Heat pump system with bi-flow expansion device

Abstract

A reversible heat pump system with one bi-flow expansion device. A four-way valve in the refrigerant circuit may be configured in either a cooling mode or a heating mode. In the cooling mode, a compressor is operable to flow a refrigerant out a compressor outlet and through the bi-flow expansion device in a first direction. In the heating mode, the compressor is operable to flow the refrigerant out the compressor outlet and through the bi-flow expansion device in a second direction, opposite the first direction. Thus, only one thermal expansion device is needed for a reversible heat pump heating, ventilation, and air conditioning (HVAC) system without the need for bypass lines and check valves around the bi-flow expansion device. Further, if an accumulator is included before the compressor, the bi-flow expansion device may be controlled to store at least some refrigerant in the accumulator, thus allowing the evaporator superheat to be lower than if the accumulator were not used.

1 . A heating, ventilation, and air conditioning (HVAC) system comprising:
 an outdoor heat exchanger operable as an evaporator in a heating mode;   an indoor heat exchanger operable as the evaporator in a cooling mode;   one bi-flow expansion device;   a compressor operable to flow a refrigerant through the outdoor heat exchanger, the indoor heat exchanger and the bi-flow expansion device in a refrigerant circuit; and   a four-way valve in the refrigerant circuit and configurable such that the compressor is operable to flow a refrigerant out a compressor outlet and through the bi-flow expansion device in a first direction in the cooling mode and configurable such that the compressor is operable to flow the refrigerant out the compressor outlet and through the bi-flow expansion device in a second direction, opposite the first direction, in the heating mode.   
     
     
         2 . The HVAC system of  claim 1 , wherein the HVAC system is a rooftop HVAC system. 
     
     
         3 . The HVAC system of  claim 1 , wherein the HVAC system is a variable refrigerant flow heat pump system. 
     
     
         4 . The HVAC system of  claim 1 , further comprising a filter drier located in the refrigerant circuit located on either side of the bi-flow expansion device. 
     
     
         5 . The HVAC system of  claim 1 , further comprising an accumulator in the refrigerant circuit before the compressor inlet. 
     
     
         6 . The HVAC system of  claim 5 , wherein the accumulator allows collection of the liquid refrigerant such that the bi-flow expansion device may be configured to lower a superheat of the evaporator compared to not including the accumulator. 
     
     
         7 . The HVAC system of  claim 5 , wherein the bi-flow expansion device is configurable to store refrigerant in the accumulator if there is a refrigerant charge imbalance in the refrigerant circuit. 
     
     
         8 . The HVAC system of  claim 1 , further comprising an outdoor section comprising the outdoor heat exchanger and the bi-flow expansion device. 
     
     
         9 . The HVAC system of  claim 1 , further comprising an indoor section comprising the indoor heat exchanger and the bi-flow expansion device. 
     
     
         10 . The HVAC system of  claim 1 , wherein the bi-flow expansion device comprises a thermostatic expansion valve (TXV). 
     
     
         11 . The HVAC system of  claim 10 , wherein the TXV comprises a bleed port. 
     
     
         12 . The HVAC system of  claim 10 , wherein the TXV comprises a balanced port design. 
     
     
         13 . The HVAC system of  claim 10 , further comprising a sensing bulb and an equalizer line in communication with the TXV. 
     
     
         14 . The HVAC system of  claim 1 , wherein the bi-flow expansion device is configurable to control flow of the refrigerant through the evaporator such that a superheat of the evaporator is as close to zero as possible while maintaining a superheat control at the compressor. 
     
     
         15 . The HVAC system of  claim 1 , wherein the bi-flow expansion device comprises an electronic expansion valve (EXV). 
     
     
         16 . The HVAC system of  claim 15 , further comprising at least one of a temperature sensor or a pressure sensor operable to provide temperature and pressure measurement data usable to control the EXV. 
     
     
         17 . A method of operating a heating, ventilation, and air conditioning (HVAC) system, comprising:
 configuring a four-way valve and operating a compressor in a cooling mode to flow a refrigerant out a compressor outlet and through an outdoor heat exchanger, one bi-flow expansion device, and an indoor heat exchanger in a first direction in a refrigerant circuit with the indoor heat exchanger operating as an evaporator; and   configuring the four-way valve and operating the compressor in a heating mode to flow the refrigerant out the compressor outlet and through the indoor heat exchanger, the one bi-flow expansion device, and the outdoor heat exchanger in a second direction, opposite the first direction, in the refrigerant circuit with the outdoor heat exchanger operating as the evaporator.   
     
     
         18 . The method of  claim 17 , wherein the HVAC system is a rooftop HVAC system. 
     
     
         19 . The method of  claim 17 , wherein the HVAC system is a variable refrigerant flow heat pump system. 
     
     
         20 . The method of  claim 17 , further comprising filtering and drying the refrigerant in the refrigerant circuit using a filter drier located on either side of the bi-flow expansion device. 
     
     
         21 . The method of  claim 17 , further comprising collecting refrigerant in an accumulator located in the refrigerant circuit before the compressor. 
     
     
         22 . The method of  claim 21 , further comprising collecting refrigerant in the accumulator to lower a superheat of the evaporator compared to not including the accumulator. 
     
     
         23 . The method of  claim 20 , further comprising configuring the bi-flow expansion device to store refrigerant in the accumulator if there is a refrigerant charge imbalance in the refrigerant circuit. 
     
     
         24 . The method of  claim 17 , further comprising controlling refrigerant flow through the evaporator using the bi-flow expansion device such that a superheat of the evaporator is as close to zero as possible while maintaining a superheat control at the compressor. 
     
     
         25 . The method of  claim 17 , wherein the bi-flow expansion device comprises a thermostatic expansion valve (TXV) 
     
     
         26 . The method of  claim 25 , wherein the TXV comprises bleed port. 
     
     
         27 . The method of  claim 25 , wherein the TXV comprises a balanced port design. 
     
     
         28 . The method of  claim 25 , further comprising controlling the operation of the TXV using a sensing bulb and an equalizer line. 
     
     
         29 . The method of  claim 17 , wherein the bi-flow expansion device comprises an electronic expansion valve (EXV). 
     
     
         30 . The method of  claim 29 , further comprising controlling the EXV using at least one of temperature data from a temperature sensor or pressure data from a pressure sensor.