System and method for monitoring compressor floodback

1. A system comprising:

a compressor connected to an evaporator;

a suction sensor that outputs a suction temperature signal corresponding to a suction temperature of refrigerant entering the compressor;

a control module connected to the suction sensor, said control module determining a saturated evaporator temperature based on a speed of the compressor, calculating a suction superheat temperature based on the saturated evaporator temperature and the suction temperature, monitoring a floodback condition of the compressor by comparing the suction superheat temperature with a predetermined threshold, and, when the suction superheat temperature is less than or equal to the predetermined threshold, increasing the speed of the compressor or decreasing an opening of an expansion valve associated with the compressor.

2. The system of claim 1 wherein the predetermined threshold is zero degrees Fahrenheit.

3. The system of claim 1 wherein the control module increases the speed of the compressor when the suction superheat temperature is less than or equal to the predetermined threshold.

4. The system of claim 1 wherein the control module decreases the opening of the expansion valve when the suction superheat temperature is less than or equal to the predetermined threshold.

5. The system of claim 1 further comprising a condenser connected to the compressor and the evaporator, wherein the control module determines a discharge line temperature corresponding to a temperature of refrigerant leaving the compressor, determines a saturated condenser temperature, and determines the saturated evaporator temperature as a function of the saturated condenser temperature, the discharge line temperature, and the speed of the compressor.

6. The system of claim 5 wherein the control module receives compressor power data and determines the saturated condenser temperature as a function of the compressor power data, the speed of the compressor, and the saturated evaporator temperature.

7. The system of claim 6 wherein the control module performs multiple iterations of determining the saturated condenser temperature and the saturated evaporator temperature to achieve convergence.

8. The system of claim 1 wherein the control module determines a discharge line temperature corresponding to a temperature of refrigerant leaving the compressor, receives compressor power data, and determines the saturated evaporator temperature as a function of the compressor power data, the speed of the compressor, and the discharge line temperature.

9. The system of claim 1 further comprising a condenser connected to the compressor and the evaporator, wherein the control module determines a saturated condenser temperature, determines a mass flow of the compressor, and determines the saturated evaporator temperature as a function of the speed of the compressor, the saturated condenser temperature, and the mass flow.

10. A method comprising:

determining, with a control module, a saturated evaporator temperature of an evaporator based on a speed of a compressor connected to the evaporator;

receiving, with the control module, a suction temperature signal that corresponds to a suction temperature of refrigerant entering the compressor;

calculating, with the control module, a suction superheat temperature based on the saturated evaporator temperature and the suction temperature;

monitoring, with the control module, a floodback condition of the compressor by comparing the suction superheat with a predetermined threshold; and

increasing the speed of the compressor or decreasing an opening of an expansion valve, with the control module, when the suction superheat temperature is less than or equal to the predetermined threshold.

11. The method of claim 10 wherein the predetermined threshold is zero degrees Fahrenheit.

12. The method of claim 10 wherein the control module increases the speed of the compressor when the suction superheat temperature is less than or equal to the predetermined threshold.

13. The method of claim 10 wherein the control module decreases the opening of the expansion valve when the suction superheat temperature is less than or equal to the predetermined threshold.

14. The method of claim 10 further comprising determining, with the control module, a discharge line temperature corresponding to a temperature of refrigerant leaving the compressor, determining a saturated condenser temperature of a condenser connected to the evaporator and the compressor, and determining the saturated evaporator temperature as a function of the saturated condenser temperature, the discharge line temperature, and the speed of the compressor.

15. The method of claim 14 further comprising receiving, with the control module, compressor power data and determining the saturated condenser temperature as a function of the compressor power data, the speed of the compressor, and the saturated evaporator temperature.

16. The method of claim 15 further comprising performing multiple iterations of determining the saturated condenser temperature and determining the saturated evaporator temperature to achieve convergence.

17. The method of claim 10 further comprising determining, with the control module, a discharge line temperature corresponding to a temperature of refrigerant leaving the compressor, receiving compressor power data, and determining the saturated evaporator temperature as a function of the compressor power data, the speed of the compressor, and the discharge line temperature.

18. The method of claim 10 further comprising determining, with the control module, a saturated condenser temperature of a condenser connected to the evaporator and the compressor, determining a mass flow of the compressor, and determining the saturated evaporator temperature as a function of the speed of the compressor, the saturated condenser temperature, and the mass flow.