Tracking difference of biogenic carbon in ecoinvent cut-off models (by classification vs. EN15804 add-on)

Question

Hi

I've just recently obtained access to the EN15804 add-on database for ecoinvent v3.8, for which reason I have been modelling in the system model 'cut-off, by classification' previously. 

In the transfer of my preliminary results from the previous system model into the EN15804, I've stubled upon some magnitude differenes, which appear to be due to the tracking of biogenic carbon - I might overlook some obvious explanation, but anyhow, I'd appriciate some input to the issue. 

Taking an example in the process of 'sawing, softwood | sawnwood', I've been looking into the input and output of the processes in both system models, and they appear similar, considering flows and magnitudes of flows. But when looking into the contribution trees of the processes, respectively in the two system models, some of the biogenic carbon in the cut-off, by classification, appear to be attributed differently. 

In both system model processes, a negative input elementary flow of 'Carbon dioxide, non-fossil, resource correction' is added after economic allocation in order to re-balance the non-fossil carbon dioxide resource extraction. This input, appears as direct emissions in the cut-off, by classification system model - but seems to be disregarded in the EN15804. 

Am I overlooking an obvious attribution explanation, that differs from the two system models, or is there a tracking difference/error somewhere? :) 

Best,

Sarah

Answer 1

Dear Sarah,

yes, this ecoinvent elementary flow "Carbon dioxide, non-fossil, resource correction" is in ecoinvent 3.8 and 3.9. But it seems that this flow is missing in the EN15804_A2_2020_3 method. In the "non-EN15804" method (for example EF 3.1), the characterisation factors for this flow is not needed since it is zero, same as for "Carbon dioxide, in air" and "Carbon dioxide, non-fossil". However, in the EN15804 method it receives the same characterisation factor as "Carbon dioxide, in air" (for example: -1). It is a resource input which needs to be subtracted from the impact result in GWP-biogenic and GWP-total. We will add it in the EN15804 add-on database and method.

You can also add it by yourself to GWP biogenic and GWP total. Just click on the methods and add the flow in the characterisation factors window with a factor of -1. In case you use openLCA2 and the impact direction of the method is set to "Output", you give it a factor of 1, since it will receive a negative sign automatically. It needs to lower the impact results, which you can double check in the impact results window.

Best wishes,

Conrad

Comments

Hi Conrad
Thanks for this, I'll add/edit it in my model, and will be aware of the factors - I'm using openLCA 2 :)

Best,
Sarah