Determining reference flows
The reference flows are the specific product flows for each of the compared product alternatives.
The reference flow is thus a quantified amount of the product(s), including product parts, necessary for a specific product system to deliver the performance described by the functional unit.
For a composite product, the reference flow will typically be identical to the list of the product parts, multiplied by a factor to scale it to the functional unit. The purpose of the reference flows is to translate the abstract functional unit into specific product flows for each of the compared systems, so that product alternatives are compared on an equivalent basis, reflecting the actual consequences of the potential product substitution or alternatives.
Important aspects to address in relation to the reference flow for alternatives are:
- Difference in performance of product systems,
- Differences in price and time consumption (rebound effect)
- Effects on overall productivity of society.
- The reference flows must include any difference that involves additional processes in one or more of the analysed product systems.
- When to include effects on the overall productivity of society and the overall societal rate of growth in a consequential LCA?
- Ignoring the rebound effect will lead to either under- or over-estimation of the effects of new technologies.
- An example on how to identify the system activities with the aim to model the reference flow for re-used bicycles.