Methods for detecting surge in centrifugal compressors

1. A method for detecting surge in a refrigeration system, said refrigeration system including a centrifugal compressor having an impeller and a compressor entrance, an evaporator that receives a fluid refrigerant, a suction line that flows said refrigerant from said evaporator to said compressor entrance, said evaporator including a heat-exchange coil supplied with a liquid through a supply line entering said evaporator, said liquid disposed in a heat-exchange relationship with said refrigerant within said evaporator, the method comprising automatically and periodically performing the steps of:

measuring a fluid temperature of said liquid proximate said supply line entering said evaporator;

measuring a refrigerant temperature of said refrigerant proximate said compressor entrance;

using said fluid temperature and said refrigerant temperature to detect surge in said refrigeration system by computing a value indicative of a temperature difference between said fluid temperature and said refrigerant temperature; and

comparing said value to a set point temperature.

2. The method of claim 1 , wherein the step of using said fluid temperature and said refrigerant temperature to detect surge comprises:

generating a compressor-status parameter indicative of an operating condition of said centrifugal compressor;

deriving a set point parameter from said compressor-status parameter;

computing a value indicative of a temperature difference between said fluid temperature and said refrigerant temperature; and

comparing said value to said set point parameter.

3. The method of claim 2 , wherein said operating condition of said centrifugal compressor is selected from a set consisting of: off-state, starting and normal running.

4. A method for detecting surge in a centrifugal compressor having a compressor entrance in fluid communication with an evaporator, said evaporator adapted to receive a fluid refrigerant and disposed in a heat-exchange relationship with a liquid entering said evaporator at a suction entrance and flowing through a heat-exchange coil located in said evaporator, said method comprising automatically and periodically performing the steps of:

generating a compressor-status parameter which defines an operating condition for said centrifugal compressor;

calculating a set point parameter in accordance with said compressor-status parameter;

positioning a first temperature sensor proximate said compressor entrance to measure a refrigerant temperature;

positioning a second temperature sensor near said suction entrance to measure a liquid temperature; and

using said liquid temperature, said refrigerant temperature and said set point temperature to detect surge.

5. A method for detecting surge in a centrifugal compressor having a compressor entrance fluidly connected to an evaporator, said evaporator flowing a refrigerant, said refrigerant received from a condenser and disposed in heat-exchange relationship with a liquid entering said evaporator at a suction entrance, said method comprising automatically and periodically performing the steps of:

determining a first thermodynamic parameter at a first location within said liquid proximate said evaporator entrance;

determining a second thermodynamic parameter at a second location within said refrigerant proximate said compressor; and

detecting surge from said first and said second thermodynamic parameters by computing a value indicative of a parameter difference between said first thermodynamic parameter and said second thermodynamic parameters: and comparing said value to a set point parameter.

6. The method of claim 5 , wherein the first thermodynamic parameter is temperature.

7. The method of claim 5 , wherein the second thermodynamic parameter is temperature.

8. The method of claim 5 , wherein the step of detecting surge further comprises:

periodically determining an operational condition of said centrifugal compressor; and

obtaining a parameter indicative of surge from said first thermodynamic parameter, said second thermodynamic parameter and said operational condition.

9. The method of claim 8 , wherein said operational condition of said compressor is selected from a set consisting of: off-state, starting and normal running.

10. An apparatus for detecting surge in a centrifugal compressor in fluid communication with an evaporator at a compressor entrance, said evaporator flowing a refrigerant fluid in heat-exchange relationship with a liquid entering said evaporator proximate a evaporator suction entrance, said apparatus comprising:

means for detecting a first temperature of said refrigerant proximate said compressor entrance;

means for detecting a second temperature of said liquid proximate said evaporator suction entrance;

means for determining a differential between said first temperature and said second temperatures; and

means for detecting surge by comparing said differential to a set point parameter.

11. The apparatus of claim 10 , wherein said means for detecting said first temperature is a temperature sensor.

12. The apparatus of claim 11 , wherein said means for detecting said second temperature is a temperature sensor.

13. The apparatus of claim 10 , wherein said means for determining said differential and said means for detecting surge are implemented as an operative arrangement selected from the set consisting of: analog circuitry, a digital processor, software, firmware or any combination thereof.

14. The apparatus of claim 13 , wherein said means for determining said differential controls an operation condition of said centrifugal compressor responsive to said differential.

15. A method for detecting surge in a centrifugal compressor connected in series and in fluid communication with an evaporator at a compressor entrance, said evaporator flowing a refrigerant fluid in heat-exchange relationship with a liquid entering said evaporator proximate a evaporator suction entrance, said method comprising the step of:

periodically comparing a temperature differential between a first temperature measured in said refrigerant fluid proximate said compressor entrance and a second temperature measured in said liquid proximate said evaporator suction entrance to a set point temperature indicative of an operating condition of said centrifugal compressor.

16. The method of claim 15 , wherein said operating condition of said centrifugal compressor is selected from a set consisting of: off-state, starting and normal running.

17. A method for detecting surge in a centrifugal compressor connected in series and in fluid communication with an evaporator at a compressor entrance, said evaporator flowing a refrigerant fluid in heat-exchange relationship with a liquid entering said evaporator proximate a evaporator suction entrance, said method comprising the step of:

periodically comparing a rate of change of a temperature differential between a first temperature measured in said refrigerant fluid proximate said compressor entrance and a second temperature measured in said liquid proximate said evaporator suction entrance to a set point temperature indicative of an operating condition of said centrifugal compressor.

18. The method of claim 17 , wherein said operating condition of said centrifugal compressor is selected from a set consisting of: off-state, starting and normal running.

19. A method of detecting surge in a centrifugal compressor having an impeller and a compressor entrance in fluid communication with said impeller, said compressor entrance connected to a evaporator, said evaporator adapted to receive refrigerant from a condenser, said refrigerant disposed in heat-exchange relationship with a liquid entering said evaporator at a evaporator suction entrance and flowing within a heat-exchange coil disposed in said evaporator, the method comprising the steps of:

monitoring a first temperature of said refrigerant before said refrigerant enters said compressor entrance;

monitoring a second temperature of said liquid before said liquid enters said evaporator suction entrance; and

detecting surge from calculations involving said first temperature, said second temperature and a set point temperature.

20. The method of claim 19 , wherein the step of detecting surge from calculations comprises the steps of:

detecting surge responsive to a deviation of a temperature difference between said first temperature and said second temperature from a set point parameter indicative of an operating condition of said centrifugal compressor by a selected amount.

21. The method of claim 20 , wherein said deviation of said temperature difference from said set point is measured by an operative arrangement selected from the set consisting of: analog circuitry, a digital processor, software, firmware or any combination thereof.

22. The method of claim 20 , wherein said operating condition of said centrifugal compressor is selected from a set consisting of: off-state, starting and normal running.

23. A method for detecting surge in a refrigeration system, said refrigeration system including a centrifugal compressor means having an impeller and a compressor entrance, an evaporator means for receiving a fluid refrigerant, a suction line for flowing said refrigerant from said evaporator means to said compressor entrance, said evaporator means including a heat-exchange coil means supplied with a liquid through a supply line entering said evaporator means, said liquid disposed in a heat-exchange relationship with said refrigerant within said evaporator means, the method comprising automatically and periodically performing the steps of:

measuring a fluid temperature of said liquid proximate said supply line entering said evaporator means;

measuring a refrigerant temperature of said refrigerant proximate said compressor entrance;

using said fluid temperature and said refrigerant temperature to detect surge in said refrigeration system by periodically determining an operational condition of said centrifugal compressor means; and

obtaining a parameter indicative of surge from said fluid temperature, said refrigerant temperature and said operational condition.

24. The method of claim 23 , wherein said step of measuring said fluid temperature comprises the steps of:

positioning a first temperature sensor proximate said supply line entering said evaporator.

25. The method of claim 23 , wherein said step of measuring said refrigerant temperature comprises the steps of:

positioning a second temperature sensor proximate said compressor entrance.

26. The method of claim 23 , wherein said operational condition of said compressor is selected from a set consisting of: off-state, starting and normal running.

27. The method of claim 23 , wherein the step measuring said refrigerant temperature includes the step of:

positioning a second temperature sensor in said suction line in the vicinity of said compressor entrance.

28. The method of claim 23 , wherein the step measuring said refrigerant temperature includes the step of:

positioning a second temperature sensor proximate said impeller.