Patent Publication Number: US-9897357-B2

Title: Isentropic expansion device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 62/036,800 filed on Aug. 13, 2014 by Stephen S. Hancock, and entitled “Isentropic Expansion Device,” the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND 
     Heating, ventilation, and air conditioning systems (HVAC systems) generally comprise one or more heat exchangers generally referred to as “condensers” that may be comprise a condenser coil, and may be associated with one or more compressors and a fan assembly. In operation, a compressor may compress refrigerant and discharge superheated refrigerant (i.e., refrigerant at a temperature greater than a saturation temperature of the refrigerant) to the condenser coil. As the refrigerant passes through the condenser coil, a fan assembly may be configured to selectively force air into contact with the condenser coil. In response to the air contacting the condenser coil, heat may be transferred from the refrigerant to the air, thereby desuperheating and condensing the refrigerant and/or otherwise reducing a temperature of the refrigerant. 
     Refrigerant may generally exit the condenser coil in a liquid phase and/or a gaseous and liquid mixed phase. The refrigerant may thereafter be delivered from the condenser coil to a refrigerant expansion device where the refrigerant pressure is reduced. The resulting pressure drop in the expansion device results in the saturation temperature of the refrigerant dropping. The resulting lower pressure refrigerant can then be selectively discharged into a so-called evaporator coil of the HVAC system that may provide a cooling function. 
     SUMMARY 
     In an embodiment, a heating, ventilation, and air conditioning (HVAC) system comprises a heat exchanger, and an expansion device disposed upstream and in fluid communication with the heat exchanger. The expansion device comprises a pressure recovery portion. The expansion device may be configured to receive a liquid refrigerant and isentropically or substantially isentropically expand the refrigerant. The heat exchanger may be configured to absorb heat from an external fluid. The HVAC system may also include a second expansion device in fluid communication with the expansion device. The second expansion device may comprise at least one of: an electronically controlled motor driven electronic expansion valve (EEV), a thermostatic expansion valve, an isenthalpic expansion valve, a capillary tube assembly, or an orifice. The second expansion device may comprise an isentropic or substantially isentropic expansion device. The refrigerant expansion device may comprise a flow section and an expansion section. A diameter of the flow section and a diameter of the expansion section may be equal at an intersection of the flow section and the expansion section. 
     In an embodiment, a heating, ventilation, and air conditioning (HVAC) system comprises a refrigerant expansion device that comprises a pressure recovery portion. The refrigerant expansion device may comprise an isentropic expansion device or a substantially isentropic expansion device. The refrigerant expansion device may comprise an inlet section, a flow section, and an expansion section. A diameter of the flow section and a diameter of the expansion section may be equal at an intersection of the flow section and the expansion section. The diameter of the expansion section may increase over its length in a direction of flow. A length of the expansion section may be between about 3 and about 15 times a final diameter of the expansion section. A shoulder may not be present between the flow section and the expansion section. 
     In an embodiment, a method of operating a heating, ventilation, and air conditioning (HVAC) system, the method comprises receiving a refrigerant at a first pressure at an expansion device, passing the refrigerant through the expansion device in an isentropic or substantially isentropic expansion, and passing the refrigerant to a downstream heat exchanger at a second pressure. The second pressure is less than the first pressure. The refrigerant may be received at the expansion device as a liquid. Passing the refrigerant through the expansion device may comprise passing the refrigerant through a flow section, and passing the refrigerant through an expansion section. The expansion section may be located downstream from the flow section. Passing the refrigerant through the flow section may comprise passing the refrigerant through the flow section in a choked flow condition. Passing the refrigerant through the expansion device may also include flashing a portion of the refrigerant from a liquid state to a vapor state within the flow section. The method may also include absorbing heat in the downstream heat exchanger, and evaporating at least a portion of the refrigerant in the downstream heat exchanger in response to absorbing the heat. A thermodynamic quality of the refrigerant passing to the downstream heat exchanger may be between about 0.01 and about 0.25. 
     These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description: 
         FIG. 1  is simplified schematic diagram of an HVAC system according to an embodiment of the disclosure. 
         FIG. 2  is a simplified cross-sectional view of an expansion device according to an embodiment of the disclosure. 
         FIG. 3  is a simplified cross-sectional view of another expansion device according to an embodiment of the disclosure. 
         FIG. 4  is a simplified schematic diagram of another HVAC system according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals, respectively. In addition, similar reference numerals may refer to similar components in different embodiments disclosed herein. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is not intended to limit the invention to the embodiments illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed herein may be employed separately or in any suitable combination to produce desired results. 
     HVAC systems are being improved in order to provide increased efficiency and cooling capacity. Disclosed herein is an HVAC system that utilizes an expansion device having a pressure recovery portion, which reduces losses in the expansion of the two phase refrigerant stream to improve system efficiency. In some embodiments, an orifice type expansion device can be used. As the refrigerant flows through the orifice, the pressure drops and a portion of the refrigerant may flash from a liquid to a vapor. The use of an orifice may result in a turbulent flow within and downstream of the expansion device. The resulting energy loss may result in a refrigerant having a reduced ability to absorb heat within a downstream heat exchanger. 
     In contrast to an isenthalpic expansion device described above, the expansion device disclosed herein may reduce the expansion losses associated with the refrigerant passing through the expansion device. For example, the expansion device may comprise a pressure recovery portion that may allow the refrigerant to expand in a controlled manner and reduce the amount of turbulence present. The controlled expansion may result in a lower vapor content of the refrigerant leaving the expansion device and a corresponding improvement in energy and process efficiency. The expansion device can be used in conjunction with other expansion devices and/or used in series to provide for a more controlled pressure drop while reducing the overall energy losses associated with an orifice type expansion device. 
     Referring now to  FIG. 1 , a simplified schematic diagram of an HVAC system  100  is shown according to an embodiment of the disclosure. HVAC system  100  generally comprises an indoor unit  102 , an outdoor unit  104 , and a system controller  106 . The system controller  106  may generally control operation of the indoor unit  102  and/or the outdoor unit  104 . 
     The HVAC system  100  illustrated in  FIG. 1  may be referred to as a split system in some contexts, where the split system  100  comprises an indoor unit  102  located separately from the outdoor unit  104 . While a split system is described herein, the systems and methods described herein may be equally applicable to other HVAC systems as well. In some embodiments of an HVAC system  100 , the system  100  may comprise a package system in which one or more of the components of the indoor unit  102  and one or more of the components of the outdoor unit  104  are carried together in a common housing or package. In still other embodiments, the HVAC system  100  may comprise a ducted system where the indoor unit  102  is remotely located from the conditioned zones, thereby requiring air ducts to route the circulating air. 
     Indoor unit  102  generally comprises an indoor heat exchanger  108 , an indoor fan  110 , and an expansion device  112 . The indoor heat exchanger  108  is configured to allow heat exchange between a refrigerant carried within internal tubing of the indoor heat exchanger  108  and fluids that contact the indoor heat exchanger  108  but that are kept segregated from the refrigerant. In a cooling mode, the refrigerant received within the indoor heat exchanger  108  can be cooler than the fluid passing over the exterior of the indoor heat exchanger  108 . The resulting heat absorption by the refrigerant within the indoor heat exchanger may result in the vaporization of the refrigerant within the indoor heat exchanger  108 . For this reason, the indoor heat exchanger may be referred to as an evaporator or evaporator exchanger in some contexts. Various types of exchangers can be used as the indoor heat exchanger  108  including, but not limited to, a plate fin heat exchanger, a spine fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger. 
     The indoor fan  110  serves to create the flow of the fluid that contacts the indoor heat exchanger  108 . In general, the indoor fan  110  drives an air flow over the exterior of the indoor heat exchanger  108  tubes as well as driving the ventilation system to circulate the air within the indoor environment. While described as a fan, various types of fans and blowers can be used as the indoor fan  110 . In an embodiment, the indoor fan  110  may be a centrifugal blower comprising a blower housing, a blower impeller at least partially disposed within the blower housing, and a blower motor configured to selectively rotate the blower impeller. In other embodiments, the indoor fan  110  may comprise a mixed-flow fan and/or any other suitable type of fan. The indoor fan  110  may be configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the indoor fan  110  may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the indoor fan  110 . In yet other embodiments, the indoor fan  110  may be a single speed fan. 
     The expansion device  112  is configured to receive a relatively high-pressure refrigerant from the outdoor heat exchanger  114  and reduce the pressure of the refrigerant (e.g., expanding the refrigerant) as measured across the expansion device  112  prior to the refrigerant entering the indoor heat exchanger  108 . In this embodiment, the expansion device  112  is disposed between and is in fluid communication with the outlet of the outdoor heat exchanger  114  and the inlet of the indoor heat exchanger  108 . In some embodiments, the expansion device  112  may also control an amount of refrigerant passing through the expansion device  112 . The pressure reduction results in a cooling of the refrigerant, which is then used to absorb heat into the refrigerant in the indoor heat exchanger  108  while correspondingly cooling the fluid (e.g., the indoor air) passing over the indoor heat exchanger  108 . 
     Referring to the cross-sectional view illustrated in  FIG. 2 , an embodiment of an expansion device  200  is shown in greater detail. The expansion device  200  comprises a generally cylindrical body  202  defining an interior flowpath  204 . The expansion device  200  may comprise an upstream end  208  that receives refrigerant from the outdoor heat exchanger  114  and a downstream end  206  that provides fluid communication with the interior heat exchanger  108 . Each end  206 ,  208  may be coupled to a refrigerant line and may or may not be in fluid communication with an additional expansion or control device. The body  202  may be constructed of any suitable materials. The expansion device  200  may be integrally formed from a single body  202  portion, although it will be appreciated by one of ordinary skill in the art that the various sections of the expansion device  200  may be contained in separate components that are coupled together. 
     The interior flowpath  204  is positioned within the body  202  to provide fluid communication through the expansion device  200 . The interior flowpath  204  may be positioned concentrically within the body  202  and may be cylindrical in shape, however, in some embodiments, the shape of the interior flowpath may vary to some degree. The diameter of the interior flowpath  204  may be chosen to provide the desired fluid flow rate and fluid velocity at the appropriate operating conditions (e.g., pressure, temperature, etc.) and refrigerant type. 
     As shown in  FIG. 2 , the body  202  may be configured to provide several flow sections of the interior flowpath  204 . For example, the interior flowpath  204  may comprise an inlet section  212 , a flow section  214 , and an expansion section  216 . Refrigerant flowing into the expansion device  200  may first flow through the inlet section  212 . The inlet section  212  may have a decreasing diameter  217  along its length  218  between the upstream end  208  of the body  202  and the interface with the flow section  214 . The diameter  217  may decrease gradually (e.g., over a curved surface) or may decrease in one or more steps, which may correspond to one or more sharp edges. In an embodiment, the diameter  220  of the flow section  214  may extend to the upstream end  208  of the expansion device  200 , in which case the inlet section  212  may not be considered to be present. The flow section  214  may have a relatively uniform diameter  220  along its length  219 . The expansion section  216  may extend from the flow section to the downstream end  206  of the body. The diameter of the expansion section  216  may be greater than the diameter  220  of the flow section  214  and may be relatively uniform along its length  222 . 
     In the embodiment illustrated in  FIG. 2 , the diameter  220  of the flow section  214  is less than the diameter  224  of the expansion section  216 , thereby creating a shoulder  226  at the intersection of the flow section  214  and the expansion section  216 . The shoulder  226  may be formed as an edge disposed perpendicular to the central longitudinal axis of the interior flowpath  204 . In an embodiment, the shoulder may be formed of a generally flat edge that may be tilted up to about  30  degrees from a plane perpendicular to the longitudinal axis of the interior flowpath  204 . The relatively sharp transition between the flow section  214  and the expansion section may result in a relatively uncontrolled expansion of the refrigerant. 
     The expansion device  200  may result in an isenthalpic or substantially isenthalpic expansion. In this embodiment, the refrigerant may enter the expansion device  200  through the upstream end  208 . The refrigerant may be in the liquid phase, though a minor portion of the refrigerant may be in a vapor phase if the outdoor heat exchanger  114  does not entirely condense the refrigerant. As the refrigerant enters the inlet section  212 , the refrigerant may flow into the flow section  214 . The flow section  214  may be sized to result in a desired pressure drop. The pressure within the refrigerant may drop within the flow section  214 , and a portion of the refrigerant may flash from a liquid state to a vapor state. The properties of the flow section  214  and/or the resulting flashing of the refrigerant may result in a choked flow condition of the refrigerant within the flow section  214 . In this condition, the flow rate of the refrigerant through the flow section  214  is substantially independent of the downstream pressure. As the refrigerant passes out of the flow section, the refrigerant may rapidly expand into the expansion section  216  due to the presence of the shoulder  226 . The resulting turbulence may result in a conversion of the energy in the refrigerant stream into heat, which results in the refrigerant stream leaving the expansion device  200  having an increased thermodynamic quality and a decreased ability to absorb heat in the indoor heat exchanger. As used herein, the thermodynamic quality refers to the mass fraction in a saturated mixture that is vapor. For example, the refrigerant leaving the expansion device  200  may comprise a thermodynamic quality between about 0.15 and 0.3. Further, the resulting expansion of the refrigerant through the expansion device  200  may reduce the overall efficiency of the system  100  due to the uncontrolled nature of the expansion as it passes from the flow section  214  to the expansion  216  of between about 0.5% and about 5%. The resulting efficiency loss or reduction may hold true for other isenthalpic expansion devices as well. 
     In some embodiments, the expansion device may comprise a pressure recovery portion that may reduce the efficiency loss associated with an isenthalpic or isenthalpic type expansion device. In an embodiment, the expansion device may comprise a flow section coupled to an expansion section having a smooth transition between the two sections that does not result in a shoulder. Further, the expansion section may have a continuous expansion along its length to provide for a controlled expansion of the refrigerant passing therethrough. The smooth transition and/or the continuous expansion may be referred to as a pressure recovery portion or section. 
     As shown in the cross-sectional view of  FIG. 3 , another embodiment of an expansion device  300  is shown in greater detail. The expansion device  300  illustrated in  FIG. 3  is similar to the expansion device  200  illustrated in  FIG. 2 , and similar components will not be described in detail in the interest of clarity and brevity. The expansion device  300  comprises a generally cylindrical body  302  defining an interior flowpath  304 . The expansion device  300  may comprise an upstream end  308  that receives refrigerant from the outdoor heat exchanger  114  and a downstream end  306  that provides fluid communication with the interior heat exchanger  108 . Each end  306 ,  308  may be coupled to a refrigerant line and may or may not be in fluid communication with an additional expansion or control device. The body  302  may be constructed of any suitable materials. The expansion device  300  may be integrally formed from a single body  302  portion, although it will be appreciated by one of ordinary skill in the art that the various sections of the expansion device  300  may be contained in separate components that are coupled together. 
     The interior flowpath  304  is positioned within the body  302  to provide fluid communication through the expansion device  300 . The interior flowpath  304  may be positioned concentrically within the body  302  and may generally be cylindrical in shape, however, in some embodiments, the shape of the interior flowpath may vary to some degree. The diameter of the interior flowpath  304  may vary along the length of the expansion device  300  and may be chosen to provide the desired fluid flow rate and fluid velocity at the appropriate operating conditions (e.g., pressure, temperature, etc.) and refrigerant type. 
     As shown in  FIG. 3 , the body  302  may be configured to provide several flow sections of the interior flowpath  304 . For example, the interior flowpath  304  may comprise an inlet section  312 , a flow section  314 , and an expansion section  316 . The inlet section  312  and the flow section  314  may be the same or similar to the inlet and flow sections described with respect to  FIG. 2  (e.g., the inlet section  212 , and the flow section  214 ). Refrigerant flowing into the expansion device  300  may first flow through the inlet section  312 . The inlet section  312  may have a decreasing diameter  317  along its length  318  between the upstream end  308  of the body  302  and the interface with the flow section  314 . The diameter  317  may decrease gradually (e.g., over a curved surface) or may decrease in one or more steps, which may correspond to one or more sharp edges. In an embodiment, the diameter  320  of the flow section  314  may extend to the upstream end  308  of the expansion device  300 , in which case the inlet section  312  may not be considered to be present. The flow section  314  may have a relatively uniform diameter  320  along its length  319 . 
     The expansion section  316  may extend from the flow section to the downstream end  306  of the body  302 . The diameter  324  of the expansion section  316  may be approximately the same as the diameter  320  of the flow section  314  at the upstream end of the expansion section  316 . As a result, the transition from the flow section  314  to the expansion section  316  may be relatively uniform or smooth. The diameter  324  of the expansion section  316  may vary over the length  322  of the expansion section  316 . As shown in  FIG. 3 , the diameter  324  may increase linearly from the upstream end of the expansion section  316  to the downstream end  306  of the expansion device  300 . In some embodiments, the diameter  324  may expand non-linearly over the length  322  of the expansion section  316 . For example, the diameter  324  may expand and present a concave or convex curve as viewed from within the interior flowpath. The diameter  324  may comprise a curved surface having a constant or variable radius of curvature. Further, combinations of these types of shapes may also be possible. For example, the diameter may increase over a curved surface for a portion of the length  322  of the expansion section  316  while increasing linearly over another portion of the length  322  of the expansion section  316 . 
     In an embodiment, the diameters and lengths of the inlet section  312 , the flow section  314 , and/or the expansion section  316  may vary. In an embodiment, the length  319  and diameter  320  of the flow section  314  may be selected to provide for a desired pressure drop and/or a choked flow condition of the refrigerant within the flow section  314 . In general, the length  319  of the flow section  314  may be greater than about three times its diameter  320 , alternatively greater than about four times its diameter  320 . The diameter  320  of the flow section  314  may be measured as the minimum diameter of the flow section  314  when the diameter  320  varies over the length  319  of the flow section  314 . The length  322  of the expansion section  316  may range from about three to about fifteen times the largest diameter  324  of the expansion section  316 . 
     The expansion device  300  may result in an isentropic or substantially isentropic expansion. As used herein, an isentropic expansion is one that occurs at a substantially constant entropy. A substantially isentropic expansion may occur with an entropy change of less than about 90%, alternatively less than about 95%, or alternatively less than about 98%. In this embodiment, the refrigerant may enter the expansion device  300  through the upstream end  308 . The refrigerant may be in the liquid phase, though a portion of the refrigerant may be in a vapor phase if the outdoor heat exchanger  114  does not entirely condense the refrigerant. As the refrigerant enters the inlet section  312 , the refrigerant may flow into the flow section  314 . The flow section  314  may be sized to result in a desired pressure drop. The pressure within the refrigerant may drop within the flow section  314 , and a portion of the refrigerant may flash from a liquid state to a vapor state. The properties of the flow section  314  and/or the resulting flashing of the refrigerant may result in a choked flow condition of the refrigerant within the flow section  314 . As the refrigerant passes out of the flow section  314 , the refrigerant may gradually expand into the expansion section  316  due to the gradually increasing diameter  324  of the expansion section  322  and/or the smooth transition between the flow section  314  and the expansion section  316 . 
     The gradual expansion may reduce or limit the amount of turbulence occurring during the expansion. As a result, the refrigerant stream leaving the expansion device  300  may have a decreased thermodynamic quality, a lower enthalpy, and an increased ability to absorb heat in the indoor heat exchanger. In an embodiment, the refrigerant leaving the expansion device  300  may comprise a thermodynamic quality that is less than about 0.2, or less than about 0.15. While a lower thermodynamic quality is desired, some amount of vapor may still be formed due to the reduction in pressure within the expansion device  300 . As a result, the thermodynamic quality may be at least about 0.05 or at least about 0.1. Further, the resulting expansion of the refrigerant through the expansion device  300  may increase the overall efficiency of the system  100  relative to an isenthalpic expansion device between about 0.5% and about 3%. 
     Returning to  FIG. 1 , the expansion device  112  may comprise at least one device comprising a pressure recovery portion such as the expansion device  300  described with respect to  FIG. 3  above. In some embodiments, an expansion device  112  comprising a pressure recovery portion may be used in parallel or in series with additional expansion devices. One or more of the additional expansion devices may also comprise a pressure recovery portion. For example, expansion devices such as expansion device  300  described with respect to  FIG. 3  may be used in series, and each expansion device may reduce the pressure of the refrigerant a desired amount. Staging the pressure reduction may result in an increased efficiency due to the reduced turbulence and/or energy loss in each stage relative to a single expansion process. 
     In some embodiments, an expansion device  112  comprising a pressure recovery portion may be used in parallel or in series with additional expansion devices that do not comprise a pressure recovery section. Additional expansion devices can include, but are not limited to, an electronically controlled motor driven electronic expansion valve (EEV), a thermostatic expansion valve, an isenthalpic expansion valve, a capillary tube assembly, an orifice and/or any other suitable expansion device or metering device. The use of the expansion device comprising the pressure recovery portion may improve the overall efficiency of the system by providing a portion of the pressure drop in a controlled process. For example, a portion of the pressure drop may occur in an isentropic or substantially isentropic process. In some embodiments, the expansion device  112  may comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass. 
     The outdoor unit  104  generally comprises an outdoor heat exchanger  114 , a compressor  116 , and an outdoor fan  118 . The outdoor heat exchanger  114  is configured to allow heat exchange between a refrigerant carried within internal tubing of the outdoor heat exchanger  114  and fluids (e.g., outdoor air) that contact the outdoor heat exchanger  114  but that are kept segregated from the refrigerant. In a cooling mode, the refrigerant received within the outdoor heat exchanger  114  through inlet line  115  can be warmer than the fluid passing over the exterior of the outdoor heat exchanger  114 . The resulting heat loss by the refrigerant within the outdoor heat exchanger  114  may result in the partial or complete condensation of the refrigerant within the outdoor heat exchanger  114 . For this reason, the outdoor heat exchanger  114  may be referred to as a condenser or condenser exchanger in some contexts. Various types of exchangers can be used as the outdoor heat exchanger  114  including, but not limited to, a plate fin heat exchanger, a spine fin heat exchanger, a microchannel heat exchanger, or any other suitable type of heat exchanger. 
     While the outdoor heat exchanger  114  is described as being outside or outdoors, the outdoor heat exchanger  114  does not have to be installed physically outdoors. For example, the outdoor heat exchanger  114  can be installed within a building while having ducting to contact exterior air with the outdoor heat exchanger  114 . In some embodiments, the heat exchange between the outdoor heat exchanger  114  and the exterior or outdoor air can occur directly or indirectly via an intermediate heat transfer fluid. 
     The compressor  116  can be disposed between and in fluid communication with the outlet of the indoor heat exchanger  108  and the inlet of the outdoor heat exchanger  114 . The compressor  116  may be configured to receive the refrigerant from the indoor heat exchanger  108  through line  119 , compress the refrigerant, and pass the refrigerant to the outdoor heat exchanger  114  through line  115 . As the refrigerant is compressed, the pressure and temperature of the refrigerant may rise, thereby allow the heat to be released from the refrigerant within the outdoor heat exchanger  114 . Various types of compressors are known and may be suitable for use with the system  100 . In an embodiment, the compressor  116  may comprise a multiple speed scroll type compressor configured to selectively pump refrigerant at a plurality of mass flow rates. In some embodiments, the compressor  116  may comprise a modulating compressor capable of operation over one or more speed ranges, a reciprocating type compressor, a single speed compressor, and/or any other suitable refrigerant compressor and/or refrigerant pump. 
     In an embodiment, the outdoor heat exchanger  114  may comprise a condensing section and a subcooling section. As used herein, subcooling refers to a reduction in the temperature of the refrigerant below is saturation temperature (e.g., its condensation temperature) at the pressure within the outdoor heat exchanger  114 . The condensing section may comprise a main coil, and the subcooling section may comprise a subcooling coil. The terms main coil and subcooling coil can refer to any type of heat exchanger and not meant to describe or be limited to any particular design. In an embodiment, the main coil and the subcooling coil can be two separate heat exchangers, or in some embodiments, they can be combined in various ways, for example by sharing common heat transfer fins. The heat transfer fins may be constructed of metal or any other thermally conductive material to allow for the transfer of heat from the tubes into the heat transfer fins and consequently to the external fluid flowing over the heat transfer fins. 
     The outdoor fan  118  serves to create the flow of the fluid that contacts the outdoor heat exchanger  114 . In general, the outdoor fan  118  drives an air flow over the exterior of the outdoor heat exchanger  118  tubes. While described as a fan, various types of fans and blowers can be used as the indoor fan  110 . In an embodiment, the outdoor fan  118  may be an axial fan comprising a fan blade assembly and fan motor configured to selectively rotate the fan blade assembly. In other embodiments, the outdoor fan  118  may comprise a mixed-flow fan, a centrifugal blower, and/or any other suitable type of fan and/or blower. The outdoor fan  118  is configured as a modulating and/or variable speed fan capable of being operated at many speeds over one or more ranges of speeds. In other embodiments, the outdoor fan  118  may be configured as a multiple speed fan capable of being operated at a plurality of operating speeds by selectively electrically powering different ones of multiple electromagnetic windings of a motor of the outdoor fan  118 . In yet other embodiments, the outdoor fan  118  may be a single speed fan. 
     The outdoor fan  118  may be configured to draw air through the outdoor heat exchanger  118  and/or blow air into the outdoor heat exchanger  118 . While illustrated as being above the outdoor exchanger  114 , the outdoor fan  118  may be disposed below, within, or adjacent the outdoor heat exchanger  114 . In some embodiments, the outdoor fan  118  may be configured to create an air flow pattern over the outdoor heat exchanger  114  such that the air passes over the subcooling section prior to passing over the condensing section, thereby creating a counter-current flow pattern within the outdoor heat exchanger  114 . In some embodiments, a cross-current flow pattern may be established where the external fluid (e.g., the outdoor air) is drawn across the subcooling section and the condensing section. Any other suitable flow patterns or configurations are also possible. 
     The system controller  106  may display information related to the operation of the HVAC system  100  and may receive user inputs related to operation of the HVAC system  100 . However, the system controller  106  may further be operable to display information and receive user inputs tangentially and/or unrelated to operation of the HVAC system  100 . The system controller  106  may generally comprise a touchscreen interface for displaying information and for receiving user inputs. In some embodiments, the system controller  106  may not comprise a display and may derive all information from inputs from remote sensors and remote configuration tools. In some embodiments, the system controller  106  may comprise and/or be coupled to a temperature sensor and may further be configured to control heating and/or cooling of zones associated with the HVAC system  100 . In some embodiments, the system controller  106  may be configured as a thermostat for controlling supply of conditioned air to one or more zones associated with the HVAC system  100 . 
     In some embodiments, the system controller  106  may also selectively communicate with an indoor controller  124  of the indoor unit  102 , with an outdoor controller  126  of the outdoor unit  104 , and/or with other components of the HVAC system  100 . In some embodiments, the system controller  106  may be configured for selective bidirectional communication over a communication bus  128 . In some embodiments, portions of the communication bus  128  may comprise a three-wire connection suitable for communicating messages between the system controller  106  and one or more of the HVAC system  100  components configured for interfacing with the communication bus  128 . Still further, the system controller  106  may be configured to selectively communicate with HVAC system  100  components and/or any other device  130  via a communication network  132 . In some embodiments, the communication network  132  may comprise a telephone network, and the other device  130  may comprise a telephone. In some embodiments, the communication network  132  may comprise the Internet, and the other device  130  may comprise a smartphone and/or other Internet-enabled mobile telecommunication device. In other embodiments, the communication network  132  may also comprise a remote server. 
     The indoor controller  124  may be carried by the indoor unit  102  and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller  106 , the outdoor controller  126 , and/or any other device  130  via the communication bus  128  and/or any other suitable medium of communication. In some embodiments, the indoor controller  124  may be configured to receive information related to a speed of the indoor fan  110 , transmit a control output to an electric heat relay, transmit information regarding an indoor fan  110  volumetric flow-rate, communicate with and/or otherwise affect control over an air cleaner, and communicate with an indoor expansion device controller. In some embodiments, the indoor controller  124  may be configured to communicate with an indoor fan controller and/or otherwise affect control over operation of the indoor fan  110 . 
     The outdoor controller  126  may be carried by the outdoor unit  104  and may be configured to receive information inputs, transmit information outputs, and otherwise communicate with the system controller  106 , the indoor controller  124 , and/or any other device via the communication bus  128  and/or any other suitable medium of communication. In some embodiments, the outdoor controller  126  may be configured to receive information related to an ambient temperature associated with the outdoor unit  104 , information related to a temperature of the outdoor heat exchanger  114 , and/or information related to refrigerant temperatures and/or pressures of refrigerant entering, exiting, and/or within the outdoor heat exchanger  114  and/or the compressor  116 . In some embodiments, the outdoor controller  126  may be configured to transmit information related to monitoring, communicating with, and/or otherwise affecting control over the outdoor fan  118 , a compressor sump heater, a solenoid of the reversing valve, a relay associated with adjusting and/or monitoring a refrigerant charge of the HVAC system  100 , a position of the indoor metering device  112 , and/or a position of the outdoor metering device  120 . The outdoor controller  126  may further be configured to communicate with a compressor drive controller that is configured to electrically power and/or control the compressor  116 . 
     In operation, the HVAC system  100  may be used in a cooling mode in which heat is absorbed by refrigerant at the indoor heat exchanger  108  and heat is rejected from the refrigerant at the outdoor heat exchanger  114 . In the cooling mode, a cooled and pressurized refrigerant may be received at the expansion device  112  through line  117 . The refrigerant received at the expansion device  112  from the outdoor heat exchanger  114  may comprise a refrigerant that is primarily or completely in the liquid refrigerant. The expansion device  112  may reduce the pressure of the refrigerant as measured from upstream of the expansion device  112  (e.g., in line  117 ) to downstream of the expansion device  112  (e.g., in line  121 ). The pressure differential across the expansion device  112  may allow the refrigerant downstream of the expansion device  112  to expand and/or at least partially convert to a two-phase (gas/liquid) mixture. 
     In an embodiment, the refrigerant received at the expansion device  112  from the outdoor heat exchanger  114  may be expanded in an isentropic process in the expansion device  112 . In some embodiments, the expansion device  112  may comprise a pressure recovery section. For example, the expansion device  112  may comprise a flow section upstream of an expansion section. The diameter of the flow section and the expansion section may be substantially the same at the intersection of the two sections, thereby providing a relatively smooth transition without any shoulder between the sections. The expansion section may then expand in diameter from an upstream end to a downstream end. The expansion in the diameter may be relatively smooth so that the refrigerant can expand along the length of the expansion section with a reduced amount of turbulence relative to an expansion device comprising a shoulder or sharp edge. 
     When the expansion device  112  comprises a pressure recovery section, the refrigerant may enter the expansion device  112  through an upstream end. The refrigerant may be in the liquid phase, though a minor portion of the refrigerant may be in a vapor phase if the outdoor heat exchanger  114  does not entirely condense the refrigerant. The refrigerant may flow through a flow section, which may be sized to result in a desired pressure drop. The pressure within the refrigerant may drop within the flow section, and a portion of the refrigerant may flash from a liquid state to a vapor state. The properties of the flow section and/or the resulting flashing of the refrigerant may result in a choked flow condition of the refrigerant within the flow section. As the refrigerant passes out of the flow section, the refrigerant may gradually expand into the expansion section due to the gradually increasing diameter of the expansion section and/or the smooth transition between the flow section and the expansion section. As a result, the refrigerant stream leaving the expansion device  112  may have an decreased thermodynamic quality, a lower enthalpy, and an increased ability to absorb heat in the indoor heat exchanger relative to a refrigerant passing through an expansion device having a sharp edge such as an isenthalpic expansion device. In an embodiment, the refrigerant leaving the expansion device  112  may comprise a thermodynamic quality that is less than about 0.2, or less than about 0.15, and in some embodiments, the thermodynamic quality may be at least about 0.05 or at least about 0.1. In some embodiments, the refrigerant may pass through one or more additional expansion device or flow metering devices that may comprise a portion of the expansion device  112  and/or are associated with the expansion device  112 . 
     The two phase refrigerant may pass from the expansion device  112  and enter the indoor heat exchanger  108  through line  121 . As the refrigerant passes through the indoor heat exchanger  108 , the indoor fan  110  may be operated to move air into contact with the indoor heat exchanger  108 , thereby transferring heat to the refrigerant from the air surrounding the indoor heat exchanger  108 . The liquid portion of the two phase mixture may evaporate and the temperature of the refrigerant may rise in the indoor heat exchanger  108 . 
     The refrigerant may pass out of the indoor heat exchanger  108  through line  119  and enter the compressor  116 . The compressor  116  may operate to compress the refrigerant and pump the resulting relatively high temperature and high pressure compressed refrigerant from the compressor  116  to the outdoor heat exchanger  114  through line  115 . As the refrigerant is passed through the outdoor heat exchanger  114 , the outdoor fan  118  may be operated to move a fluid (e.g., outdoor air) into contact with the outdoor heat exchanger  114 , thereby transferring heat from the refrigerant to the air surrounding the outdoor heat exchanger  114 . The refrigerant entering the outdoor heat exchanger  114  may primarily comprise a vapor and the refrigerant passing out of the outdoor heat exchanger  114  may primarily comprise liquid phase refrigerant. The refrigerant may flow from the outdoor heat exchanger  114  to the expansion device  112  to repeat the process. 
     While the HVAC system described above refers to a system that can generally be used in a cooling mode, the use of the system comprising an expansion valve having a pressure recovery portion (e.g., an isentropic expansion valve) can also be used in a reversible HVAC system  400  as shown in the embodiment depicted in  FIG. 4 . The simplified diagram of the HVAC system  400  is similar in many respect to the HVAC described with respect to  FIG. 1 , and accordingly, similar components will not be described for the sake or brevity. In an embodiment, the HVAC system  400  may comprise a so-called heat pump system that may be selectively operated to implement one or more substantially closed thermodynamic refrigeration cycles to provide a cooling functionality and/or a heating functionality. The HVAC system  400  may generally comprise an indoor unit  402 , an outdoor unit  404 , and a controller  106 . The system controller  106  may generally comprise those component described above with respect to the controllers. 
     The indoor unit  402  generally comprises an indoor heat exchanger  108 , an indoor fan  110 , and an indoor metering device  412 . The indoor heat exchanger  108  and the indoor fan  110  may be the same or similar to the elements described herein. The indoor metering device  412  may be similar to the expansion device  112  described herein. For example, the indoor metering device  412  may comprise an expansion device comprising a pressure recovery section. For example, the indoor metering device  412  may comprise the expansion device  300  as described with respect to  FIG. 3 . The indoor metering device  412  may also comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the indoor metering device  412  is such that the indoor metering device  412  is not intended to meter or otherwise substantially restrict flow of the refrigerant through the indoor metering device  412 . 
     The outdoor unit  404  generally comprises an outdoor heat exchanger  114 , a compressor  116 , an outdoor fan  118 , an outdoor metering device  420 , and a reversing valve  422 . The outdoor heat exchanger  114 , the compressor  116 , and the outdoor fan  118  may be the same as or similar to any of the corresponding components described herein. The outdoor metering device  420  may be similar to the expansion device  112  described with respect to  FIGS. 1 and 3 . For example, the outdoor metering device  420  may comprise an expansion device comprising a pressure recovery section. For example, the outdoor metering device  420  may comprise the expansion device  300  as described with respect to  FIG. 3 . The outdoor metering device  420  may also comprise and/or be associated with a refrigerant check valve and/or refrigerant bypass for use when a direction of refrigerant flow through the outdoor metering device  420  is such that the outdoor metering device  420  is not intended to meter or otherwise substantially restrict flow of the refrigerant through the outdoor metering device  420 . 
     The reversing valve  422  may be configured to selectively control or alter a flow path of refrigerant in the HVAC system  400  as described in greater detail below. In an embodiment, the reversing valve  422  may comprise so-called four-way reversing valve. The reversing valve  422  may comprise an electrical solenoid or other device configured to selectively move a component of the reversing valve  422  between operational positions. 
     As schematically illustrated in  FIG. 4 , the HVAC system  400  is shown configured for operating in a so-called cooling mode in which heat is absorbed by refrigerant at the indoor heat exchanger  108  and heat is rejected from the refrigerant at the outdoor heat exchanger  114 . In some embodiments, the compressor  116  may be operated to compress refrigerant and pump the relatively high temperature and high pressure compressed refrigerant from the compressor  116  to the outdoor heat exchanger  114  through the reversing valve  422  and to the outdoor heat exchanger  114 . As the refrigerant is passed through the outdoor heat exchanger  114 , the outdoor fan  118  may be operated to move air into contact with the outdoor heat exchanger  114 , thereby transferring heat from the refrigerant to the air surrounding the outdoor heat exchanger  114 . The refrigerant leaving the outdoor heat exchanger  114  may primarily comprise liquid phase refrigerant. The refrigerant may flow from the outdoor heat exchanger  114  to the indoor metering device  412  through and/or around the outdoor metering device  420  which does not substantially impede flow of the refrigerant in the cooling mode. The indoor metering device  412  may meter passage of the refrigerant through the indoor metering device  412  so that the refrigerant downstream of the indoor metering device  412  is at a lower pressure than the refrigerant upstream of the indoor metering device  412 . In an embodiment, the indoor metering device  412  comprises an expansion device having a pressure recovery section. For example, the indoor metering device  412  may comprise a isentropic expansion device. The pressure differential across the indoor metering device  412  may allow the refrigerant downstream of the indoor metering device  412  to expand and/or at least partially convert to a two-phase (vapor and gas) mixture. 
     The two phase refrigerant may enter the indoor heat exchanger  108 . As the refrigerant is passed through the indoor heat exchanger  108 , the indoor fan  110  may be operated to move air into contact with the indoor heat exchanger  108 , thereby transferring heat to the refrigerant from the air surrounding the indoor heat exchanger  108 , and causing evaporation of the liquid portion of the two phase mixture. The refrigerant leaving the indoor heat exchanger  108  may thereafter re-enter the compressor  116  after passing through the reversing valve  422 . 
     The HVAC system  400  may also be operated in the so-called heating mode. In this configuration, the reversing valve  422  may be controlled to alter the flow path of the refrigerant, the indoor metering device  412  may be disabled and/or bypassed, and the outdoor metering device  420  may be enabled. In the heating mode, refrigerant may flow from the compressor  116  to the indoor heat exchanger  108  through the reversing valve  422 , the refrigerant may be substantially unaffected by the indoor metering device  412 , the refrigerant may experience a pressure differential across the outdoor metering device  420 . In an embodiment, the outdoor metering device  420  comprises an expansion device having a pressure recovery section. For example, the outdoor metering device  420  may comprise a isentropic expansion device. After passing through the outdoor metering device  420  and having the pressure of the refrigerant reduced, the refrigerant may pass through the outdoor heat exchanger  114 , and the refrigerant may reenter the compressor  116  after passing through the reversing valve  422 . Most generally, operation of the HVAC system  400  in the heating mode reverses the roles of the indoor heat exchanger  108  and the outdoor heat exchanger  114  as compared to their operation in the cooling mode. In the heating mode, heat may be released from the refrigerant in the indoor heat exchanger  108  and absorbed by the outdoor heat exchanger  114 . 
     At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R l , and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R l +k*(R u −R l ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention.