildings are operated within changing industrial and environmental systems; the simultaneous evaluation of these dynamic systems is recognized as a need in LCA. At the whole building level, LCA of buildings has also failed to account for internal impacts due to indoor environmental quality (IEQ). The two key contributions of this work are 1) the development of an explicit framework for DLCA and 2) the inclusion of IEQ impacts related to both occupant health and productivity. DLCA was defined as “an approach to LCA which explicitly incorporates dynamic process modeling in the context of temporal and spatial variations in the surrounding industrial and environmental systems.” IEQ impacts were separated into three types: 1) chemical impacts, 2) nonchemical health impacts, and 3) productivity impacts. Dynamic feedback loops were incorporated in a combined energy/IEQ model, which was applied to an illustrative case study of the Mascaro Center for Sustainable Innovation (MCSI) building at the University of Pittsburgh. Data were collected by a system of energy, temperature, airflow and air quality sensors, and supplemented with a post-occupancy building survey to elicit occupants’ qualitative evaluation of IEQ and its impact on productivity. The IEQ+DLCA model was used to evaluate the tradeoffs or co-benefits of energy-savings scenarios. Accounting for dynamic variation changed the overall results in several LCIA categories - increasing nonrenewable energy use by 15% but reducing impacts due to criteria air pollutants by over 50%. Internal respiratory effects due to particulate matter were up to 10% of external impacts, and internal cancer impacts from VOC inhalation were several times to almost an order of magnitude greater than external cancer impacts. An analysis of potential energy saving scenarios highlighted tradeoffs between internal and external impacts, with some energy savings coming at a cost of negative impacts on either internal health, productivity or both. Findings support including both internal and external impacts in green building standards, and demonstrate an improved quantitative LCA method for the comparative evaluation of building designs.
Collinge, W.C., Landis, A.E., Jones, A., Schaefer, L., Bilec, M.M. (2013). “A Dynamic Life Cycle Assessment: Framework and Application to an Institutional Building.” International Journal of Life Cycle Assessment, 18(3), 538-552. http://dx.doi.org/10.1007/s11367-012-0528-2
Collinge, W.O., DeBlois, J., Landis, A.E., Schaefer, L.A., Bilec, M.M. (2016). “A hybrid dynamic-empirical building energy modeling approach for an existing campus building.” ASCE Journal of Architectural Engineering. 04015010. http://dx.doi.org/10.1061/(ASCE)AE.1943-5568.0000183
Impact of Lifetime on U.S. Residential Building Life Cycle Assessment Results
Residential building lifetime data that presents existing trends in the U.S. was analyzed. Results indicate that residential building lifetime in the U.S. is currently 61 years. Existing LCAs rely heavily on estimates for residential building lifetime, and choices are usually made arbitrarily. This study is the first time mean residential building lifetime has been calculated from a large, reliable sample and used in LCA.
Lifetime of buildings and products presented in the current study should not be taken as static values. Future trends, occupant behavior, population demographics, regulatory policies, or development of new technologies have the potential to alter both lifetime and emissions of buildings and building products. The increasing trend in the age of demolished residential buildings was demonstrated in the current study. Ranges of values supported by statistical analysis were used throughout the study to compensate for some of the uncertainties associated with variables. The use of distributions that are based on past reported values, instead of deterministic values chosen arbitrarily for lifetime of buildings and building products improves the objectivity of a life cycle study that assumes average conditions when project specific data are not available. More data on environmental emissions of interior finishes is also a necessary step towards more robust results.
Interior renovation energy consumption for the residential model that was developed by using average U.S. conditions was found to have a mean of 220 GJ over the life cycle of the model. Using published data on energy consumption during pre-use and use phase of residential buildings enabled comparisons to be made among interior renovation impacts and other life cycle phases. Ratio of interior renovation to pre-use energy consumption was calculated to have a mean of 34% for a model regular home and 22% for a low-energy home. Ratio of interior renovation to life cycle energy consumption of residential buildings was calculated to have a mean of 3.9% for a model regular home and 7.6% for a low-energy home.
Life cycle impacts of regular buildings are dominated by use phase emissions. However, this is likely to change as buildings become more energy efficient during their use phase. An increase in the number of low-energy buildings would decrease the use phase emissions of residential buildings, increasing the relative importance of interior renovation over the life cycle of a residential building. Such an increase would necessitate more focus on interior finishes in a building LCA.
Due to its influence on product lifetime and emissions, the effects of consumer behavior related to interior finishes needs to be better quantified in order to improve accuracy of residential building LCA. Since lifetime information plays an important role in life cycle studies, and since consumer behavior can greatly influence product lifetime, developing a model that can accurately predict product lifetime by including the effects of technical factors as well as consumer behavior becomes a necessity. Such a tool would not only improve the accuracy of building LCA studies, but also of product comparison studies as well.
Without fully understanding and quantifying the underlying problems, it is not possible to develop effective environmental impact reducing strategies for the built environment. While collecting data for product lifetime, it was noticed that a product’s actual lifetime was usually different than what the product was designed for, and was determined by the effects of consumer behavior. Therefore, studying the supply chain from the initial design phase down to individual consumer preferences could open new opportunities to reduce the environmental footprint of products and still maintain economy.
Whole Building Life Cycle Assessment of a Living Building
Life cycle assessment (LCA) is a tool to quantify the environmental impacts of a product or system. This tool is used to assess environmental impacts of buildings over their lifespan. 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.
Frick Environmental Center's south-facing façade
Net-zero energy and water does not ensure net-zero carbon
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.