Using supplier-provided LCA and EPD impact results in your own LCA models is a challenging task from a scientific perspective.
Each impact assessment method uses its own specific characterization factors and different assumptions for how elementary flows are translated into calculated impact results. Because of this, results from different impact methods are not comparable with each other and cannot be converted with a "factor". For example you cannot calculate the climate change impact results in EF3.1 if your supplier has given you the climate change results in IPCC 2021. You would need the whole inventory to be able to do it accurately.
The good news is that there are various strategies as a workaround to be able to use your data from your suppliers' impact assessment results.
This guide outlines various strategic approaches and their limitations for incorporating external impact data into your LCA models.
Strategies for uploading/using supplier data
Modelling a representative LCA + one of the following "add-ons":
Impact overrides
Only works on a cycle level for a given category
Impact exchange adjustment
Great for representing the reported structure
Requires exporting or viewing the results to be able to calculate the needed adjustment
Scaling the input to match the reported result
Can only be scaled based on 1 impact category
Limiting assumption: All the impact categories follow the same curve, which is really often not the case
Difficult to use correctly and it makes the inputs more difficult to understand
Requires exporting or viewing the results to be able to calculate the needed adjustment
Empty cycles with overrides or impact exchanges
Quicker to make, will not show correct result with any other categories
Adding results with proxy exchanges
Gives results in every category
Gives the false illusion that the results are correct
The main impact driver might be a different exchange than the chosen proxy
Uploading your EPD results using an excel file
One great way to upload your EPD results in bulk is to use the "update in batch" or "replicator" features in combination with the impact overrides.
You can download this spreadsheet to use it as a starting point to upload EPD or LCA results from your suppliers. It includes detailed instructions on how to use it and two of the most commonly used impact method to get you started.