Method for operating a heat exchanger unit

A method for operating a heat exchanger unit with a process fluid flowing therethrough and having a first pump, a second pump and a fan rotatable in a range of fan speeds, the heat exchanger unit operable in an OFF operating mode in which the first pump, the second pump and the fan are in an OFF state, a DRY operating mode in which the fan is in an ON state and the first pump and the second pump are in the OFF state, an EVAPORATIVE operating mode in which the fan, the first pump and the second pump are in the ON state and a WATER EFFICIENT operating mode in which the fan and the first pump are in the ON state and the second pump is in the OFF state, the method comprising the steps of:

• determining a current physical characteristic of the process fluid at or adjacent a process fluid outlet of the heat exchanger unit;
• predetermining a desired physical characteristic of the process fluid at which the process fluid is desired to exit the heat exchanger unit;
• and
• determining if the current physical characteristic of the process fluid is greater than the desired physical characteristic of the process fluid or if the current physical characteristic of the process fluid is less than the desired physical characteristic of the process fluid such that:
• if the current physical characteristic of the process fluid is greater than the desired physical characteristic of the process fluid, then either the current fan speed is incrementally increased or the current fan speed is set at a predetermined low set point fan speed, or
• if the current physical characteristic of the process fluid is less than the desired physical characteristic of the process fluid, then either the current fan speed is incrementally decreased or the current fan speed is set at a predetermined high set point fan speed or the OFF operating mode is activated, with the predetermined high set point fan speed being larger than the predetermined low set point fan speed.