The objective of the present work was to determine the coffee bean Guardiola dryer operating conditions that minimized the energy consumption (Q) and maximized the process thermal efficiency. A mechanistic coffee bean drying model was solved for a complete mixed assumption to simulate the drying. The simulated results reproduced the experimental results obtained with a 7.60 m³ Guardiola dryer loaded with 2675 kg of wet green coffee grains. The thermal second law efficiency of the drying was calculated with an expression that takes into account the exergy air carries before entering the dryer. For the same coffee load, and with restrictions on grain's temperature (T_β<45°C), final water content (X_β<11%) and water activity (a_w<0.80), the drying was simulated for several air fluxes and temperatures to find the optimum drying conditions (T_γ =80°C and G_γ=6560 kg air.h^-1). A 15.80% reduction in energy consumption was achieved when optimization results were compared with the normal operation conditions.