Hvac with back-pressure limiting expansion device

Abstract

A fluid conditioning system includes a compressor, a first heat exchanger, a second heat exchanger, and a first expansion device, and a second expansion device fluidly connected to form a closed loop through which a working fluid circulates. The first expansion device is associated with operation of the fluid conditioning system in a first mode and the second expansion device is associated with operation of the fluid conditioning system in a second mode. The second expansion device is a thermostatic expansion device. An accumulator is fluidly connected to the closed loop upstream from the compressor relative to a flow of the working fluid. A back pressure regulator is fluidly coupled to the first heat exchanger, the second heat exchanger, and the second expansion device.

What is claimed is: 
     
         1 . A fluid conditioning system comprising:
 a compressor, a first heat exchanger, a second heat exchanger, and a first expansion device, and a second expansion device fluidly connected to form a closed loop through which a working fluid circulates, wherein the first expansion device is associated with operation of the fluid conditioning system in a first mode, and the second expansion device is associated with operation of the fluid conditioning system in a second mode, the second expansion device being a thermostatic expansion device;   an accumulator fluidly connected to the closed loop upstream from the compressor relative to a flow of the working fluid; and   a back pressure regulator fluidly coupled to the first heat exchanger and the second heat exchanger, second expansion device.   
     
     
         2 . The fluid conditioning system of  claim 1 , wherein an internal working fluid volume of the first heat exchanger is greater than the internal working fluid volume of the second heat exchanger such that the fluid conditioning system has a charge imbalance. 
     
     
         3 . The fluid conditioning system of  claim 2 , wherein the second heat exchanger is a microchannel heat exchanger. 
     
     
         4 . The fluid conditioning system of  claim 2 , further comprising a reversing valve such that the working fluid is movable through the closed loop in a first direction associated with the first mode of operation and in an opposite, second direction associated with the second mode of operation. 
     
     
         5 . The fluid conditioning system of  claim 4 , wherein the first mode is a cooling mode and the second mode is a heating mode. 
     
     
         6 . The fluid conditioning system of  claim 4 , wherein the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator is located at the outdoor unit. 
     
     
         7 . The fluid conditioning system of  claim 4 , wherein the back pressure regulator is configured such that working fluid bypasses the back pressure regulator during the cooling mode. 
     
     
         8 . The fluid conditioning system of  claim 2 , wherein a first portion of the working fluid is provided to the thermostatic expansion device and a second portion of the working fluid is provided to the back pressure regulator, wherein the first portion of the working fluid and the second portion of the working fluid are mixed within the closed loop. 
     
     
         9 . The fluid conditioning system of  claim 8 , wherein a first branch extends downstream from the thermostatic expansion device and a second branch extends downstream from the back pressure regulator, the first branch and the second branch being joined at a mixing location arranged upstream from the first heat exchanger relative to a second direction of flow of the working fluid, wherein the first portion of the working fluid and the second portion of the working fluid are mixed at the mixing location. 
     
     
         10 . A method of operating a fluid conditioning system, comprising:
 providing a closed loop circuit including a compressor, a first heat exchanger, a first expansion device, a second expansion device, and a second heat exchanger, wherein the second expansion device is a thermostatic expansion device;   operating the fluid conditioning system in a first mode;   during the first mode, circulating a working fluid through the compressor, the first heat exchanger, the first expansion device, and the second heat exchanger of the closed loop circuit in a first direction;   operating the fluid conditioning system in a second mode; and   during the second mode, circulating the working fluid through the compressor, the second heat exchanger, the second expansion device, and the first heat exchanger of the closed loop circuit in a second direction, the closed loop including a back pressure regulator arranged in parallel with the second expansion device and circulating the working fluid through the closed loop circuit during the second mode includes dividing the working fluid into a first portion provided to the second expansion device and a second portion provided to the back pressure regulator.   
     
     
         11 . The method of  claim 10 , further comprising adjusting a position of a reversing valve of the closed loop to transform the fluid conditioning system from operating in the first mode to operating in the second mode. 
     
     
         12 . The method of  claim 10 , wherein during operation in the first mode, the working fluid bypasses the second expansion device and the back pressure regulator. 
     
     
         13 . The method of  claim 10 , further comprising collecting liquid working fluid within an accumulator during operation in the second mode. 
     
     
         14 . The method of  claim 10 , further comprising adjusting a position of the back pressure regulator to maintain a pressure upstream from the back pressure regulator at a desired threshold. 
     
     
         15 . The method of  claim 14 , wherein adjusting the position of the back pressure regulator includes increasing the second portion provided to the back pressure regulator in response to an increase in the pressure at an inlet of the thermostatic expansion device. 
     
     
         16 . The method of  claim 14 , wherein adjusting the position of the back pressure regulator reduces superheat of the working fluid upstream from the compressor. 
     
     
         17 . The method of  claim 10 , wherein an internal working fluid volume of the first heat exchanger is greater than the internal working fluid volume of the second heat exchanger such that the fluid conditioning system has a charge imbalance. 
     
     
         18 . The method of  claim 10 , wherein the second heat exchanger is a microchannel heat exchanger. 
     
     
         19 . The method of  claim 10 , wherein the fluid conditioning system is a heat pump having an indoor unit and an outdoor unit and the back pressure regulator is located at the outdoor unit.