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Life Cycle Assessment:History and Framework
H. Scott Matthews
Civil and Environmental Engineering
Carnegie Mellon University
Course Comments
• Brief (re)-Intros• Projects• Intended to help you start practicing• Will summarize, not repeat, what is
found in readings• Make sure you know ‘definitions’ from
ISO documents
Life-Cycle Assessment (LCA)• A concept and methodology to evaluate the environmental effects of
a product or activity holistically, by analyzing the whole life cycle of a particular product, process, or activity (U.S. EPA, 1993).
• LCA studies analyze the environmental aspects and potential impacts throughout a product's life cycle (e.g., cradle-to-grave) from raw material acquisition through production, use and disposal (ISO).
LCA Uses
• Process analysis• Material selection• Product evaluation• Product comparison• Policy-making• Measuring performance• Marketing
Components of LCA -3 or 4 I’s
• Inventory• Impact Assessment• Interpretation (and Improvement)
• We’ll do a lot with #1, then #2, and come back to #2 at end of course
• Regardless, need to learn terminology first before doing anything else..
Components and Criteria
• Criteria:– Spatial, Temporal– Design– Functional unit– Significance/magnitude– Uncertainty
• ISO documents a framework (not a recipe); LCAs may or may not consider all points above
Criticisms / Limitations• Data reliability and quality is questionable.• Models based on assumptions.• Problem boundaries are arbitrary. • Scale issues - global -> local, etc.• Uncertainty is everywhere• Spatial and temporal issues• Comparisons between studies difficult• No single, accepted method
Important Note on Context
• LCA should be one part of a broad environmental assessment
• If comparing with LCA, all assumptions and methods should be consistent– Especially problematic for validating
against external studies
Definitions
• Big set of definitions in ISO framework documents (e.g., p.1 of ISO 14040)
• Won’t review all of them here, but you need to know them.
• Big ones to know are unit process, elementary flows, inputs, outputs
Definitions• Elementary flows - material or energy
entering or leaving the system, directly to/from the environment, without human transformation
• Unit process - smallest portion of a product being studied for which LCI data available
• Inputs / Outputs - materials or energy entering or leaving a unit process
Scope Considerations
• Setting all the parameters for study– e.g., functional unit, boundaries, data, etc.– Whether it will be critically reviewed
• May be iterative (update in progress)• Supports product system diagram
– Realize LCA can be used for ‘products’, ‘processes’, ‘systems’, etc.
• Functional unit definition ensures unit consistency for validation and comparison
Product Systems
• Collections of unit processes, elementary flows, and product flows
• Also shows system boundary• Processes, flows maybe in / out of bounds
– In: fuel, energy, materials, …– Out: emissions, waste, …
Simple Example - Tree
SunlightCO2
O2
Wood
Environ- ment
Tree EnergySystem?Wate
r
If we wanted to do a life cycle inventory of a tree, we could draw the boundary in one of several places
More Complex Example
• We manufacture a part for new automobiles and ship it in cardboard boxes
• Currently, we “ship and forget it”• Generates significant box waste• We want to reduce waste - how?• What are tradeoffs?
Original System
ManufactureSystem
PackagingTransport/Delivery
Energy
Emissions, Cardboard Box Waste
Car Assembly
Part
Energy
Cardboard Manuf.
UnboxedPart
Raw Mats, Energy
Emissions,Waste
BoxedPart
Packaging Takeback System
Manuf.System
PartPackaging
Transport/Delivery
Emissions, (Less?) Cardboard Waste
Car Assembly
Cardboard Manuf.
Unboxed Part
Empty Box
Transp/Logistics
Reused Box
Energy
Emissions
Packaging Takeback System
• Our new system uses less cardboard– Thus less waste, manufacturing impacts
• But uses more transportation to retrieve used boxes– Thus more energy use, emissions
• Unclear whether this tradeoff is beneficial• Perfect application for LCI/LCA
Example Goal/Scope• Goal: “To determine whether the new system is
better than the old”– More detail: which inventory items? How to assess?– Maybe air emissions, energy use, waste generated– Would a better goal originally have been to do LCA of
old system and suggest improvements?• Scope: Fairly detailed description of both
systems, items in/out of boundaries– e.g., might exclude impacts of product (relevant?)– But include packaging/logistics/reuse of systems
Next Step: Inventory
• In general, just “good research”• “Look up the data, add it up”
– However, data availability varies widely• Consider inputs, outputs of interest
– In: energy, resources, etc.– Out: emissions, waste, etc.
• Also may be iterative• Allocation an issue
Inventory Process
• Iterative• Collect/validate• Matching data with
unit processes/ functional units/etc
• See “sample forms” on pp.16-20 of ISO 14041 PDF.
Allocation
• Hard to assign “one to one” linkages between units and inputs-outputs
• Need standard/specified way to distribute (allocate) them– mass balance method– Physical properties– Economic value ratio?
• What allocations needed for packaging takeback system?
Inventory Interpretation• How do results fit goal/scope?• Assessment of data quality• Sensitivity analysis on inputs/outputs
Data Sheet Exercise
• Break into small groups (2-3 max)• Using samples provided (from ISO
14041) summarize data for:– Getting to school– Doing a homework assignment / writing a
paper– Reading a book chapter– Something else similar
Impact Assessment
• We’ll come back to this later in course• Classification• Characterization• Weighting (e.g. taking an inventory of
various toxics, then weighted by toxicity)– Assumed that existing weighting methods
can be used (not developed as part of LCA)
Resources
• Don’t despair, you do not need to collect all of your own data for LCAs, for example:– US NREL LCI Database (various):
http://www.nrel.gov/lci/– BEES (construction materials):
http://www.bfrl.nist.gov/oae/software/bees.html
• Slightly ahead of schedule in content, but you should look at these for ideas before finalizing ideas and scope for Course Project