I am wondering how to model parasitic energy demand in openLCA. In the anaerobic digestion system I am modelling, biogas is used to generate electricity. Some of the electricity generated is used by the system. Furthermore all of the heat generated is used also by the digester. I have tried to implement this with electricity/ heat generated as outputs in the third process in the product system used as a providers for the electricity/ heat inputs in the second process. However this does not appear to work as this results in negative values for environmental impacts for the second process when calculated.
Maybe I am making this too complicated and can exclude the parasitic demand in the model? I am using a consequential approach, so the net electricity that goes to the grid is accounted for as an avoided product.
When creating the product system, I select auto-link processes and prefer default providers.
Any thoughts on this would be appreciated.
Many thanks, Ciara