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apparently a similar question has previously been asked in this forum but I have not found a satisfying answer yet.

I created a product system of a production process that has 0,15 kg of its output product as a quantitative reference. It's main provider process (tier 1) needs 0,1575 kg of pre-product due to  losses. The provider of this pre-product (tier 2) needs 1,46 times it's mass output of pre-product from its provider (0,23 kg). This last provider (tier 3) needs 2,5 times as much raw product as it's output so 0,23*2,5 =0,575 kg. In my understanding, this means, that I need 0,575 kg of raw product to produce 0,15 kg of final product. When I calculate the product system of the initial production process for 0,15 kg of final product, the "required amount" column of my contribution tree tells me that I need 0,44 kg of raw product though. I am wondering why the contribution tree does not match the required inputs of my processes. I have tried this for other processes and product systems and I get similar results. Am I missing some fundamental concept here?

I appreciate any help and ideas.
in openLCA by (140 points)

1 Answer

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by (5.6k points)
Hello Lars,

If you have the contribution tree, you should be able to see where the error is. Expand the tree's branches and see what mass inputs and outputs are under each process.

Furhtermore, be aware that when you create the product system and do the calculation, that you identify exactly the required amount in the target amount box.

If you have the option of including a picture, it would be easier to help you troubleshoot.

Good luck
by (140 points)
Hello Matias,

thank you for your help and your explanations! I found the problem which was an allocation factor between two outputs of a process in the supply chain (I did not know this because I did not create the processes myself but entered an existing project). Anyway, the contribution tree does not indicate if an allocation took place as far as I know which means it is hard to trace by-products mass and impact wise in hindsight. This would be a nice feature I think...