A maior rede de estudos do Brasil

Grátis
314 pág.
LCA part3

Pré-visualização | Página 36 de 50

amount of clothes optically white (= functional unit)1.
Lindfors et al. (1995a) argue that a “performance quality standard (if any), e.g. a certain level of
corrosion protection provided by an industrial paint system” should be taken into account in quantifying
the reference flow. This is supported by the work of Udo de Haes et al. (1996). In line with the proposal
of Udo de Haes et al., three types of system performance can be distinguished:
a) Standard performance refers to a known standard (national, e.g. DIN, or international, e.g. CEN),
describing a standardised test applicable to all equivalent products: for example, the amount of
detergent required to wash to a certain degree of cleanness a certain quantity of clothes with a
certain degree of soiledness at temperature X, at Y degrees of hardness, etc.
b) Recommended performance refers to manufacturers’ recommendations on product operating
mode: for example, the detergent dosage indicated on the packaging.
c) Actual performance refers to the actual performance which will often depend on the consumer
behaviour, e.g. the average detergent dosage used by the consumer based on consumer studies.
 
1 Note that the functional unit and reference flow are different quantities. On the basis of one functional unit,
different reference flows will usually be quantified for each (product) system analysed. Only in exceptional
cases will reference flows and functional unit be the same, but this will then generally limit the number of
products that can be compared.
Part 3: Scientific background May 200181
This actual performance can be taken as an average or as a range, which may a significant factor in
the final LCA results. The latter might be used to provide environmental advice to consumers, etc.
 Several examples of reference flows are described In the textbox.
 
 
 In the case of a multifunctional unit, the reference flows must be quantified in such a way that they fulfil
all the functions included in the functional unit. This may imply that, although one of the functions can
already be fulfilled using smaller amounts of the reference flow, the amount of reference flow has to be
further increased to fulfil the other functions. If this is not acceptable, to the commissioning or interested
parties, for example, the multifunctional problem should be solved by allocation (including system
expansion) rather than by including the extra functions in the functional unit.
Paint
Reference flows are typically expressed as the number of litres required for covering the surface area as
defined by the functional unit. For example, in a standardised test, paint A may be determined to cover 8.7
m2 per litre, thus requiring 2.3 litres to cover the 20 m2 of the functional unit, provided the conditions in the
standardised test are similar to those required by the functional unit (with regard to surface type and
opacity).
Hand-drying
In a comparison of paper towels versus an electrical hand drier, it may be irrelevant to use a standardised
test based on the technical properties of the paper such as mass, absorption power and tensile strength, if
the actual weight of paper used depends on the dispenser design. A more appropriate measure would
then be data collected by weighing the paper stock at the start and end of a suitable period in which the
number of hands dried are determined by electronic surveillance of actual wash basins located in relevant
institutions. Similarly, technical specifications of an electrical hand-drier, such as the volume of air and its
temperature, may be irrelevant as a basis for calculating the reference function, if the actual running time of
the device is determined by other factors, e.g. a built-in timer. Then, all that is needed is the running time
and the electrical capacity of the equipment.
Refrigerators
For long-lived products, such as refrigerators with lifetimes of 10 or 20 years, technology development may
be a factor that cannot be disregarded. One refrigerator with a lifetime of 20 years cannot simply be
compared to two successive, present-day refrigerators with a lifetime of 10 years. The refrigerators
available 10 years from now are certain to be more energy-efficient than current models; the energy
efficiency of the second refrigerator in the 10+10 years option must be established by projecting trends,
while that of the 20 years option is fixed.
A comparison of refrigerators may be based on their internal and/or external volume. Although the primary
function is obviously related to the internal volume, the external volume may a determining factor if the
refrigerator is to be fitted in an existing kitchen. If an identical external volume is demanded, the internal
volume may differ because of differences in insulation thickness. This can only be adjusted for by
assuming differences in user behaviour (e.g. more frequent shopping trips, storage of certain items
outside the refrigerator, adding another, smaller refrigerator elsewhere in the house). Each of these
changes in behaviour will involve changes in different processes, which will then have to be included in the
study. If, on the other hand, an identical internal volume is demanded, a change in insulation thickness may
require adjustments in the physical surroundings of the refrigerator (the other kitchen furniture). If both the
internal and external volume must be equal, there is obviously no adjustment feasible to accommodate the
change in insulation thickness. As this demonstrates, the choice of required functions also determines the
possible alternatives to be included in the study.
 
Beverage packaging
100,000 half-litre one-way bottles may technically fulfil the same function of protecting 50,000 litres of
beverage as 125,000 0.4-litre returnable bottles with a reuse rate of 90%. For the consumer, however, the
difference in volume may be indistinguishable. If the consumer takes ‘a bottle to be a bottle’, total
consumption of the beverage will decrease when the returnable bottles are introduced. In this case, the
packaging cannot be studied independent of its contents. In this example there should also be iteration
back to the “selection of relevant function(s)” step, or, alternatively, the goal of the study should be redefined,
allowing for a comparison of beverage plus packaging taking into account the changes in consumption.
Source: ISO/TR 14049 (1998). For even more examples see also ISO/TR 14049 (1998).
Part 3: Scientific background 82 May 2001
Although the examples and phrasing of ISO/TR 14049 certainly provide a degree of insight, they still do
not pin down precisely what a reference flow is or how it relates to a functional unit. Let us therefore
expand and focus the discussion a little more. Consider a comparison of two systems for lighting a room
with the same amount of light: an incandescent lamp and a fluorescent lamp. Suppose we have defined
the functional unit as lighting a standard room for 1 year with a certain flux of light. The flow diagrams of
the two product alternatives then contain the two use processes as follows (see Figure 2.4.1).
lighting with
incandescent
lamp
electricity
production
incandescent
lamp
production
disposal of
incandescent
lamp
3
incandescent
lam
ps
3 discarded
incandescent lam
ps
1000 hours of
light w
ith
incandescent
lam
p
fluorescent
lamp
production
electricity
production
lighting with
fluorescent
lamp
200 kW
h
electricity
disposal of
fluorescent
lamp
1000 hours of
light w
ith
fluorescent lam
p
2 discarded
fluorescent lam
ps
100 kW
h
electricity
2 fluorescent
lam
ps
reference flows
reference processes/use processes
functional unit: "1000 hours of light"
Figure 2.4.1: Flow diagrams, functional unit, reference/use processes and reference flows for two
alternative (hypothetical) lighting systems.
Following the ISO examples, the reference flows would be 3 incandescent lamps for the first system and
2 fluorescent lamps for the second.