Mixing unit and system processes in a product system

[pascal.lesage]

Dear forum,

I find the "prefer" option in the "build supply chain" function of the model graph tab extremely useful. However, I seem to hit a problem when I mix unit and system processes (using ecoinvent v3.1, at least).

Case 1) If I choose an ecoinvent v3.1 Unit process, "building a supply chain", whether one tier or completely, will always connect to Unit processes, even if I "preferred" System processes.

Case 2) Say I have a unit process of my own, using ecoinvent v3.1 for background data, I can definitely "building a supply chain" "preferring" System processes. However, say I want to examine in more detail a particularly important contributor, I would want to be able to change one of the System processes for a Unit process and then "build a supply chain" for that specific input "preferring" System processes. This does not work - it necessarily links to unit processes.

Is this known/expected behaviour, or am I doing something wrong?

Thanks!
Pascal

[KevinP]

Hello everyone,

we seem to have the same problem as Pascal and before opening another post, I'd like to bring some more attention to his.

We are using openLCA 1.4.2 and the probas database. Our assignment is to design an ecobalance for the production and use of t-shirts. We mostly use system processes, but for the transport distances we are using unit processes.

Now the problem is, that we cannot link all of the system processes to the unit process. Let's say our transport unit process has 4 inputs, then we can usually link 1-2 of the system processes but the others won't work. We can't drag&drop them in the model graph, nor can we find another way to add them. Going further, every unit process has 2-3 other unit processes as input and we cannot add system processes to these unit processes either, which results in a ton of work load.

Is there a fix to this problem?


Thanks!
Kevin

[aciroth]

Hi Kevin,
well the ProBas database is not fully linked, meaning that it contains processes which link to products which do not exist in the database, and thus the supply chain needs to be completed manually, which can indeed be quite some work. You are referring to the ProBas or the ProBas+ database?
Best wishes,
Andreas

[KevinP]

Hi Andreas,
thanks for your response. We are using the probas database. We do have the required system processes for the inputs, but we simply cannot link them to our supply chain. Also when we try to connect them with our model, the programm has some strange errors like connections pointing into random corners, or even a complete crash of the programm. We are kind of frustrated right now...

[aciroth]

If the processes are using different products, they cannot be combined directly (between ProBas and another database or between ProBas and your own processes). One solution is to create an intermediate "handshake" process which has one product as input and the ProBas product as output, and link these with the database and with ProBas.
Kind of frustrated: The model graph can be difficult if you have a larger system, if you use the default provider feature in the process editor (input/output sheet) for establishing the default connection, you avoid working with the entire model all the time.
Hth,
Andreas