Energy Efficiency Ratio or EEF is inversely related to the operating cost whereby increased EEF means decreased OC (operating cost).
Say for instance:
Energy efficiency ratio (EER) of ACs: The ratio between the cooling capacity and the power input of the Air Conditioners (ACs) .
For instance, if a 1 TR (3500 W) AC consumes 1000 watts, then the EER of the Air Conditioners is 3.5 W/W. Air Conditioners (ACs) with high EER consume less power.