Difference between system process and unit process

Question

Hi,
I am curious about the difference between system process and unit process when modeling in openLCA. It was written in the manual that it depends on the database, but what it really means?
Thank you for your answers in advance!
Kind regards,
Norbert

Answer 1

Hi Norbert, your question is explained in our PET bottle example http://www.openlca.org/wp-content/uploads/2016/10/1.5-Basic-Modelling.pdf

Processes are sets of interacting activities that transform inputs into outputs. Every process is defined by an output flow as a quantitative reference with the flow type “product flow”, which is either selected or created when creating a project. openLCA distinguishes two types of processes:

• Unit Processes: smallest unit analysed for which input and output data are quantified
• System Processes (LCI): unit for which input and output data are aggregated (an aggregated life cycle result saved as a process)

System processes in the model graph are framed with a double line (left), unit processes are framed with one line (right).

Whether you are dealing with a system process or a unit process is also indicated by the symbol before the process. Purple background, white letter = system process; White background, purple letter = unit process;

 

openLCA allows to save product systems or unit processes as system processes/life cycle inventories. A how-to is available via the following link: https://twitter.com/openLCA/status/1059756126466641921

Answer 2

Hi Norbert,
a system process is simply an aggregated life cycle result saved as a process; some databases mostly contain one sort of these processes, unit or system processes, but strictly speaking it does not depend on the database.
Hth,
Andreas