Hi, you can follow the procedure in the following paper:
Ahmad Fudholi, Kamaruzzaman Sopian, Mohammad H. Yazdi, Mohd Hafidz Ruslan, Mohamed Gabbasa, and Hussein A. Kazem, “Performance analysis of solar drying system for red chili”, Elsevier-Solar Energy SE (ISSN: 01425919), Vol. 99, January 2014, pp 47–54.
In order to calculate the overall exergy efficiency, you need to defined what's the useful output from the overall process and then divided by the exergy input or fuel. So it's not clear from the question which is useful or how the system works.
I am totally agree with Sattam, but I think you want going to partial calculation exergy efficiency for all elements individually in your process and than you can go to calculation of overall exergy efficiency? In that case you must follow of energy/exergy flow for partial elements, their input and output and etc