Superheat and sub-cooling control of refrigeration system

Abstract

A refrigeration vapor compression system including a compressor, an electronic expansion valve with closed loop feedback into a controller, sensors to measure and monitor the system superheat and sub-cooling, and condenser fans controlling the flow of air through the condensing coils, the refrigeration system is operated in at least one of two functional modes to either give priority control to the level of superheat in the system or maintain a minimum level of sub-cooling in the system.

1 . A refrigerant vapor compression system comprising:
 a compressor;   first and second heat exchangers fluidly coupled to the compressor;   a variable orifice expansion valve located between the first and second heat exchangers;   at least one sensor for sensing operating conditions of the system related to a system superheat level and a system subcooling level;   a controller operative to receive sensed data from the at least one sensor and, based at least in part thereon, control at least one system component to optimize system performance, the controller configured to:
 monitor the system superheat level to determine whether the system superheat level is within a prescribed range of a system superheat setpoint; 
 monitor the system subcooling level to determine whether the system subcooling level is within a prescribed range of a system subcooling setpoint; and, 
 iteratively:
 adjust at least one system setting to restore the system subcooling level to within the prescribed range of the system subcooling setpoint while the system superheat level is within its prescribed range; 
 increment the system superheat setpoint when either the system subcooling level or the system superheat level cannot be maintained within their respective prescribed ranges; and 
 adjust at least one system setting to achieve the incremented superheat setpoint. 
 
   
     
     
         2 . The system of  claim 1 , wherein the at least one sensor for sensing operating conditions of the system related to a system superheat level and a system subcooling level includes at least one of a refrigerant temperature sensor, refrigerant pressure sensor or an ambient temperature sensor, the controller being configured to receive information from the at least one sensor and use the information for monitoring the system superheat level or system subcooling level. 
     
     
         3 . The system of  claim 2 , wherein the controller includes a memory containing a look-up table, the look-up table including at least one of a superheat setpoint value or a subcooling setpoint value corresponding to at least one sensed operating condition, and wherein the controller is further configured to determine at least one of the system superheat setpoint or the system subcooling setpoint by looking up a superheat setpoint value or a subcooling setpoint value using the at least one sensed operating condition. 
     
     
         4 . The system of  claim 1 , further comprising a condenser fan, wherein the controller is configured to adjust a speed of the condenser fan to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         5 . The system of  claim 4 , wherein the controller is configured to optimize the condenser fan speed by reducing the speed of the condenser fan when the system subcooling level exceeds the system subcooling setpoint. 
     
     
         6 . The system of  claim 1 , further comprising a variable output compressor, wherein the controller is configured to adjust an output capacity of the compressor to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         7 . The system of  claim 1 , wherein the controller is configured to adjust the expansion valve to maintain the system superheat level within a prescribed range of the system superheat setpoint. 
     
     
         8 . A method of optimizing a refrigerant vapor compression system having a compressor, first and second heat exchangers fluidly coupled to the compressor, a variable orifice expansion valve located between the first and second heat exchangers, and at least one sensor for sensing operating conditions of the system related to a system superheat level and a system subcooling level, the method comprising:
 monitoring the system superheat level to determine whether the system superheat level is within a prescribed range of a system superheat setpoint;   monitoring the system subcooling level to determine whether the system subcooling level is within a prescribed range of a system subcooling setpoint; and,   iteratively:
 adjusting at least one system setting to restore the system subcooling level to within the prescribed range of the system subcooling setpoint while the system superheat level is within its prescribed range; 
 incrementing the system superheat setpoint when either the system subcooling level or the system superheat level cannot be maintained within their respective prescribed ranges; and 
 adjusting at least one system setting to achieve the incremented superheat setpoint. 
   
     
     
         9 . The method of  claim 8 , wherein the monitoring the system superheat or system subcooling includes using at least one sensor for sensing system superheat or system subcooling. 
     
     
         10 . The method of  claim 9 , wherein the at least one sensor for sensing system superheat or system subcooling includes at least one of a refrigerant temperature sensor, refrigerant pressure sensor or an ambient temperature sensor. 
     
     
         11 . The method of  claim 8 , further comprising assigning an initial system superheat value and system subcooling value at system startup based at least in part on at least one of an ambient temperature, refrigerant line temperature or refrigerant line pressure sensed by the at least one sensor. 
     
     
         12 . The method of  claim 8 , further comprising adjusting a speed of a variable speed condenser fan to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         13 . The method of  claim 8 , further comprising adjusting an output capacity of the compressor to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         14 . The method of  claim 8 , further comprising adjusting the expansion valve to maintain the system superheat within a prescribed range of the system superheat setpoint. 
     
     
         15 . An electronic control unit for controlling an associated expansion valve of a refrigerant vapor compression system having a compressor, first and second heat exchangers fluidly coupled to the compressor, a condenser fan, a variable orifice expansion valve located between the first and second heat exchangers, and at least one sensor for sensing operating conditions of the system related to a system superheat level and a system subcooling level, the electronic control unit comprising:
 an input for receiving data from the at least one sensor;   an output for sending a control signal to at least one of the condenser fan, the expansion valve, or the compressor;   a memory that stores computer-executable instructions; and   a processor configured to execute the computer-executable instructions to generate the control signal, the instructions comprising:
 monitoring the system superheat level to determine whether the system superheat level is within a prescribed range of a system superheat setpoint; 
 monitoring the system subcooling level to determine whether the system subcooling level is within a prescribed range of a system subcooling setpoint; and, 
   iteratively:
 adjusting at least one system setting to restore the system subcooling level to within the prescribed range of the system subcooling setpoint while the system superheat level is within its prescribed range; 
 incrementing the system superheat setpoint when either the system subcooling level or the system superheat level cannot be maintained within their respective prescribed ranges; and 
 adjusting at least one system setting to achieve the incremented superheat setpoint. 
   
     
     
         16 . The electronic control unit of  claim 15 , wherein the processor is further configured to assign an initial system superheat value and system subcooling value at system startup based at least in part on at least one of an ambient temperature, refrigerant line temperature or refrigerant line pressure sensed by the at least one sensor. 
     
     
         17 . The electronic control unit of  claim 15 , wherein the processor is further configured to adjust a speed of the variable speed condenser fan to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         18 . The electronic control unit of  claim 15 , wherein the processor is further configured adjust an output capacity of the compressor to maintain the system subcooling level within the prescribed range of the system subcooling setpoint. 
     
     
         19 . The electronic control unit of  claim 15 , wherein the processor is further configured to adjust the expansion valve to maintain the system superheat within a prescribed range of the system superheat setpoint. 
     
     
         20 . A refrigerant vapor compression system comprising:
 a compressor;   first and second heat exchangers fluidly coupled to the compressor;   a variable orifice expansion valve located between the first and second heat exchangers;   at least one sensor for sensing operating conditions of the system related to a system superheat level and a system subcooling level;   and means to receive sensed data from the at least one sensor and, based at least in part thereon, control at least one of the compressor or variable orifice expansion valve to maintain system performance, the means configured to:
 monitor the system superheat level to determine whether the system superheat level is within a prescribed range of a system superheat setpoint; 
 monitor the system subcooling level to determine whether the system subcooling level is within a prescribed range of a system subcooling setpoint; and, 
 iteratively:
 adjust at least one system setting to restore the system subcooling level to within the prescribed range of the system subcooling setpoint while the system superheat level is within its prescribed range; 
 increment the system superheat setpoint when either the system subcooling level or the system superheat level cannot be maintained within their respective prescribed ranges; and 
 adjust at least one system setting to achieve the incremented superheat setpoint.