Page 151 - Materials Chemistry, Second Edition

3.5 Data Aggregation and Units 135

LCIs. The praxis in The International Journal of Life Cycle Assessment allows only
SI (Syst` eme International) units as well as their multiples and a few other units
authorized by SI, so kilowatt hour, day, hour, minute (ISO 1000, 177) DIN 1301). 178)
As such, besides the use of Joule and its multiples (in LCI mostly as MJ), also
kilowatt hour (1 kWh ≡ 3.6 MJ) is allowed to distinguish electrical energy (mostly
given in kilowatt hour) from other forms of energy. Inadmissible for this journal
is the use of obsolete US-American units, for example, the BTU (British Thermal
Unit), calorie, pound, gallon and miles. 179)
Heijungs 180) shows by examples how important it is to comply with the rules, in
LCA also. SI also regulates the designations of units and the prefixes. Heijungs
further points to the problem of dimensionless quantity (physicists say, such
a quantity is of dimension 1). These are usually quotients, for example, the
‘dimensionless Henry coefficient’; here, an additional note or a clear designation
helps, like ‘air/water-distribution coefficient’.

Box 3.1 Units

According to The International Journal of Life Cycle Assessment, Instructions for
authors 181) .
Only use metric units (SI) and some other units specified in ISO 1000. The
Syst` eme International d’unit´ es, the modern variant of the meter convention,
comprises the following fundamental units: meter, kilograms, second, ampere,
Kelvin, mol and candela and a set of derived units (e.g. Newton for force, Joule
for energy, Watt for power and Pascal for pressure). A complete list is part of
ISO 1000/ISO 80 000.
Examples of permitted additional units, which do not belong to SI, are hectare
3
2
4
(= 10 m ), symbol ha; litre (= dm ), symbol: l or L; day (= 86 400 s), symbol
d; hour (= 3600 s), symbol h; minute (= 60 s), symbol min; kilometre per hour
−1
(km h ); metric ton (= 1000 kg, Mg), symbol t; Watt hour and multiples, like
kWh, MWh and GWh (in LCIs only to differentiate electricity from other forms
−3
of energy). Furthermore, decibel (dB); mol per litre (mol dm ), symbol mol l −1
−1
or mol L ; electron volt (eV) and its multiples, like keV, MeV and GeV (only
common for the energy of elementary particles and photons).
◦
◦
However, degree Celsius, symbol C, defined by 0 C ≡ 273.15 Kelvin (K) belongs
to SI.
The data sets related to a unit process or a phase of the life cycle are not to be
lost due to the aggregation of data over the entire life cycle. This is important for
the detection – and possibly improvement of – those unit processes or life cycle

177) ISO 1000 is now part of ISO 80 000 (2009).
178) Deutsche Normen, 1978a,b; International Standard Organization (ISO), 1998b.
179) Such units can, of course, be used in LCA studies of regional importance and for audiences
unaware of metric/SI units.
180) Heijungs, 2005.
181) http://www.springer.com/environment/journal/11367.