In openLCA, you should be able to do Monte Carlo simulation as follows:
Create a product system in openLCA that includes the processes that you want to model.
Set up the input data for the product system, including the amounts of each flow and the parameters for each process.
Open the Monte Carlo simulation window by going to the "Tools" menu and selecting "Monte Carlo simulation."
Select the product system that you want to analyze and specify the number of iterations to run.
Set up the distribution types and parameters for the input variables that you want to include in the simulation. You can choose from several different distribution types, incl normal, uniform, and triangular.
Run the simulation by clicking "Start". The simulation should generate a set of results for each iteration.
View and analyze the results using openLCA's graphical tools.
Alternatively, if you have Microsoft Excel, you can also set up Monte Carlo in Excel and I explain how to do that in the attached.
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