Is it necessary to create multiple processes to model them in a product system?

Question

Hello openLCA users,

I hope somebody more experienced than me can explain the diffrence between processes and product systems in terms of calculating and modelling.

I am creating an LCA for a cleaning product using EF_secondarydata_201908 database and EF LCIA method. The cleaning product I am analysing doesn´t have many ingredients, and therefore therefore the flows are quite straightforward: there are 5 raw materials, some transportation, packaging, and electricity usage.

I am thinking to only create one process, and from that to create one product system which will have all the inputs, and the output would be the cleaning product.

The second option I have in mind is to create 3 different processes representing:
1. Production (= raw materials, energy, transportation),
2. Packaging ( = materials for producing the packaging, energy, and transportation),
3. Use (=packaging becomes waste, cleaning product becomes wastewater)

After that to create one product system for each process, and then to create one final product system consisting of these 3 product systems.

Are these two options any different in terms of calculating the environmental impact? What I´m thinking is that it only makes a difference in modeling, i.e. maybe the second option is better for presenting the flows and processes visually.?

And secondly, when I am creating processes, should I create unit processes or system processes?

Thanks in advance for any response.

Kind regards,

Katerina

Answer 1

Generally, the results will not differ, independent of whether you have multiple processes in your product system or just one "black-box" process which aggregates all the flows.

You are right: in terms of transparency, presentation and analysis, it is always beneficial to model a system as close to reality as possible (real world independent activities, such as production and use are represented by multiple processes in openLCA). Also, this allows you to re-use modelled processes. Maybe you want to model a product system in the future, which uses the same production and packaging, but a different user behavior? In this case you can re-use the already created processes.

One important tip:

• - create the three processes in a way, that they are connected. meaning: output flow of production is an input flow for packaging, ... output flow of packaging is an input flow for use
• this way, you only have to create one product system, which incorporates all three processes.

I think, you should create unit processes.

Comments

Thank you so much, Julian! Your answer is very helpful.
And could you by any chance also tell me how to "update" an already created product system after editing its processes? Is it even possible?

---

Actually when I create one product system incorporating three different processes which are linked as you are suggesting, I get different (lower) numbers in the impact analys than when I created it one one "black-box" process or a product system consisting of three product systems. And I believe it is because the reference process of this product system is only the production process even though I added the other two processes in the model graph and linked their providers. How do I create a product system incorporating all three processes equally?

---

This shouldn't happen. If all amounts and flows are equal, you should and will get the same results.

One possible reason might be that the flow amounts are not the same due to your process specifications (think of: you specified your production process for 1 kg, but in the end your product system only needs 0.5 kg of product etc).

And concerning your other question: you can always create a new product system, after you have made changes to processes.