Variable speed condenser fan control system

1. A controller comprising:

a first input that receives a signal indicating an energy consumption value of a compressor;

a second input that receives a signal indicating an energy consumption value of a variable speed condenser fan;

a third input that receives a signal indicating an ambient temperature;

a fourth input that receives a signal indicating a condenser temperature;

an output that provides a control signal to said variable speed condenser fan;

a memory that stores a temperature difference set-point; and

a processor in communication with said inputs, said output and said memory, that calculates a difference between said ambient temperature and said condenser temperature, compares said difference with said temperature difference set-point, controls said variable speed condenser fan based on said comparison, monitors said energy consumption values, and modulates said temperature difference set-point to minimize energy consumption.

2. The controller of claim 1 wherein said variable speed condenser fan is driven by a variable frequency drive and wherein said control signal indicates a frequency of electrical power for said variable frequency drive to deliver to an electric motor of said variable speed condenser fan.

3. The controller of claim 2 wherein said energy consumption value of said variable speed condenser fan comprises an electrical current value received from said variable frequency drive.

4. The controller of claim 2 wherein said energy consumption value of said variable speed condenser fan comprises an electrical power value received from said variable frequency drive.

5. The controller of claim 2 wherein said processor:

sets said temperature difference set-point to an initial value;

records a first energy consumption value resulting from said initial value;

sets said temperature difference set-point to a different value;

records a second energy consumption value resulting from said different value;

compares said first energy consumption value with said second energy consumption value; and

modulates said temperature difference set-point based on said energy consumption comparison.

6. The controller of claim 5 wherein said processor calculates a first ratio based on said first energy consumption value and a first ambient temperature and a second ratio based on said second energy consumption value and a second ambient temperature, and modulates said temperature difference set-point based on a comparison of said first and second ratios.

7. The controller of claim 6 wherein said processor calculates an energy ratio difference as a difference between said first ratio and said second ratio, calculates a set-point difference as a difference between said initial value and said different value, calculates a comparison factor as one of a product and a quotient of said energy ratio difference and said set-point difference, and modulates said temperature difference set-point based on said comparison factor.

8. The controller of claim 7 wherein said processor determines a sign of said comparison factor and modulates said temperature difference set-point based on said sign.

9. The controller of claim 1 wherein said processor:

sets said temperature difference set-point to an initial value;

changes said temperature difference set-point in an initial direction; and

determines a resulting energy consumption change;

wherein said processor changes said temperature difference set-point in an opposite direction of said initial direction when said resulting energy consumption change is positive and changes said condenser set-point in said initial direction when said resulting energy consumption change is negative.

10. A method comprising:

monitoring an energy consumption of at least one of a compressor and a variable speed condenser fan of a condenser of a refrigeration system;

monitoring an ambient temperature;

monitoring a temperature of said condenser;

calculating a difference between said ambient temperature and said temperature of said condenser;

comparing said difference with a temperature difference set-point;

controlling said variable speed condenser fan based on said comparing; and

modulating said temperature difference set-point to minimize said energy consumption.

11. The method of claim 10 wherein said controlling said variable speed condenser fan includes generating a control signal indicating a frequency of electrical power for a variable frequency drive to deliver to an electric motor of said variable speed condenser fan.

12. The method of claim 11 wherein said monitoring said energy consumption includes receiving an electrical current value from said variable frequency drive.

13. The method of claim 11 wherein said monitoring said energy consumption includes receiving an electrical power value from said variable frequency drive.

14. The method of claim 11 further comprising:

setting said temperature difference set-point to an initial value;

recording a first energy consumption value resulting from said initial value;

setting said temperature difference set-point to a different value;

recording a second energy consumption value resulting from said different value;

comparing said first energy consumption value with said second energy consumption value;

modulating said temperature difference set-point based on said comparing.

15. The method of claim 14 further comprising:

calculating a first ratio based on said first energy consumption value and a first ambient temperature;

calculating a second ratio based on said second energy consumption value and said second ambient temperature;

wherein said modulating said temperature difference set-point includes modulating said temperature difference set-point based on comparing said first and second ratios.

16. The method of claim 15 further comprising:

calculating a ratio difference as a difference between said first and second ratio;

calculating a set-point difference as a difference between said initial value and said different value;

calculating a comparison factor as one of a product and a quotient of said ratio difference and said set-point difference;

wherein said modulating said temperature difference set-point includes modulating said temperature difference set-point based on said comparison factor.

17. The method of claim 16 further comprising:

determining a sign of said comparison factor;

wherein said modulating said temperature difference set-point includes modulating said temperature difference set-point based on said sign.