Page 103 - Materials Chemistry, Second Edition

88 A. Bjørn et al.

reference flow is the amount of product that is needed to realise the functional unit.
For example, as shown in Table 8.1, 0.67 L of paint A is required to realise the
functional unit in Fig. 8.4, while the same functional unit is realised with 0.15 L of
paint B. The reference flow is typically different qualitatively and quantitatively for
different products compared on the basis of a functional unit, due to differences in
product properties and characteristics (e.g. viscosity and tear resistance of a paint).
The reference flow is the starting point for the ensuing LCI analysis phase of an
LCA (see Chap. 9), because it determines all the product flows required throughout
the life cycle of the product system studied and their associated elementary flows
(resource uses and emissions). It is very important not to confuse a reference flow
with a functional unit (see Example 1 in Box 8.1). The former can only be known
when the latter is correctly defined. One should, for example, never base an LCA on
the comparison of 1 L of two different paints, unless a correctly defined functional
unit has shown that the reference flows of the compared paints are quantitatively
identical. It is important to understand the use situation in order to correctly define
reference flows. For example, to define reference flows in a comparison of a dis-
posable cardboard cup and a ceramic cup, the LCA practitioner must understand the
number of times the two cups are used before they are discarded and how the
ceramic cup is cleaned (by hand or dishwasher, and the associated consumption of
detergent and water and its temperature). Tables 8.1 and 8.2 include functional unit
and corresponding reference flows for the example of outdoor wall paint and the
window frame case study (Chap. 39), respectively.

8.5 LCI Modelling Framework and Handling
of Multifunctional Processes

This part of the scope definition deals with the choice of an appropriate LCI
modelling framework and ways to handle multifunctional processes. These choices
must be made in accordance with the goal definition, particularly the identified
decision context (Situation A, B or C, see Sect. 7.3), and they have a strong
influence on the inventory analysis, the LCA results and their interpretation.

8.5.1 Secondary Functions and Multifunctional Processes

To understand why different LCI modelling frameworks exist we first need to
consider that a product system often delivers other types of function than the type
dealt with in Tables 8.1 and 8.2. The functions of Tables 8.1 and 8.2 all relate to
obligatory or positioning properties and are intended functions made available to
product users by, e.g. companies selling the products. They are called primary
functions. In addition to those, secondary functions can also emerge in the life cycle