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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.