Active charge control methods for vapor cycle refrigeration or heat pump systems

Abstract

Vapor compression systems are supplemented with a charge control loop that includes a discharge control valve, a transfer pump, and a mass storage vessel configured to add or remove refrigerant to or from the refrigeration loop during operation to optimize efficiency according to variations in thermal load. Methods for operating the vapor control systems include adjusting the refrigerant charge in the refrigeration loop by activating the discharge control valve to remove refrigerant or by activating the transfer pump to add refrigerant, thereby maintaining optimal pressure and temperature conditions in the refrigeration loop over large variations in environmental temperatures. Refrigerant removed from the refrigeration loop through the discharge control valve may be held in the mass storage vessel until subsequently being added back into the refrigeration loop by the transfer pump.

What is claimed is: 
     
         1 . A vapor compression system comprising:
 a refrigeration loop configured to transfer heat from a load location to a rejection apparatus at a rejection location, the refrigeration loop comprising components in fluidic communication through refrigeration lines containing a refrigerant, the components comprising a compressor, a condenser, an expansion valve, and an evaporator at the load location;   a charge control loop having an extraction connection and an injection connection to the refrigeration loop, both the extraction connection and the injection connection placing the charge control loop in fluidic communication with the refrigeration loop between the condenser and the expansion valve, the charge control loop comprising a discharge control valve, a transfer pump, and a mass storage vessel between the discharge control valve and the transfer pump, wherein:
 the discharge control valve is controllably configured to allow refrigerant to pass from the refrigeration loop through the extraction connection and into the mass storage vessel; and 
 the transfer pump is controllably configured to inject refrigerant from the mass storage vessel into the refrigeration loop through the injection connection; 
   a high-side sensor that measures a high-side pressure and compressor discharge temperature of a high-pressure side of the refrigeration loop;   a sink sensor that measures a sink temperature of the refrigeration loop; and   a control apparatus electronically coupled to the compressor, the at least one expansion valve, the discharge control valve, the transfer pump, the high-side sensor, and the sink sensor.   
     
     
         2 . The vapor compression system of  claim 1 , wherein:
 the compressor compresses the refrigerant from the low-pressure side of the refrigeration loop and delivers the refrigerant to the high-pressure side of the refrigeration loop;   the condenser condenses at least a portion of the refrigerant from the compressor to produce chilled refrigerant, the condenser being in thermal communication with the rejection location via the rejection apparatus;   the expansion valve has an adjustable opening through which the chilled refrigerant from the condenser expands and is delivered back to the low-pressure side; and   the evaporator at the load location transfers heat from the heat load to the refrigerant arriving from the expansion valve and delivers the refrigerant back to the compressor.   
     
     
         3 . The vapor compression system of  claim 1 , wherein the vapor compression system is a multiple-load vapor compression system comprising a plurality load locations and an evaporator at each load location. 
     
     
         4 . A method for controlling a vapor compression system, wherein the vapor compression system comprises:
 a refrigeration loop configured to transfer heat from a load location to a rejection apparatus at a rejection location, the refrigeration loop comprising components in fluidic communication through refrigeration lines containing a refrigerant, the components comprising a compressor, a condenser, an expansion valve, and an evaporator at the load location;   a charge control loop having an extraction connection and an injection connection to the refrigeration loop, both the extraction connection and the injection connection placing the charge control loop in fluidic communication with the refrigeration loop between the condenser and the expansion valve, the charge control loop comprising a discharge control valve, a transfer pump, and a mass storage vessel between the discharge control valve and the transfer pump, wherein:
 the discharge control valve is controllably configured to allow refrigerant to pass from the refrigeration loop through the extraction connection and into the mass storage vessel; and 
 the transfer pump is controllably configured to inject refrigerant from the mass storage vessel into the refrigeration loop through the injection connection; 
   a high-side sensor that measures a high-side pressure and compressor discharge temperature of a high-pressure side of the refrigeration loop;   a sink sensor that measures a sink temperature of the refrigeration loop; and   a control apparatus electronically coupled to the compressor, the at least one expansion valve, the discharge control valve, the transfer pump, the high-side sensor, and the sink sensor   
       the method comprising:
 selecting a saturated discharge temperature set-point; 
 selecting an approach high set-point; 
 operating the vapor compression system to transfer heat from the load location to the rejection location; 
 polling the sink temperature from the sink sensor; 
 polling the high-side pressure and compressor discharge temperature from the high-side sensor; 
 determining an approach as a temperature difference between the sink temperature polled from the sink sensor and the compressor discharge temperature polled from the high-side sensor; 
 determining a saturated-discharge temperature, the saturated discharge temperature being determined from the high-side pressure polled from the high-side sensor; 
 adjusting continually with the control apparatus, while the vapor compression system is operating, one or more of:
 the discharge control valve in response to the temperature difference so as to adjust flow of refrigerant to from the refrigeration loop through the extraction connection and into the mass storage vessel; and 
 the transfer pump in response to the saturated-discharge temperature differential so as to adjust flow of refrigerant from the mass storage vessel into the refrigeration loop through the injection connection. 
 
 
     
     
         5 . The method of  claim 4 , wherein adjusting continually with the control apparatus comprises:
 adjusting the transfer pump to add refrigerant from the mass storage vessel into the refrigeration loop through the injection connection if the approach exceeds the approach high set-point; and   adjusting the discharge control valve to allow refrigerant to pass from the refrigerant loop through the extraction connection and into the mass storage vessel if the saturated discharge temperature exceeds the saturated discharge temperature set-point.   
     
     
         6 . The method of  claim 5 , wherein the approach high set-point is approximately 4° F. to approximately 15° F. 
     
     
         7 . The method of  claim 5 , wherein, the method further comprises:
 selecting an approach low set-point; and   adjusting the discharge control valve to allow refrigerant to pass from the refrigerant loop through the extraction connection and into the mass storage vessel if the approach falls below the approach low set-point.   
     
     
         8 . The method of  claim 7 , wherein the approach low set-point is approximately 1° F. to approximately 5° F. 
     
     
         9 . The method of  claim 5 , wherein adjusting the transfer pump comprises adding from about 0.25 pounds of refrigerant to about 10 pounds of refrigerant from the mass storage vessel into the refrigeration loop through the injection connection when the approach exceeds the approach high set-point during polling. 
     
     
         10 . The method of  claim 5 , wherein adjusting the discharge control valve comprises removing from about 0.25 pounds of refrigerant to about 10 pounds of refrigerant from the refrigeration loop through the extraction connection and into the mass storage vessel when the saturated discharge temperature exceeds the saturated discharge temperature set-point during polling. 
     
     
         11 . The method of  claim 7 , wherein adjusting the discharge control valve comprises removing from about 0.25 pounds of refrigerant to about 10 pounds of refrigerant from the refrigeration loop through the extraction connection and into the mass storage vessel when the approach falls below the approach low set-point during polling. 
     
     
         12 . The method of  claim 4 , wherein, the method further comprises adjusting continually with the control apparatus while the vapor compression system is operating one or more of:
 a capacity of the compressor so as to maintain with respect to the evaporator load a maximum low-side pressure as measured by a low-side sensor; and   the adjustable opening of the expansion valve so as to maintain the load temperature measured by the load sensor within the desired set-point temperature range.   
     
     
         13 . The method of  claim 12 , wherein the low-side sensor is between the evaporator and the compressor. 
     
     
         14 . The method of  claim 12 , wherein the high-side sensor is between the condenser and the expansion valve. 
     
     
         15 . The method of  claim 12 , wherein the rejection apparatus is chosen from fans, vents, variable bypass paths, and closed cooling loops. 
     
     
         16 . The method of  claim 12 , wherein the load location is an enclosed space that is cooled by the vapor compression system. 
     
     
         17 . The method of  claim 12 , wherein the load location is chosen from a radar apparatus, an aircraft, an electronic apparatus, a cabin environment, a cockpit environment, a weapon, a galley, a fluidic apparatus containing lubrication fluids, and a fuel compartment containing a fuel. 
     
     
         18 . The method of  claim 12 , wherein the rejection location is the environment. 
     
     
         19 . The method of  claim 12 , wherein the rejection location is an intermediate rejection location from which additional heat is removable to an ultimate rejection location, the intermediate rejection location being chosen from chilled water, a fuel tank, an air stream, and a body of water. 
     
     
         20 . The method of  claim 19 , wherein the ultimate rejection location is the environment.