Comparative Analysis of Life Cycle Inventory
Techniques and Development of a Quantitative
Uncertainty Analysis Procedure
Deidre Wolff
School of Civil and Building Services Engineering
Prof. Aidan Duffy
Prof. Geoff Hammond
Nov. 29, 2013
Life Cycle Assessment (LCA)
‘The compilation and evaluation of the inputs,
outputs, and potential environmental impacts of
a product system throughout its life cycle’
(ISO 14044, 2006)
Life Cycle Assessment (LCA)
Goal
Definition and
Scope
Inventory
Analysis
Four Stages:
• Goal and Scope Definition
Interpretation
• Life Cycle Inventory (LCI)
• Life Cycle Impact
Assessment (LCIA)
• Interpretation
Impact
Assessment
(ISO 14040)
7
Motivation
LCA is often used in decision-making processes
and to inform policy
LCA involves using expert judgement,
assumptions, data of poor quality, allocation
and weighting
 These all introduce uncertainty
Uncertainty is often ignored in LCA studies
due to lack of knowledge and/or time and
budget constraints
Objectives
1. Conduct Process, Input-Output, and Hybrid LCA of a simple
system, quantifying overall uncertainty for each model
2. Compare the results obtained using different LCI methods
3. Develop a technique to make comparisons between studies that
have applied different LCI methods
4. Apply methodology to a building, using a Bill of Quantities (BoQ)
as a data source
5. Determine a suitable LCI and uncertainty analysis methodology
to apply to all LCA studies in the built environment
What is uncertainty?
Errors originating from inaccurate
measurements, lack of data, and model
assumptions (Huijbregts, 1998)
The problem of using information that is
unavailable, wrong, unreliable, or that shows a
certain degree of variability (Heijungs, 2004)
Uncertainty Classification in LCA
Parameter
•
data uncertainty
•
arises due to incomplete knowledge of true value of data, lack of data
or measurement error
Model
•
unknown interactions between model formulations, due to
simplification, derivation of characterization factors, aggregation of
data into impact categories
Scenario
•
due to decisions made during the LCA, such as choice in system
boundary, functional unit, allocation, weighting factors
LCA Overall Steps...
Goal and Scope
LCI
LCIA
Interpretation
System
Boundary
Data
Collection
Choose
Impact
Categories
Identify
Significant
Issues
Scale Data to
FU/ Ref Flow
Characterization
Factors
FU and
Reference
Flow
Allocation
Procedure
LCI/LCIA
Method
Assumptions
Weighting
Methods
Contribution/
Sensitivity
Analysis
Uncertainty
Analysis
(Reap et al, 2008)
Case-study: Process LCA
Goal and Scope:
Determine the overall Global Warming
Potential for the production of an electric kettle,
using data from EcoInvent Database.
System boundary is cradle-to-gate, including
raw material extraction and manufacturing of
the materials used for the production of a kettle.
The system boundary is simplified, as the
overall goal of the LCA is to quantify the
uncertainty.
Case-study: Process LCA
Energy Input
Raw
Material
Extraction
Energy Input
Transport to
production
facility
Energy Input
Assembly of
Electric Kettle
Energy Input
Emissions to Air
Emissions to Air
Energy Input
Transport of
Electric Kettle
to Consumer
Energy Input
Emissions to Air
Disposal/
Recycling
Emissions to Air
Emissions to Air
Use Phase
Emissions to Air
System Diagram
Stainless
Steel
437 g
Polypropylen
e
245.5 g
Silicone
The emissions
associated with energy
consumed during these
steps has been ignored
for simplification
Body of
Kettle
682.9 g
0.4 g
Stainless
Steel
15 g
Polypropylene
310.2 g
Copper
41.9 g
Polyamide
3.5 g
Assembly
Electrical
Component
355.6 g
1038.5 g
Kettle
Process LCI and LCIA Results
LCI Data
Emissions to Air
Quantity
Unit
CO2 Biogenic HPD
2.79E-02 kg
CO2 Biogenic LPD
2.58E-03 kg
CO2 Biogenic Unspecified
1.13E-03 kg
CO2 Fossil lower strat and upper trop
3.52E-08 kg
CO2 Fossil unspecified
3.23E-01 kg
CO2 Fossil HPD
2.16E+00 kg
CO2 Fossil LPD
4.57E-01 kg
CO2 Land Transformation, LPD
4.49E-05 kg
SF6 LPD
4.16E-11 kg
SF6 Unspecified
3.65E-08 kg
N2O LPD
7.46E-06 kg
N2O lower strat and upper trop
3.36E-13 kg
N2O HPD
2.67E-05 kg
N2O Unspecified
7.77E-06 kg
Methane biogenic LPD
8.20E-06 kg
Methane biogenic HPD
2.72E-05 kg
Methane biogenic Unspecified
1.86E-05 kg
Methane fossil LPD
4.78E-03 kg
Methane fossil lower strat and upper trop 5.60E-13 kg
Methane fossil HPD
6.68E-03 kg
Methane fossil Uspecified
3.57E-06 kg
CF4 HPD (PFCs)
2.28E-11 kg
CF4 Unspecified (PFCs)
2.29E-07 kg
C2F6 HPD (PFCs)
2.03E-10 kg
C2F6 Unspecified (PFCs)
2.55E-08 kg
CHF3 HPD (HCFCs)
8.11E-12 kg
LCIA
Total
Characterization Factor CO2-equivalents
3.16E-02
1
3.16E-02
2.94E+00
1
2.94E+00
4.49E-05
3.65E-08
1
22800
4.49E-05
8.33E-04
4.19E-05
298
1.25E-02
5.40E-05
25
1.35E-03
1.15E-02
25
2.87E-01
2.29E-07
7390
1.69E-03
2.57E-08
12200
3.13E-04
8.11E-12
14800
1.20E-07
3.277
Total GWP:
Contribution Analysis
Contribution Analysis
Contribution of Body Component Material to
Overall GWP
Contribution to Overall GWP (%)
70.0%
Methane (Fossil HPD)
60.0%
Methane (Fossil LPD)
50.0%
CO2 (Fossil LPD)
40.0%
CO2 (Fossil HPD)
30.0%
CO2 (Fossil Unspecified)
20.0%
10.0%
0.0%
Polypropylene
Stainless Steel
Silicone
Sensitive Parameters
Sensitive Parameter
Raw EcoInvent Data
Contribution to
Overall GWP
(%)
Mean Value (kg
CO2-eq per
Kettle)
Emission
Kettle Part
and
Material
CO2 (Fossil)
Electrical,
Polyprop.
15.9%
CO2 (Fossil)
Body,
Polyprop.
CO2 (Fossil)
Body,
Stainless
Steel
Mean (kg)
Minimum (kg)
Maximum
(kg)
0.519
1.673
1.670
1.676
12.6%
0.410
1.673
1.670
1.676
56.5%
1.842
4.212
3.673
4.865
Sensitivity Analysis
Next Steps…
• Quantify Uncertainty
• Identify scenario and model uncertainty
• Is it necessary to quantify scenario and model
uncertainty in all cases?
Thank You!
Any Questions?