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I hope this question hasn't been asked before.

I exported a database in CSV from SimaPro and then imported it into OpenLCA.

I then built a product system in OpenLCA from a random process (Polycarbonate production) and compared its inventory results with the ones obtained from SimaPro for the same process.

The number of elementary flows for the two inventories is identical, however, some minor differences are present in the amounts (1-5 % differences, with most of them being <1%).

I struggle to understand why this is happening, as I'm expecting to obtain exactly the same inventory for the two identical processes with two identical databases.

Any ideas on why this is happening?

Thank you in advance!


in openLCA by (120 points)

1 Answer

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by (92.9k points)

Hi, this is an often-discussed topic, with the same model, and the same flows, SimaPro and openLCA provide almost the same results, and not exactly the same, for several reasons:

  • SimaPro calculates (or calculated, in verison 9.1x I think when I last checked) with single precision but with a smart, commercial library that switches the decimal based on the size of the quantitative number, openLCA calculates with double precision (see e.g. https://web.archive.org/web/20120325162206/http://www.psc.edu/general/software/packages/ieee/ieee.php). The difference is larger for numerically less stable calculations, such as substracting to large amounts.
  • Both softwares use a different algorithm, a simplified / approximated matrix inversion calculation with each will have different result

More severly, though, the export could be affected, by

  • truncation of SImaPro names in the SimaPro csv
  • possibly different units that are not mapped
  • maybe formulas that are ill-specified or also processes that are ill-specified in the csv export due to special characters in the SimaPro csv

You can perform a validation of the database to check whether formulas are not ok. You should use openLCA version 2 for this, and export the SimaPro LCIA methods (or, map flows).

Hope this helps!