A demand flow device configured to interface with a chilled water plant controller to optimize performance of one or more chilled water plant components over a range of demand conditions is disclosed. The demand flow device includes a communication device configured to receive sensor data associated with the one or more chilled water plant components, wherein the sensor data measures operational variables of the chilled water plant. The demand flow device further includes a demand flow controller in communication with the communication device. The demand flow controller is configured to utilize the received sensor data to: determine an optimal pressure setpoint as a function of a desired chilled water delta T; control a chilled water flow rate through the one or more chiller water plant components as a function of the optimal pressure setpoint and the desired chilled water delta T; and adjust, via the chilled water plant controller, the optimal pressure setpoint, in response to one or more detected triggering events, to perform a critical zone reset of the desired chilled water delta T.