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Hello

I do not know why there is a difference in results obtained by process direct calculation and results from process system calculation. I used the same method IPCC 2021.

See pictures enclosed.

Process results

Product system results

I can not explain this big difference.

in openLCA by (790 points)

2 Answers

+1 vote
by (6.3k points)
edited by
Please take a random process from ecoinvent 3.9.1 (a process which is original from ecoinvent without any user modifications) and perform a "direct calculation" and create a product system with "only link default providers". You will get the same results for direct calculation, for product system calculations and I guess for SimaPro (I assume they implemented IPCC 2021 similar or equal to the ecoinvent 3.9.1 IPCC 2021 implementation). Together with your own foreground processes, of course, there are possibilities that your providers might be different in direct calculation, product system calculation and SimaPro, since it depends on your own provider settings inside the processes and your providers from auto-linking or from manual linking in the model graph.

I can see from your picture, that Transporto and Materiali (the last two processes) are equal in the direct calculation and in the product system calculation. So you have to check in your other processes, if you have set exactly the same providers in your own foreground processes and in the same way in the model graph of your created product system. The "direct calculation" takes always the default providers (one fixed "hardwired" provider per exchange). The product system creates a new linking, depending on the user setting (ignore default providers, prefer default providers, only link default providers). You can also try to check your calculations with "only link default providers".
0 votes
by (122k points)
Hi, the direct calculation assumes a simple system as it is used in SimaPro and was used in ecoinvent 2, where every product is "hardwired" to one process. If your database is different (which is often the case as this is somewhat inconvenient and inflexible) then you will get different results, most likely, as providers are ignored in the direct calculation.
by (790 points)
I’m using Ecoinvent database.
I think that direct calcultation without providers must have result lower than the product system one.
It’s not what I’m obtaining.
I used the same model in Simapro (both models are based on Ecoinvent 3.9.1 and IPCC 2021) and the result of GHG emission is much higher than the one calculated in openLCA product system. Simapro 163tCO2e - openLCA 125 tCO2e the difference of 38 tCO2e is unacceptable.
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