Difference in results for quantitive reference flow being product flow or waste flow

Question

Hello,

I've created two process with exaclty the same inputs and outputs, the only difference being the reference flow. The first is 1 m3 of a product flow and the other is 1 m3 of a waste flow.

The results are very different, the process with the waste flow has a higher impact. In the contribution tree, i see that this is due to the flow type of the reference flow.

Why are the results so different? It's almost twice the value.

Thank you for your help!

Answer 1

Hi,

Unfortunately, openLCA technically allows what you did. I guess you did not participate in openLCA training or read the manual. A process has a reference (product) flow in the output and a waste treatment (waste) flow in the input. If you follow that logic, you get the same impacts.

I think I recreated what you did, by adding the waste flow as reference, but still having the product flow there and choosing it as the reference flow for the product system. This leads indeed to weird results. But it makes no sense to model this way.

Best