System and method for level control in a flash tank

Abstract

A control algorithm is provided for controlling an economizer circuit in a chiller system. The control algorithm adjusts the position of a feed valve in the economizer circuit in response to measured system operating parameters to maintain a level of liquid refrigerant in a flash tank of the economizer circuit. The measured system operating parameters can include the load of the compressor and the pressure and temperature of refrigerant in the flash tank.

1 . A method for controlling an economizer circuit in a chiller system, the method comprising the steps of: 
 providing an economizer circuit for a chiller system having a flash tank, an inlet line, and a feed valve, the feed valve being disposed in the inlet line and being configured to control flow of refrigerant to the flash tank;    measuring at least one system operating parameter for the chiller system;    calculating a valve position for the feed valve in response to the measured at least one system operating parameter; and    adjusting the feed valve to the calculated valve position to control the level of liquid refrigerant in the flash tank.    
   
   
       2 . The method of  claim 1 , wherein the at least one system operating parameters is selected from a load of the compressor, a pressure of refrigerant in the flash tank, or a temperature of refrigerant in the flash tank.  
   
   
       3 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the load on the compressor by determining a system capacity from an entering fluid temperature and a leaving fluid temperature in the evaporator  
   
   
       4 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the load on the compressor by sensing the flow of liquid through the evaporator  
   
   
       5 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the load on the compressor by measuring a speed of the compressor.  
   
   
       6 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the load on the compressor by sensing an operating frequency of the variable speed drive.  
   
   
       7 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the load on the compressor by sensing the position of a slide valve in the compressor.  
   
   
       8 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the pressure of the refrigerant in the flash tank by sensing the pressure in the flash tank  
   
   
       9 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the temperature of the refrigerant in the flash tank by sensing the temperature in the flash tank.  
   
   
       10 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the pressure of the refrigerant in the flash tank by sensing a suction pressure and a discharge pressure in the compressor.  
   
   
       11 . The method of  claim 2 , wherein the step of measuring at least one system operating parameter includes determining the temperature of the refrigerant in the flash tank by sensing a suction temperature and a discharge temperature of the refrigerant in the compressor.  
   
   
       12 . The method of  claim 1 , wherein the step of calculating a valve position includes comparing the measured at least one system operating parameter to entries in a map to determine the position for the feed valve.  
   
   
       13 . The method of  claim 12 , wherein the map correlates the measured at least one system operating parameter and at least one additional criteria with operating positions for the feed valve.  
   
   
       14 . The method of  claim 13 , wherein the at least one additional criteria is selected from the group consisting of at least one cross-sectional flow area for the feed valve corresponding with at least one operating position of the feed valve, at least one actuation requirement of a motor for adjusting the operating position of the feed valve, and performance of the compressor at a plurality of measured operating parameters based over a range of system operating conditions.  
   
   
       15 . The method of  claim 14 , wherein the ranges of system operating parameters are based on measured or calculated mapping of the compressor.  
   
   
       16 . A liquid level control system for an economizer circuit having a feed valve being disposed in an inlet line and configured to control flow of refrigerant to a flash tank, the control system comprising: 
 a map of a plurality of operating positions of the feed valve, each operating position of the plurality of operating positions being associated with a predetermined position of the feed valve and an amount of refrigerant in the flash tank corresponding to a flow rate of the predetermined position, the map configured to correlate the plurality of feed valve operating positions with a plurality of predetermined system operating parameters;    a microprocessor, the microprocessor being configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank; and    wherein the microprocessor generates a control signal to position the adjustable valve arrangement of a refrigeration system based on the map the to control the operation of the feed valve.    
   
   
       17 . The system of  claim 16 , wherein the map is generated from test data that determines an operating position for the valve in response to particular system operating parameters or conditions.  
   
   
       18 . The system of  claim 16 , wherein the map is generated from calculated data that determines an operating position for the valve in response to particular system operating parameters or conditions.  
   
   
       19 . The system of  claim 16 , also including at least one upper level switch to determine a refrigerant level of the flash tank above a predetermined maximum refrigerant level, and at least one lower level switch to determine a predetermined minimum refrigerant level, the upper and lower level switches configured to generate a signal to indicate to the microprocessor when the level of exceeds a respective maximum or minimum refrigerant level.  
   
   
       20 . The system of  claim 16 , wherein the predetermined system operating parameters is selected from a load of the compressor, a pressure of the refrigerant in the flash tank, or a temperature of the refrigerant in the flash tank.  
   
   
       21 . The system of  claim 20 , wherein the load on the compressor is determined by determining a system capacity by sensing an entering liquid temperature and a leaving liquid temperature in the evaporator.  
   
   
       22 . The system of  claim 20 , wherein the load on the compressor is determined by at least on of sensing the flow of liquid through the evaporator, measuring a speed of the compressor, sensing an operating frequency of the variable speed drive, or sensing the position of a slide valve in the compressor.  
   
   
       23 . The system of  claim 20 , wherein the pressure of the refrigerant in the flash tank is determined by at least one of sensing the pressure in the flash tank or sensing a suction pressure and a discharge pressure in the compressor.  
   
   
       24 . The system of  claim 20 , wherein the temperature of the refrigerant in the flash tank is determined by at least one of sensing the temperature in the flash tank or sensing a suction temperature and a discharge temperature of the refrigerant in the compressor.  
   
   
       25 . A chiller system comprising: 
 a refrigerant circuit with a compressor, a condenser arrangement, an expansion valve and an evaporator arrangement connected in a closed refrigerant loop;    an economizer circuit connected to the refrigerant circuit, the economizer circuit comprising a flash tank, an inlet line, and a feed valve, the feed valve being disposed in the inlet line and being configured to control flow of refrigerant to the flash tank; and a control panel comprising: 
 a map of a plurality of operating positions of the feed valve, each operating position of the plurality of operating positions being associated with a predetermined position of the feed valve and an amount of refrigerant in the flash tank corresponding to a flow rate of the predetermined position, the map configured to correlate the plurality of feed valve operating positions with a plurality of predetermined system operating parameters;  
 a microprocessor, the microprocessor being configured to control the position of the feed valve to control the level of liquid refrigerant in the flash tank; and  
 wherein the microprocessor generates a control signal to position the feed valve based on the map.