Stand-alone data is a term that describes the set of information developed to standardize or normalize the subsystem module input and output for the product, process, or activity being analyzed. (A subsystem is an individual step or process that is part of the defined system.) Stand-alone data must be developed for each subsystem to fit the subsystems into a single system. Two goals are necessary to achieve in this step:
Presenting data for each subsystem consistently by reporting the same product output from each subsystem Developing the data in terms of the life cycle of only the product being examined in the inventory
A standard unit of output must be determined for each subsystem. All data could be reported in terms of producing a certain number of pounds, kilograms, or tons of a subsystem product.
Once the data are at a consistent reporting level, the analyst must determine the energy and material requirements and the environmental releases attributed to the production of each coproduct using a technique called coproduct allocation. One commonly used allocation method is based on relative weight. Figure 3.4.5 illustrates this technique.
Once the input and output of each subsystem are allocated, the analyst can establish the numerical relationships of the subsystems within the entire system flow diagram. This process starts at the finished product of the system and works backward; it uses the relationships of the material input and product output of each subsystem to compute the input requirements from each of the preceding subsystems.
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