Life Cycle Assessment:The ABC’s

H. Scott Matthews

Civil and Environmental Engineering

Carnegie Mellon University

Brainstorming Exercise• Break into groups of 5• Draw process flow diagrams for producing 5

products:– Can of Coca Cola– Steel– Water– Electricity– Coal

• Make them as comprehensive and inclusive as you feel comfortable.

A - 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?

Allocation (cont.)• Ideally, avoid it

– Separate into subprocesses– Divide and conquer (only allocate from 1)

• Example: CMU produces 30 CEE graduates per year. How to model student production of the university?– There are ~30 departments, assume each produces

one?– One of the 30 departments is CEE, and produces all

of the graduates– This sounds trivial, but is a common mistake!

Source: ISO 14041, Appendix B

Allocation Rules (cont.)

• Else expand system boundaries!• Allocate by physical relationship

– Allocate incinerated waste emissions of cadmium only to waste products containing cadmium

– Mass or volume for transport allocation

• See other examples in ISO 14041, App B

Structure of a Process-based LCA Model

process

processprocess

process

process

process

process

process process

process

processprocess

process

process

sub-system1

process

process process process

processprocess process

sub-system2

B - The Boundary Issue• Where to set the boundary of the LCA?• Include all processes, but at least the most

important processes if there are time and financial constraints – Which are the least and most important?– Often do not know until you’re done!– Draw boundaries around processes, number of

flows tracked, life cycle stages, time, ..?– Maybe combinations of the above

C - Circularity Effects• Circularity effects in the economy must be accounted for: cars are made

from steel, steel is made with iron ore, coal, steel machinery, etc. Iron ore and coal are mined using steel machinery, energy, etc...

emissions

product

system boundary

RESOURCES

waste

Special Notes - Public Studies• Follow ISO-prescribed format on reporting the results• Use external peer-reviewers to ensure validity• Incorporate, as necessary, comments of reviewers• Much like an academic journal publication process!• Be careful with comparative assertions (i.e., “A is

better than B”)– Cannot just use LCIA results, weighting methods

“Process-based LCA” Tools

• BEES (NIST, construction-oriented)• NREL LCI (Ongoing)• Swiss ecoinvent ($1500)

– http://www.ecoinvent.ch/en/index.htm

• SimaPro ($2000-$4000)• GaBi ($1000-$3000)• Links on Website

Data Sources - Heart of Tools

• All of these tools are ‘front ends’ to databases

• The data is the important part• The interface is just there to help• Should examine data documentation to

guide you towards what you need

Reporting

• Need to document everything you’ve done, especially assumptions.

• See ISO 14041 document (Section 8)