I've started from scratch to see if I rebuild the model, to see what the problem is. It appears there's something wrong in the Monte Carlo if you have an input product which is also an output product. I use a lot of dummy processes to keep things clear in my models, especially when I want to correct an ecoinvent process which has the wrong output value. So this issue has caused me a lot of problems.
To replicate what I did, try this...
Create process A with an input of:
1kg carbon dioxide, liquid: market for carbon dioxide, liquid | carbon dioxide, liquid | Cutoff, U - RER (1;4;1;1;1)
1m3 compressed air, 1200 kPa gauge: market for compressed air, 1200 kPa gauge | compressed air, 1200 kPa gauge | Cutoff, U - GLO (1;4;1;1;1)
1kg potassium nitrate: market for potassium nitrate | potassium nitrate | Cutoff, U - GLO (1;4;1;1;1)
1kg water, deionised, from tap water, at user : market for water, deionised, from tap water, at user | water, deionised, from tap water, at user | Cutoff, U - Europe without Switzerland (1;4;1;1;1)
With an output flow you create of, say 1000 kg algae (these are made up numbers to demonstrate something).
Then make process B, which takes in 1000kg of algae and outputs 1000kg of algae
Create process C which takes in 1000kg of algae and outputs 1000kg of algae
Make sure A->B->C by setting the providers right.
The compare the Quick Analysis and Monte Carlo. They'll be different for B and C by a factor of 1000, because the models is based on the production of 1000kg of algae, and the Monte Carlo gets confused which process to take figures from if a flow goes through several processes.
I tried this with EcoInvent 3.5 and OpenLCA 1.7.4, but it happens with other versions.
Anyone want to confirm this happens? Any idea why????