Page 104 - Materials Chemistry, Second Edition

8 Scope Definition 89

of a product system. Secondary functions are unintended functions that usually
have low or no relevance to the users of a product, meaning that they are not
contributing to the obligatory or positioning properties. Instead, secondary func-
tions are relevant to other systems of the technosphere that the studied product
system interacts with. The existence of secondary functions reflects the fact that
some processes are multifunctional. A process is multifunctional when it provides
more than one function, meaning that it either delivers more than one product
output and/or provides more than one service. An example of a multifunctional
process that delivers more than one product output is animal husbandry where the
cow may deliver both milk, meat, hide, bone meal and other products with an
economic value. The production of the hide is an example of a secondary function
of the husbandry from the perspective of the user of a bottle of milk, since hide is
neither an obligatory nor a positioning property of the milk. An example of a
multifunctional process that both deliver more than one product output and provide
more than one service is waste incineration. It provides the multiple services of
getting rid of many different types of wastes (the obligatory property) and can
deliver both electricity and heat while doing so. Thus, secondary functions of a
product that is disposed of by incineration are the production of heat and electricity.
These secondary functions are relevant from the perspective of the energy system
that the product system interact with because a change in the volume of discarded
products that is incinerated leads to a change in the amount of energy generated
from incineration.
Multifunctional processes constitute a methodological challenge in LCA, which
is based on the idea of analysing individual product systems based on the primary
functions they provide in order to determine the environmental impact from the
product. In the real world, there is hardly any product system that exists in isolation.
As soon as a by-product arises from a multifunctional process (e.g. animal hus-
bandry), it is economic common sense to try to utilise it, often in a different context
from the product system being analysed in the LCA. This means that the process
becomes part of another product system as well, and that the environmental impacts
from the process can no longer be fully ascribed to the product system studied.

8.5.2 The ISO 14044 Hierarchy to Solving
Multifunctionality

In order to solve multifunctionality issues, the ISO 14044 standard presents a
hierarchy of solutions. These solutions can both be used to make different product
systems functionally comparable and to represent a single product system in a
hotspot analysis. The levels of the hierarchy are presented below and the hierarchy
is summarised as a decision tree in Fig. 8.5. Chapter 9 shows how to use to ISO
hierarchy in practice when constructing an LCI.