Page 123 - Materials Chemistry, Second Edition

108 A. Bjørn et al.

Table 8.5 Geographical scope for life cycle stages and central unit processes in the window
frames case study
Stage Window type
Wood Wood/aluminium PVC Wood/composite
Materials Metal ores: not known
Crude oil: Norway, Russia, Middle East
Forestry: Finland – –
Manufacturing Glass pane: Sweden
Wood frame: Wood frame: PVC frame: Composite
Scandinavia Scandinavia Germany frame: Germany
Other Other elements: Other Other elements:
elements: mainly Europe elements: mainly Europe
Europe mainly
Europe
Assembly: Denmark
Use (heat Mainly Mainly Europe Mainly
supply) Scandinavia, Scandinavia, Scandinavia
Germany Germany
Disposal The same as the use stage

involving clothes washing in Vietnam the unit process for a certain waste water
treatment process in Thailand may be a good approximation for a Vietnamese unit
process if the treatment efficiency is the same, because of the climatic similarities
between the two countries. If needed, the proxy process may be adjusted to better
represent the actual process of the product system. Chapter 9 elaborates on the
choices related to geographical representativeness when constructing an inventory
model. The influence of a low geographical representativeness on the conclusionsof
the study must be evaluated in the interpretation of the LCA results (see Chap. 12).

8.7.2 Time-Related Representativeness

Just as two processes delivering the same product output can be different if they
occur in different locations, they can also be different if they occur at different
times. This is due to technological innovation and development, which often tends
to lead to more efficient processes over time, meaningless input (energy, material
and resource flows) and sometimes also less unwanted by-products (waste to be
treated and emissions) per unit of output. The time-related representativeness
reflects how well the inventory data represents the actual processes regarding the
time (e.g. year) they occur. Technological innovation is “faster” in some sectors
than others. Therefore, a unit process that reflects the situation 10 years prior to the
occurrence of the process in the product system can have a high time-related
representativeness if it belongs to a mature sector with little technological