Allocation problems

Question

Hello,

I have a model, which can be simplified in the below image. So, I have two products, z_A and z_B, they come from Process 2A and 2B respectively. 

Process 2A uses x from Process 1

Process 2B uses y from Process 1

Process 1 produces x and y, which have different weights and different values. 

So, I want to run a product systems for the Process 2A, and a seperate one for Process 2B. How do I make sure that the impacts for x and y are allocated correctly for Process 2A and Process 2B? I've tried using physical allocation within OpenLCA and the impacts of x and y are split equally, despite the different weights, meaning that the impacts of Process 2A and Process 2B hare identical, when they shouldn't by

Thanks!

Tom

Answer 1

After a longer explanation of the allocation in general I realise that the issue may be slightly different here - we'll come back to the question

Answer 2

`Process 1` is a multi-output process and you can define allocation factors related to the products `x` and `y` in `Process 1`. Say we have also an elementary flow `e` in `Process 1`:

We can allocate a fraction of the amount of `e` to each product `x` and `y` via allocation factors:

Now, when you calculate e.g. a product system with `Process 2A` which just takes `x` as an input:

you can select the allocation method in the calculation setup:

Depending which method you choose, the corresponding allocation factors are applied. For the example, `physical allocation` results in:

and `economic allocation` in:

Note that allocation factors are also applied to input product amounts so that you can allocate impacts of the supply chain too etc. The best is maybe just to try it out in openLCA. Also, in the next openLCA version it will be possible to use formulas for allocation factors so that you can bind allocation factors to product properties via parameters etc. 

Comments

Brilliant, thanks, that all makes perfect sense, and works when I make simple models. However, when I apply this to my more complex model, the economic allocation works perfectly, but the physical does not, just giving a 50/50 equal split. I'm using Econinvent 3.3 within OpenLCA 1.10.2, are there any known bugs with the physical allocation?

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Hello, I have the same problem as you. When doing the impact assessment by physical allocation, the impacts are identical for both output products (e.g. x and y).
Have you been able to get a solution to this?