How to aggregate processes to reflect the impacts of different stages ?

Question

Hello,

I am conducting a LCA of a product composed by different parts, and as a beginner with OpenLCA I have a few questions regarding the aggregation of some processes.

The different parts are produced in various placed, then transported to a single location to be assembled (see the simplified diagram below). In order to better understand the impact of the various stage of the life cycle, I am looking for a way to aggregate the processes included in the manufacturing stage, and the processes related to the transportation stage of the parts before the assembly stage.

I am considering two option for this aggregation, but I am not sure of which one could be better, and if there is another way to do so that would be more suited :

Option A : nested product systems

I tried to use "sub-product systems", one for the manufacturing stage, and one for the transport stage.

But I need to set a reference process, i.e. the process producing the main outputs a sub-product system, which is complicated because I have many processes involved in each sub-product system (at least one for each part manufactured or transported), and each one is equally important. How do I choose which process should be set as the reference process of the sub-product system ? The one with the most important impacts ? Or can I choose it arbitrarily ?

Option B : grouping the results

The other option I am considering is to calculate the entire product system and using the grouping option once the results have been processed. This option seems better, since it is more flexible, but I have several identical processes involved at various stage of the life cycle (e.g transports and electricity), and the grouping option aggregate the overall impact of these processes. Thus, I am not able to isolate at a specific stage the impacts generated by a specific process used in several stages, since these processes appear only once in the selection panel of the Grouping tab .

For example, in my simplified diagram, the process "Transport by lorry" appears both in each process related to the transport of the parts stage, and at the distribution stage. But in the grouping tab, I have only one "Transport by lorry" process which aggregate the impacts generated by the transport of each parts and the distribution stages. Yet I would like to distinguish the impacts generated by the use of lorry transportation at these two stages separatly.

I am considering duplicating these shared processes, and rename them in order to have one specific for each stage, but I am not sure it's a good idea.

Plus, I am not sure that the grouping option include upstream impacts even if I choose the "Analysis" option when launching the calculation.

Is one of these options better than the other ? Or is there another way to proceed ?

Thank you in advance for your answers !

Answer 1

Hello, I am curious if you found your solution. I also thought of these two options, but as you said, it is not evident.

Anyone could give guidance regarding this?