How to model an input fucntional unit?

Question

I'm looking at a product system for biogas, and I'm wondering how to have a functional unit based on the quantity of feedstock going into the system i.e. as an input at the start. In openLCA, when you create a product system, you select a reference process at the end of the supply chain, in my case electricity produced.

In the openLCA manual it says:

9.2 Product system tabs contents

9.2.1 General information

Here you can change the name of the product system as well as add a description (optional). In the "Reference" section you can see the reference process and make changes to the reference product, flow property, unit and the target amount. The target amount should be selected in accordance with your functional unit.

Does this mean that any functional unit must be a reference process at the end of the supply chain?

Thanks

Ciara

Answer 1

Hi Ciara,

Does this mean that any functional unit must be a reference process at the end of the supply chain?

Yes and no; the functional unit must be in the last process of your system, in the reference process, but it can be at the input side of this process (which makes typically sense if the flow is a waste flow)

Comments

Thanks Andreas, calling it an "input" functional is confusing in this sense, I understand that the FU can be an input or output in the last process.

Is there a workaround when the reference process you are interested in is at the start of your system?

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Ah - since LCA does not consider time, I probably should have written "top" or so instead of last; I think you will rarely have this top process as literally first / bottom process, e.g.: first process cast copper wire; used in maybe 200 different processes to produce 200 pre-products  which are again used in maybe 1000 different other processes - right? You will always try to model the process where the supply chain somehow culminates.