The control logic is based on the following two temperature differences.
1. is the temperature difference between the condensate leaving the ACC and the steam temperature at the turbine exhaust. If this temperture difference is below a certain limit the control system can increase the fan speeds, if possible. if the temperature difference is too big fans have to be reduced in speed or switched off as we are undercooling.
2. the second temperture difference is the temperature difference between the extraction of the incondensables and the steam temperture at the turbine exhaust. if this difference is too big the fans of the secondary cells have to be reduced in speed as the secondary bundles are cooling the steam too much.