Not matcing required amounts in contribution tree and defined processes

Question

Hi,

I noticed that when I run my model and at the same time consider allocation for my model, the required amount shown in the contribution tree is not correct and is less than the actual amount I defined in my model. I know this is because of the allocation factor, but I cannot remove the allocation factor from my model. Do you have any idea how I can solve this? Currently, except for the total results, none of the results shown in the contribution tree are reliable for me because the required amount assigned to each process is not correct.

Thank you & Kind regards,

Mahsa

Answer 1

If I understand correctly, you want to see results (e.g. in the contribution tree) without allocation factors applied? If so, this can be achieved by setting allocation to "none" in the calculation properties:

Of course, I would say, also with allocation applied the result you see in the UI is "correct" (but reflecting the allocation).

Best wishes,

Andreas

Comments

Hi,
Thank you for your response. But this is not my question. I will explain with an example.  in my model, I assign 0.165 kg to an input flow in a multi-output process and consider a mass allocation. This means my output value will be less than 0.165 kg, for example, 0.145 kg. I expect to see 0.145 kg as the required amount in the contribution tree, but I see (for example) 0.123 kg. Why is this number changing (from 0.145 to 0.123 kg)? How is openLCA calculating 0.123 kg? I checked and this is not changing according to the allocation factor.
Kind regards,
Mahsa

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Hi Masha, I see; the contribution tree somehow turns the entire system which is often heavily looped (i.e., contains many loops, processes calling themselves again basically) into a tree structure, where the different branches of the tree do not loop back. If a certain process is in this way visited from different pathways in the life cycle, the tree shows these as separate branches, and splits the amounts as well. So I am suspecting that you have this situation in your model, and will have the same process several times in your tree. Also, if the process is not multi-functional, the result is not affected by the allocation.

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Hi Andreas,
Exactly! My model is a complicated model with several loops. However I cannot simplify it or exclude the allocation factor. How can I see the correct environmental impacts now in my model? Right now, most of the numbers I see in the contribution tree are wrong and I have to adjust them manually, but you know better that it is impossible to do this for all flows and processes in a complex LCA model.
Regards,
Mahsa

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I would say openLCA does it correctly, but you seem certain that not - maybe post a screenshot or several ones to describe the situation?

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Hi,
I do not see any option here to upload a screenshot.
My concern is that when the contribution tree shows the CO2 emission for a required amount that is not the input value I defined in the model, all the CO2 emissions of processes that end up in this final process are calculated wrong. e.g. the contribution tree is calculating  0.5 kgco2-eq for process number 5 for a required amount of 0.1 kg of an input. However, I have defined 0,17 kg of input in the process. I can adjust the co2 emission values for 0,17 kg. But, If I want to see the CO2 emission of process 4, this amount is calculated based on 0.5 kgco2-eq! The same applies to process 3, 2, and 1.  In my model, I have around 50 processes (with at least 4-5 flows in each process). For my project, I need to know the CO2 emission of most of processes.