Page 53 - Materials Chemistry, Second Edition

2.2 Scope 37

2.2.5
The Functional Unit
2.2.5.1 Definition of a Suitable Functional Unit and a Reference Flow
Although data acquisition initially does not need a fU – conversion of other
reference units to the fU can be made later – it is urgently recommended to specify
a fU already at the beginning of an LCA and, if necessary, to make adjustments
later. If serious problems already arise within the definition of the fU, this indicates
an unsatisfactory understanding of the system, serious data leaks or that LCA may
not be a suitable method for solving the individual problem.
The quantitative determination of fU and reference flow is, to a certain degree,
arbitrary. In the example of Section 1.1.3 (beverage packaging), it is unimportant
whether the fU ‘defined supply quantity beverage for customer consumption’
is defined for 1000, 100 or 1 l 27) packed beverage. 28) Results would only vary in
their numerical values by the appropriate factors (1000 : 1 respectively 100 : 1).
This is without consequences if different packaging systems using the same fU
are compared with one another. A variant that has been recommended in Dutch
guidelines 29) for detailed LCA is the use of annual quantities or similar realistic
data as a basis for determining the fU. In the example of beverage packaging, this
would mean the annual quantity (e.g. in million litres) of a certain kind of beverage
to be eligible for that type of packaging. According to the point of interest, a special
product of the commissioner or the sum of similar products would be concerned.
In the first case, the manufacturer or bottler would be interested, whereas in the
second case, probably a trade association or a national environmental protection
authority would be interested.
In comparative studies of products of high life time, such as, for example, floor
coverings, a length of use time must be included into the description of function.
It is important that early in the study, functions and performance of the product
systems are correctly defined. The functions of a floor covering consist of providing
the ground of an interior with specific characteristics (protection of supporting
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surface, accessibility, etc.). Thus the fU can be defined as follows: 1 m floor is
covered for a period of 30 a, for a defined stress.
fU = area of the floor covering (e.g.1m ) for one period (e.g.30a)
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In the next step, the defined fU must be applied to the product variants to
be examined, and thus a reference flow of data acquisition be defined. The
following fictitious example clarifies this approach by the example of two plastics
(‘plastic A’ and ‘plastic B’). As floor coverings contain beside the base material,
for example, fillers, softeners, and so on, and as production as well as disposal of
the floor covering can be neglected here, this arithmetical example for illustrating

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27) One litre (SI: 1 l ≡ 1dm ) equals 1.75 pints (UK) or 2.13 pints (US); in international LCA studies
only SI units should be used (ISO 1000).
28) A practical unit should be chosen; micro pint would not be wrong but absurd.
29) Guin´ ee et al. (2002).