Refrigerant charge and control method for heat pump systems

Abstract

A heat pump system comprises a compressor, at least one expansion valve, an accumulator for storing a volume of liquid refrigerant therein, a liquid refrigerant indicator connected to the accumulator to indicate an appropriate refrigerant charge in cooling and heating modes, and a controller. The controller is configured to determine a target compressor discharge pressure based on measured outdoor air temperature and control the compressor discharge pressure by modulating the position of the at least one expansion valve, wherein the higher the target discharge pressure target, the less liquid refrigerant is left in the accumulator. The accumulator can be sized to always have capacity to hold excess refrigerant during heating operations, and can include a charge level indicator so as to allow proper charge of the system in the field without additional tools.

What is claimed is: 
     
         1 . A heat pump system comprising:
 a compressor;   at least one expansion valve;   a liquid refrigerant indicator connected to the accumulator to indicate an appropriate refrigerant charge in cooling and heating modes;   an accumulator continuously storing a volume of liquid refrigerant therein; and   a controller configured to determine a target compressor discharge pressure based on outdoor air temperature and control the compressor discharge pressure by modulating the position of the at least one expansion valve, wherein the higher the target discharge pressure target, the less liquid refrigerant is left in the accumulator.   
     
     
         2 . The heat pump system of  claim 1 , further comprising:
 an indoor heat exchanger; and   an outdoor heat exchanger in fluid communication with indoor heat exchanger;   wherein the at least one expansion valve is arranged between and modulates the flow of the refrigerant between the indoor heat exchanger and the outdoor heat exchanger.   
     
     
         3 . The heat pump system of  claim 1 , wherein modulating a position of the at least one expansion valve comprises opening and/or closing the at least one expansion valve causing an orifice size of the valve to increase or decrease. 
     
     
         4 . The heat pump system of  claim 1 , wherein the accumulator has an element that is configured to indicate a desired amount for the volume of liquid refrigerant within the accumulator. 
     
     
         5 . The heat pump system of  claim 4 , wherein the element is positioned such the volume of the liquid refrigerant when filled to the desired amount comprises at least a charge difference volume between a cooling mode of system operation and a heating mode of system operation and a reserve volume to prevent the accumulator from being dry or over flow. 
     
     
         6 . The heat pump system of  claim 5 , wherein the element is positioned to indicate the volume of the liquid refrigerant that is appropriate regardless of a current mode of system operation and regardless of a season in which refrigerant is contemplated to be added to the system. 
     
     
         7 . The heat pump system of  claim 4 , wherein the element comprises two elements spaced from one another, each of the two elements indicating the volume of liquid refrigerant in the accumulator that is appropriate based upon both a current mode of system operation and one season in which refrigerant is contemplated to be added to the system. 
     
     
         8 . The heat pump system of  claim 1 , wherein the volume of liquid refrigerant in the accumulator comprises at least twice as much refrigerant as a volume difference in refrigerant utilized by the system between a cooling mode of system operation and a heating mode of system operation. 
     
     
         9 . The heat pump system of  claim 1 , wherein the controller is further configured to determine an indoor air temperature and the compressor discharge pressure is derived from the indoor air temperature. 
     
     
         10 . The heat pump system of  claim 1 , wherein in a heating mode of system operation, an indoor air temperature is utilized in controlling the compressor discharge pressure, and wherein in a cooling mode of system operation, the outdoor air temperature is utilized in controlling the compressor discharge pressure. 
     
     
         11 . The heat pump system of  claim 1 , wherein the controller is further configured to determine a potential for an overflowed accumulator and increase a compressor discharge pressure target which modulates the position of the at least one expansion valve to a more closed position when the overflowed accumulator is detected. 
     
     
         12 . The heat pump system of  claim 1 , wherein the at least one expansion valve comprises an assembly of two or more expansion valves, each of the two or more expansion valves having an associated check valve. 
     
     
         13 . A method comprising:
 storing a volume of liquid refrigerant continuously within an accumulator during operation of the heat pump, the volume of liquid refrigerant comprising an appropriate amount for both a heating mode and a cooling mode of operation of a heat pump;   determining an outdoor air temperature and a compressor discharge pressure; and   controlling the compressor discharge pressure based upon the determined outdoor air temperature; wherein the volume of the liquid refrigerant within the accumulator changes based upon the discharge pressure.   
     
     
         14 . The method of  claim 13 , further comprising:
 increasing a compressor discharge pressure target to modulate the position of the at least one expansion valve to prevent a overflowed accumulator; and   issuing one of a warning or turning off the heat pump system if the target discharge pressure reaches a predetermined high limit to prevent compressor damage.   
     
     
         15 . The method of  claim 13 , further comprising indicating a desired amount for the volume of liquid refrigerant within the accumulator. 
     
     
         16 . The method of  claim 15 , wherein the indicating is independent of a current mode of heat pump operation and a season in which refrigerant is contemplated to be added to the heat pump. 
     
     
         17 . The method of  claim 15 , wherein the indicating is dependent upon both a current mode of heat pump operation and a season in which refrigerant is contemplated to be added to the heat pump. 
     
     
         18 . The method of  claim 13 , further comprising determining an indoor air temperature and deriving the compressor discharge pressure from the indoor air temperature. 
     
     
         19 . The method of  claim 13  further comprising:
 controlling the compressor discharge pressure based upon an indoor air temperature in a heating mode of heat pump operation; and 
 controlling the compressor discharge pressure based upon the determined outdoor air temperature in a cooling mode of heat pump operation. 
 
     
     
         20 . An accumulator comprising:
 a housing configured to house a continuous volume of liquid refrigerant during both a heating mode and a cooling mode of operation of a heat pump; and   an element that is configured to indicate a desired amount for the volume of the liquid refrigerant within the accumulator.   
     
     
         21 . The accumulator of  claim 20 , wherein the element is positioned such the volume of the liquid refrigerant when filled to the desired amount comprises at least a liquid refrigerant charge difference volume between a cooling mode of heat pump operation and a heating mode of heat pump operation and a reserve volume to prevent the accumulator from being dry or overflow. 
     
     
         22 . The heat pump system of  claim 20 , wherein the element is positioned to indicate the volume of the liquid refrigerant that is appropriate regardless of a current mode of system operation and regardless of a season in which refrigerant is contemplated to be added to the system. 
     
     
         23 . The heat pump system of  claim 20 , wherein the element comprises two elements spaced from one another, each of the two elements indicating the volume of liquid refrigerant in the accumulator that is appropriate based upon both a current mode of system operation and one season in which refrigerant is contemplated to be added to the system.