Page 204 - Materials Chemistry, Second Edition

190 R.K. Rosenbaum et al.

• Baseline reference scenario, such as another product system (e.g. expressing the
“environmental space” occupied by this product system relative to a similar
reference system using best available technology)

Using one of the first three reference systems listed above is also referred to as
external normalisation. Using the last reference system in the list is also called
internal normalisation when the reference scenario is one of the compared alter-
natives, such as the best or worse of all compared options or the baseline scenario
representing, e.g. a current situation that is intended to be improved or a virtual or
ideal scenario representing a goal to be reached. Normalised impact scores, when
using internal normalisation, are often communicated as percentages relative to the
reference system. In the illustrative case on window frames in Chap. 39 an internal
normalisation is applied using the wooden frame window as reference (indexing it
to 100%) to reveal how the studied alternatives compare to this baseline choice. The
study also applies external normalisation in order to compare the size of the dif-
ferent midpoint impact scores with the European person equivalent impact scores
that is provided as default normalisation references for the LCIA method applied in
the study (the ILCD method).
In practice, an LCIA method generally provides normalisation factors for use
with its characterisation factors. The normalisation factors should be calculated
using the same characterisation factors for the reference inventory as used for the
inventory of the product system. Normalisation factors from different LCIA
methods thus cannot be mixed or combined with characterisation factors from
another LCIA method. This means that as an LCA practitioner you are usually
limited to the reference system chosen by the LCIA method developers.
Normalisation is applied using normalisation factors (NF). These are essentially
calculated per impact category by conducting an LCI and LCIA on the reference
system, i.e. quantifying all environmental interventions E for all elementary flows
i for the reference system and applying the characterisation factors CF per ele-
mentary flow i, respectively, for each impact category c. Although not obligatory,
the normalisation reference is typically divided by the population P of the reference
region r, in order to express the NF per average inhabitant of the reference region
(per capita impacts or “person equivalents”). This way, a total impact of the ref-
erence system per impact category is calculated, resulting in one NF per impact
category c:
P 1
ð CF i E i Þ
i
NF c ¼ ð10:2Þ
P r
Ensuring consistency, the LCI data used to calculate a NF need to represent a
common reference year and duration of activity (typically one year, being the
reference year) for all impact categories. This results in NF having a unit expressing
an impact per person and year, also referred to as person equivalent. A normalised
impact score NS for a product system is calculated by multiplying the calculated
impact score IS for the product system by the relevant NF per impact category c: