Life Cycle Assessment
A product-oriented method
for sustainability analysis
UNEP LCA Training Kit
Module g – Multifunctionality, allocation & system boundaries
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Contents
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The problem
Definitions and typologies
Solutions to the
multifunctionality problem
Allocation according to ISO
System boundary and
allocation
Economic allocation
Conclusion
The problem (1)
• There are processes which have more than one function
– “multifunctional processes”
function 1
not a function
coal
generator
not a function
function 2
electricity
electricity production
with cogeneration
of heat (CHP)
heat
fly ash
not a function
The problem (2)
sodium chloride
(NaCl)
electricity
electrolysis of
sodium chloride
chlorine
(Cl2)
caustic soda
(NaOH)
hydrogen gas
(H2)
3 functions
The problem (3)
crude oil
refinery process
naphtha
kerosene
heavy fuel oil
3 functions
The problem (4)
• Two problems;
– How should the environmental impacts of these processes
be allocated to the different product systems involved?
– Which processes belong to the product system studied
and which do not?
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Definitions and typologies (1)
• Functional flow
– any of the flows of a unit process that constitute its goal
• product outflows of a production process
• waste inflows of a waste treatment process
• Multifunctional process
– a unit process yielding more than one functional flow
• co-production (multi-output)
• combined waste processing (multi-input)
• recycling (input-output)
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Definitions and typologies (2)
1 functional flow
product
product
product
general
process
waste
waste
product
single-output process
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Definitions and typologies (3)
2 functional flows
product
product
product
general
process
product
waste
product
multi-output process
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Definitions and typologies (4)
1 functional flow
waste
product
waste
general
process
waste
waste
product
single-input process
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Definitions and typologies (4)
2 functional flows
waste
waste
waste
general
process
waste
waste
product
multi-input process
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Definitions and typologies (5)
2 functional flows
waste
product
product
general
process
waste
waste
product
input-output process
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Definitions and typologies (6)
4 functional flows
waste
waste
product
general
process
product
waste
product
multi-input-output process
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Definitions and typologies (7)
• Allocation problem
– partitioning (the inputs and outputs of) unit processes
among product systems
• Multifunctionality problem
– a broader issue cutting right across LCA inventory
modelling
• what are the functional flows of every process?
• which processes are multi-functional processes?
• how to resolve the problems related to that?
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Definitions and typologies (8)
• Problem
– whenever a product system needs product 1, it also
produces product 2
• Possible solutions
– more refined data collection
– system expansion
– substitution
– partitioning (=allocation)
– surplus
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Definitions and typologies (9)
• (More refined data collection)
– … not really allocation, but more re-iteration of data
collection
• System expansion
– add extra function(s) to the functional unit
– … but are you still doing the LCA of a product?
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Definitions and typologies (10)
• Substitution method
– defining an “avoided” process with subsequent “avoided”
interventions/impacts
– … but which process is avoided?
• Partitioning method
– effectively splitting the multifunctional process into several
monofunctional processes
– … but what basis for splitting?
• (Surplus method)
– ignoring co-products
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Solutions to the multifunctionality problem (1)
• Allocation problem is artefact of wishing to isolate one function
• Artefacts can only be cured in an artificial way; there is no
“correct” way, even not in theory
• Solution should be consistent in itself, and with main
modelling principles
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Solutions to the multifunctionality problem (2)
equipment
• What to do with the
extra heat?
coal mining
steel
generator production
coal
generator
electricity production
fly ash
heat
fly ash treatment
gypsum
electricity
Solutions to the multifunctionality problem (3)
• Two main strategies for dealing with multifunctionality:
– accept extra functions as composite reference flow
(“system expansion”)
– get rid of extra functions by an extra modeling step
(“allocation”)
• subtracting “avoided” burdens (“substitution”)
• allocating only part of burden to function needed
(“partitioning”)
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Solutions to the multifunctionality problem (3)
equipment
• System expansion
– change system
boundary
– include extra
function(s) in
functional unit
– must also do this for
the other alternatives
coal mining
steel
generator production
coal
generator
electricity production
fly ash
heat
electricity
fly ash treatment
gypsum
composite functional unit:
2 reference flows
Solutions to the multifunctionality problem (4)
equipment
steel
Draf t
• Substitution
coal mining
generator production
– change system
boundary
– add extra
coal
coal
generator
process
– subtract
“avoided”
heat production electricity production
process
– with
fly ash heat
electricity
consequences heat
avoids
upstream and
downstream
fly ash treatment
gypsum
avoided process
Solutions to the multifunctionality problem (5)
equipment
• Partitioning
– allocate only a part
of the process to
the function
considered
– with consequences
upstream and
downstream
coal mining
steel
generator production
coal
generator
electricity production
fly ash
heat
fly ash treatment
gypsum
electricity
allocate only part of the
inputs and outputs to
single function
Solutions to the multifunctionality problem (6)
• Comparison of solutions on three aspects:
functional unit
flow diagram
process data
system expansion revised
(for all alternatives)
enlarged
(for other alternatives)
same
substitution
same
enlarged
same
(with avoided processes)
partitioning
same
same
changed
(by multiplying with
allocation factors)
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Solutions to the multifunctionality problem (7)
• Problems with the three solutions:
problem
system expansion you don’t answer the question you started with
substitution
which processes are avoided?
partitioning
what are the allocation factors?
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Allocation according to ISO (1)
Draf t
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Allocation according to ISO (2)
• Step 1: Wherever possible, allocation should be avoided by:
– dividing the unit process to be allocated into two or more
sub-processes and collecting the input and output data
related to these sub-processes
– expanding the product system to include the additional
functions related to the co-products
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Allocation according to ISO (3)
• Step 2: Partition inputs and outputs in a way which reflects the
underlying physical relationships between them
– not necessarily mass of molar flows
• Step 3: Partition inputs and outputs in a way which reflects
other relationships between then
– e.g., in proportion to the economic value of the products
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Allocation according to ISO (4)
Draf t
• System expansion versus substitution
A.-M. Tillman et al. Choice of system boundaries in life cycle assessment. Journal of Cleaner Production 2:1 (1994), p.24
System boundary and allocation (1)
price < 0
electricity production
fly ash
waste treatment
electricity
TV use
reference flow
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System boundary and allocation (2)
price > 0
electricity production
heat
chemical plant
electricity
TV use
reference flow
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System boundary and allocation (3)
generator plant
coal mining
generator
coal
electricity production
price > 0
reference flow
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System boundary and allocation (4)
pallet production
coal mining
wood waste
coal
electricity production
price < 0
reference flow
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System boundary and allocation (5)
• Price/direction determines:
– if a process is to be included
– if allocation is needed for a process
– extent to which a process in included
• There is something to say for economic allocation
– price<0: exclude
– price>0: include a bit
– price>>0: include a lot
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System boundary and allocation (6)
price
price>>
> 00
<
electricity production
waste
co-product
by-product
downstream process
electricity
TV use
reference flow
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Economic allocation (1)
• Allocation factors based on shares in proceeds
– no absolute values needed
– any monetary unit, if the same
– any base year, if the same
total amount produced 
economic value/unit
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Economic allocation (2)
• Problems
– market prices not known
– fluctuating prices
– inflation
– trends in real prices
– market distortions
– markets not yet existing
– …
• Some solutions suggested in CML’s Handbook on LCA
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Conclusions
• Transparency crucial in drawing system boundaries and
solving the multifunctionality problem
– what are the flow diagrams of the systems?
– which flows are goods, which are wastes?
– where are the multifunctional processes?
– how is the multifunctionality problem solved in each of
these?
• system expansion: what is the function added? (also in the
other alternatives)
• substitution: what is the avoided process?
• partitioning: what are the allocation factors?
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