Page 101 - Materials Chemistry, Second Edition

86 A. Bjørn et al.
shopping back example above). In the window frame case study the “how well?”
question was partly addressed quantitatively by defining a visible light transmit-
tance (the fraction of light that a window allows into the building) of at least 0.7 in
the functional unit. The magnitude of the quantitative aspects in the functional unit
can be chosen more or less arbitrarily. However, for the users of an LCA, it often
makes the most sense to relate it to the magnitudes of typical use by a person, a
family or a community. In the example of Fig. 8.4 it would be less intuitive to relate
2
to a functional unit involving the complete coverage of 1 km primed outdoor wall,
while a good magnitude in the functional unit for a study of waste incinerators
could be the household waste generated by the municipality in one year.
The qualitative aspects cover the way in which the function is provided and are
often not easily quantifiable and sometimes not even clear-cut. The “what?” and
“where” questions require qualitative answers. In the example of Fig. 8.4 the
“what?” question is answered by “complete coverage of primed outdoor wall” and
the “where?” question by “Germany”. Other qualitative aspects are often used to
answer the “how well?” question. These could be legal requirements, e.g. fire safety
measures in a car or an office building, or technical standards, e.g. RAL code 3020
for the colour of paint. References to relevant legal requirements and technical
standards in the functional unit are helpful, because they ensure comparability
through adherence to the standard. To fully address the “how well?” question
subjective or ambiguous elements related to user perception (e.g. fashion) are often
important to include, to ensure comparability of different products. For example,
products may be discarded by users although they still fulfil their technical func-
tions because they are no longer perceived as fashionable. For this reason, it is
important to understand which aspects of a studied product’s function, including
non-technical aspects such as fashion, that are perceived as important by users.
LCA practitioners carrying out a study are therefore advised to consult the users of
the product or service that is studied to ensure that the definition of the functional
unit captures their perception of the product’s functionality. Those non-technical
aspects that differ between compared products should either be included in the
functional unit or considered separately in the interpretation phase of the LCA (see
Chap. 12).
The authors of this chapter have over the years encountered many types of
mistakes in the definition of functional units. Box 8.1 provides selected examples of
such mistakes and explains what is wrong with them and what needs to be con-
sidered to prevent making them.

Box 8.1: Common Types of Mistakes when Defining the Functional Unit
1. Assuming that same physical quantity of product equals the same
function:
Example: “1 kg of packaging material”
Explanation: A physical quantity, such as mass, is not a function. The
mass required to provide a packaging function often depends on the material.