Electronic expansion valve superheat recovery for a variable speed compressor system

Abstract

A method of operating an electronic expansion valve of a heating, ventilation, air conditioning and refrigeration system includes detecting superheat of an evaporator of the heating, ventilation, air conditioning and refrigeration system and calculating a derivative of evaporator superheat with respect to time. The derivative of evaporator superheat with respect to time is compared to a selected derivative range, and the electronic expansion valve is closed at a rapid closure step increment higher than a normal closure step increment if the derivative is within the selected derivative range.

What is claimed is: 
     
         1 . A method of operating an electronic expansion valve of a heating, ventilation, air conditioning and refrigeration system comprising:
 detecting superheat of an evaporator of the heating, ventilation, air conditioning and refrigeration system;   calculating a derivative of evaporator superheat with respect to time;   comparing the derivative of evaporator superheat with respect to time to a selected derivative range; and   closing the electronic expansion valve at a rapid closure step increment higher than a normal closure step increment if the derivative is within the selected derivative range.   
     
     
         2 . The method of  claim 1 , further comprising:
 repeating calculation of the derivative of evaporator sump superheat with respect to time at a selected time interval;   repeating comparison of the derivative of evaporator sump superheat with respect to time to the selected derivative range; and   maintaining the closure of the electronic expansion valve at the rapid closure step increment as long as the derivative is within the selected derivative range.   
     
     
         3 . The method of  claim 2 , wherein the selected time interval is in the range of about 2 seconds to 30 seconds. 
     
     
         4 . The method of  claim 3 , wherein the selected time interval is 5 seconds. 
     
     
         5 . The method of  claim 1 , further comprising closing the electronic expansion valve at the normal closure step increment slower than the rapid closure step increment if the derivative is outside of the selected derivative range. 
     
     
         6 . The method of  claim 1 , wherein the selected derivative range is between about 0.05 and 0.5 degrees Rankin/sec. 
     
     
         7 . The method of  claim 1 , wherein the rapid closure step increment is selected to minimize a time duration of low or constant evaporator sump superheat. 
     
     
         8 . The method of  claim 7 , wherein minimizing the time duration of low or constant evaporator sump superheat reduces oil depletion of a compressor sump of the heating, ventilation, air conditioning and refrigeration system. 
     
     
         9 . A heating, ventilation, air conditioning and refrigeration system, comprising:
 a compressor, the compressor cooled via cooling fluid circulated therethrough from a compressor sump;   a condenser;   an expansion valve;   an evaporator;   a refrigerant pathway to fluidly connect the compressor, the condenser, the expansion valve and the evaporator, a volume of refrigerant circulating through the refrigerant pathway; and   a controller operably connected to the evaporator and the expansion valve configured to:
 detect superheat of the evaporator; 
 calculate a derivative of evaporator superheat with respect to time; 
 compare the derivative of evaporator superheat with respect to time to a selected derivative range; and 
 close the electronic expansion valve at a rapid closure step increment higher than a normal closure step increment if the derivative is within the selected derivative range. 
   
     
     
         10 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the controller is configured to:
 Repeat calculation of the derivative of evaporator superheat with respect to time at a selected time interval;   repeat comparison of the derivative of evaporator superheat with respect to time to the selected derivative range; and   maintain the closure step increment of the electronic expansion valve at the rapid closure step increment as long as the derivative is within the selected derivative range.   
     
     
         11 . The heating, ventilation, air conditioning and refrigeration system of  claim 10 , wherein the selected time interval is in the range of about 2 seconds to 30 seconds. 
     
     
         12 . The heating, ventilation, air conditioning and refrigeration system of  claim 11 , wherein the selected time interval is 5 seconds. 
     
     
         13 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the controller is configured to close the electronic expansion valve at the normal closure step increment slower than the rapid closure step increment if the derivative is outside of the selected derivative range. 
     
     
         14 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the selected derivative range is between about 0.05 and 0.5 degrees Rankin/sec. 
     
     
         15 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the rapid first rate is selected to minimize a time duration of low or constant compressor sump superheat. 
     
     
         16 . The heating, ventilation, air conditioning and refrigeration system of  claim 15 , wherein minimizing the time duration of low or constant compressor sump superheat reduces oil depletion of the compressor sump. 
     
     
         17 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the compressor is a variable speed compressor. 
     
     
         18 . The heating, ventilation, air conditioning and refrigeration system of  claim 9 , wherein the expansion valve is an electronic expansion valve.