Patent Publication Number: US-11041679-B2

Title: Energy recovery wheel assembly for an HVAC system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 62/794,933, entitled “ENERGY RECOVERY WHEEL ASSEMBLY FOR AN HVAC SYSTEM,” filed Jan. 21, 2019, which is herein incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     This disclosure relates generally to heating, ventilation, and/or air conditioning (HVAC) systems. Specifically, the present disclosure relates to an energy recovery wheel for HVAC units. 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present techniques, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light and not as an admission of any kind. 
     A heating, ventilation, and/or air conditioning (HVAC) system may be used to thermally regulate an environment, such as a building, home, or other structure. The HVAC system generally includes a vapor compression system that includes heat exchangers, such as a condenser and an evaporator, which transfer thermal energy between the HVAC system and the environment. In many cases, the HVAC system may direct a continuous flow of fresh outdoor air into a building to provide ventilation and improved air quality within the building, while stale return air of the building is discharged into an ambient environment, such as the atmosphere. The HVAC system may include an energy recovery wheel that is configured to recover energy from the return air prior to discharging the return air into the atmosphere, thus improving an efficiency of the HVAC system. 
     For example, the energy recovery wheel may be situated within and configured to rotate relative to a flow path of the return air and a flow path of the outdoor air. The energy recovery wheel typically includes heat transfer elements that are configured to transition between the return air flow path and the outdoor air flow path of the HVAC system as the energy recovery wheel rotates. The heat transfer elements are generally porous and enable air flowing therethrough to absorb thermal energy from or release thermal energy to the heat transfer elements. In cases when the HVAC system is operating in a cooling mode, the return air discharging from the building may be cooler than the outdoor air entering the HVAC system. Accordingly, when the energy recovery wheel rotates, the heat transfer elements may cyclically absorb thermal energy from the warmer outdoor air and subsequently release the absorbed thermal energy to the cooler return air passing through the return air flow path. As a result, the energy recovery wheel may pre-cool the outdoor air before the outdoor air flows through the rest of the HVAC system. In some cases, it is desirable to temporarily suspend operation of the energy recovery wheel, such as when a temperature of the outdoor air entering the HVAC system is substantially equal to a temperature of the return air discharging from the building. Unfortunately, the deactivated energy recovery wheel may hinder air flow along the outdoor air flow path and the return air flow path and may thus reduce an overall operational efficiency of the HVAC system. 
     SUMMARY 
     The present disclosure relates to an energy recovery wheel for a heating, ventilation, and/or air conditioning (HVAC) system. The energy recovery wheel includes a frame that is positioned within a passage of the HVAC system. The frame is configured to rotate about an axis of the passage relative to the HVAC system and includes an opening that is configured to transmit an air flow. The energy recovery wheel also includes a heat transfer element coupled to the frame and positioned within the opening, where the heat transfer element is permeable and configured to transition between a closed orientation to occlude the opening and direct the air flow across the heat transfer element and an open orientation to substantially unblock the opening and mitigate interaction between the air flow and the heat transfer element. 
     The present disclosure also relates to an energy recovery wheel for a heating, ventilation, and/or air conditioning (HVAC) system, where the energy recovery wheel includes an inner frame disposed within an air flow path of the HVAC system. The inner frame is positioned within the air flow path and is rotatable with respect to the HVAC system, and a plurality of dividers extend from the inner frame. The energy recovery wheel further includes a plurality of matrix segments configured to transfer heat and moisture between air flows, where each matrix segment of the plurality of matrix segments is mounted between a pair of dividers of the plurality of dividers, such that each matrix segment is configured to pivot relative to the inner frame. 
     The present disclosure also relates to an energy recovery wheel for a heating, ventilation, and/or air conditioning (HVAC) system, where the energy recovery wheel includes a frame disposed within a passage of the HVAC system, and the frame is rotatable about an axis of the passage relative to the HVAC system. The frame includes a central hub, an outer ring disposed about the central hub, and a plurality of spokes extending between the central hub and the outer ring to form an opening therebetween. The energy recovery wheel further includes a matrix segment pivotably coupled to the frame and mounted within the opening, where the matrix segment is permeable and configured rotate relative to the frame between a closed configuration to occlude the opening and an open orientation to substantially unblock the opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a perspective view of an embodiment of a building that may utilize a heating, ventilation, and/or air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure; 
         FIG. 2  is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure; 
         FIG. 3  is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure; 
         FIG. 4  is a schematic diagram of an embodiment of a vapor compression system that may be used in an HVAC system, in accordance with an aspect of the present disclosure; 
         FIG. 5  is a perspective view of an embodiment of an HVAC enclosure having an energy recovery wheel assembly, in accordance with an aspect of the present disclosure; 
         FIG. 6  is an exploded perspective view of an embodiment of an energy recovery wheel assembly, in accordance with an aspect of the present disclosure; 
         FIG. 7  is a perspective view of an embodiment of an energy recovery wheel assembly having an energy recovery wheel in a closed configuration, in accordance with an aspect of the present disclosure; 
         FIG. 8  is a front view of an embodiment of an energy recovery wheel assembly, in accordance with an aspect of the present disclosure; 
         FIG. 9  is a perspective view of an embodiment of a pin of an energy recovery wheel, in accordance with an aspect of the present disclosure; 
         FIG. 10  is a perspective view of an embodiment of a guide ring of an energy recovery wheel, in accordance with an aspect of the present disclosure; 
         FIG. 11  is an expanded perspective view of an embodiment of an energy recovery wheel assembly, in accordance with an aspect of the present disclosure; 
         FIG. 12  is a perspective view of an embodiment of an energy recovery wheel assembly having an energy recovery wheel in an open configuration, in accordance with an aspect of the present disclosure; 
         FIG. 13  is a front view of an embodiment of an energy recovery wheel assembly having an energy recovery wheel in an open configuration, in accordance with an aspect of the present disclosure; and 
         FIG. 14  is a perspective view of an embodiment of an HVAC enclosure having an energy recovery wheel in an open configuration, in accordance with an aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments of the present disclosure will be described below. These described embodiments are only examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     As briefly discussed above, a heating, ventilation, and/or air conditioning (HVAC) system may be used to regulate certain climate parameters within a space of a building, home, or other suitable structure. In particular, the HVAC system may be used to exhaust stale return air from a building while simultaneously directing fresh and conditioned outdoor air into the building. Accordingly, a continuous supply of fresh, conditioned air may be circulated through an interior of the building to improve or maintain an air quality within the building. In some cases, the HVAC system may direct the return air discharging from the building across an energy recovery wheel, which may be configured to recover thermal energy from the return air before the return air is released into an ambient environment, such as the atmosphere. 
     For example, in some embodiments, the HVAC system may include an enclosure having a partition that extends along an interior of the enclosure to divide the enclosure into an outdoor air flow path and a return air flow path. Respective fans or blowers may be used to direct the fresh outdoor air along the outdoor air flow path and direct the stale return air along the return air flow path. The partition may include an opening formed therein, which enables the energy recovery wheel to extend through the partition and span across the outdoor air flow path and the return air flow path. Accordingly, the outdoor air and the return air may flow across respective portions of the energy recovery wheel. The energy recovery wheel may include a plurality of heat transfer elements that are configured absorb and/or release thermal energy and/or moisture from the outdoor air and return air flows. The energy recovery wheel may be configured to rotate relative to the enclosure, such that the heat transfer elements may cyclically rotate into and out of the outdoor air flow path and the return air flow path. In this manner, the energy recovery wheel may transfer thermal energy and/or moisture from the outdoor air flowing along the outdoor air flow path to the return air flowing along the return air flow path, and vice versa. 
     As an example, in embodiments where the HVAC system is operating in a cooling mode, a temperature of the outdoor air entering the enclosure may be warmer than a temperature of the return air discharging from the building. The relatively cool return air may absorb thermal energy from the heat transfer elements of the energy recovery wheel positioned within the return air flow path, thereby decreasing a temperature of these heat transfer elements. Due to the rotational motion of the energy recovery wheel within the HVAC system, the cooled heat transfer elements may gradually rotate out of the return air flow path and into the outdoor air flow path. Accordingly, upon transitioning into the outdoor air flow path, the cooled heat transfer elements may absorb thermal energy from the warmer outdoor air flowing thereacross. As a result, the energy recovery wheel may be used to pre-cool or pre-condition the outdoor air before the outdoor air reaches other heat exchange components of the HVAC system, such as an evaporator assembly. 
     In certain cases, the outdoor air may also include a relatively high humidity value, as compared to a humidity value of the return air. In such cases, the energy recovery wheel may be used to dehumidify the outdoor air entering the HVAC system by transferring moisture from the outdoor air to the return air, in accordance with the techniques discussed above. That is, the heat transfer elements of the energy recovery wheel may be configured to absorb and release moisture, in addition to the absorption and release of thermal energy. 
     In some cases, it may be desirable to temporarily deactivate the energy recovery wheel, such as when a temperature value of the outdoor air entering the HVAC system is substantially equal to a temperature value of the return air discharging from the building. Indeed, in such cases, the energy recovery wheel may be ineffective to transfer thermal energy between the outdoor air flow and the return air flow of the HVAC system. Unfortunately, the inactive energy recovery wheel may restrict air flow along the outdoor air flow path and the return air flow path, which may increase a load on the fans or blowers configured to direct the outdoor air and the return air along the outdoor air flow path and the return air flow path, respectively. As a result, the inactive energy recovery wheel may increase a power consumption of these fans, and thus, reduce an overall operational efficiency of the HVAC system. 
     It is now recognized that reducing fluid restrictions generated by the inactive energy recovery wheel along the outdoor air flow path and the return air flow path of the HVAC system may decrease a load on the fan(s) or blower(s) that are configured to direct air flows along the outdoor air flow path and return air flow path. Accordingly, embodiments of the present disclosure are directed toward an energy recovery wheel that is transitionable between an operational configuration, in which substantially all air flowing along the outdoor air flow path and the return air flow path is directed across heat transfer elements of the energy recovery wheel, and a non-operational configuration, in which substantially all air flowing along the outdoor air flow path and return air flow path may bypass the heat transfer elements of the energy recovery wheel. By enabling air to bypass the heat transfer elements during non-operational periods of the energy recovery wheel, the fluid restrictions previously created by the inactive energy recovery wheel may be reduced or eliminated during non-operational periods of the energy recovery wheel. In this manner, a load on the fans or blowers associated with the outdoor and return air flow paths may be reduced, which may enhance an overall efficiency of the HVAC system. 
     For example, the energy recovery wheel may include a frame that is configured to rotate relative to an enclosure of the HVAC system. The frame may include a plurality of openings formed therein, which are each configured to receive a corresponding heat transfer element of the energy recovery wheel. Each of the heat transfer elements may be rotatably mounted to the frame via one or more pins, which enable the heat transfer elements to rotate relative to the frame. In particular, the heat transfer elements may be transitionable between a closed configuration, where the heat transfer elements occlude the openings within the frame, and an open configuration, where the heat transfer elements substantially unblock the openings of the frame. Accordingly, when the heat transfer elements transition to the closed configuration, the fans of the HVAC system may force substantially all air flowing along the outdoor air flow path and the return air flow path across the heat transfer elements of the energy recovery wheel. Conversely, when the heat transfer elements are positioned in the open configuration, air flowing along the outdoor air flow path and the return air flow path may bypass the heat transfer elements and may flow directly through the openings within the frame. These and other features will be described below with reference to the drawings. 
     Turning now to the drawings,  FIG. 1  illustrates an embodiment of a heating, ventilation, and/or air conditioning (HVAC) system for environmental management that may employ one or more HVAC units. As used herein, an HVAC system includes any number of components configured to enable regulation of parameters related to climate characteristics, such as temperature, humidity, air flow, pressure, air quality, and so forth. For example, an “HVAC system” as used herein is defined as conventionally understood and as further described herein. Components or parts of an “HVAC system” may include, but are not limited to, all, some of, or individual parts such as a heat exchanger, a heater, an air flow control device, such as a fan, a sensor configured to detect a climate characteristic or operating parameter, a filter, a control device configured to regulate operation of an HVAC system component, a component configured to enable regulation of climate characteristics, or a combination thereof. An “HVAC system” is a system configured to provide such functions as heating, cooling, ventilation, dehumidification, pressurization, refrigeration, filtration, or any combination thereof. The embodiments described herein may be utilized in a variety of applications to control climate characteristics, such as residential, commercial, industrial, transportation, or other applications where climate control is desired. 
     In the illustrated embodiment, a building  10  is air conditioned by a system that includes an HVAC unit  12 . The building  10  may be a commercial structure or a residential structure. As shown, the HVAC unit  12  is disposed on the roof of the building  10 ; however, the HVAC unit  12  may be located in other equipment rooms or areas adjacent the building  10 . The HVAC unit  12  may be a single package unit containing other equipment, such as a blower, integrated air handler, and/or auxiliary heating unit. In other embodiments, the HVAC unit  12  may be part of a split HVAC system, such as the system shown in  FIG. 3 , which includes an outdoor HVAC unit  58  and an indoor HVAC unit  56 . 
     The HVAC unit  12  is an air cooled device that implements a refrigeration cycle to provide conditioned air to the building  10 . Specifically, the HVAC unit  12  may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit  12  is a rooftop unit (RTU) that conditions a supply air stream, such as environmental air and/or a return air flow from the building  10 . After the HVAC unit  12  conditions the air, the air is supplied to the building  10  via ductwork  14  extending throughout the building  10  from the HVAC unit  12 . For example, the ductwork  14  may extend to various individual floors or other sections of the building  10 . In certain embodiments, the HVAC unit  12  may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes. In other embodiments, the HVAC unit  12  may include one or more refrigeration circuits for cooling an air stream and a furnace for heating the air stream. 
     A control device  16 , one type of which may be a thermostat, may be used to designate the temperature of the conditioned air. The control device  16  also may be used to control the flow of air through the ductwork  14 . For example, the control device  16  may be used to regulate operation of one or more components of the HVAC unit  12  or other components, such as dampers and fans, within the building  10  that may control flow of air through and/or from the ductwork  14 . In some embodiments, other devices may be included in the system, such as pressure and/or temperature transducers or switches that sense the temperatures and pressures of the supply air, return air, and so forth. Moreover, the control device  16  may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building  10 . 
       FIG. 2  is a perspective view of an embodiment of the HVAC unit  12 . In the illustrated embodiment, the HVAC unit  12  is a single package unit that may include one or more independent refrigeration circuits and components that are tested, charged, wired, piped, and ready for installation. The HVAC unit  12  may provide a variety of heating and/or cooling functions, such as cooling only, heating only, cooling with electric heat, cooling with dehumidification, cooling with gas heat, or cooling with a heat pump. As described above, the HVAC unit  12  may directly cool and/or heat an air stream provided to the building  10  to condition a space in the building  10 . 
     As shown in the illustrated embodiment of  FIG. 2 , a cabinet  24  encloses the HVAC unit  12  and provides structural support and protection to the internal components from environmental and other contaminants. In some embodiments, the cabinet  24  may be constructed of galvanized steel and insulated with aluminum foil faced insulation. Rails  26  may be joined to the bottom perimeter of the cabinet  24  and provide a foundation for the HVAC unit  12 . In certain embodiments, the rails  26  may provide access for a forklift and/or overhead rigging to facilitate installation and/or removal of the HVAC unit  12 . In some embodiments, the rails  26  may fit into “curbs” on the roof to enable the HVAC unit  12  to provide air to the ductwork  14  from the bottom of the HVAC unit  12  while blocking elements such as rain from leaking into the building  10 . 
     The HVAC unit  12  includes heat exchangers  28  and  30  in fluid communication with one or more refrigeration circuits. Tubes within the heat exchangers  28  and  30  may circulate refrigerant, such as R- 410 A, through the heat exchangers  28  and  30 . The tubes may be of various types, such as multichannel tubes, conventional copper or aluminum tubing, and so forth. Together, the heat exchangers  28  and  30  may implement a thermal cycle in which the refrigerant undergoes phase changes and/or temperature changes as it flows through the heat exchangers  28  and  30  to produce heated and/or cooled air. For example, the heat exchanger  28  may function as a condenser where heat is released from the refrigerant to ambient air, and the heat exchanger  30  may function as an evaporator where the refrigerant absorbs heat to cool an air stream. In other embodiments, the HVAC unit  12  may operate in a heat pump mode where the roles of the heat exchangers  28  and  30  may be reversed. That is, the heat exchanger  28  may function as an evaporator and the heat exchanger  30  may function as a condenser. In further embodiments, the HVAC unit  12  may include a furnace for heating the air stream that is supplied to the building  10 . While the illustrated embodiment of  FIG. 2  shows the HVAC unit  12  having two of the heat exchangers  28  and  30 , in other embodiments, the HVAC unit  12  may include one heat exchanger or more than two heat exchangers. 
     The heat exchanger  30  is located within a compartment  31  that separates the heat exchanger  30  from the heat exchanger  28 . Fans  32  draw air from the environment through the heat exchanger  28 . Air may be heated and/or cooled as the air flows through the heat exchanger  28  before being released back to the environment surrounding the HVAC unit  12 . A blower assembly  34 , powered by a motor  36 , draws air through the heat exchanger  30  to heat or cool the air. The heated or cooled air may be directed to the building  10  by the ductwork  14 , which may be connected to the HVAC unit  12 . Before flowing through the heat exchanger  30 , the conditioned air flows through one or more filters  38  that may remove particulates and contaminants from the air. In certain embodiments, the filters  38  may be disposed on the air intake side of the heat exchanger  30  to prevent contaminants from contacting the heat exchanger  30 . 
     The HVAC unit  12  also may include other equipment for implementing the thermal cycle. Compressors  42  increase the pressure and temperature of the refrigerant before the refrigerant enters the heat exchanger  28 . The compressors  42  may be any suitable type of compressors, such as scroll compressors, rotary compressors, screw compressors, or reciprocating compressors. In some embodiments, the compressors  42  may include a pair of hermetic direct drive compressors arranged in a dual stage configuration  44 . However, in other embodiments, any number of the compressors  42  may be provided to achieve various stages of heating and/or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit  12 , such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other things. 
     The HVAC unit  12  may receive power through a terminal block  46 . For example, a high voltage power source may be connected to the terminal block  46  to power the equipment. The operation of the HVAC unit  12  may be governed or regulated by a control board  48 . The control board  48  may include control circuitry connected to a thermostat, sensors, and alarms. One or more of these components may be referred to herein separately or collectively as the control device  16 . The control circuitry may be configured to control operation of the equipment, provide alarms, and monitor safety switches. Wiring  49  may connect the control board  48  and the terminal block  46  to the equipment of the HVAC unit  12 . 
       FIG. 3  illustrates a residential heating and cooling system  50 , also in accordance with present techniques. The residential heating and cooling system  50  may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system  50  is a split HVAC system. In general, a residence  52  conditioned by a split HVAC system may include refrigerant conduits  54  that operatively couple the indoor unit  56  to the outdoor unit  58 . The indoor unit  56  may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit  58  is typically situated adjacent to a side of residence  52  and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The refrigerant conduits  54  transfer refrigerant between the indoor unit  56  and the outdoor unit  58 , typically transferring primarily liquid refrigerant in one direction and primarily vaporized refrigerant in an opposite direction. 
     When the system shown in  FIG. 3  is operating as an air conditioner, a heat exchanger  60  in the outdoor unit  58  serves as a condenser for re-condensing vaporized refrigerant flowing from the indoor unit  56  to the outdoor unit  58  via one of the refrigerant conduits  54 . In these applications, a heat exchanger  62  of the indoor unit  56  functions as an evaporator. Specifically, the heat exchanger  62  receives liquid refrigerant, which may be expanded by an expansion device, and evaporates the refrigerant before returning it to the outdoor unit  58 . 
     The outdoor unit  58  draws environmental air through the heat exchanger  60  using a fan  64  and expels the air above the outdoor unit  58 . When operating as an air conditioner, the air is heated by the heat exchanger  60  within the outdoor unit  58  and exits the unit at a temperature higher than it entered. The indoor unit  56  includes a blower or fan  66  that directs air through or across the indoor heat exchanger  62 , where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork  68  that directs the air to the residence  52 . The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence  52  is higher than the set point on the thermostat, or a set point plus a small amount, the residential heating and cooling system  50  may become operative to refrigerate additional air for circulation through the residence  52 . When the temperature reaches the set point, or a set point minus a small amount, the residential heating and cooling system  50  may stop the refrigeration cycle temporarily. 
     The residential heating and cooling system  50  may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers  60  and  62  are reversed. That is, the heat exchanger  60  of the outdoor unit  58  will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor unit  58  as the air passes over outdoor the heat exchanger  60 . The indoor heat exchanger  62  will receive a stream of air blown over it and will heat the air by condensing the refrigerant. 
     In some embodiments, the indoor unit  56  may include a furnace system  70 . For example, the indoor unit  56  may include the furnace system  70  when the residential heating and cooling system  50  is not configured to operate as a heat pump. The furnace system  70  may include a burner assembly and heat exchanger, among other components, inside the indoor unit  56 . Fuel is provided to the burner assembly of the furnace system  70  where it is mixed with air and combusted to form combustion products. The combustion products may pass through tubes or piping in a heat exchanger, separate from heat exchanger  62 , such that air directed by the blower  66  passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system  70  to the ductwork  68  for heating the residence  52 . 
       FIG. 4  is an embodiment of a vapor compression system  72  that can be used in any of the systems described above. The vapor compression system  72  may circulate a refrigerant through a circuit starting with a compressor  74 . The circuit may also include a condenser  76 , an expansion valve(s) or device(s)  78 , and an evaporator  80 . The vapor compression system  72  may further include a control panel  82  that has an analog to digital (A/D) converter  84 , a microprocessor  86 , a non-volatile memory  88 , and/or an interface board  90 . The control panel  82  and its components may function to regulate operation of the vapor compression system  72  based on feedback from an operator, from sensors of the vapor compression system  72  that detect operating conditions, and so forth. 
     In some embodiments, the vapor compression system  72  may use one or more of a variable speed drive (VSDs)  92 , a motor  94 , the compressor  74 , the condenser  76 , the expansion valve or device  78 , and/or the evaporator  80 . The motor  94  may drive the compressor  74  and may be powered by the variable speed drive (VSD)  92 . The VSD  92  receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor  94 . In other embodiments, the motor  94  may be powered directly from an AC or direct current (DC) power source. The motor  94  may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor. 
     The compressor  74  compresses a refrigerant vapor and delivers the vapor to the condenser  76  through a discharge passage. In some embodiments, the compressor  74  may be a centrifugal compressor. The refrigerant vapor delivered by the compressor  74  to the condenser  76  may transfer heat to a fluid passing across the condenser  76 , such as ambient or environmental air  96 . The refrigerant vapor may condense to a refrigerant liquid in the condenser  76  as a result of thermal heat transfer with the environmental air  96 . The liquid refrigerant from the condenser  76  may flow through the expansion device  78  to the evaporator  80 . 
     The liquid refrigerant delivered to the evaporator  80  may absorb heat from another air stream, such as a supply air stream  98  provided to the building  10  or the residence  52 . For example, the supply air stream  98  may include ambient or environmental air, return air from a building, or a combination of the two. The liquid refrigerant in the evaporator  80  may undergo a phase change from the liquid refrigerant to a refrigerant vapor. In this manner, the evaporator  80  may reduce the temperature of the supply air stream  98  via thermal heat transfer with the refrigerant. Thereafter, the vapor refrigerant exits the evaporator  80  and returns to the compressor  74  by a suction line to complete the cycle. 
     In some embodiments, the vapor compression system  72  may further include a reheat coil in addition to the evaporator  80 . For example, the reheat coil may be positioned downstream of the evaporator relative to the supply air stream  98  and may reheat the supply air stream  98  when the supply air stream  98  is overcooled to remove humidity from the supply air stream  98  before the supply air stream  98  is directed to the building  10  or the residence  52 . 
     It should be appreciated that any of the features described herein may be incorporated with the HVAC unit  12 , the residential heating and cooling system  50 , or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications. 
     As noted above, certain HVAC systems may include an energy recovery wheel that is configured to transfer thermal energy and/or moisture between two air flows, such as a flow of fresh outdoor air entering the HVAC system and a flow of stale return air discharging from the HVAC system. The energy recovery wheel may be disposed upstream of certain heat exchange components of the HVAC system, such as an evaporator or a furnace, and may be used to pre-condition the outdoor air before the outdoor air flows across these components. Accordingly, the energy recovery wheel may improve an operational efficiently of the HVAC system by recovering energy from return air that is typically exhausted from a cooling load, such as a building or other structure, directly into an ambient environment. 
     In certain cases, operation of the energy recovery wheel may be temporarily deactivated to suspend the transfer of thermal energy and/or moisture between the outdoor air and the return air flows. In conventional HVAC systems, the outdoor air flow and the return air flow are typically forced across heat transfer elements of the energy recovery wheel even when the energy recovery wheel is inactivate. Unfortunately, forcing the outdoor air and the return air across the inactive energy recovery wheel may increase a load on fan(s) or blower(s) configured to direct the outdoor air and return air through the HVAC system. As a result, the inactive energy recovery wheel may reduce an overall operational efficiency of the HVAC system. Therefore, embodiments of the present disclosure are directed toward an energy recovery wheel assembly having an energy recovery wheel that is transitionable between an operational configuration, where the outdoor air and return air flows are directed across heat transfer elements of the energy recovery wheel, and a non-operational configuration, where the outdoor air and the return air flows may bypass the heat transfer elements of the energy recovery wheel. In this manner, the energy recovery wheel assembly may allow substantially unrestricted air flow across the energy recovery wheel during non-operational periods of the energy recovery wheel. 
     With the foregoing in mind,  FIG. 5  is a perspective view of an embodiment of an energy recovery wheel (ERW) assembly  100  that is positioned within an enclosure  102  of a heating, ventilating, and/or air conditioning (HVAC) system  104 . It should be noted that the HVAC system  104  may include embodiments or components of the HVAC unit  12  shown in  FIG. 2 , embodiments or components of the residential heating and cooling system  50  shown in  FIG. 3 , a rooftop unit (RTU), or any other suitable HVAC system. To facilitate discussion, the ERW assembly  100  and its respective components will be described with reference to a longitudinal axis  106 , a vertical axis  108 , and a lateral axis  110 . 
     As discussed in detail below, the HVAC system  104  may be configured to circulate a flow of conditioned air through a cooling load  112 , such as a conditioned space within a building, residential home, or any other suitable structure. The HVAC system  104  may include a vapor compression system, such as the vapor compression system  72 , which enables the HVAC system  104  to regulate one or more climate parameters within the cooling load  112 . In particular, the HVAC system  104  may be configured to maintain a desired air quality, air humidity, and/or air temperature within the cooling load  112 . 
     As shown in the illustrated embodiment, the enclosure  102  may include a partition  116  that divides an interior of the enclosure  102  into an outdoor air flow path  118  and a return air flow path  120 . The ERW assembly  100  may extend through an opening of the partition  116  to enable an energy recovery wheel  122  of the ERW assembly  100  to span across at least a portion of the outdoor air flow path  118  and the return air flow path  120 . As discussed in detail herein, this configuration may enable the energy recovery wheel  122  to transfer thermal energy and/or moisture between air flows that may respectively traverse the outdoor air flow path  118  and the return air flow path  120 . As used herein, the “energy recovery wheel  122 ” may also refer to the entire ERW assembly  100  in subsequent discussion. 
     For clarity, it should be appreciated that a portion of the energy recovery wheel  122  that is disposed within the outdoor air flow path  118  will be referred to herein as a first portion  128  of the energy recovery wheel  122 , while a portion of the energy recovery wheel  122  that is disposed within the return air flow path  120  will be referred to herein as a second portion  130  of the energy recovery wheel  122 . It is important to note that, because the energy recovery wheel  122  may rotate during operation of the HVAC system  104 , a particular section or segment of the energy recovery wheel  122  may continuously rotate into and out of the outdoor air flow path  118  and the return air flow path  120 . Specifically, the energy recovery wheel  122  may rotate about a central axis  132  of the energy recovery wheel  122 , which may extend generally parallel to the longitudinal axis  106 . Accordingly, as used herein, the first portion  128  of the energy recovery wheel  122  refers to the portion of the energy recovery wheel  122  that is disposed within the outdoor air flow path  118  at a particular instance in time, while the second portion  130  of the energy recovery wheel  122  is refers to the portion of the energy recovery wheel  122  that is disposed within the return air flow path  120  at that same instance in time. In other words, particular sections of the energy recovery wheel  122  that correspond to the first portion  128  and the second portion  130  may be transient as the energy recovery wheel  122  rotates relative to the outdoor air flow path  118  and the return air flow path  120 . 
     The HVAC system  104  may include one or more fans or blowers that are configured to draw a flow of outdoor air  138  into the outdoor air flow path  118  via an outdoor air inlet  140  of the enclosure  102 . The fans may direct the outdoor air  138  along the outdoor air flow path  118  and across the first portion  128  of the energy recovery wheel  122  in a first direction  142  that is generally parallel to the longitudinal axis  106 . As discussed below, the first portion  128  of the energy recovery wheel  122  may transfer thermal energy and/or moisture to the outdoor air  138 , or may absorb thermal energy and/or moisture from the outdoor air  138 , such that the outdoor air  138  discharges from the first portion  128  as supply air  144 . Thereafter, the supply air  144  may flow across one or more heat exchange components (not shown) of the HVAC system  104  to further condition the supply air  144 . Then, the supply air  144  may flow toward the cooling load  112  via an inlet duct, represented by dashed lines  146 , of the HVAC system  104 , which fluidly couples the outdoor air flow path  118  to the cooling load  112 . 
     The return air flow path  120  may receive a flow of return air  148  from the cooling load  112  via a return air duct, represented by dashed lines  149 , of the HVAC system  104 , which fluidly couples the return air flow path  120  to the cooling load  112 . In some embodiments, an exhaust fan or exhaust blower of the HVAC system  104  may facilitate drawing the return air  148  across the second portion  130  of the energy recovery wheel  122  in a second direction  150  that is generally opposite the first direction  142 . The exhaust blower of the HVAC system  104  may force the return air  148  through an exhaust air outlet  152  of the enclosure  102  as exhaust air  154 . 
     As noted above, in embodiments where a relatively large temperature differential exits between the outdoor air  138  and the return air  148 , the energy recovery wheel  122  may be operable to recover thermal energy from the return air  148  before the return air  148  discharges from the HVAC system  104 . Particularly, the energy recovery wheel  122  may include a plurality of heat transfer elements  160  that facilitate the transfer of thermal energy from the outdoor air  138  to the return air  148 , or vice versa. The heat transfer elements  160  may be formed from a permeable matrix material, a porous material, a desiccant material, and/or any other suitable heat and/or moisture absorbing material. For example, in embodiments where the HVAC system  104  is operating in a cooling mode, a temperature of outdoor air  138  entering the enclosure  102  may be relatively high, while a temperature of the previously-conditioned return air  148  is relatively low. Accordingly, relatively cool return air  148  flowing across heat transfer elements  160  of the second portion  130  of the energy recovery wheel  122  may absorb thermal energy from these heat transfer elements  160  and, thus, reduce a temperature of the heat transfer elements  160 . Upon traversing the second portion  130  of the energy recovery wheel  122 , the return air  148 , which has increased in temperature, may exhaust from the HVAC system  104  via the exhaust air outlet  152  as the exhaust air  154 . 
     As the energy recovery wheel  122  rotates about the central axis  132 , the cooled heat transfer elements  160  within the return air flow path  120  may transition into the outdoor air flow path  118 . The heat transfer elements  160  entering the outdoor air flow path  118  may therefore absorb thermal energy from the warmer outdoor air  138  flowing thereacross. As such, the energy recovery wheel  122  may cool or pre-condition the outdoor air  138  by absorbing thermal energy from the outdoor air  138 . That is, the energy recovery wheel  122  may pre-condition the outdoor air  138  by effectively transferring thermal energy from the outdoor air  138  to the return air  148 . It should be noted that the energy recovery wheel  122  may alternatively be used to transfer energy from the return air  148  to the outdoor air  138 , for example, in embodiments where the HVAC system  104  is operating in a heating mode, rather than a cooling mode. 
     As discussed in detail below, the heat transfer elements  160  may be rotatably or pivotably mounted to the energy recovery wheel  122 , thereby enabling the energy recovery wheel  122  to transition between an operational configuration  161 , in which the outdoor air  138  and the return air  148  are forced across the heat transfer elements  160 , and a non-operational configuration  163 , as shown in  FIGS. 12-14 , in which the outdoor air  138  and the return air  148  may bypass the heat transfer elements  160 . Accordingly, in the non-operational configuration  163 , the energy recovery wheel  122  may enable substantially unrestricted air flow along the outdoor air flow path  118  and the return air flow path  120 , such that a pressure drop across the energy recovery wheel  122  may be reduced or substantially eliminated. 
       FIG. 6  is an exploded perspective view of an embodiment of the ERW assembly  100 . As shown in the illustrated embodiment, the ERW assembly  100  includes an outer frame, referred to herein as a shroud  162 , which includes a passage  164  formed therein. The passage  164  defines an air flow path  165  through the shroud  162  and may be configured to receive the energy recovery wheel  122 . Particularly, the energy recovery wheel  122  may be positioned within the passage  164  such that the central axis  132  of the energy recovery wheel  122  aligns with a centerline  166  of the passage  164 . The energy recovery wheel  122  may be rotatably coupled to the shroud  162  and may be configured to rotate relative to the shroud  162  about the central axis  132  and the centerline  166 . For example, an actuator  168 , such as an electric motor, a pneumatic motor, a hydraulic motor, or other suitable actuator, may be used to drive rotation of the energy recovery wheel  122  within the shroud  162 . The actuator  168  may be coupled to the energy recovery wheel  122  via an arrangement of gears, a belt or rope drive system, or any other suitable power transmission system. An outer diameter of the energy recovery wheel  122  may be substantially equal to an inner diameter of the passage  164 . Accordingly, in an assembled configuration  170 , as shown in  FIG. 7 , of the ERW assembly  100 , air flow between the shroud  162  and the energy recovery wheel  122  may be substantially blocked. 
     As shown in the illustrated embodiment, the energy recovery wheel  122  includes a frame  172  that is configured to receive and support the heat transfer elements  160 . The frame  172  includes a central hub  174  that is positioned concentrically within an outer ring  176  of the frame  172 . A plurality of dividers, also referred to herein as a plurality of spokes  178 , may extend radially from the central hub  174  and may couple to the outer ring  176 . Accordingly, the central hub  174 , the outer ring  176 , and the spokes  178  may cooperate to form a plurality of receptacles  180  that each define an air flow path or an opening  182  through the energy recovery wheel  122 . Each of the receptacles  180  may be configured to receive one of the heat transfer elements  160  of the energy recovery wheel  122 . A geometric shape of the heat transfer elements  160  may be substantially similar to a geometric shape of the receptacles  180 . Accordingly, airflow between the frame  172  and the heat transfer elements  160  may be substantially blocked when the heat transfer elements  160  are positioned in closed configurations  184 , as shown in  FIG. 7 , within the receptacles  180 , such as when the energy recovery wheel  122  is in the operational configuration  161 . 
     For clarity, in the closed configurations  184  of the heat transfer elements  160 , respective first permeable end surfaces  188  and respective second permeable end surfaces  190  (e.g., as shown in  FIG. 12 ) of each of the heat transfer elements  160  may be oriented substantially perpendicular to a direction of air flow through the openings  182 . Therefore, in the operational configuration  161  of the energy recovery wheel  122 , substantially all air flowing along the outdoor air flow path  118  and the return air flow path  120  may be directed across the heat transfer elements  160 . In other words, when the heat transfer elements  160  are in their respective closed configurations  184 , the outdoor air  138 , the return air  148 , or both, may flow across or through the heat transfer elements  160  from the first permeable end surfaces  188  to the second permeable end surfaces  190 , or vice versa. 
     As shown in the illustrated embodiment, the heat transfer elements  160  and the receptacles  180  may each include a generally pie-shaped perimeter. However, it should be noted that, in other embodiments, the heat transfer elements  160  and the receptacles  180  may include any other suitable perimeter or geometric cross-section. Moreover, although the energy recovery wheel  122  includes eight heat transfer elements  160  in the illustrated embodiment, in other embodiments, the energy recovery wheel  122  may include any other suitable quantity of heat transfer elements  160 . For example, in some embodiments, the energy recovery wheel may include 1, 2, 3, 4, 6, 8, 12, or more than 12 heat transfer elements  160 . 
     As discussed in detail below, the heat transfer elements  160  may be rotatably coupled to the frame  172  via a plurality of pins  192 . Indeed, the pins  192  may be configured to block translational movement of the heat transfer elements  160  relative to the frame  172 , while enabling the heat transfer elements  160  to rotate or pivot relative to the frame  172  between the closed configurations  184  and respective open configurations  194 , as shown in  FIGS. 12-14 . The ERW assembly  100  includes a guide ring  196  that is configured to engage with the pins  192  and drive rotation of the pins  192 . The guide ring  196  may be rotatably coupled to the frame  172 , the shroud  162 , or both, such that the guide ring  196  may rotate independently of the frame  172  and the shroud  162 . As discussed below, rotational motion of the guide ring  196  relative to the frame  172  may enable the guide ring  196  to impart rotational motion to the pins  192 . In this manner, the guide ring  196  may enable the pins  192  to rotate the heat transfer elements  160  between the closed and open configurations  184 ,  194 . In some embodiments, the guide ring  196  may be concentrically aligned with the frame  172  and may be configured to abut an end face  198  of the frame  172 . 
       FIG. 8  is a front view of an embodiment of the ERW assembly  100 . As noted above, each of the heat transfer elements  160  may engage with and pivotably couple to the frame  172  via the pins  192 . For conciseness, the engagement between a first heat transfer element  200  of the heat transfer elements  160  and the frame  172  will be discussed below. However, it should be noted that pins  192  may rotatably or pivotably couple the remaining heat transfer elements  160  to the frame  172  in a substantially similarly manner as the first heat transfer element  200 . With the forgoing in mind, the pins  192  corresponding to the first heat transfer element  200  may include an inner pin  202  and an outer pin  206 . The inner pin  202  may be rigidly coupled to a first end portion  204  or radially inner portion of the first heat transfer element  200  and may be rotatably coupled to the central hub  174 . The outer pin  206  may be rigidly coupled to a second end portion  208  or radially outer portion of the first heat transfer element  200  and may be rotatably coupled to the outer ring  176 . The pins  192  may extend along an axis  210  that extends radially from the central hub  174  relative to the central axis  132 . That is, the axis  210  may extend generally orthogonal to or radially outward from the central axis  132  of the energy recovery wheel  122 . Accordingly, the pins  192  may enable the first heat transfer element  200  to rotate about the axis  210  relative to the frame  172  between the closed configuration  184  and the open configuration  194 . 
     It should be noted that, in some embodiments, the inner pin  202  may be rotatably coupled to the first heat transfer element  200  and may be rigidly coupled to the central hub  174 . In other embodiments, the inner pin  202  may be rotatably coupled to both the first heat transfer element  200  and the central hub  174 . In some embodiments, the axis  210  may symmetrically bisect the first heat transfer element  200 . That is, in such embodiments, arc portions  212  of the first heat transfer element  200  that extend from either side of the axis  210 , at a common point along the axis  210 , to the spokes  178  adjacent the first heat transfer element  200  may be substantially equal. However, in other embodiments, the axis  210  may extend though the first heat transfer element  200  in any other suitable manner, such that the arc portions  212  at a common point along the axis  210  may be unequal to one another. Moreover, it should be noted that, in certain embodiments of the ERW assembly  100 , a single pin  192  may be used to rotatably couple the first heat transfer element  200  to the frame  172  instead of the inner and outer pins  202 ,  206 . For example, the first heat transfer element  200  may be rotatably coupled to the frame  172  via a single pin  192  that extends through the first heat transfer element  200  from the central hub  174  to the outer ring  176 . 
     In some embodiments, the outer pin  206  may include a drive arm  216  that extends from the outer pin  206  along the second direction  150  and engages with the guide ring  196 . That is, the drive arm  216  may extend past the end face  198  of the frame  172  in the second direction  150 , thereby enabling the drive arm  216  to engage with the guide ring  196 . As discussed in detail below, the engagement between the drive arm  216  and the guide ring  196  enables the guide ring  196  to rotate the outer pin  206  about the axis  210  when the guide ring  196  rotates about the central axis  132 . In this manner, the guide ring  196  enables the outer pin  206  to transition the first heat transfer element  200  between the closed configuration  184  and the open configuration  194 . 
       FIG. 9  is a perspective view of an embodiment of the outer pin  206 . As shown in the illustrated embodiment, the outer pin  206  includes a shaft  220  that extends from a first end portion  222  of the outer pin  206  to a second end portion  224  of the outer pin  206 . That shaft  220  includes a first section  226  that is configured to rotatably couple to the outer ring  176  of the frame  172  and a second section  227  that may be configured to rigidly couple to the first heat transfer element  200  or a frame of the first heat transfer element  200 . The drive arm  216  may extend generally cross-wise from the shaft  220  and may include a tracing peg  228  that extends from the drive arm  216  toward the first end portion  222  of the outer pin  206 . In some embodiments, the tracing peg  228  may include a generally circular cross-section and may extend generally parallel to the shaft  220 . The tracing peg  228  may be configured to engage with a slot  230 , as shown in  FIG. 10 , of the guide ring  196 , such that rotational motion of the guide ring  196  about the central axis  132  may cause the tracing peg  228  to translate along the slot  230 . 
     To better illustrate,  FIG. 10  is a perspective view of an embodiment of the guide ring  196 . For clarity, it should be noted that guide ring  196  may include a plurality of slots  230  that are each configured to engage with a respective outer pin  206  of the heat transfer elements  160 . However, for conciseness, the slot  230  corresponding to the outer pin  206  of the first heat transfer element  200  will be discussed below. As shown in the illustrated embodiment, the slot  230  may extend along the guide ring  196  in a counter-clockwise direction  231  from a first axial end portion  232 , which may abut the end face  198  of the frame  172  of the guide ring  196 , toward a second axial end portion  234  of the guide ring  196 . Although the slot  230  is shown as extending substantially linearly along a length  236  of the slot  230 , it should be noted that, in other embodiments, the slot  230  may include any other suitable slope or profile. For example, in some embodiments, the slot  230  may include a curved profile that extends from an initiating end  240  of the slot  230  to a terminal end  242  of the slot  230 . In any case, the tracing peg  228  may be configured to engage with the slot  230  and to slide along the length  236  of the slot  230  when the guide ring  196  rotates relative to the frame  172 . 
     To better illustrate the engagement between the outer pin  206  and the guide ring  196 ,  FIG. 11  is a perspective view of an embodiment of the ERW assembly  100 . It should be noted that the first heat transfer element  200  has been removed from its respective receptacle  180  to better show the outer pin  206  and the guide ring  196 . In the illustrated embodiment, the guide ring  196  is positioned in a first orientation  250  relative to the frame  172 . In the first orientation  250 , markers  252  on the guide ring  196  and the frame  172  may be radially aligned with one another. In the first orientation  250  of the guide ring  196 , the tracing peg  228  may be positioned at or proximate to the initiating end  240  of the slot  230 , such that the outer pin  206  is positioned at a first angular orientation with respect to the axis  210 . Specifically, in the first angular orientation, the outer pin  206  may position the first heat transfer element  200  in the closed configuration  184 , such that the first heat transfer element  200  occludes the opening  182  defined by the receptacle  180  of the first heat transfer element  200 . 
     To transition the first heat transfer element  200  from the closed configuration  184  to the open configuration  194 , the guide ring  196  may rotate about the central axis  132  in a clockwise direction  254  relative to the frame  172 . In particular, the guide ring  196  may rotate to a second orientation  256 , as shown in  FIG. 12 , where the markers  252  are radially offset from one another. As an example, the guide ring  196  may rotate approximately 15 degrees about the central axis  132  in the clockwise direction  254  to transition from the first orientation  250  to the second orientation  256 . However, in other embodiments, the guide ring  196  may rotate by an angular increment that is less than or greater than 15 degrees when transitioning between the first and second orientations  250 ,  256 . In any case, rotating the guide ring  196  from the first orientation  250  to the second orientation  256  causes the tracing peg  228  to translate along the profile of the slot  230  from the initiating end  240  to the terminal end  242  of the slot  230 . As a result, the drive arm  216  translates along the slot  230  and thereby rotates the outer pin  206  in a counter-clockwise direction  258  about the axis  210  relative to the central hub  174 . The rotation of the outer pin  206 , which is rigidly attached to the first heat transfer element  200 , drives rotation of the first heat transfer element  200  from the closed configuration  184  to the open configuration  194 . That is, the outer pin  206  may rotate the first heat transfer element  200  in the counter-clockwise direction  258  about the axis  210 , relative to the central hub, from the closed configuration to  184  to the open configuration  194 . Accordingly, the first heat transfer element  200  may substantially unblock the opening  182  defined by the receptacle  180  of the first heat transfer element  200  and enable substantially unrestricted air flow therethrough. 
     To transition the first heat transfer element  200  from the open configuration  194  to the closed configuration  184 , the guide ring  196  may rotate in the counter-clockwise direction  231  about the central axis  132  from the second orientation  256  to the first orientation  250 . Accordingly, the guide ring  196  will rotate the outer pin  206  in the a clockwise direction  270  about the axis  210 , with respect to the central hub  174 , such that the outer pin  206  transitions the first heat transfer element  200  from the open configuration  194  to the closed configuration  184 . That is, the outer pin  206  rotates the first heat transfer element  200  in the clockwise direction  270  about the axis  210  from the open configuration  194  to the closed configuration  184 . 
     In accordance with the techniques discussed above, the guide ring  196  may be configured to rotate each of the heat transfer elements  160  in a same direction about their respective axes  210  from the closed configurations  184  to the open configurations  194 . Similarly, the guide ring  196  may be configured to rotate each of the heat transfer elements  160  in a same direction about their respective axes  210  from the open configurations  194  to the closed configurations  184 . However, it should be noted that, in some embodiments, the slots  230  of the guide ring  196  may be formed such that rotation of the guide ring  196  in a particular direction imparts rotation to a first subset of the heat transfer elements  160  in a first direction about the corresponding axes  210 , while imparting rotation to a second subset of the heat transfer elements  160  in a second direction in about the corresponding axes  210 , where the second direction is opposite to the first direction. As an example, in such embodiments, a first subset of the heat transfer elements  160  may be configured to transition from respective closed configurations  184  to respective open configurations  194  by rotating about the respective axes  210  in the counter-clockwise direction  258 , while a second subset of the heat transfer elements  160  may be configured to transition from the respective closed configurations  184  to the respective open configurations  194  by rotating about the respective axes  210  in the clockwise direction  270 . In certain embodiments, in the closed configurations  184 , the heat transfer elements  160  may be disposed within the passage  164  of the shroud  162 . Conversely, in the open configurations  194 , respective tip portions  272 , as shown in  FIG. 12 , of the heat transfer elements  160  may protrude axially from the passage  164  relative to the central axis  132 . 
     As mentioned above,  FIG. 12  is a perspective view of an embodiment of the energy recovery wheel  122  in the non-operational configuration  163 , in which each of the heat transfer elements  160  is positioned in their respective open configuration  194 . In some embodiments, the first and second permeable end surfaces  188 ,  190  of the heat transfer elements  160  may be oriented substantially parallel to a direction of air flow through the openings  182  when in the heat transfer elements  160  are oriented in the open configurations  194 . That is, in the open configurations  194 , the heat transfer elements  160  may be rotated approximately ninety degrees in the counter-clockwise direction  258  about their respective axes  210  with respect to the closed configurations  184 , such that the heat transfer elements  160  substantially unblock the openings  182  defined by the receptacles  180 . 
     For example,  FIG. 13  is a front view of an embodiment of the energy recovery wheel  122  in the non-operational configuration  163 . As shown in the illustrated embodiment, when the heat transfer elements  160  are positioned in the open configurations  194 , the heat transfer elements  160  may substantially unblock to openings  182  to enable substantially unimpeded air flow across the energy recovery wheel  122 . In this manner, the energy recovery wheel  122  may reduce fluid restrictions along the outdoor air flow path  118  and/or the return air flow path  120  during inactive operational periods of the energy recovery wheel  122 . That is, in the open configurations  194  of the heat transfer elements  160 , a substantially negligible amount of air may flow through the heat transfer elements  160  between the first permeable end surfaces  188  and the second permeable end surfaces  190  of the heat transfer elements  160 , thereby reducing a pressure drop across the energy recovery wheel  122 . 
     The ERW assembly  100  may include an actuator  274  that is configured to selectively rotate the guide ring  196  relative to the frame  172  between the first and second orientations  250 ,  256 , and thus, may be used to adjust a position of the heat transfer elements  160 . In some embodiments, the actuator  274  may be coupled to the frame  172  of the energy recovery wheel  122  and may be configured to rotate with the frame  172  during normal operation of the energy recovery wheel  122 . In other embodiments, the actuator  274  may be coupled to the shroud  162  or to a portion of the enclosure  102  of the HVAC unit  12 . As an example, the actuator  274  may include an electric motor that is coupled to the shroud  162  and is configured to drive rotation of the guide ring  196  via a set of gears or a belt system. In other embodiments, the actuator  274  may include a linear actuator or a servo motor that is operable to rotate the guide ring  196  between the first and second orientations  250 ,  256 . In further embodiments, any other suitable actuator  274  may be used to drive rotation of the guide ring  196 . 
     In certain embodiments, the actuator  274  may be configured to axially translate the guide ring  196  along the central axis  132  relative to the shroud  162 , instead of rotating the guide ring  196  about the central axis  132  relative to the shroud  162 . Translating the guide ring  196  axially along the central axis  132  may enable the guide ring  196  to transition the heat transfer elements  160  between the respective closed configurations  184  and the respective open configurations  194  in a manner similar to that discussed above. Indeed, axial translation of the guide ring  196  relative to the shroud  162  may similarly cause the tracing pegs  228  of the outer pins  206  to slide along the slots  230  of the guide ring  196  between the respective initiating ends  240  and the respective terminating ends  242  of the slots  230 . Accordingly, the engagement between the tracing pegs  228  and the slots  230  may cause the guide arms  216 , and thus the outer pins  206  coupled thereto, to rotate about the axes  210  in the counter-clockwise direction  258  or in the clockwise direction  270 . Therefore, by axially translating the guide ring  196  along the central axis  132 , the actuator  274  may transition the heat transfer elements  160  between the respective closed and open configurations  184 ,  194 . 
       FIG. 14  is a perspective view of the enclosure  102  of the HVAC system  104 , illustrating the energy recovery wheel  122  in the non-operational configuration  163 . In some embodiments, the ERW assembly  100  may include a sensor  280  that is communicatively coupled to a controller  282  of the HVAC system  104 , such as the control device  16  or the control panel  82 , and is configured to provide feedback to the controller  282  indicative of an operating parameter of the ERW assembly  100 , such as an orientation of the energy recovery wheel  122  with respect to the enclosure  102  or the shroud  162 . In some embodiments, the controller  282  may be operatively coupled to the actuators  168 ,  276  and may be configured to instruct the actuator  168  to transition the energy recovery wheel  122  to a non-interfering position  284  before instructing the actuator  274  to transition the heat transfer elements  160  from the closed configurations  184  to the open configurations  194 . Specifically, in the non-interfering position  284  of the energy recovery wheel  122 , a pair  288  of the spokes  178  may be aligned and/or coplanar with the partition  116  of the enclosure  102 . Accordingly, the controller  282  may ensure that the heat transfer elements  160  are precluded from contact with the partition  116  when transitioning from the closed configurations  184  to the open configuration  194 . That is, the controller  282  may instruct the actuator  274  to transition the heat transfer elements  160  from the closed configurations  184  to the open configurations  194  upon receiving feedback from the sensor  280  indicating that actuator  168  has transitioned the energy recovery wheel  122  to the non-interfering position  284 . 
     It should be appreciated that one or more control transfer devices, represented by dashed lines  286 , such as wires, cables, wireless communication devices, and the like, may communicatively couple the actuators  168 ,  274 , the sensor  280 , or any other components of the ERW assembly  100  and/or the HVAC system  104  to the controller  282 . The controller  282  may include a processor  290 , such as a microprocessor, which may execute software for controlling the components of the ERW assembly  100  and/or the HVAC system  104 . Moreover, the processor  290  may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICS), or some combination thereof. 
     For example, the processor  290  may include one or more reduced instruction set (RISC) processors. The controller  282  may also include a memory device  292  that may store information such as control software, look up tables, configuration data, and so forth. The memory device  292  may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device  292  may store a variety of information and may be used for various purposes. For example, the memory device  292  may store processor-executable instructions including firmware or software for the processor  290  execute, such as instructions for controlling the components of the ERW assembly  100  and/or the HVAC system  104 . In some embodiments, the memory device  292  is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processor  290  to execute. The memory device  292  may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The memory device  292  may store data, instructions, and any other suitable data. 
     As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for reducing fluid restrictions along the outdoor air flow path  118  and the return air flow path  120  of an HVAC unit during inactive operational periods of the energy recovery wheel  122 . In particular, the disclosed energy recovery wheel  122  is configured to transition between the operational configuration  161  and the non-operational configuration  163  to enable or substantially preclude, respectively, air flow across the heat transfer elements  160 . By mitigating fluid restrictions along the outdoor air flow path  118  and the return air flow path  120  during inactive operational periods of the energy recovery wheel  122 , the energy recovery wheel  122  may reduce a load on fans or blowers of the HVAC system  104  during such inactive operational periods, and thus, enhance an overall operational efficiency of the HVAC system  104 . The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems. 
     While only certain features and embodiments of the present disclosure have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the present disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode of carrying out the present disclosure, or those unrelated to enabling the claimed embodiments. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.