Economized device control for refrigeration systems

Abstract

Methods and systems for operating a refrigeration unit are provided. The methods and systems include measuring a first characteristic of a refrigeration unit, calculating a compressor middle stage pressure based on the first measured characteristic, determining if a first comparison and a second comparison are satisfied based on the first measured characteristic and the calculated compressor middle stage pressure, and opening an economizer solenoid valve when the first comparison and the second comparison are satisfied.

What is claimed is: 
     
         1 . A method for operating a refrigeration unit, the method comprising:
 measuring a first characteristic of a refrigeration unit;   calculating a compressor middle stage pressure based on the first measured characteristic;   determining if a first comparison and a second comparison are satisfied based on the first measured characteristic and the calculated compressor middle stage pressure; and   opening an economizer solenoid valve when the first comparison and the second comparison are satisfied.   
     
     
         2 . The method of  claim 1 , wherein the first characteristic comprises a plurality of characteristics. 
     
     
         3 . The method of  claim 2 , wherein the first characteristic comprises a flash tank pressure, a compressor suction pressure, and a discharge port pressure. 
     
     
         4 . The method of  claim 3 , wherein the compressor middle stage pressure is calculated based on the compressor suction pressure and the discharge port pressure as P mid =k 1 ×(P suc ×P dis ) k     2   +k 3 , wherein k 1 , k 2 , k 3  are known parameters. 
     
     
         5 . The method of  claim 1 , wherein the first characteristic comprises a flash tank pressure, the first comparison comprises comparing the calculated compressor middle stage pressure with a critical pressure modified by a first pressure constant, and the second comparison comprises comparing the flash tank pressure with the critical pressure. 
     
     
         6 . The method of  claim 1 , further comprising:
 monitoring a second characteristic;   determining if a third comparison or a fourth comparison are satisfied based on the second characteristic; and   closing the economizer solenoid valve when either the third comparison or the second comparison are satisfied.   
     
     
         7 . The method of  claim 6 , wherein the second characteristic is at least one of (i) a time that a flash tank pressure exceeds a critical pressure modified by a first pressure constant and (ii) the flash tank pressure. 
     
     
         8 . The method of  claim 7 , wherein the third comparison is satisfied if the time that the flash tank pressure exceeds the critical pressure modified by the first pressure constant exceeds a predetermined time. 
     
     
         9 . The method of  claim 7 , wherein the fourth comparison is satisfied if the flash tank pressure exceeds the critical pressure modified by a second pressure constant. 
     
     
         10 . The method of  claim 6 , further comprising, after closing the economizer solenoid valve, determining if the economizer solenoid valve should be opened again. 
     
     
         11 . A refrigeration unit comprising:
 at least one sensor configured to measure a first characteristic of the refrigeration unit;   a controller configured to calculate a compressor middle stage pressure based on the first characteristic the controller further configured to determine if a first comparison and a second comparison is satisfied based on the first characteristic and the calculated compressor middle stage pressure; and   an economizer solenoid valve configured to open when the first comparison and the second comparison are satisfied.   
     
     
         12 . The refrigeration unit of  claim 11 , wherein the first characteristic comprises a plurality of characteristics. 
     
     
         13 . The refrigeration unit of  claim 12 , further comprising a flash tank, wherein the first characteristic comprises a flash tank pressure, a compressor suction pressure, and a discharge port pressure. 
     
     
         14 . The refrigeration unit of  claim 13 , wherein the compressor middle stage pressure is calculated based on the compressor suction pressure and the discharge port pressure as P mid =k 1 ×(P suc ×P dis ) k     2   +k 3 , wherein k 1 , k 2 , k 3  are known parameters. 
     
     
         15 . The refrigeration unit of  claim 11 , further comprising a flash tank, wherein the first characteristic comprises a flash tank pressure, the first comparison comprises comparing the calculated compressor middle stage pressure with a critical pressure modified by a first pressure constant, and the second comparison comprises comparing the flash tank pressure with the critical pressure. 
     
     
         16 . The refrigeration unit of  claim 11 , wherein the controller is configured to determine if a third comparison or a fourth comparison are satisfied and wherein the economizer solenoid valve is configured to close when either the third comparison or the second comparison are satisfied. 
     
     
         17 . The refrigeration unit of  claim 16 , wherein the controller is configured to monitor a second characteristic, wherein the second characteristic is at least one of (i) a time that a flash tank pressure exceeds a critical pressure modified by a first pressure constant and (ii) the flash tank pressure 
     
     
         18 . The refrigeration unit of  claim 17 , wherein the third comparison is satisfied if the time that the flash tank pressure exceeds the critical pressure modified by the first pressure constant exceeds a predetermined time. 
     
     
         19 . The refrigeration unit of  claim 17 , wherein the fourth comparison is satisfied if the flash tank pressure exceeds the critical pressure modified by a second pressure constant. 
     
     
         20 . The refrigeration unit of  claim 16 , wherein the controller is further configured to determine if the economizer solenoid valve should be opened again after the economizer solenoid valve is closed.