How do I choose between unit and system libraries?

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As an LCA practitioner, you are free to choose between unit and system processes when doing an LCA. The final results will not be influenced. So, why choose one or the other? There are important considerations to take into account. If you want to understand better the difference between the two, please read this article.

How to decide between unit and system processes?

Whether you choose unit or system processes, the results of your LCA will be the same. However, there are advantages to using either.
For unit processes, the advantages are:

  • It is easier to browse through the network and analyze the supply chain, as unit process contains links to other processes. For example, you can use them to do an environmental hotspots analysis.
  • Unit processes can be used for uncertainty analyses, as they include probability distributions (e.g. lognormal) of inventory data.

The advantages of using system processes are:

  • System processes improve the calculation speed in SimaPro.
  • A way to deal with confidential data. Datasets may be transformed into a single system process. This way, all the underlying details are removed, and no confidentiality issues should arise.
  • Additionally, datasets may be offered as an average for a sector instead of individual datasets for individual manufacturers.

Which approach to choose?

Although both versions are available for users on the ecoinvent website, some LCA software tools provide only the system processes. In SimaPro, both versions are available for use. Still, you may think your project would benefit from both the advantages of unit processes and system processes. Luckily, with SimaPro, you do not have to make a final choice right away. You can combine benefits, so you get optimal calculation speed while retaining the options to analyze the supply chain, the hotspots and the uncertainty.
How? By easily being able to switch from unit to system processes and back in your LCA model. In SimaPro, that takes literally two clicks when indicating the preferences for your analysis. This way, you can have the best of both worlds! Check out this video on switching libraries.