Environmental Engineering Reference
In-Depth Information
instances where a material with a higher EE is justified when the life cycle
costs that also include maintenance and replacement costs are taken into
account. For instance, an aluminum window with an EE ~ 5500 (MJ/m
2
)
and a carbon emission (GWP) 279 (kg/m
2
) will have several times the
service lifetime of a comparable wooden window with the lower EE of
approximately 230-490 (MJ/m
2
) and a GWP of only 12-25 (kg/m
2
)
(Hammond andJones,2008a). Similarly, amaterial withahigherEEmight
be justified when a smaller quantity of it can be used to provide the same
functionalityasthematerialitreplaces.Inanyeventasdiscussedin
Chapter
carbon emissions and reusability of materials need to be considered.
Estimates of EE for different plastics (US data) are shown in
Figure 4.9
. The
estimates for common plastics are not that different from each other and
valuebeingdependentonthespecificsourcesofenergyusedinmanufacture
and on the technology used can be somewhat different in other parts of
the world. For instance, the comparable energy calculations in the
PlasticsEurope database are 4-13% lower for common plastics such as PE,
PP, PVC, and PS. The cradle-to-gate values for EE in the figure for neat
plastics resins will change if they are compounded with additives.
