Page 95 - Materials Chemistry, Second Edition

3.2 Energy Analysis 79

The efficiency thus serves as weighting factor. During data procurement of
single processes in the enterprise, mainly the partial amounts of the final energy
consumption will be determinable. As the energy is usually purchased, invoices
can be evaluated, and on the basis of machine data and running times the final
energy consumption can be calculated or be measured by electric meters. For
LCAs, however, the primary energy demand is essential. For instance, g = 0.2 will
result in a fivefold higher primary energy demand (because 80% of the primary
energy, usually in the form of waste heat, are lost).
With the above stated formulas, the CED can also be determined without a
complete life cycle inventory. The latter would require the consideration of all input
and output categories. The determination of CED is therefore often regarded as a
methodology of its own, 52) although VDI 4600 refers to a fU and LCA in general.
The CED determination within the inventory analysis is done using the sum of
energy sources and is often split into a CED fossil and a CED renewable .

3.2.2.3 Balancing Boundaries
The CED is a very useful aggregated quantity which provides a good overview on
the integrated primary energy demand of a product system.
It has been argued that the determination of CED in case of certain forms of
primary energy (nuclear energy, solar energy, and wind energy) is ambiguous. 53)
A convention is needed on how to define primary energy, in particular, with
respect to solar energy. Solar radiation hitting the earth’s surface has so far not
been assessed; therefore wood and similar renewable energy carriers and materials
have not been evaluated in regard of their primary energy potential. This is also
true for hydropower, which is an indirect form of solar energy and is quantified in
the form of potential energy. Because of the high (approximately 85%) efficiency in
the conversion of potential energy of the water into electrical energy, the electricity
itself (starting from the power station) can be defined as primary energy, as a first
approximation. For the energy supply to the consumer, corrections due to varying
losses depending upon distance and voltage and wire losses must be made in the
calculations. The available generic data records 54) provide various options.
For nuclear energy the CED is calculated using the thermal efficiency of electricity
generation: the primary energy is thus defined as the energy stored in the fissile
atomic nuclei. Here and in the case of solar energy a convention is certainly needed,
which should be specified in the form of a standard. VDI 4600 does not propose
rules on how to deal with these forms of primary energy in the context of LCA. In
ISO 14044 an aggregation of energy to CED is not expressly mentioned contrary to
a year-long practice. The Dutch guideline of 2001 provides CED as an option. 55)

52) Wrisberg et al., 2002.
53) Frischknecht, 1997.
54) Fritsche et al., 1997 and updates : Globales Emissions-Modell Integrierter Systeme (GEMIS
4.3) (downloaded 2 May, 2007) http://www.oeko.de/service/gemis/de/index.htm; Version of 2010 is
Gemis 4.7; ecoinvent 1, 2004a; Frischknecht et al., 2005.
55) Guin´ ee et al., 2002.