Superheat control for a refrigerant vapor compression system

Abstract

A refrigerant vapor compression system includes a compressor, an expansion valve, a compressor speed sensor operatively connected to the compressor, an ambient temperature sensor, and a controller operatively coupled to the expansion valve, compressor speed sensor and ambient temperature sensor. The controller including a superheat control that is configured and disposed to selectively activate the expansion valve to establish a desired superheat value based on a speed of the compressor as sensed by the compressor speed sensor and ambient temperature as sensed by the ambient temperature sensor.

What is claimed is: 
     
         1 . A refrigerant vapor compression system comprising:
 a compressor;   an expansion valve;   a compressor speed sensor operatively connected to the compressor;   an ambient temperature sensor; and   a controller control operatively coupled to the expansion valve, compressor speed sensor and ambient temperature sensor, the controller including a superheat control configured and disposed to selectively activate the expansion valve to establish a desired superheat value based on a speed of the compressor as sensed by the compressor speed sensor and ambient temperature as sensed by the ambient temperature sensor.   
     
     
         2 . The refrigerant vapor compression system according to  claim 1 , wherein the controller includes a memory having stored therein a look-up table, the look-up table including a plurality of superheat values that are correlated to ambient temperature and compressor speed. 
     
     
         3 . The refrigerant vapor compression system according to  claim 2 , wherein the expansion valve is a variable orifice expansion valve. 
     
     
         4 . The refrigerant vapor compression system according to  claim 1 , wherein the controller includes a transient operation control that establishes the predicted expansion valve position to provide the desired superheat value following a transient system change. 
     
     
         5 . The refrigerant vapor compression system according to  claim 4 , wherein the transient system change includes one of a compressor speed change, a system initialization, and an exit from a defrost mode. 
     
     
         6 . The refrigerant vapor compression system according to  claim 1 , wherein the controller includes a flooding control that selectively operates the expansion valve based upon a sensed partial flooding condition of the evaporator. 
     
     
         7 . The refrigerant vapor compression system according to  claim 6 , wherein the flooding control shifts the expansion valve toward a closed position upon detecting a partial flooding condition. 
     
     
         8 . The refrigerant vapor compression system according to  claim 1 , wherein the superheat control comprises a proportional-integrated-derivative (PID) controller. 
     
     
         9 . A method of controlling superheat in a refrigerant vapor compression system, the method comprising:
 sensing ambient temperature;   detecting operational speed of a compressor of the refrigerant vapor compression system; and   establishing a desired superheat value based on ambient temperature and operational speed of the compressor.   
     
     
         10 . The method of  claim 9 , wherein establishing the desired superheat value comprises selectively operating an expansion valve of the refrigerant vapor compression system. 
     
     
         11 . The method of  claim 10 , wherein selectively operating the expansion valve of the refrigerant vapor compression system comprises establishing a desired orifice of the expansion valve. 
     
     
         12 . The method of  claim 9 , further comprising: retrieving the desired superheat value from a look-up table stored in a memory, the superheat value being correlated to compressor speed and ambient temperature in the look-up table. 
     
     
         13 . The method of  claim 12 , further comprising: interpolating the desired superheat value. 
     
     
         14 . The method of  claim 9 , further comprising: establishing a predicted superheat value following a transient system change. 
     
     
         15 . The method of  claim 14 , wherein the predicted superheat value is established for a predetermined period of time. 
     
     
         16 . The method of  claim 14 , wherein the predicted superheat value is established following one of a compressor speed change, a system initialization, and one of an entry into and an exit from a defrost mode. 
     
     
         17 . The method of  claim 14 , wherein the predicted superheat value is based upon a predicted steady state operation of the refrigerant vapor compression system following the transient operating parameter change. 
     
     
         18 . The method of  claim 9 , further comprising:
 detecting a partial evaporator flooding condition; and   shifting an evaporator valve of the refrigerant vapor compression system toward a closed position based on the detected partial evaporator flooded condition.   
     
     
         19 . The method of  claim 18 , wherein detecting a partial evaporator flooded condition comprises detecting a frosted condition on at least a portion of the evaporator. 
     
     
         20 . The method of  claim 18 , further comprising: maintaining the expansion valve in the closed position until the refrigerant vapor compression system enters a defrost mode.