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So I created this product system for the life cycle of a wood plastic composite. The reference process is P18 EoL, which is basically a dummy process I created so the waste management process isn't the reference process because it is a multi-ouput process and it does.

I wanted to create a waste management process where I can send part of the waste to the landfill, incineration or recycling by using parameters. It works well for the incineration and the landfill but the recycling process does not show up in the contribution tree at all. So i decided to create a loop and use the recycled material as a feedstock for the blender process. It still does not show up in the results/contribution tree.

As a workaround I created a product system with the recycling process as a reference process and the recycled plastic output being the reference flow. Now it works but I don't really like it that way because this is not my functional unit and I find this to be an... odd approach. Any other ways to do this? I am using the ELCD database.

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Hi, good question; basically you are using the two products of your P13 waste collection process in your system, and thus the contribution of the second product supply chain depends on how you specify the allocation for this process, and also, if its supply chain has at all any impacts.

I made a simple example: A process produces heat and electricity, the heat is used in the system, in a simple intermediate process that has only CO2 emissions:

(you also see that you can "shorten" the connections in the model graph, uncheck "route" in the model graph layout:


The co-generation process has these allocation factors:

Now, when I calculate the system, I get different results, depending on which allocation method I select

..and also, in the calculated inventory, I see "leftover" product, heat, if the amount of heat the system needs does not exactly fit to the amount of heat the system produces:

But the heat "pathway" is in considered in the calculation, and I see it e.g. in the contribution tree:

So this works, but you will need to address the heat-excess production with a system expansion e.g., which you can steer via a parameter, to be considered exactly to the extent too much heat is produced in your system. For your approach, you can even combine both product systems into one, but probably have excess product (like my heat) there, too. So you could apply system expansion in both, to have only truly one product in each system, but I agree that this is a bit funny.

Good luck!