Environmental Engineering Reference
In-Depth Information
thermodynamic equivalent of the invested muscular
exertion or the maximalist option of finding the total
existential energy requirements? And how can the mental
(inventive or managerial) component be reduced to a
common energy denominator?
These challenges have no satisfactory solutions. Conse-
quently, I focus first on general approaches, achieve-
ments, and limitations of energy accounting and then on
the energy costs of energy (surely one of the most deci-
sive determinants of a civilization's achievements and
prospects) and on the energy costs (energy intensity or
embodied energy) of basic material inputs. Food is, of
course, the most indispensable human energy input, and
the fuel and electricity subsidies used in modern farming
are reviewed in the closing sections of this chapter. Most
of the pioneering studies of energy costs and subsequent
energy analyses for a large variety of industrial products
are gathered in volumes by Boustead and Hancock
(1979) and Brown, Hamel, and Hedman (1996). En-
ergy analyses also are an important component of life cy-
cle assessments (LCA) of products, structures, or services
(Frankl and Rubik 2000; EEA 1998).
There are three basic approaches to the quantification
of energy costs. Input-output analysis is a variant of stan-
dard econometric analysis based on input-output tables.
A square sectoral matrix of national economic activity in
a given year is used to extract the values of direct and in-
direct energy inputs, and these in turn are converted into
physical energy equivalents by using prevailing fuel and
electricity prices. A limitation of this approach is that sec-
toral aggregates may reach only heterogeneous catego-
ries (elevators, drugs, steel) and not particular products.
In contrast, process energy analysis first identifies the se-
quence of physical operations required to produce a par-
ticular item, then accounts for all significant material and
energy inputs into the process, and finally assigns energy
equivalents to direct energy inputs and energy costs of
materials. The first two parts of the exercise are of great
heuristic value and indispensable for any successful
improvements in managing the analyzed process. The
third, hybrid approach combines the input-output and
the process analysis approaches (Treloar 1997).
The choice of system boundaries determines the out-
come. Limiting the analysis to direct energy inputs used
in the final process stage may suffice in cases of simple
processing. In other cases, contributing costs diminish
rapidly with every successive stage, and limiting the anal-
ysis to direct energy inputs and to the best values of en-
ergy costs of all major material inputs may be satisfactory.
In order to calculate the energy cost of making a poly-
ethylene grocery bag, we do not need to know the en-
ergy cost of building a blast furnace that will operate for
half a century and whose two-week's worth of pig iron
output will be eventually made into steel to build an off-
shore platform used to extract natural gas. But in some
cases, truncation errors can be large; two detailed reanal-
yses illustrate their extent for steel and an apartment
building. Lenzen and Dey (2000) showed that an input-
output analysis of the Australian steel industry yielded an
average twice as large (40.1 GJ/t) as did a process analy-
sis (19 GJ/t). And Lenzen and Treloar (2002) used
input-output analysis to demonstrate that the embodied
energy in a four-story Swedish apartment building should
be about twice as large as the value derived by a two-
stage process analysis by B
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rjesson and Gustavsson
(2000), with the greatest differences for structural iron
(@17 GJ/t vs. @6 GJ/t) and plywood (@9 GJ/t vs. 3
GJ/t). When analyzing the energy cost in the automo-
bile industry, it is imperative to go well beyond the cost
of assembly. In order to account for energies embodied
