Page 99 - Materials Chemistry, Second Edition

84 A. Bjørn et al.

outdoor paints may be based on the functional unit: “Complete coverage of 1 m 2
primed outdoor wall for 10 years in Germany in a uniform colour at 99.9%
opacity”. This is not to say that all LCAs on paint should have this functional unit.
In other cases, for example, a particular colour or sheen may be considered an
important function and should be included in the functional unit. It is important to
understand that the functional unit should always include a function and not simply
be a physical quantity, such as 1 kg, 1L or 1 MJ. For example, it would be wrong to
compare paints on the basis of a functional unit of “1L paint”, since an identical
quantity of different paints may deliver different functions, e.g. in terms of area of
wall that can be covered, or the quality and duration of the coverage. Figure 8.4
illustrates how this functional unit is composed of answers to the five questions
presented above.
It is important to define the functional unit right because it significantly influ-
ences the way LCA is performed, its results and interpretation, especially in
comparative studies (see Sect. 8.9). This is because the functional unit serves as a
reference point for deciding which unit processes to include and to what extent they
are drawn upon. It is therefore essential to ensure that the functional unit fully
captures the relevant functional aspects of the studied systems. In the following
paragraphs, we provide some guidance for defining a correct functional unit.
To get started, two concepts from the product development field are generally
useful. These are obligatory properties and positioning properties. The obligatory
properties are features that the product must possess for any user to perceive it as a
product (e.g. ability to cover and protect the wall against the weather for an outdoor
wall paint) and may also include legally required features (e.g. a car must have seat
belts). These can usually be expressed in technical terms. The positioning prop-
erties, on the other hand, are optional features of a product, which can be used to
position it as more attractive to the consumer in the competition with other similar
products. Examples include price, colour, comfort, convenience, image, fashion and
aesthetic aspects of the product. Positioning properties often vary from consumer to
consumer as opposed to obligatory properties. Tables 8.1 and 8.2 show an example
of obligatory and positioning properties for an outdoor wall paint and the window
frame case study (Chap. 39), respectively.
After having listed the obligatory and positioning properties they need to be
transformed into the functional unit, i.e. they should be used to address the

Complete coverage of 1 m 2 primed outdoor wall for 10 years in Germany

For how long/
What? How much? What? Where?
how many times?
in a uniform color at 99 .9 % opacity

How well?
Fig. 8.4 Example of a functional unit composed of five questions