cascade controller will modulate the surface fans in order to meet the calculated target demand flow the surface fan controller is a cascade controller fig3 items 58 59 that optimizes the surface fan speeds in order to minimize energy consumption while assuring all levels to obtain their calculated target demand flow and maintaining a set maximum regulator opening this maximum regulator opening is the cascade controller setpoint it is assumed that all surface fans are driven by a variable frequency drive as an example if the surface fans cascade controller setpoint is set at 80 opening maximum for any air flow regulator the surface fans will be modulated in order to assure that any level air flow regulator will be at and not exceed this 80 maximum opening the surface fans cascade controller calculates a common modulated fan speed for all fans this speed is then split by a ratio to intake fans and to another ratio to exhausts fans the booster fan controller is a cascade controller over the air flow regulator controller it will modulate the booster fan speed based on set maximum air flow regulator opening for example if the cascade controller setpoint is set at 70 this means that when the booster fan will be modulated upward when the regulator position exceeds 70 the optimized mine ventilation system has the following control modes fig3 item 54 man a fixed fan speed or regulator position setpoint is entered by the surface operator the fan speed and or regulator position not modulated automatically the simulation model.