Refrigeration system with mechanical subcooling

1. A refrigeration system comprising:

a primary compressor receives refrigerant from an evaporator and delivers refrigerant to a condenser;

a subcooling compressor delivers refrigerant to the condenser;

a subcooler receives refrigerant from the condenser;

a first refrigerant flow path through the subcooler, the first refrigerant flow path delivers a portion of the refrigerant to the evaporator;

a second refrigerant flow path through the subcooler, the second refrigerant flow path delivers a remainder of the refrigerant to the subcooling compressor;

a first sensor for measuring a first operating condition of the refrigeration system corresponding to a primary evaporating temperature;

a second sensor for measuring a second operating condition of the refrigeration system corresponding to a condensing temperature; and

a controller operable to control operation of the subcooling compressor, the controller varying operation of the subcooling compressor based upon the first and second operating conditions, the controller calculating a desired subcooler evaporating temperature required for highest efficiency operation of the refrigeration system based upon the primary evaporating temperature and the condensing temperature to maintain the subcooler evaporating temperature such that the refrigeration system operates at a point of highest efficiency.

2. The refrigeration system of claim 1 wherein the primary compressor comprises a plurality of primary compressors, the primary compressors receive refrigerant from the evaporator and deliver refrigerant to the condenser.

3. The refrigeration system of claim 1 wherein the first sensor measures a primary evaporating pressure.

4. The refrigeration system of claim 1 wherein the second sensor measures a condensing pressure.

5. The refrigeration system of claim 1 , and further comprising a third sensor for measuring a third operating condition of the refrigeration system corresponding to a subcooler evaporating temperature wherein the controller varies operation of the subcooling compressor to maintain the measured subcooler evaporating temperature at the desired subcooler evaporating temperature.

6. The refrigeration system of claim 5 wherein the third sensor measures a subcooler evaporating pressure.

7. The refrigeration system of claim 1 wherein the controller stores a plurality of coefficients of performance for a range of particular operating conditions of the refrigeration system, each coefficient of performance corresponding to a desired subcooler evaporating temperature, and further wherein the controller determines a highest coefficient of performance from the plurality of coefficients of performance and varies operation of the subcooling compressor to achieve the desired subcooler evaporating temperature.

8. The refrigeration system of claim 1 wherein the controller controls operation of the subcooling compressor by adjusting running speed of the subcooling compressor.

9. The refrigeration system of claim 1 wherein the primary compressor comprises a reciprocating compressor.

10. The refrigeration system of claim 1 wherein the subcooling compressor comprises a reciprocating compressor.

11. A refrigeration system comprising:

a primary compressor receives refrigerant from an evaporator and delivers refrigerant to a condenser;

a subcooling compressor delivers refrigerant to the condenser;

a subcooler receives refrigerant from the condenser, the subcooler includes a first refrigerant flow path that delivers a portion of the refrigerant to the evaporator and a second refrigerant flow path that delivers a remainder of the refrigerant to the subcooling compressor;

a controller operable to control operation of the subcooling compressor;

a first sensor measures a first operating condition of the refrigeration system, the first sensor being coupled to the controller and the first operating condition corresponding to a primary evaporating temperature of the refrigeration system; and

a second sensor measures a second operating condition of the refrigeration system, the second sensor being coupled to the controller and the second operating condition corresponding to a condensing temperature of the refrigeration system,

wherein based upon the first operating condition measured by the first sensor and the second operating condition measured by the second sensor, the controller controls operation of the subcooling compressor to obtain highest efficiency operation of the refrigeration system.

12. The refrigeration system of claim 11 wherein the primary compressor comprises a plurality of primary compressors, the primary compressors receiving refrigerant from the evaporator and delivering refrigerant to the condenser.

13. The refrigeration system of claim 11 wherein the first sensor measures a primary evaporating pressure.

14. The refrigeration system of claim 11 wherein the second sensor measures a condensing pressure.

15. The refrigeration system of claim 11 wherein the controller calculates an optimum subcooler evaporating temperature for highest efficiency operation of the refrigeration system based upon the primary evaporating temperature and the condensing temperature.

16. The refrigeration system of claim 15 wherein the controller controls operation of the subcooling compressor to maintain the optimum subcooler evaporating temperature.

17. The refrigeration system of claim 15 , and further comprising a third sensor that measures a third operating condition of the refrigeration system, the third sensor being coupled to the controller and the third operating condition corresponding to a subcooler evaporating temperature, wherein the controller controls operation of the subcooling compressor to maintain the measured subcooler evaporating temperature substantially equal to the optimum subcooler evaporating temperature.

18. The refrigeration system of claim 15 wherein the controller stores a plurality of coefficients of performance for a range of particular operating conditions of the refrigeration system, each coefficient of performance corresponding to a desired subcooler evaporating temperature, and further wherein the controller determines a highest coefficient of performance from the plurality of coefficients of performance and controls the subcooling compressor to achieve the desired subcooler evaporating temperature.

19. The refrigeration system of claim 11 wherein the controller controls operation of the subcooling compressor by adjusting running speed of the subcooling compressor.

20. The refrigeration system of claim 11 wherein the primary compressor comprises a reciprocating compressor.

21. The refrigeration system of claim 11 wherein the subcooling compressor comprises a reciprocating compressor.

22. A control system for managing operation of a subcooling compressor in a refrigeration system, the control system comprising:

a controller coupled to the subcooling compressor and operable to control operation of the subcooling compressor;

a first sensor measures a first operating condition of the refrigeration system, the first sensor being coupled to the controller and the first operating condition corresponding to a primary evaporating temperature of the refrigeration system;

a second sensor measures a second operating condition of the refrigeration system, the second sensor being coupled to the controller and the second operating condition corresponding to a condensing temperature of the refrigeration system; and

wherein based upon the first operating condition measured by the first sensor and the second operating condition measured by the second sensor, the controller controls operation of the subcooling compressor to obtain highest efficiency operation of the refrigeration system.

23. The control system of claim 22 wherein the controller controls operation of the subcooling compressor by adjusting running speed of the subcooling compressor.

24. The control system of claim 22 wherein the first sensor measures a primary evaporating pressure.

25. The control system of claim 22 wherein the second sensor measures a condensing pressure.

26. The control system of claim 22 wherein the controller calculates an optimum subcooler evaporating temperature for highest efficiency operation of the refrigeration system based upon the primary evaporating temperature and the condensing temperature.

27. The control system of claim 26 wherein the controller controls operation of the subcooling compressor to maintain the optimum subcooler evaporating temperature.

28. The control system of claim 26 , and further comprising a third sensor that measures a third operating condition of the refrigeration system, the third sensor being coupled to the controller and the third operating condition corresponding to a subcooler evaporating temperature, wherein the controller controls operation of the subcooling compressor to maintain the measured subcooler evaporating temperature substantially equal to the optimum subcooler evaporating temperature.

29. The control system of claim 26 wherein the controller stores a plurality of coefficients of performance for a range of particular operating conditions of the refrigeration system, each coefficient of performance corresponding to a desired subcooler evaporating temperature, and further wherein the controller determines a highest coefficient of performance from the plurality of coefficients of performance and controls the subcooling compressor to achieve the desired subcooler evaporating temperature.