HVAC systems and methods with low pressure operation

Abstract

A heating, ventilation, and air conditioning (HVAC) system includes a working fluid circuit having a compressor configured to circulate a working fluid along the working fluid circuit and a suction conduit configured to direct the working fluid to the compressor. The HVAC system also includes a first pressure sensor configured to detect a first pressure of the working fluid along the suction conduit and a second pressure sensor configured to detect a second pressure of the working fluid along the suction conduit. The HVAC system is configured to adjust operation of the compressor in response to detection of the first pressure of the working fluid below a first threshold value, and to adjust operation of a fan of the HVAC system in response to detection of the second pressure of the working fluid below a second threshold value

Description

BACKGROUND

[0001] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described 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 admissions of prior art.

[0002] A heating, ventilation, and / or air conditioning (HVAC) system may be used to thermally regulate an environment, such as a space within a building, home, or other structure. The HVAC system generally includes a vapor compression system having heat exchangers, such as a condenser and an evaporator, which transfer thermal energy between the HVAC system and the environment. Typically, a compressor is fluidly coupled to a working fluid circuit of the vapor compression system and is configured to circulate a working fluid (e.g., refrigerant) between the condenser and the evaporator. In this way, the compressor facilitates heat exchange between the working fluid, the condenser, and the evaporator. In some cases, working fluid flow through the working fluid circuit may be reversible, such that the condenser is operable as an evaporator (e.g., a heat absorber), and the evaporator is operable a condenser (e.g., a heat rejector). Accordingly, the HVAC system may operate as a heat pump system in multiple operating modes (e.g., a cooling mode, a heating mode) to provide both heating and cooling to the building with one working fluid circuit. In some application, the HVAC system may include a reheat heat exchanger, which, together with the evaporator, is positioned along an air flow path of the HVAC system. The evaporator and the reheat heat exchanger may operate concurrently to facilitate dehumidification and temperature regulation of an air flow traveling along the air flow path and entering a building serviced by the HVAC system. Accordingly, the HVAC system may facilitate supply of a temperature regulated and dehumidified air flow to the building. Unfortunately, existing HVAC systems may be susceptible to inefficiencies and / or operational interruptions in certain operating conditions.SUMMARY

[0003] A summary of certain embodiments disclosed herein is set forth below. It should be noted that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

[0004] In one embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a working fluid circuit having a compressor configured to circulate a working fluid along the working fluid circuit and a suction conduit configured to direct the working fluid to the compressor. The HVAC system also includes a first pressure sensor configured to detect a first pressure of the working fluid along the suction conduit and a second pressure sensor configured to detect a second pressure of the working fluid along the suction conduit. The HVAC system is configured to adjust operation of the compressor in response to detection of the first pressure of the working fluid below a first threshold value, and to adjust operation of a fan of the HVAC system in response to detection of the second pressure of the working fluid below a second threshold value.

[0005] In another embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a working fluid circuit having a compressor, a suction conduit configured to direct a working fluid to the compressor, and a heat exchanger configured to place the working fluid in a heat exchange relationship with an air flow. The HVAC system also includes a fan configured to force the air flow across the heat exchanger, a pressure switch configured to detect a first pressure of the working fluid along the suction conduit, where the pressure switch is configured to actuate in response to detection of the first pressure below a first threshold value, and a pressure sensor configured to detect a second pressure of the working fluid along the suction conduit. The HVAC system is configured to adjust operation of the fan in response to detection of the second pressure of the working fluid below a second threshold value, and the second threshold value is greater than the first threshold value.

[0006] In a further embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a compressor configured to circulate a working fluid along a working fluid circuit, a suction conduit of the working fluid circuit configured to direct the working fluid to the compressor, a heat exchanger of the working fluid circuit configured to place the working fluid in a heat exchange relationship with an air flow, and a fan configured to force the air flow across the heat exchanger. The HVAC system also includes a first pressure switch configured to detect a first pressure of the working fluid along the suction conduit, where the first pressure switch is configured to interrupt supply of power to the compressor in response to detection of the first pressure below a first threshold value. The HVAC system further includes a second pressure switch configured to detect a second pressure of the working fluid along the suction conduit, where the second pressure switch is configured to interrupt supply of power to the fan in response to detection of the second pressure below a second threshold value, and the second threshold value is greater than the first threshold value.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0008] FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0009] FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

[0010] FIG. 3 is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

[0011] FIG. 4 is a schematic diagram of an embodiment of a vapor compression system used in an HVAC system, in accordance with an aspect of the present disclosure;

[0012] FIG. 5 is a schematic diagram of an embodiment of an HVAC system including a reheat circuit, in accordance with an aspect of the present disclosure;

[0013] FIG. 6 is a schematic diagram of an embodiment of an HVAC system including a reheat circuit, in accordance with an aspect of the present disclosure;

[0014] FIG. 7 is a schematic diagram of an embodiment of an HVAC system including a heat pump system, in accordance with an aspect of the present disclosure;

[0015] FIG. 8 is a schematic diagram of an embodiment of an HVAC system including a heat pump system, in accordance with an aspect of the present disclosure; and

[0016] FIG. 9 is a schematic of an embodiment of a control system for an HVAC system, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0017] One or more specific embodiments of the present disclosure will be described below. These described embodiments are 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'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.

[0018] When introducing elements of various embodiments of the present disclosure, the articles “a,”“an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0019] As used herein, the terms “approximately,”“generally,” and “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to mean that the property value may be within + / −5%, within + / −4%, within + / −3%, within + / −2%, within + / −1%, or even closer, of the given value. Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to mean that the given feature is within + / −5%, within + / −4%, within + / −3%, within + / −2%, within + / −1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Further, it should be understood that mathematical terms, such as “planar,”“slope,”“perpendicular,”“parallel,” and so forth are intended to encompass features of surfaces or elements as understood to one of ordinary skill in the relevant art, and should not be rigidly interpreted as might be understood in the mathematical arts. For example, a “planar” surface is intended to encompass a surface that is machined, molded, or otherwise formed to be substantially flat or smooth (within related tolerances) using techniques and tools available to one of ordinary skill in the art. Similarly, a surface having a “slope” is intended to encompass a surface that is machined, molded, or otherwise formed to be oriented at an angle (e.g., incline) with respect to a point of reference using techniques and tools available to one of ordinary skill in the art.

[0020] As briefly discussed above, a heating, ventilation, and air conditioning (HVAC) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC system may include a vapor compression system that operates to transfer thermal energy between a working fluid, such as a refrigerant, and a fluid to be conditioned, such as air. The vapor compression system includes heat exchangers, such as a condenser and an evaporator, which are fluidly coupled to one another via one or more conduits of a working fluid loop or circuit. A compressor may be used to circulate the working fluid through the conduits and other components of the working fluid circuit (e.g., an expansion device) and, thus, enable the transfer of thermal energy between components of the working fluid circuit (e.g., between the condenser and the evaporator) and one or more thermal loads (e.g., an environmental air flow, a supply air flow).

[0021] In some embodiments, the HVAC system may include a heat pump (e.g., a heat pump system, a reverse-cycle heat pump) having a first heat exchanger (e.g., a heating and / or cooling coil, an indoor coil, the evaporator) positioned within or otherwise fluidly coupled to the space to be conditioned, a second heat exchanger (e.g., a heating and / or cooling coil, an outdoor coil, the condenser) positioned in or otherwise fluidly coupled to an ambient environment (e.g., the atmosphere), and a pump (e.g., the compressor) configured to circulate the working fluid (e.g., refrigerant) between the first and second heat exchangers to enable heat transfer between the thermal load and the ambient environment, for example. The heat pump system is operable to provide both cooling or heating to the space to be conditioned (e.g., a room, zone, or other region within a building) by adjusting a flow of the working fluid through the working fluid circuit.

[0022] For example, during operation of the heat pump system in a cooling mode, the compressor may direct working fluid through the working fluid circuit and the first and second heat exchangers in a first flow direction. While receiving working fluid in the first flow direction, the first heat exchanger, which may be positioned within the space to be conditioned, may operate as an evaporator. Thus, working fluid flowing through the first heat exchanger may absorb thermal energy from an air flow (e.g., supply air flow) directed to the space. Further, the second heat exchanger, which may be positioned in the ambient environment surrounding the heat pump system, may operate as a condenser to reject the heat absorbed by the working fluid flowing from the first heat exchanger (e.g., to an ambient air flow directed across the second heat exchanger). In this way, the heat pump system may facilitate cooling of the space or other thermal load serviced by (e.g., in thermal communication with) the first heat exchanger.

[0023] Conversely, during operation in a heating mode, a reversing valve (e.g., switch-over valve) enables the compressor to direct working fluid through the working fluid circuit and the first and second heat exchangers in a second flow direction, opposite the first flow direction. While receiving working fluid in the second flow direction, the first heat exchanger may operate as a condenser instead of an evaporator, and the second heat exchanger may operate as an evaporator instead of a condenser. As such, the first heat exchanger may receive (e.g., from the second heat exchanger) a flow of heated working fluid to reject heat to thermal load serviced by the first heat exchanger (e.g., an air flow directed to the space) and, thus, facilitate heating of the thermal load. In this way, the heat pump system may facilitate either heating or cooling of the thermal load based on the selected operational mode of the heat pump system (e.g., based on a flow direction of working fluid along the working fluid circuit).

[0024] During operation of the HVAC system in a cooling mode, the first heat exchanger (e.g., evaporator, indoor coil) cools an air flow (e.g., supply air flow), which may cause moisture suspended or contained within the air flow to condense. For example, moisture condensed from the air flow may accumulate on a surface of the first heat exchanger as condensate. The condensate may flow along the first heat exchanger and drip into a drain pan that may be positioned beneath the first heat exchanger (e.g., with respect to a direction of gravity). As such, a humidity level of the flow of conditioned air discharging from the first heat exchanger may be less than a humidity level of the air flow received by the evaporator. The fan may direct the cooled, dehumidified air discharging from the first heat exchanger along an air flow path and toward a conditioned space, such as a room in a building. In this manner, the HVAC system may operate to regulate a temperature and / or humidity level within an interior of the building.

[0025] In some cases, it may be desirable to reduce a humidity level within the conditioned space without substantially adjusting a current temperature within the conditioned space (e.g., without heating or cooling an interior of a building). For example, in certain cases, a temperature within the building (e.g., a temperature within one or more rooms, zones, or other spaces of the building) may be within a threshold range of a designated target temperature setpoint, while a humidity level within the building may exceed a designated target humidity level setpoint beyond an acceptable tolerance. In such situations, it may be desirable to operate the HVAC system in a dehumidification mode, in which the HVAC system may operate to dehumidify the building without substantially heating or cooling the conditioned space within building.

[0026] To facilitate operation in the dehumidification mode, the HVAC system may include a reheat circuit having a reheat heat exchanger (e.g., reheat coil, third heat exchanger) that is fluidly coupled to the vapor compression system (e.g., working fluid circuit) and is configured to reheat (e.g., increase a temperature of) the cooled, dehumidified air discharging from the first heat exchanger before the air is directed into the building or other conditioned space. For example, the reheat heat exchanger may be positioned within the air flow path and downstream of the first heat exchanger (e.g., evaporator), such that the reheat heat exchanger may receive the cooled, dehumidified air discharging from the first heat exchanger. The compressor may be configured to receive, from the first heat exchanger, a flow of heated working fluid that has previously absorbed thermal energy from the supply air flow. The compressor may compress the working fluid received from the first heat exchanger, which adds more heat to the working fluid. The heated working fluid may be directed from the compressor toward and through a reheat valve (e.g., a three-way valve, hot gas reheat valve, modulating value) that is adjustable to direct at least a portion of the heated working fluid to the reheat heat exchanger, while directing a remaining portion of the heated working fluid toward the second heat exchanger (e.g., condenser). As such, the cooled, dehumidified air discharged from the first heat exchanger and directed across the reheat heat exchanger may re-absorb thermal energy from the heated working fluid circulating through the reheat heat exchanger. Accordingly, the reheat heat exchanger may increase a temperature of the cooled, dehumidified air discharged from the first heat exchanger prior to delivery of the dehumidified air to the conditioned space. The working fluid discharged from the reheat heat exchanger may be directed along the working fluid circuit toward another portion of the working fluid circuit, such as upstream of the compressor and / or first heat exchanger (e.g., evaporator) and downstream of the second heat exchanger (e.g., condenser).

[0027] Unfortunately, in certain operating conditions, the HVAC system may operate inefficiently and / or may be susceptible to operational interruptions. For example, during cold ambient (e.g., atmospheric) conditions, a pressure of the working fluid circulated within the working fluid circuit may fall below an acceptable or desirable level. In traditional HVAC systems, low pressure levels of working fluid within the working fluid circuit may cause inefficient operation and / or operational interruption (e.g., “tripping”) of the HVAC system. In some instances, operation of the HVAC system may be suspended, and intervention by a technician or operator of the HVAC system may be prompted. Further, in some HVAC systems, such as HVAC systems including a heat pump system, the second heat exchanger (e.g., condenser, outdoor coil) of the HVAC system may be susceptible to formation of frost (e.g., freezing condensate, freezing moisture) on the second heat exchanger during operation of the HVAC system (e.g., in a heating mode, in a reheat mode). Indeed, formation of frost on outdoor coils of existing HVAC systems may result in operational inefficiencies and / or operational interruptions.

[0028] Accordingly, embodiments of the present disclosure are directed to systems and methods that enable improved operation of HVAC systems, such as HVAC systems having a reheat circuit and / or HVAC systems having a heat pump system, during operational conditions and / or modes that may induce low pressures of working fluid within the HVAC system. For example, an HVAC system having a reheat circuit may include a pressure switch (e.g., hot gas reheat [HGRH] pressure switch) configured to detect a pressure of working fluid at an inlet or suction line of the compressor. The pressure switch may be an additional or second pressure switch that is incorporated with another pressure switch (e.g., low-pressure switch) of the working fluid circuit. The HGRH pressure switch may be actuated based on a detection of a pressure of the working fluid at the inlet (e.g., suction conduit) of the compressor that is below a threshold pressure, which may be a pressure that is above a corresponding threshold pressure associated with the low-pressure switch. In accordance with present techniques, actuation of the HGRH pressure switch may initiate an interruption in operation of a fan (e.g., outdoor fan) of the HVAC system that is configured to direct an air flow (e.g., ambient air flow) across the second heat exchanger (e.g., condenser, outdoor coil). Therefore, the fan may not force the ambient air flow across the second heat exchanger, which may reduce transfer of thermal energy between the ambient air flow and the working fluid circulated through the second heat exchanger. As a result, a pressure of the working fluid within the working fluid circuit may increase, which may avoid actuation of the low-pressure switch of the HVAC system and subsequent operational interruption of the HVAC system. In this way, the disclosed techniques enable improved operation of the HVAC system having the reheat circuit.

[0029] Also in accordance with present techniques, an HVAC system having a heat pump system may include a pressure switch (e.g., defrost pressure switch) configured to detect a pressure of working fluid at an inlet or suction conduit of the compressor. The pressure switch may be an additional or second pressure switch that is incorporated with another pressure switch (e.g., low-pressure switch) of the working fluid circuit. The defrost pressure switch may be actuated based on a detection of a pressure of the working fluid at the inlet of the compressor that is below a threshold pressure, which may be a pressure that is above a corresponding threshold pressure associated with the low-pressure switch. Actuation of the defrost pressure switch may initiate an interruption in operation of a fan (e.g., indoor fan) of the HVAC system that is configured to direct an air flow (e.g., supply air flow) across the first heat exchanger (e.g., indoor coil). Therefore, the fan may not force the supply air flow across the first heat exchanger, which may reduce transfer of thermal energy between the supply air flow and the working fluid circulated through the first heat exchanger. As a result, a pressure of the working fluid within the working fluid circuit may increase, which may increase a temperature of the working fluid directed through the second heat exchanger (e.g., outdoor coil) and thereby reduce formation of frost or other frozen liquid on the second heat exchanger. In this way, the disclosed techniques enable improved operation (e.g., reduced operational interruptions) of the HVAC system including the heat pump system. While the present techniques are described in the context of controlling air flow via operation control of fans or blowers, it should be appreciated that other components may additionally or alternatively be utilized to control air flow, such as dampers, louvers, and so forth.

[0030] Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and air conditioning (HVAC) system for environmental management that employs one or more HVAC units in accordance with the present disclosure. 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.

[0031] In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12, which may be a heat pump or may include a reheat system, in accordance with present embodiments. 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.

[0032] 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 working fluid circuit configured to operate in different modes. In other embodiments, the HVAC unit 12 may include one or more working fluid circuits (e.g., refrigeration circuits) for cooling an air stream and an electric heating system for heating the air stream.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more working fluid circuits (e.g., refrigerant circuits). Tubes within the heat exchangers 28 and 30 may circulate a working fluid (e.g., a refrigerant), such as R-410A, 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 working fluid 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 working fluid to ambient air, and the heat exchanger 30 may function as an evaporator where the working fluid absorbs heat to cool an air flow. 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 an electric heating system 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.

[0037] 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.

[0038] The HVAC unit 12 also may include other equipment for implementing the thermal cycle. Compressors 42 increase the pressure and temperature of the working fluid before the working fluid 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 configuration44. 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.

[0039] 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.

[0040] FIG. 3 is a cutaway perspective view of an embodiment of 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 working fluid conduits 54 (e.g., refrigerant conduits) that operatively couple the indoor HVAC unit 56 to the outdoor HVAC unit 58. The indoor HVAC unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor HVAC 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 block leaves and other debris or contaminants from entering the outdoor HVAC unit 58. The working fluid conduits 54 transfer working fluid between the indoor HVAC unit 56 and the outdoor HVAC unit 58, typically transferring primarily liquid working fluid in one direction and primarily vaporized working fluid in an opposite direction.

[0041] When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor HVAC unit 58 serves as a condenser for re-condensing vaporized working fluid flowing from the indoor HVAC unit 56 to the outdoor HVAC unit 58 via one of the working fluid conduits 54. In these applications, a heat exchanger 62 of the indoor unit functions as an evaporator. Specifically, the heat exchanger 62 receives liquid working fluid, which may be expanded by an expansion device, and evaporates the working fluid before returning it to the outdoor HVAC unit 58.

[0042] The outdoor HVAC unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor HVAC unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor HVAC unit 58 and exits the unit at a temperature higher than it entered. The indoor HVAC unit 56 includes a blower or fan 66 that directs air through or across the 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 the 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 the set point minus a small amount, the residential heating and cooling system 50 may stop the refrigeration cycle temporarily.

[0043] 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 HVAC unit 58 will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor HVAC unit 58 as the air passes over the heat exchanger 60. The heat exchanger 62 will receive a flow of air directed therethrough and will heat the air by condensing the working fluid.

[0044] In some embodiments, the indoor HVAC unit 56 may include a heating system 70 (e.g., electric heating system). For example, the indoor HVAC unit 56 may include the heating system 70 when the residential heating and cooling system 50 is not configured to operate as a heat pump. The heating system 70 may include one or more electric heating coils, among other components, inside the indoor HVAC unit 56. The electric heating coils may convert electrical energy to thermal energy, such that air directed across the electric heating coils is heated. The heated air may then be routed from the heating system 70 to the ductwork 68 for heating the residence 52.

[0045] FIG. 4 is schematic of 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 working fluid (e.g., 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.

[0046] 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.

[0047] The compressor 74 compresses a working fluid 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 working fluid vapor delivered by the compressor 74 to the condenser 76 may transfer heat to a fluid directed across the condenser 76, such as ambient or environmental air 96. The working fluid vapor may condense to a working fluid liquid in the condenser 76 as a result of thermal heat transfer with the environmental air 96. The liquid working fluid from the condenser 76 may flow through the expansion device 78 to the evaporator 80.

[0048] The liquid working fluid delivered to the evaporator 80 may absorb heat from another air stream, such as a supply air flow 98 provided to the building 10 or the residence 52. For example, the supply air flow 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid working fluid in the evaporator 80 may undergo a phase change from the liquid working fluid to a working fluid vapor. In this manner, the evaporator 80 may reduce the temperature of the supply air flow 98 via thermal heat transfer with the working fluid. Thereafter, the vapor working fluid exits the evaporator 80 and returns to the compressor 74 by a suction line to complete the cycle.

[0049] In some embodiments, the vapor compression system 72 may further include a reheat heat exchanger. In the illustrated embodiment, the reheat heat exchanger is represented as part of the evaporator 80. The reheat heat exchanger is positioned downstream of the evaporator 80 relative to the supply air flow 98 and may reheat the supply air flow 98 when the supply air flow 98 is overcooled to remove humidity from the supply air flow 98 before the supply air flow 98 is directed to the building 10 or the residence 52.

[0050] 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 flow 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.

[0051] As briefly discussed above, embodiments of the present disclosure are directed to an HVAC system configured to enable improved operation during operating conditions that may otherwise cause low pressures of working fluid within a working fluid circuit of the HVAC system. For example, the disclosed techniques may be incorporated with HVAC systems having a reheat circuit and / or a heat pump system. To provide context for the following discussion, FIG. 5 is a schematic of an embodiment of an HVAC system 100 that includes a reheat circuit 102, in accordance with present techniques. It should be appreciated that the HVAC system 100 may include embodiments or components of the HVAC unit 12 shown in FIGS. 1 and 2, embodiments or components of the split residential heating and cooling system 50 shown in FIG. 3, a rooftop unit (RTU), or any other suitable air handling unit or HVAC system.

[0052] In the illustrated embodiment, the HVAC system 100 includes a working fluid circuit 104 (e.g., refrigerant circuit, vapor compression circuit, vapor compression system) having an evaporator 106 (e.g., indoor coil, first heat exchanger, indoor heat exchanger, cooling coil), a condenser 108 (e.g., outdoor coil, second heat exchanger, outdoor heat exchanger), a compressor 110, and an expansion valve 112. The reheat circuit 102 includes a reheat heat exchanger 114 (e.g., reheat coil). As will be appreciated, the reheat circuit 102 may be considered as a portion of the working fluid circuit 104 and / or a portion of the working fluid circuit 104 may be considered as a portion of the reheat circuit 102. The HVAC system 100 further includes a blower 116 (e.g., fan, supply air fan) configured to draw an air flow 118 (e.g., supply air flow) sequentially across the evaporator 106 and the reheat heat exchanger 114. In other words, the reheat heat exchanger 114 is disposed downstream of the evaporator 106 with respect to a direction of the air flow 118.

[0053] During operation of the HVAC system 100, the blower 116 may force the air flow 118 across the evaporator 106 to enable cooled working fluid circulating through one or more coils or tubes of the evaporator 106 to absorb thermal energy from the air flow 118. The evaporator 106 may absorb an amount of thermal energy from the air flow 118 that is sufficient to cause moisture suspended within the air flow 118 to condense (e.g., on the evaporator 106). Accordingly, the air flow 118 discharged from the evaporator 106 may be a cooled, dehumidified air flow 120 having a temperature value and a humidity level that are less than a temperature value and a humidity level of the air flow 118 received by the evaporator 106.

[0054] The evaporator 106 may discharge, via a conduit 122 (e.g., a suction conduit, suction line) of the working fluid circuit 104, a flow of heated working fluid that has absorbed thermal energy from the air flow 118. The heated working fluid may flow through the conduit 122 and toward the compressor 110 of the working fluid circuit 104. The compressor 110 may compress the working fluid, which adds heat to the working fluid, and direct the heated working fluid through a reheat valve 124 (e.g., three-way valve, modulating valve) disposed along the working fluid circuit 104. The reheat valve 124 is configured to regulate diversion (e.g., division, apportionment) of the heated working fluid between the condenser 108 and the reheat heat exchanger 114 of the HVAC system 100, as discussed further below.

[0055] The condenser 108 may include one or more tubes or coils that are configured to facilitate heat exchange between heated working fluid received from the reheat valve 124 and the ambient environment. For example, the HVAC system 100 may include one or more fans 126 (e.g., condenser fans, outdoor fans) that are configured to draw an air flow 128 (e.g., ambient air flow) across the condenser 108. Accordingly, the air flow 128 may absorb thermal energy from the working fluid circulating through the condenser 108, thereby cooling and condensing the working fluid before the working fluid is discharged from the condenser 108 via a conduit 130 (e.g., liquid conduit portion) of the working fluid circuit 104. The cooled working fluid discharged from the condenser 108 may be directed along the conduit 130, through the expansion valve 112, and to the evaporator 106 to cool the air flow 118.

[0056] In certain embodiments, one or more check valves 132 may be disposed along conduits of the working fluid circuit 104 and / or the reheat circuit 102. The check valves 132 are configured to block working fluid flow through the conduits in undesired directions (e.g., in an upstream direction, with respect to a flow of the working fluid through the compressor 110). In some embodiments, the HVAC system 100 may additionally include one or more bleed conduits configured to redirect working fluid through the working fluid circuit 104 (e.g., from the reheat heat exchanger 114 to the compressor 110, from the conduit 130 to the reheat heat exchanger 114).

[0057] The reheat valve 124 may be a three-way valve (e.g., modulating valve, three-way modulating valve) that is configured to control respective amounts of working fluid directed from the compressor 110 to the reheat heat exchanger 114 and / or from the compressor 110 to the condenser 108. In particular, the reheat valve 124 may control flow parameters, such as a flow rate and / or a flow pressure, of the working fluid flowing from the compressor 110 into the reheat heat exchanger 114 and / or of the working fluid flowing from the compressor 110 into the condenser 108. As such, the reheat valve 124 enables operation of the HVAC system 100 in a reheat mode (e.g., dehumidification mode), in which at least a portion of the heated working fluid discharged from the compressor 110 is directed through the reheat heat exchanger 114 to reheat the cooled, dehumidified air flow 120. The reheat valve 124 also enables operation of the HVAC system 100 in a cooling mode, in which substantially no heated working fluid discharged from the compressor 110 is directed through the reheat heat exchanger 114. In the reheat or dehumidification mode, the working fluid directed through the reheat heat exchanger 114 may heat the cooled, dehumidified air flow 120 to generate a warm or “neutral” dehumidified air flow that is directed by the blower 116 toward a conditioned space 134. In the cooling mode, the cooled, dehumidified air flow 120 may not be heated by the reheat heat exchanger 114 and may be directed to the conditioned space 134 by the blower 116.

[0058] The HVAC system 100 further includes a controller 150 (e.g., a control system, a control panel, control circuitry, automation controller) that is communicatively coupled to one or more components of the HVAC system 100 (e.g., compressor 110, expansion valve 112, blower 116, fan 126, reheat valve 124) and is configured to monitor, adjust, and / or otherwise control operation of the components of the HVAC system 100. For example, one or more control transfer devices, such as wires, cables, wireless communication devices, and the like, may communicatively couple the compressor 110, the expansion valve 112, the blower 116, the fan 126, the control device 16 (e.g., a thermostat), and / or any other suitable components of the HVAC system 100 to the controller 150. That is, the compressor 110, the expansion valve 112, the blower 116, the fan 126, and / or the control device 16 may each have one or more communication components that facilitate wired or wireless (e.g., via a network) communication with the controller 150. In some embodiments, the communication components may include a network interface that enables the components of the HVAC system 100 to communicate via various protocols such as EtherNet / IP, ControlNet, DeviceNet, or any other communication network protocol. Alternatively, the communication components may enable the components of the HVAC system 100 to communicate via mobile telecommunications technology, Bluetooth®, near-field communications technology, and the like. As such, the compressor 110, the expansion valve 112, the blower 116, the fan 126, and / or the control device 16 may wirelessly communicate data between each other. In other embodiments, operational control of certain components of the HVAC system 100 may be regulated by one or more relays or switches (e.g., a 24 volt alternating current [VAC] relay).

[0059] In some embodiments, the controller 150 may be a component of or may include the control panel 82. In other embodiments, the controller 150 may be a standalone controller, a dedicated controller, or another suitable controller included in the HVAC system 100. In any case, the controller 150 is configured to control components of the HVAC system 100 in accordance with the techniques discussed herein. The controller 150 includes processing circuitry 152, such as a microprocessor, which may execute software for controlling the components of the HVAC system 100. The processing circuitry 152 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 processing circuitry 152 may include one or more reduced instruction set (RISC) processors.

[0060] The controller 150 also include a memory device 154 (e.g., a memory) that may store information, such as instructions, control software, look up tables, configuration data, etc. The memory device 154 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 154 may store a variety of information and may be used for various purposes. For example, the memory device 154 may store processor-executable instructions including firmware or software for the processing circuitry 152 execute, such as instructions for controlling components of the HVAC system 100. In some embodiments, the memory device 154 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 152 to execute. The memory device 154 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 154 may store data, instructions, and any other suitable data.

[0061] As mentioned above, the HVAC system 100 may further include one or more pressure switches configured to detect a pressure of the working fluid circulated through the HVAC system 100 (e.g., reheat circuit 102, working fluid circuit 104). For example, in the illustrated embodiment, the HVAC system 100 includes a first pressure switch 160 (e.g., low-pressure switch, first pressure sensor) and a second pressure switch 162 (e.g., hot gas reheat [HGRH] pressure switch, second pressure sensor). The first and second pressure switches 160 and 162 are configured to detect a pressure of the working fluid within the conduit 122 (e.g., suction conduit). In other words, the first and second pressure switches 160 and 162 may be configured to detect a pressure of the working fluid at an inlet 164 (e.g., suction inlet) of the compressor 110. The first and second pressure switches 160 and 162 are also configured to be actuated or “tripped” (e.g., transition from a closed configuration to an open configuration) in response to detection of a pressure of the working fluid that falls below a respective threshold pressure (e.g., trip pressure, threshold value) of the first and second pressure switches 160 and 162. That, the first pressure switch 160 (e.g., low-pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a first threshold pressure (e.g., trip pressure), and the second pressure switch 162 (e.g., HGRH pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a second threshold pressure (e.g., trip pressure). The second threshold pressure may be greater than the first threshold pressure. For example, the second threshold pressure may be greater than the first threshold pressure by approximately 5 pounds per square inch (psi), 10 psi, 15 psi, 20 psi, 25 psi, at least 10 psi, or any other suitable pressure value. In some embodiments, the first threshold pressure is approximately 50 to 60 psi, and the second threshold pressure is approximately 70 to 80 psi.

[0062] In some circumstances, the pressure of the working fluid at the inlet 164 of the compressor 110 may decrease below the first threshold pressure and / or the second threshold pressure due to operational conditions of the HVAC system 100. For example, low ambient temperatures (e.g., low temperatures of the air flow 128) may cause the pressure of the working fluid within the working fluid circuit 104 to decrease. That is, air flow 128 (e.g., ambient air flow) at low temperatures that is drawn across the condenser 108 may further reduce the temperature and / or pressure of the working fluid directed through the condenser 108, which may result in an overall decrease in the pressure of the working fluid circulated through the working fluid circuit 104 and the reheat circuit 102. Accordingly, actuation of the first pressure switch 160 or the second pressure switch 162 may induce an operational adjustment in the HVAC system 100. For example, upon detection of a pressure of the working fluid at the inlet 164 of the compressor 110 below the first threshold pressure, the first pressure switch 160 may be actuated. In some embodiments, the first pressure switch 160 (e.g., low-pressure switch) may transmit data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 160 to the controller 150. In response, the controller 150 may adjust operation of the HVAC system 100, such as by suspending operation of the compressor 110 and / or otherwise interrupting operation of the HVAC system 100.

[0063] As will be appreciated, during operation in the reheat mode discussed above, less working fluid may be directed through the condenser 108, for example, because a portion of the working fluid is directed through the reheat heat exchanger 114 by the reheat valve 124. During such operation, the HVAC system 100 may be further susceptible to low pressures of working fluid within the HVAC system 100 due to low temperatures of the air flow 128 (e.g., ambient air flow). Accordingly, embodiments of the present disclosure include the second pressure switch 162 configured to be actuated or tripped in response to detection of a working fluid pressure below the second threshold pressure that is greater than the first threshold pressure of the first pressure switch 160. In the illustrated embodiment, the second pressure switch 162 (e.g., HGRH pressure switch) is configured to interrupt supply of power to the fan 126 (e.g., outdoor fan, outdoor heat exchanger fan) configured to force the air flow 128 across the condenser 108. For example, the second pressure switch 162 may be disposed along a power conduit 166 (e.g., power line, power supply connection, signal line, 24 volt [V] power wire) configured to direct supply of power to the fan 126. In some embodiments, the power conduit 166 may be configured to direct supply of power from the controller 150 to the fan 126, as shown. Alternatively, the power conduit 166 may be configured to direct supply of power from another power source or another component of the HVAC system 100 to the fan 126.

[0064] In any case, upon detection of a working fluid pressure below the second threshold pressure, the second pressure switch 162 may open and interrupt supply of power to the fan 126 via the power conduit 166. Operation of the fan 126 may therefore be suspended, which may reduce, substantially reduce, or suspend flow of the air flow 128 across the condenser 108. In this way, heat transfer between the air flow 128 and the working fluid within the condenser 108 may be reduced, which may result in an increase in the temperature and / or pressure of the working fluid directed through the condenser 108 (e.g., less cooling of the working fluid) and thereby result in an increase in the overall pressure of the working fluid circulated through the working fluid circuit 104 and the reheat circuit 102 (e.g., including the pressure of the working fluid at the inlet 164 of the compressor 110). As the second threshold pressure is greater than the first threshold pressure of the first pressure switch 160, actuation or tripping of the first pressure switch 160 (e.g., low-pressure switch) may thereby be avoided. In this way, the HVAC system 100 may continue to operate in the reheat mode without undesired interruption in operation of the HVAC system 100 to condition the air flow 118.

[0065] In some embodiments, subsequent to actuation or tripping of the second pressure switch 162, the second pressure switch 162 may be reset or “closed” upon detection of a working fluid pressure at the inlet 164 of the compressor 110 that is greater than a second additional threshold pressure. For example, the second additional threshold pressure may be greater than the second threshold pressure (e.g., trip pressure) by approximately 25 psi, 30 psi, 35 psi, 40 psi, 45 psi, or another suitable pressure value. Upon reset of the second pressure switch 162, supply of power to the fan 126 via the power conduit 166 may resume, and operation of the fan 126 to force the air flow 128 across the condenser 108 may resume.

[0066] FIG. 6 is a schematic of another embodiment of the HVAC system 100 that includes the reheat circuit 102, in accordance with present techniques. The embodiment of FIG. 6 includes certain elements and element numbers similar to those of the embodiment described above with reference to FIG. 5, including the working fluid circuit 104, the reheat valve 124, the reheat heat exchanger 114, the first pressure switch 160 (e.g., low pressure switch), the fan 126, the condenser 108, and so forth. The HVAC system 100 also includes a pressure transducer 180 (e.g., pressure sensor) configured to detect a pressure of the working fluid within the conduit 122 and / or at the inlet 164 of the compressor 110. In some embodiments, the HVAC system 100 may also include the second pressure switch 162 discussed above in addition to the pressure transducer 180.

[0067] The HVAC system 100 also includes a variable speed drive (VSD) 182 (e.g., variable frequency drive) associated with the fan 126. As will be appreciated, the VSD 182 is configured to enable operation of the fan 126 at variable speeds. In this way, the fan 126 may operate to draw variable amounts (e.g., flow rates) of the air flow 128 across the condenser 108. The pressure transducer 180 may be communicatively coupled to the controller 150, the VSD 182, or both. In some embodiments, the pressure transducer 180 may be communicatively coupled to the controller 150, and the controller 150 may be communicatively coupled to the VSD 182 and configured to transmit control signals to the VSD 182. In any case, the HVAC system 100 is configured to adjust operation of the fan 126 in response to a pressure of the working fluid at the inlet 164 of the compressor 110 detected by the pressure transducer 180. For example, the pressure transducer 180 and / or the controller 150 may control the VSD 182 to decrease a speed of the fan 126 in response to detection of a reduction in the pressure of the working fluid at the inlet 164 of the compressor 110. In some embodiments, as the pressure of the working fluid at the inlet 164 continues to reduce or fall (e.g., below a threshold value, below the second pressure threshold), the pressure transducer 180 and / or the controller 150 may further decrease the speed of the fan 126 via control of the VSD 182. In this way, reductions in the pressure of the working fluid at the inlet 164 may result in a corresponding reduction in the speed of the fan 126 to enable a reduced an amount of the air flow 128 directed across the condenser 108. As similarly discussed above, a reduction in the amount of air flow 128 directed across the condenser 108 may result in less cooling of the working fluid in the condenser 108, which may cause an increase in the overall pressure of the working fluid within the working fluid circuit 104 and the reheat circuit 102. In some embodiments, the HVAC system 100 may instruct the VSD 182 to suspend operation of the fan 126 in response to detection of the second threshold pressure at the inlet 164 of the compressor 110 by the pressure transducer 180 and / or by the second pressure switch 162. In this way, actuation or tripping of the first pressure switch 160 (e.g., low-pressure switch) may be avoided, and the HVAC system 100 may continue to operate in the reheat mode without undesired interruption in operation of the HVAC system 100 to condition the air flow 118.

[0068] FIG. 7 is a schematic of another embodiment of the HVAC system 100, in accordance with present techniques. In the illustrated embodiment, the HVAC system 100 includes a heat pump 200 (e.g., heat pump system). The heat pump 200 may include a portion of or all of the components of the vapor compression system 72 discussed above. The heat pump 200 includes a first heat exchanger 202 (e.g., indoor heat exchanger) and a second heat exchanger 204 (e.g., outdoor heat exchanger) that are fluidly coupled to one another via a working fluid circuit 206 (e.g., one or more conduits, refrigerant circuit). The first heat exchanger 202 may be in thermal communication with (e.g., fluidly coupled to) a thermal load 208 (e.g., a room, space, and / or device) serviced by the heat pump 200, and the second heat exchanger 204 may be in thermal communication with an ambient environment 210 (e.g., the atmosphere) surrounding the HVAC system 100.

[0069] In some embodiments, a blower 212 (e.g., indoor fan) may direct a first air flow (e.g., supply air flow) across the first heat exchanger 202 to facilitate heat exchange between working fluid within the first heat exchanger 202 and the thermal load 208, while a fan 214 may direct a second air flow (e.g., ambient air flow) across the second heat exchanger 204 to facilitate heat exchange between working fluid within the second heat exchanger 204 and the ambient environment 210. An expansion device 216 (e.g., an electronic expansion valve) may be disposed along the working fluid circuit 206 between the first heat exchanger 202 and the second heat exchanger 204 and may be configured to regulate (e.g., throttle) a working fluid flow and / or a working fluid pressure differential between the first and second heat exchangers 202, 204.

[0070] The heat pump 200 also includes a compressor 218 disposed along the working fluid circuit 206. The compressor 218 is configured to direct working fluid flow through the first heat exchanger 202, the second heat exchanger 204, and remaining components (e.g., the expansion device 216) that may be fluidly coupled to the working fluid circuit 206. The working fluid circuit 206 includes a suction conduit 220 and a discharge conduit 222, and the compressor 218 is fluidly coupled to the suction conduit 220 and the discharge conduit 222. Thus, the compressor 218 may draw (e.g., intake) a working fluid flow from the suction conduit 220 and discharge (e.g., output) the working fluid flow through the discharge conduit 222.

[0071] The compressor 218 is fluidly coupled to a remainder of the working fluid circuit 206 via a reversing valve 224 (e.g., switch-over valve). In particular, the reversing valve 224 may include a first port 226 that is fluidly coupled to the suction conduit 220, a second port 228 that is fluidly coupled to the discharge conduit 222, a third port 230 that is fluidly coupled to a first conduit portion 232 of the working fluid circuit 206 extending to the first heat exchanger 202, and a fourth port 234 that is fluidly coupled to a second conduit portion 236 of the working fluid circuit 206 extending to the second heat exchanger 204.

[0072] In the illustrated embodiment, the reversing valve 224 is shown in a first configuration (e.g., heating mode configuration), in which the reversing valve 224 fluidly couples the first port 226 and the fourth port 234 and fluidly couples the second port 228 and the third port 230. The reversing valve 224 is also configured to transition to a second configuration (e.g., cooling mode configuration), in which the reversing valve 224 fluidly couples the first port 226 and the third port 230 and fluidly couples the second port 228 and the fourth port 234. In the first configuration, the reversing valve 224 enables the compressor 218 to receive a flow of working fluid from the second heat exchanger 204 and to discharge a flow of working fluid to the first heat exchanger 202. In the second configuration, the reversing valve 224 enables the compressor 218 to receive a flow of working from the first heat exchanger 202 and to discharge a flow of working fluid to the second heat exchanger 204. In this way, while in the first configuration, the reversing valve 224 enables the heat pump 200 to operate in a heating mode, in which the second heat exchanger 204 absorbs thermal energy from the ambient environment 210, and the first heat exchanger 202 rejects the absorbed thermal energy (e.g., absorbed from the ambient environment 210) to the thermal load 208 (e.g., supply air flow directed across the first heat exchanger 202) to heat the thermal load 208. In the second configuration, the reversing valve 224 enables the heat pump 200 to operate in a cooling mode, the first heat exchanger 202 absorbs thermal energy from the thermal load 208 to cool the thermal load 208 (e.g., cool the supply air flow), and the second heat exchanger 204 rejects the absorbed thermal energy (e.g., absorbed from the thermal load 208) to the ambient environment 210 (e.g., ambient air flow).

[0073] In accordance with present techniques, the HVAC system 100 may further include one or more pressure switches (e.g., pressure sensors) configured to detect a pressure of the working fluid circulated through the HVAC system 100 (e.g., heat pump 200). As similarly described above, the heat pump 200 includes a first pressure switch 250 (e.g., low-pressure switch, first pressure sensor) and a second pressure switch 252 (e.g., defrost pressure switch, second pressure sensor). The first and second pressure switches 250 and 252 are configured to detect a pressure of the working fluid within the suction conduit 220. For example, the first and second pressure switches 250 and 252 may be configured to detect a pressure of the working fluid at the first port 226 of the reversing valve 224 and / or at an inlet (e.g., suction inlet) of the compressor 218. The first and second pressure switches 250 and 252 are also configured to be actuated or “tripped” in response to detection of a pressure of the working fluid that falls below a respective threshold pressure (e.g., trip pressure) of the first and second pressure switches 250 and 252. That, the first pressure switch 250 (e.g., low-pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a first threshold pressure (e.g., trip pressure), and the second pressure switch 252 (e.g., defrost pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a second threshold pressure (e.g., trip pressure). The second threshold pressure may be greater than the first threshold pressure. For example, the second threshold pressure may be greater than the first threshold pressure by approximately 5 pounds per square inch (psi), 10 psi, 15 psi, 20 psi, 25 psi, or any other suitable pressure value. In some embodiments, the first threshold pressure is approximately 50 to 60 psi, and the second threshold pressure is approximately 70 to 80 psi.

[0074] In some circumstances, the pressure of the working fluid within the suction conduit 220 may decrease below the first threshold pressure and / or the second threshold pressure, such as in certain operating modes of the heat pump 200 and / or due to operational conditions of the HVAC system 100. For example, operation of the heat pump 200 in the heating mode and in low ambient temperatures (e.g., low temperatures of ambient air directed across the second heat exchanger 204, low temperatures of the ambient environment 210) may cause the pressure of the working fluid within the working fluid circuit 206 to decrease. That is, ambient air flow at low temperatures that is drawn across the second heat exchanger 204 may reduce the temperature and / or pressure of the working fluid directed through the second heat exchanger 204, which may result in an overall pressure decrease of the working fluid circulated through the working fluid circuit 206. In some instances, the temperature of the second heat exchanger 204 may decrease such that the second heat exchanger 204 is susceptible to formation of frost or other frozen fluid on the second heat exchanger 204. Accordingly, actuation of the first pressure switch 250 or the second pressure switch 252 may induce an operational adjustment in the heat pump 200. For example, upon detection of a pressure of the working fluid in the suction conduit 220 below the first threshold pressure, the first pressure switch 250 may be actuated. In some embodiments, the first pressure switch 250 (e.g., low pressure switch) may transmit data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 250. To this end, the heat pump 200 may include an embodiment of the controller 150 (e.g., including processing circuitry 152 and memory device 154) discussed above with reference to FIGS. 5 and 6, and the first pressure switch 250 may be communicatively coupled to the controller 150.

[0075] In response to receipt of data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 250, the controller 150 may adjust operation of the heat pump, such as by suspending operation of the compressor 218 and / or otherwise interrupting operation of the heat pump 200. As will be appreciated, during operation in the heating mode, the second heat exchanger 204 may operate as an evaporator and may reject heat from the working fluid to the ambient environment 210. Thus, in low ambient temperatures, the second heat exchanger 204 may be susceptible to formation of frost or other froze liquid, such as on a surface of the second heat exchanger 204, which may be indicated by particular low pressures of the working fluid discharged by the second heat exchanger 204 and entering the compressor 218 via the reversing valve 224 and the suction conduit 220. Accordingly, embodiments of the present disclosure include the second pressure switch 252 configured to be actuated or tripped in response to detection of a working fluid pressure below the second threshold pressure that is greater than the first threshold pressure of the first pressure switch 250. In the illustrated embodiment, the second pressure switch 252 (e.g., defrost pressure switch) is configured to interrupt supply of power to the blower 212 (e.g., indoor fan) configured to force an air flow (e.g., supply air flow) across the first heat exchanger 202. For example, the second pressure switch 252 may be disposed along a power conduit 254 (e.g., power line, power supply connection, signal line, 24 volt [V] power wire) configured to direct supply of power to the blower 212. In some embodiments, the power conduit 254 may be configured to direct supply of power from the controller 150 to the blower 212, as shown. Alternatively, the power conduit 254 may be configured to direct supply of power from another power source or another component of the heat pump 200 to the blower 212.

[0076] In any case, upon (e.g., in response to) detection of a working fluid pressure below the second threshold pressure, the second pressure switch 250 may open and interrupt supply of power to the blower 212 via the power conduit 254. Operation of the blower 212 may therefore be suspended, which may reduce, substantially reduce, or suspend flow of air (e.g., supply air) across the first heat exchanger 202. In this way, heat transfer between the supply air and the working fluid within the first heat exchanger 202 may be reduced, which may result in an increase in the temperature and / or pressure of the working fluid directed through the first heat exchanger 202 (e.g., less cooling of the working fluid) and thereby result in an increase in the overall pressure and temperature of the working fluid circulated through the working fluid circuit 206. Indeed, the pressure and temperature of the working fluid circulated through the second heat exchanger 204 may also be increased as a result, which may increase the temperature of the second heat exchanger 204 above a dew point temperature and / or maintain a temperature of the second heat exchanger 204 above the dew point temperature. In this way, frost accumulated on the second heat exchanger 204 may be melted and / or formation of frost on the second heat exchanger 204 may be avoided. As the second threshold pressure is greater than the first threshold pressure of the first pressure switch 250, actuation or tripping of the first pressure switch 250 (e.g., low-pressure switch) may thereby be avoided. In this way, the heat pump 200 may continue to operate in the heating mode without undesired interruption and / or inefficient operation of the heat pump 200 due to frost formation on the second heat exchanger 204.

[0077] In some embodiments, subsequent to actuation or tripping of the second pressure switch 252, the second pressure switch 252 may be reset or “closed” upon detection of a working fluid pressure at the suction conduit 220 that is greater than a second additional threshold pressure. For example, the second additional threshold pressure may be greater than the second threshold pressure (e.g., trip pressure) by approximately 25 psi, 30 psi, 35 psi, 40 psi, 45 psi, or another suitable pressure value. Upon reset of the second pressure switch 250, supply of power to the blower 212 via the power conduit 254 may resume, and operation of the blower 212 to draw the supply air flow across the first heat exchanger 202 may resume.

[0078] FIG. 8 is a schematic of another embodiment of the HVAC system 100 that includes the heat pump 200, in accordance with present techniques. The embodiment of FIG. 8 includes certain elements and element numbers similar to those of the embodiment described above with reference to FIG. 7, including the first heat exchanger 202, the second heat exchanger 204, the working fluid circuit 206, the reversing valve 224, the first pressure switch 250 (e.g., low pressure switch, first pressure sensor), the blower 212, and so forth. The heat pump 200 also includes a pressure transducer 260 (e.g., second pressure sensor) configured to detect a pressure of the working fluid within the suction conduit 220, at the first port 226, and / or at the inlet of the compressor 218. In some embodiments, the heat pump 200 may also include the second pressure switch 252 discussed above in addition to the pressure transducer 260.

[0079] The heat pump 200 also includes a variable speed drive (VSD) 262 (e.g., variable frequency drive) associated with the blower 212. As will be appreciated, the VSD 262 is configured to enable operation of the blower 212 at variable speeds. In this way, the blower 212 may operate to draw variable amounts (e.g., flow rates) of the supply air flow across the first heat exchanger 202. The pressure transducer 260 may be communicatively coupled to the controller 150, the VSD 262, or both. In some embodiments, the pressure transducer 260 may be communicatively coupled to the controller 150, and the controller 150 may be communicatively coupled to the VSD 262 and configured to transmit control signals to the VSD 262. In any case, the heat pump 200 is configured to adjust operation of the blower 212 in response to a pressure of the working fluid within the suction conduit 220 detected by the pressure transducer 260. For example, the pressure transducer 260 and / or the controller 150 may control the VSD 262 to decrease a speed of the blower 212 in response to detection of a reduction in the pressure of the working fluid within the suction conduit 220. In some embodiments, as the pressure of the working fluid within the suction conduit 220 continues to reduce or fall (e.g., below a threshold value, below the second pressure threshold), the pressure transducer 260 and / or the controller 150 may further decrease the speed of the blower 212 via control of the VSD 262.

[0080] In this way, reductions in the pressure of the working fluid within the suction conduit 220 may result in a corresponding reduction in the speed of the blower 212 to enable a reduction an amount of the supply air flow directed across the first heat exchanger 202. As similarly discussed above, a reduction in the amount of supply air flow directed across the first heat exchanger 202 may result in less cooling of the working fluid in the first heat exchanger 202, which may cause an increase in the overall pressure of the working fluid within the working fluid circuit 206, as well as an increase in the temperature of the second heat exchanger 204. Thus, formation of frost on the second heat exchanger 204 may be avoided and / or frost formed on the second heat exchanger 204 may be melted. In some embodiments, the heat pump 200 may instruct the VSD 262 to suspend operation of the blower 212 in response to detection of the second threshold pressure within the suction conduit 220 by the pressure transducer 260 and / or by the second pressure switch 252. In this way, actuation or tripping of the first pressure switch 250 (e.g., low-pressure switch) may be avoided, and the heat pump 200 may continue to operate in the heating mode without undesired interruption and / or inefficient operation of the heat pump 200 due to frost formation on the second heat exchanger 204.

[0081] Additionally or alternatively, in some embodiments the controller 150 may be configured to control operation of the VSD 182 based on data (e.g., feedback) from one or more sensors 264. For example, the sensors 264 may include a first sensor 266 (e.g., first temperature sensor) configured to detect an operating parameter of the second heat exchanger 204 (e.g., outdoor heat exchanger), such as a temperature of the working fluid within and / or discharged from the second heat exchanger 204, a surface temperature (e.g., coil temperature) of the second heat exchanger 204, or another suitable parameter. The sensors 264 may also include a second sensor 268 (e.g., second temperature sensor) configured to detect an operating parameter of the ambient environment 210. For example, the second sensor 268 may detect a temperature (e.g., dew point temperature) of the ambient environment 210. The sensors 264 may be communicatively coupled to the controller 264 and be configured to transmit data and / or feedback indicative of the respective parameters detected or measured by the sensors 264. Based on the data, the controller 150 may adjust operation of the heat pump 200, such as operation of the VSD 262 to adjust operation of the blower 212. In accordance with the present techniques, the controller 150 may adjust operation of the VSD 262 to control (e.g., reduce) a speed of the blower 212 based on a comparison to a detected temperature of the working fluid at the second heat exchanger 204 and / or a detected temperature of the second heat exchanger 204 relative to a detected temperature, such as a dew point temperature, of the ambient environment 210. For example, the controller 150 may operate to reduce a speed of the blower 212 in order to maintain a temperature of the second heat exchanger 204 above a dew point temperature of the ambient environment 210 and mitigate formation of frost (e.g., freezing of moisture) on the second heat exchanger 204. In some embodiments, an amount of a speed reduction of the blower 212 implemented by the controller 150 may be based on (e.g., associated with, correspond to, proportional to) a difference value between the detected temperature associated with the second heat exchanger 204 and the detected temperature (e.g., dew point temperature) of the ambient environment 210.

[0082] FIG. 9 is a schematic of an embodiment of a control system 300 that may be implemented with an embodiment of the HVAC system 100 to enable one or more of the operations described herein. The control system 300 may include one or more components similar to those described above. For example, the control system 300 may include an embodiment of the controller 150 (e.g., control board, thermostat, HVAC unit controller, transformer) and a pressure switch 302 (e.g., pressure sensor, pressure transducer, HGRH pressure switch, defrost pressure switch). For example, the pressure switch 302 may be an embodiment of the second pressure switch 162 or the second pressure switch 252 described above. It should be appreciated that the control system 300 may be implemented with any of the embodiments of the HVAC system 100 described above to enable functionalities in accordance with the present techniques.

[0083] The control system 300 also includes a contactor 304 (e.g., relay) including a coil 306 (e.g., contactor coil) and a switch 308 (e.g., contactor switch, contacts). The coil 306 is configured to receive a signal 310 (e.g., 24V signal) from the controller 150 and to be energized based on receipt of the signal 310. Energization of the coil 304 causes the switch 308 to close, which enables supply of power (e.g., 120V power, 240V power) from a power source 312 to a fan motor 314 via the switch 308 and via a power line 316 (e.g., high voltage wiring, one or more power wires). For example, upon energization, the coil 306 may cause (e.g., magnetically cause, physically cause) contacts of the switch 308 to close and establish a flow path (e.g., electrical current path) to enable supply of power from the power source 312 to the fan motor 314 via the contactor 304. The fan motor 314 may be configured to drive operation (e.g., rotation) of an embodiment of the fan 126 or an embodiment of the blower 212. In some embodiments, the power line 316 may enable transmission of power to a variable speed drive (e.g., VSD 182, VSD 262) configured to enable operation of the fan motor 314 at variable speeds.

[0084] As described above, the pressure switch 302 is configured to detect a pressure of working fluid along the conduit 122 of the working fluid circuit 104 and / or at the inlet 164 of the compressor 110. The pressure switch 302 may be a pressure switch configured to transition from a closed configuration to an open configuration (e.g., trip) in response to detection of a pressure of the working fluid below a threshold pressure (e.g., second threshold pressure value, pressure value, threshold value). In the open configuration, the pressure switch 302 may block transmission of the signal 310 from the controller 150 to the contactor 304. Thus, the coil 306 may not receive the signal 310 and may not be energized, which causes the switch 308 to remain in an open configuration or to transition from a closed configuration to the open configuration. In the open configuration, the switch 308 may block transmission of power to the fan motor 314, which suspends operation of the fan motor 314 and the fan or blower associated with the fan motor 314.

[0085] As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for operating HVAC systems, such as HVAC systems having a reheat circuit and / or HVAC systems having a heat pump system, during operational conditions and / or modes that may induce low pressures of working fluid within the HVAC system. In particular, present embodiments enable adjustment to operation of one or more fans of the HVAC system in response to detection of a pressure of a working fluid directed to an inlet of a compressor that is below a threshold pressure and without causing operational interruptions of the HVAC system typically incurred in response to detections of working fluid pressures below a certain limit. It should be understood that the technical effects and technical problems in the specification are examples and are not limiting. Indeed, it should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems.

[0086] While only certain features and embodiments 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 disclosure.

[0087] 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, or those unrelated to enablement. 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.

[0088] The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Examples

Embodiment Construction

[0017]One or more specific embodiments of the present disclosure will be described below. These described embodiments are 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'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.

[0018]When introducing elements of various embodiments of...

BACKGROUND

[0001] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described 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 admissions of prior art.

[0002] A heating, ventilation, and / or air conditioning (HVAC) system may be used to thermally regulate an environment, such as a space within a building, home, or other structure. The HVAC system generally includes a vapor compression system having heat exchangers, such as a condenser and an evaporator, which transfer thermal energy between the HVAC system and the environment. Typically, a compressor is fluidly coupled to a working fluid circuit of the vapor compression system and is configured to circulate a working fluid (e.g., refrigerant) between the condenser and the evaporator. In this way, the compressor facilitates heat exchange between the working fluid, the condenser, and the evaporator. In some cases, working fluid flow through the working fluid circuit may be reversible, such that the condenser is operable as an evaporator (e.g., a heat absorber), and the evaporator is operable a condenser (e.g., a heat rejector). Accordingly, the HVAC system may operate as a heat pump system in multiple operating modes (e.g., a cooling mode, a heating mode) to provide both heating and cooling to the building with one working fluid circuit. In some application, the HVAC system may include a reheat heat exchanger, which, together with the evaporator, is positioned along an air flow path of the HVAC system. The evaporator and the reheat heat exchanger may operate concurrently to facilitate dehumidification and temperature regulation of an air flow traveling along the air flow path and entering a building serviced by the HVAC system. Accordingly, the HVAC system may facilitate supply of a temperature regulated and dehumidified air flow to the building. Unfortunately, existing HVAC systems may be susceptible to inefficiencies and / or operational interruptions in certain operating conditions.SUMMARY

[0003] A summary of certain embodiments disclosed herein is set forth below. It should be noted that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

[0004] In one embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a working fluid circuit having a compressor configured to circulate a working fluid along the working fluid circuit and a suction conduit configured to direct the working fluid to the compressor. The HVAC system also includes a first pressure sensor configured to detect a first pressure of the working fluid along the suction conduit and a second pressure sensor configured to detect a second pressure of the working fluid along the suction conduit. The HVAC system is configured to adjust operation of the compressor in response to detection of the first pressure of the working fluid below a first threshold value, and to adjust operation of a fan of the HVAC system in response to detection of the second pressure of the working fluid below a second threshold value.

[0005] In another embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a working fluid circuit having a compressor, a suction conduit configured to direct a working fluid to the compressor, and a heat exchanger configured to place the working fluid in a heat exchange relationship with an air flow. The HVAC system also includes a fan configured to force the air flow across the heat exchanger, a pressure switch configured to detect a first pressure of the working fluid along the suction conduit, where the pressure switch is configured to actuate in response to detection of the first pressure below a first threshold value, and a pressure sensor configured to detect a second pressure of the working fluid along the suction conduit. The HVAC system is configured to adjust operation of the fan in response to detection of the second pressure of the working fluid below a second threshold value, and the second threshold value is greater than the first threshold value.

[0006] In a further embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a compressor configured to circulate a working fluid along a working fluid circuit, a suction conduit of the working fluid circuit configured to direct the working fluid to the compressor, a heat exchanger of the working fluid circuit configured to place the working fluid in a heat exchange relationship with an air flow, and a fan configured to force the air flow across the heat exchanger. The HVAC system also includes a first pressure switch configured to detect a first pressure of the working fluid along the suction conduit, where the first pressure switch is configured to interrupt supply of power to the compressor in response to detection of the first pressure below a first threshold value. The HVAC system further includes a second pressure switch configured to detect a second pressure of the working fluid along the suction conduit, where the second pressure switch is configured to interrupt supply of power to the fan in response to detection of the second pressure below a second threshold value, and the second threshold value is greater than the first threshold value.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0008] FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0009] FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

[0010] FIG. 3 is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

[0011] FIG. 4 is a schematic diagram of an embodiment of a vapor compression system used in an HVAC system, in accordance with an aspect of the present disclosure;

[0012] FIG. 5 is a schematic diagram of an embodiment of an HVAC system including a reheat circuit, in accordance with an aspect of the present disclosure;

[0013] FIG. 6 is a schematic diagram of an embodiment of an HVAC system including a reheat circuit, in accordance with an aspect of the present disclosure;

[0014] FIG. 7 is a schematic diagram of an embodiment of an HVAC system including a heat pump system, in accordance with an aspect of the present disclosure;

[0015] FIG. 8 is a schematic diagram of an embodiment of an HVAC system including a heat pump system, in accordance with an aspect of the present disclosure; and

[0016] FIG. 9 is a schematic of an embodiment of a control system for an HVAC system, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0017] One or more specific embodiments of the present disclosure will be described below. These described embodiments are 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'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.

[0018] When introducing elements of various embodiments of the present disclosure, the articles “a,”“an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0019] As used herein, the terms “approximately,”“generally,” and “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to mean that the property value may be within + / −5%, within + / −4%, within + / −3%, within + / −2%, within + / −1%, or even closer, of the given value. Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to mean that the given feature is within + / −5%, within + / −4%, within + / −3%, within + / −2%, within + / −1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Further, it should be understood that mathematical terms, such as “planar,”“slope,”“perpendicular,”“parallel,” and so forth are intended to encompass features of surfaces or elements as understood to one of ordinary skill in the relevant art, and should not be rigidly interpreted as might be understood in the mathematical arts. For example, a “planar” surface is intended to encompass a surface that is machined, molded, or otherwise formed to be substantially flat or smooth (within related tolerances) using techniques and tools available to one of ordinary skill in the art. Similarly, a surface having a “slope” is intended to encompass a surface that is machined, molded, or otherwise formed to be oriented at an angle (e.g., incline) with respect to a point of reference using techniques and tools available to one of ordinary skill in the art.

[0020] As briefly discussed above, a heating, ventilation, and air conditioning (HVAC) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC system may include a vapor compression system that operates to transfer thermal energy between a working fluid, such as a refrigerant, and a fluid to be conditioned, such as air. The vapor compression system includes heat exchangers, such as a condenser and an evaporator, which are fluidly coupled to one another via one or more conduits of a working fluid loop or circuit. A compressor may be used to circulate the working fluid through the conduits and other components of the working fluid circuit (e.g., an expansion device) and, thus, enable the transfer of thermal energy between components of the working fluid circuit (e.g., between the condenser and the evaporator) and one or more thermal loads (e.g., an environmental air flow, a supply air flow).

[0021] In some embodiments, the HVAC system may include a heat pump (e.g., a heat pump system, a reverse-cycle heat pump) having a first heat exchanger (e.g., a heating and / or cooling coil, an indoor coil, the evaporator) positioned within or otherwise fluidly coupled to the space to be conditioned, a second heat exchanger (e.g., a heating and / or cooling coil, an outdoor coil, the condenser) positioned in or otherwise fluidly coupled to an ambient environment (e.g., the atmosphere), and a pump (e.g., the compressor) configured to circulate the working fluid (e.g., refrigerant) between the first and second heat exchangers to enable heat transfer between the thermal load and the ambient environment, for example. The heat pump system is operable to provide both cooling or heating to the space to be conditioned (e.g., a room, zone, or other region within a building) by adjusting a flow of the working fluid through the working fluid circuit.

[0022] For example, during operation of the heat pump system in a cooling mode, the compressor may direct working fluid through the working fluid circuit and the first and second heat exchangers in a first flow direction. While receiving working fluid in the first flow direction, the first heat exchanger, which may be positioned within the space to be conditioned, may operate as an evaporator. Thus, working fluid flowing through the first heat exchanger may absorb thermal energy from an air flow (e.g., supply air flow) directed to the space. Further, the second heat exchanger, which may be positioned in the ambient environment surrounding the heat pump system, may operate as a condenser to reject the heat absorbed by the working fluid flowing from the first heat exchanger (e.g., to an ambient air flow directed across the second heat exchanger). In this way, the heat pump system may facilitate cooling of the space or other thermal load serviced by (e.g., in thermal communication with) the first heat exchanger.

[0023] Conversely, during operation in a heating mode, a reversing valve (e.g., switch-over valve) enables the compressor to direct working fluid through the working fluid circuit and the first and second heat exchangers in a second flow direction, opposite the first flow direction. While receiving working fluid in the second flow direction, the first heat exchanger may operate as a condenser instead of an evaporator, and the second heat exchanger may operate as an evaporator instead of a condenser. As such, the first heat exchanger may receive (e.g., from the second heat exchanger) a flow of heated working fluid to reject heat to thermal load serviced by the first heat exchanger (e.g., an air flow directed to the space) and, thus, facilitate heating of the thermal load. In this way, the heat pump system may facilitate either heating or cooling of the thermal load based on the selected operational mode of the heat pump system (e.g., based on a flow direction of working fluid along the working fluid circuit).

[0024] During operation of the HVAC system in a cooling mode, the first heat exchanger (e.g., evaporator, indoor coil) cools an air flow (e.g., supply air flow), which may cause moisture suspended or contained within the air flow to condense. For example, moisture condensed from the air flow may accumulate on a surface of the first heat exchanger as condensate. The condensate may flow along the first heat exchanger and drip into a drain pan that may be positioned beneath the first heat exchanger (e.g., with respect to a direction of gravity). As such, a humidity level of the flow of conditioned air discharging from the first heat exchanger may be less than a humidity level of the air flow received by the evaporator. The fan may direct the cooled, dehumidified air discharging from the first heat exchanger along an air flow path and toward a conditioned space, such as a room in a building. In this manner, the HVAC system may operate to regulate a temperature and / or humidity level within an interior of the building.

[0025] In some cases, it may be desirable to reduce a humidity level within the conditioned space without substantially adjusting a current temperature within the conditioned space (e.g., without heating or cooling an interior of a building). For example, in certain cases, a temperature within the building (e.g., a temperature within one or more rooms, zones, or other spaces of the building) may be within a threshold range of a designated target temperature setpoint, while a humidity level within the building may exceed a designated target humidity level setpoint beyond an acceptable tolerance. In such situations, it may be desirable to operate the HVAC system in a dehumidification mode, in which the HVAC system may operate to dehumidify the building without substantially heating or cooling the conditioned space within building.

[0026] To facilitate operation in the dehumidification mode, the HVAC system may include a reheat circuit having a reheat heat exchanger (e.g., reheat coil, third heat exchanger) that is fluidly coupled to the vapor compression system (e.g., working fluid circuit) and is configured to reheat (e.g., increase a temperature of) the cooled, dehumidified air discharging from the first heat exchanger before the air is directed into the building or other conditioned space. For example, the reheat heat exchanger may be positioned within the air flow path and downstream of the first heat exchanger (e.g., evaporator), such that the reheat heat exchanger may receive the cooled, dehumidified air discharging from the first heat exchanger. The compressor may be configured to receive, from the first heat exchanger, a flow of heated working fluid that has previously absorbed thermal energy from the supply air flow. The compressor may compress the working fluid received from the first heat exchanger, which adds more heat to the working fluid. The heated working fluid may be directed from the compressor toward and through a reheat valve (e.g., a three-way valve, hot gas reheat valve, modulating value) that is adjustable to direct at least a portion of the heated working fluid to the reheat heat exchanger, while directing a remaining portion of the heated working fluid toward the second heat exchanger (e.g., condenser). As such, the cooled, dehumidified air discharged from the first heat exchanger and directed across the reheat heat exchanger may re-absorb thermal energy from the heated working fluid circulating through the reheat heat exchanger. Accordingly, the reheat heat exchanger may increase a temperature of the cooled, dehumidified air discharged from the first heat exchanger prior to delivery of the dehumidified air to the conditioned space. The working fluid discharged from the reheat heat exchanger may be directed along the working fluid circuit toward another portion of the working fluid circuit, such as upstream of the compressor and / or first heat exchanger (e.g., evaporator) and downstream of the second heat exchanger (e.g., condenser).

[0027] Unfortunately, in certain operating conditions, the HVAC system may operate inefficiently and / or may be susceptible to operational interruptions. For example, during cold ambient (e.g., atmospheric) conditions, a pressure of the working fluid circulated within the working fluid circuit may fall below an acceptable or desirable level. In traditional HVAC systems, low pressure levels of working fluid within the working fluid circuit may cause inefficient operation and / or operational interruption (e.g., “tripping”) of the HVAC system. In some instances, operation of the HVAC system may be suspended, and intervention by a technician or operator of the HVAC system may be prompted. Further, in some HVAC systems, such as HVAC systems including a heat pump system, the second heat exchanger (e.g., condenser, outdoor coil) of the HVAC system may be susceptible to formation of frost (e.g., freezing condensate, freezing moisture) on the second heat exchanger during operation of the HVAC system (e.g., in a heating mode, in a reheat mode). Indeed, formation of frost on outdoor coils of existing HVAC systems may result in operational inefficiencies and / or operational interruptions.

[0028] Accordingly, embodiments of the present disclosure are directed to systems and methods that enable improved operation of HVAC systems, such as HVAC systems having a reheat circuit and / or HVAC systems having a heat pump system, during operational conditions and / or modes that may induce low pressures of working fluid within the HVAC system. For example, an HVAC system having a reheat circuit may include a pressure switch (e.g., hot gas reheat [HGRH] pressure switch) configured to detect a pressure of working fluid at an inlet or suction line of the compressor. The pressure switch may be an additional or second pressure switch that is incorporated with another pressure switch (e.g., low-pressure switch) of the working fluid circuit. The HGRH pressure switch may be actuated based on a detection of a pressure of the working fluid at the inlet (e.g., suction conduit) of the compressor that is below a threshold pressure, which may be a pressure that is above a corresponding threshold pressure associated with the low-pressure switch. In accordance with present techniques, actuation of the HGRH pressure switch may initiate an interruption in operation of a fan (e.g., outdoor fan) of the HVAC system that is configured to direct an air flow (e.g., ambient air flow) across the second heat exchanger (e.g., condenser, outdoor coil). Therefore, the fan may not force the ambient air flow across the second heat exchanger, which may reduce transfer of thermal energy between the ambient air flow and the working fluid circulated through the second heat exchanger. As a result, a pressure of the working fluid within the working fluid circuit may increase, which may avoid actuation of the low-pressure switch of the HVAC system and subsequent operational interruption of the HVAC system. In this way, the disclosed techniques enable improved operation of the HVAC system having the reheat circuit.

[0029] Also in accordance with present techniques, an HVAC system having a heat pump system may include a pressure switch (e.g., defrost pressure switch) configured to detect a pressure of working fluid at an inlet or suction conduit of the compressor. The pressure switch may be an additional or second pressure switch that is incorporated with another pressure switch (e.g., low-pressure switch) of the working fluid circuit. The defrost pressure switch may be actuated based on a detection of a pressure of the working fluid at the inlet of the compressor that is below a threshold pressure, which may be a pressure that is above a corresponding threshold pressure associated with the low-pressure switch. Actuation of the defrost pressure switch may initiate an interruption in operation of a fan (e.g., indoor fan) of the HVAC system that is configured to direct an air flow (e.g., supply air flow) across the first heat exchanger (e.g., indoor coil). Therefore, the fan may not force the supply air flow across the first heat exchanger, which may reduce transfer of thermal energy between the supply air flow and the working fluid circulated through the first heat exchanger. As a result, a pressure of the working fluid within the working fluid circuit may increase, which may increase a temperature of the working fluid directed through the second heat exchanger (e.g., outdoor coil) and thereby reduce formation of frost or other frozen liquid on the second heat exchanger. In this way, the disclosed techniques enable improved operation (e.g., reduced operational interruptions) of the HVAC system including the heat pump system. While the present techniques are described in the context of controlling air flow via operation control of fans or blowers, it should be appreciated that other components may additionally or alternatively be utilized to control air flow, such as dampers, louvers, and so forth.

[0030] Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and air conditioning (HVAC) system for environmental management that employs one or more HVAC units in accordance with the present disclosure. 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.

[0031] In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12, which may be a heat pump or may include a reheat system, in accordance with present embodiments. 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.

[0032] 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 working fluid circuit configured to operate in different modes. In other embodiments, the HVAC unit 12 may include one or more working fluid circuits (e.g., refrigeration circuits) for cooling an air stream and an electric heating system for heating the air stream.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more working fluid circuits (e.g., refrigerant circuits). Tubes within the heat exchangers 28 and 30 may circulate a working fluid (e.g., a refrigerant), such as R-410A, 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 working fluid 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 working fluid to ambient air, and the heat exchanger 30 may function as an evaporator where the working fluid absorbs heat to cool an air flow. 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 an electric heating system 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.

[0037] 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.

[0038] The HVAC unit 12 also may include other equipment for implementing the thermal cycle. Compressors 42 increase the pressure and temperature of the working fluid before the working fluid 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 configuration44. 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.

[0039] 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.

[0040] FIG. 3 is a cutaway perspective view of an embodiment of 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 working fluid conduits 54 (e.g., refrigerant conduits) that operatively couple the indoor HVAC unit 56 to the outdoor HVAC unit 58. The indoor HVAC unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor HVAC 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 block leaves and other debris or contaminants from entering the outdoor HVAC unit 58. The working fluid conduits 54 transfer working fluid between the indoor HVAC unit 56 and the outdoor HVAC unit 58, typically transferring primarily liquid working fluid in one direction and primarily vaporized working fluid in an opposite direction.

[0041] When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor HVAC unit 58 serves as a condenser for re-condensing vaporized working fluid flowing from the indoor HVAC unit 56 to the outdoor HVAC unit 58 via one of the working fluid conduits 54. In these applications, a heat exchanger 62 of the indoor unit functions as an evaporator. Specifically, the heat exchanger 62 receives liquid working fluid, which may be expanded by an expansion device, and evaporates the working fluid before returning it to the outdoor HVAC unit 58.

[0042] The outdoor HVAC unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor HVAC unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor HVAC unit 58 and exits the unit at a temperature higher than it entered. The indoor HVAC unit 56 includes a blower or fan 66 that directs air through or across the 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 the 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 the set point minus a small amount, the residential heating and cooling system 50 may stop the refrigeration cycle temporarily.

[0043] 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 HVAC unit 58 will serve as an evaporator to evaporate refrigerant and thereby cool air entering the outdoor HVAC unit 58 as the air passes over the heat exchanger 60. The heat exchanger 62 will receive a flow of air directed therethrough and will heat the air by condensing the working fluid.

[0044] In some embodiments, the indoor HVAC unit 56 may include a heating system 70 (e.g., electric heating system). For example, the indoor HVAC unit 56 may include the heating system 70 when the residential heating and cooling system 50 is not configured to operate as a heat pump. The heating system 70 may include one or more electric heating coils, among other components, inside the indoor HVAC unit 56. The electric heating coils may convert electrical energy to thermal energy, such that air directed across the electric heating coils is heated. The heated air may then be routed from the heating system 70 to the ductwork 68 for heating the residence 52.

[0045] FIG. 4 is schematic of 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 working fluid (e.g., 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.

[0046] 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.

[0047] The compressor 74 compresses a working fluid 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 working fluid vapor delivered by the compressor 74 to the condenser 76 may transfer heat to a fluid directed across the condenser 76, such as ambient or environmental air 96. The working fluid vapor may condense to a working fluid liquid in the condenser 76 as a result of thermal heat transfer with the environmental air 96. The liquid working fluid from the condenser 76 may flow through the expansion device 78 to the evaporator 80.

[0048] The liquid working fluid delivered to the evaporator 80 may absorb heat from another air stream, such as a supply air flow 98 provided to the building 10 or the residence 52. For example, the supply air flow 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid working fluid in the evaporator 80 may undergo a phase change from the liquid working fluid to a working fluid vapor. In this manner, the evaporator 80 may reduce the temperature of the supply air flow 98 via thermal heat transfer with the working fluid. Thereafter, the vapor working fluid exits the evaporator 80 and returns to the compressor 74 by a suction line to complete the cycle.

[0049] In some embodiments, the vapor compression system 72 may further include a reheat heat exchanger. In the illustrated embodiment, the reheat heat exchanger is represented as part of the evaporator 80. The reheat heat exchanger is positioned downstream of the evaporator 80 relative to the supply air flow 98 and may reheat the supply air flow 98 when the supply air flow 98 is overcooled to remove humidity from the supply air flow 98 before the supply air flow 98 is directed to the building 10 or the residence 52.

[0050] 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 flow 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.

[0051] As briefly discussed above, embodiments of the present disclosure are directed to an HVAC system configured to enable improved operation during operating conditions that may otherwise cause low pressures of working fluid within a working fluid circuit of the HVAC system. For example, the disclosed techniques may be incorporated with HVAC systems having a reheat circuit and / or a heat pump system. To provide context for the following discussion, FIG. 5 is a schematic of an embodiment of an HVAC system 100 that includes a reheat circuit 102, in accordance with present techniques. It should be appreciated that the HVAC system 100 may include embodiments or components of the HVAC unit 12 shown in FIGS. 1 and 2, embodiments or components of the split residential heating and cooling system 50 shown in FIG. 3, a rooftop unit (RTU), or any other suitable air handling unit or HVAC system.

[0052] In the illustrated embodiment, the HVAC system 100 includes a working fluid circuit 104 (e.g., refrigerant circuit, vapor compression circuit, vapor compression system) having an evaporator 106 (e.g., indoor coil, first heat exchanger, indoor heat exchanger, cooling coil), a condenser 108 (e.g., outdoor coil, second heat exchanger, outdoor heat exchanger), a compressor 110, and an expansion valve 112. The reheat circuit 102 includes a reheat heat exchanger 114 (e.g., reheat coil). As will be appreciated, the reheat circuit 102 may be considered as a portion of the working fluid circuit 104 and / or a portion of the working fluid circuit 104 may be considered as a portion of the reheat circuit 102. The HVAC system 100 further includes a blower 116 (e.g., fan, supply air fan) configured to draw an air flow 118 (e.g., supply air flow) sequentially across the evaporator 106 and the reheat heat exchanger 114. In other words, the reheat heat exchanger 114 is disposed downstream of the evaporator 106 with respect to a direction of the air flow 118.

[0053] During operation of the HVAC system 100, the blower 116 may force the air flow 118 across the evaporator 106 to enable cooled working fluid circulating through one or more coils or tubes of the evaporator 106 to absorb thermal energy from the air flow 118. The evaporator 106 may absorb an amount of thermal energy from the air flow 118 that is sufficient to cause moisture suspended within the air flow 118 to condense (e.g., on the evaporator 106). Accordingly, the air flow 118 discharged from the evaporator 106 may be a cooled, dehumidified air flow 120 having a temperature value and a humidity level that are less than a temperature value and a humidity level of the air flow 118 received by the evaporator 106.

[0054] The evaporator 106 may discharge, via a conduit 122 (e.g., a suction conduit, suction line) of the working fluid circuit 104, a flow of heated working fluid that has absorbed thermal energy from the air flow 118. The heated working fluid may flow through the conduit 122 and toward the compressor 110 of the working fluid circuit 104. The compressor 110 may compress the working fluid, which adds heat to the working fluid, and direct the heated working fluid through a reheat valve 124 (e.g., three-way valve, modulating valve) disposed along the working fluid circuit 104. The reheat valve 124 is configured to regulate diversion (e.g., division, apportionment) of the heated working fluid between the condenser 108 and the reheat heat exchanger 114 of the HVAC system 100, as discussed further below.

[0055] The condenser 108 may include one or more tubes or coils that are configured to facilitate heat exchange between heated working fluid received from the reheat valve 124 and the ambient environment. For example, the HVAC system 100 may include one or more fans 126 (e.g., condenser fans, outdoor fans) that are configured to draw an air flow 128 (e.g., ambient air flow) across the condenser 108. Accordingly, the air flow 128 may absorb thermal energy from the working fluid circulating through the condenser 108, thereby cooling and condensing the working fluid before the working fluid is discharged from the condenser 108 via a conduit 130 (e.g., liquid conduit portion) of the working fluid circuit 104. The cooled working fluid discharged from the condenser 108 may be directed along the conduit 130, through the expansion valve 112, and to the evaporator 106 to cool the air flow 118.

[0056] In certain embodiments, one or more check valves 132 may be disposed along conduits of the working fluid circuit 104 and / or the reheat circuit 102. The check valves 132 are configured to block working fluid flow through the conduits in undesired directions (e.g., in an upstream direction, with respect to a flow of the working fluid through the compressor 110). In some embodiments, the HVAC system 100 may additionally include one or more bleed conduits configured to redirect working fluid through the working fluid circuit 104 (e.g., from the reheat heat exchanger 114 to the compressor 110, from the conduit 130 to the reheat heat exchanger 114).

[0057] The reheat valve 124 may be a three-way valve (e.g., modulating valve, three-way modulating valve) that is configured to control respective amounts of working fluid directed from the compressor 110 to the reheat heat exchanger 114 and / or from the compressor 110 to the condenser 108. In particular, the reheat valve 124 may control flow parameters, such as a flow rate and / or a flow pressure, of the working fluid flowing from the compressor 110 into the reheat heat exchanger 114 and / or of the working fluid flowing from the compressor 110 into the condenser 108. As such, the reheat valve 124 enables operation of the HVAC system 100 in a reheat mode (e.g., dehumidification mode), in which at least a portion of the heated working fluid discharged from the compressor 110 is directed through the reheat heat exchanger 114 to reheat the cooled, dehumidified air flow 120. The reheat valve 124 also enables operation of the HVAC system 100 in a cooling mode, in which substantially no heated working fluid discharged from the compressor 110 is directed through the reheat heat exchanger 114. In the reheat or dehumidification mode, the working fluid directed through the reheat heat exchanger 114 may heat the cooled, dehumidified air flow 120 to generate a warm or “neutral” dehumidified air flow that is directed by the blower 116 toward a conditioned space 134. In the cooling mode, the cooled, dehumidified air flow 120 may not be heated by the reheat heat exchanger 114 and may be directed to the conditioned space 134 by the blower 116.

[0058] The HVAC system 100 further includes a controller 150 (e.g., a control system, a control panel, control circuitry, automation controller) that is communicatively coupled to one or more components of the HVAC system 100 (e.g., compressor 110, expansion valve 112, blower 116, fan 126, reheat valve 124) and is configured to monitor, adjust, and / or otherwise control operation of the components of the HVAC system 100. For example, one or more control transfer devices, such as wires, cables, wireless communication devices, and the like, may communicatively couple the compressor 110, the expansion valve 112, the blower 116, the fan 126, the control device 16 (e.g., a thermostat), and / or any other suitable components of the HVAC system 100 to the controller 150. That is, the compressor 110, the expansion valve 112, the blower 116, the fan 126, and / or the control device 16 may each have one or more communication components that facilitate wired or wireless (e.g., via a network) communication with the controller 150. In some embodiments, the communication components may include a network interface that enables the components of the HVAC system 100 to communicate via various protocols such as EtherNet / IP, ControlNet, DeviceNet, or any other communication network protocol. Alternatively, the communication components may enable the components of the HVAC system 100 to communicate via mobile telecommunications technology, Bluetooth®, near-field communications technology, and the like. As such, the compressor 110, the expansion valve 112, the blower 116, the fan 126, and / or the control device 16 may wirelessly communicate data between each other. In other embodiments, operational control of certain components of the HVAC system 100 may be regulated by one or more relays or switches (e.g., a 24 volt alternating current [VAC] relay).

[0059] In some embodiments, the controller 150 may be a component of or may include the control panel 82. In other embodiments, the controller 150 may be a standalone controller, a dedicated controller, or another suitable controller included in the HVAC system 100. In any case, the controller 150 is configured to control components of the HVAC system 100 in accordance with the techniques discussed herein. The controller 150 includes processing circuitry 152, such as a microprocessor, which may execute software for controlling the components of the HVAC system 100. The processing circuitry 152 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 processing circuitry 152 may include one or more reduced instruction set (RISC) processors.

[0060] The controller 150 also include a memory device 154 (e.g., a memory) that may store information, such as instructions, control software, look up tables, configuration data, etc. The memory device 154 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 154 may store a variety of information and may be used for various purposes. For example, the memory device 154 may store processor-executable instructions including firmware or software for the processing circuitry 152 execute, such as instructions for controlling components of the HVAC system 100. In some embodiments, the memory device 154 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 152 to execute. The memory device 154 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 154 may store data, instructions, and any other suitable data.

[0061] As mentioned above, the HVAC system 100 may further include one or more pressure switches configured to detect a pressure of the working fluid circulated through the HVAC system 100 (e.g., reheat circuit 102, working fluid circuit 104). For example, in the illustrated embodiment, the HVAC system 100 includes a first pressure switch 160 (e.g., low-pressure switch, first pressure sensor) and a second pressure switch 162 (e.g., hot gas reheat [HGRH] pressure switch, second pressure sensor). The first and second pressure switches 160 and 162 are configured to detect a pressure of the working fluid within the conduit 122 (e.g., suction conduit). In other words, the first and second pressure switches 160 and 162 may be configured to detect a pressure of the working fluid at an inlet 164 (e.g., suction inlet) of the compressor 110. The first and second pressure switches 160 and 162 are also configured to be actuated or “tripped” (e.g., transition from a closed configuration to an open configuration) in response to detection of a pressure of the working fluid that falls below a respective threshold pressure (e.g., trip pressure, threshold value) of the first and second pressure switches 160 and 162. That, the first pressure switch 160 (e.g., low-pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a first threshold pressure (e.g., trip pressure), and the second pressure switch 162 (e.g., HGRH pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a second threshold pressure (e.g., trip pressure). The second threshold pressure may be greater than the first threshold pressure. For example, the second threshold pressure may be greater than the first threshold pressure by approximately 5 pounds per square inch (psi), 10 psi, 15 psi, 20 psi, 25 psi, at least 10 psi, or any other suitable pressure value. In some embodiments, the first threshold pressure is approximately 50 to 60 psi, and the second threshold pressure is approximately 70 to 80 psi.

[0062] In some circumstances, the pressure of the working fluid at the inlet 164 of the compressor 110 may decrease below the first threshold pressure and / or the second threshold pressure due to operational conditions of the HVAC system 100. For example, low ambient temperatures (e.g., low temperatures of the air flow 128) may cause the pressure of the working fluid within the working fluid circuit 104 to decrease. That is, air flow 128 (e.g., ambient air flow) at low temperatures that is drawn across the condenser 108 may further reduce the temperature and / or pressure of the working fluid directed through the condenser 108, which may result in an overall decrease in the pressure of the working fluid circulated through the working fluid circuit 104 and the reheat circuit 102. Accordingly, actuation of the first pressure switch 160 or the second pressure switch 162 may induce an operational adjustment in the HVAC system 100. For example, upon detection of a pressure of the working fluid at the inlet 164 of the compressor 110 below the first threshold pressure, the first pressure switch 160 may be actuated. In some embodiments, the first pressure switch 160 (e.g., low-pressure switch) may transmit data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 160 to the controller 150. In response, the controller 150 may adjust operation of the HVAC system 100, such as by suspending operation of the compressor 110 and / or otherwise interrupting operation of the HVAC system 100.

[0063] As will be appreciated, during operation in the reheat mode discussed above, less working fluid may be directed through the condenser 108, for example, because a portion of the working fluid is directed through the reheat heat exchanger 114 by the reheat valve 124. During such operation, the HVAC system 100 may be further susceptible to low pressures of working fluid within the HVAC system 100 due to low temperatures of the air flow 128 (e.g., ambient air flow). Accordingly, embodiments of the present disclosure include the second pressure switch 162 configured to be actuated or tripped in response to detection of a working fluid pressure below the second threshold pressure that is greater than the first threshold pressure of the first pressure switch 160. In the illustrated embodiment, the second pressure switch 162 (e.g., HGRH pressure switch) is configured to interrupt supply of power to the fan 126 (e.g., outdoor fan, outdoor heat exchanger fan) configured to force the air flow 128 across the condenser 108. For example, the second pressure switch 162 may be disposed along a power conduit 166 (e.g., power line, power supply connection, signal line, 24 volt [V] power wire) configured to direct supply of power to the fan 126. In some embodiments, the power conduit 166 may be configured to direct supply of power from the controller 150 to the fan 126, as shown. Alternatively, the power conduit 166 may be configured to direct supply of power from another power source or another component of the HVAC system 100 to the fan 126.

[0064] In any case, upon detection of a working fluid pressure below the second threshold pressure, the second pressure switch 162 may open and interrupt supply of power to the fan 126 via the power conduit 166. Operation of the fan 126 may therefore be suspended, which may reduce, substantially reduce, or suspend flow of the air flow 128 across the condenser 108. In this way, heat transfer between the air flow 128 and the working fluid within the condenser 108 may be reduced, which may result in an increase in the temperature and / or pressure of the working fluid directed through the condenser 108 (e.g., less cooling of the working fluid) and thereby result in an increase in the overall pressure of the working fluid circulated through the working fluid circuit 104 and the reheat circuit 102 (e.g., including the pressure of the working fluid at the inlet 164 of the compressor 110). As the second threshold pressure is greater than the first threshold pressure of the first pressure switch 160, actuation or tripping of the first pressure switch 160 (e.g., low-pressure switch) may thereby be avoided. In this way, the HVAC system 100 may continue to operate in the reheat mode without undesired interruption in operation of the HVAC system 100 to condition the air flow 118.

[0065] In some embodiments, subsequent to actuation or tripping of the second pressure switch 162, the second pressure switch 162 may be reset or “closed” upon detection of a working fluid pressure at the inlet 164 of the compressor 110 that is greater than a second additional threshold pressure. For example, the second additional threshold pressure may be greater than the second threshold pressure (e.g., trip pressure) by approximately 25 psi, 30 psi, 35 psi, 40 psi, 45 psi, or another suitable pressure value. Upon reset of the second pressure switch 162, supply of power to the fan 126 via the power conduit 166 may resume, and operation of the fan 126 to force the air flow 128 across the condenser 108 may resume.

[0066] FIG. 6 is a schematic of another embodiment of the HVAC system 100 that includes the reheat circuit 102, in accordance with present techniques. The embodiment of FIG. 6 includes certain elements and element numbers similar to those of the embodiment described above with reference to FIG. 5, including the working fluid circuit 104, the reheat valve 124, the reheat heat exchanger 114, the first pressure switch 160 (e.g., low pressure switch), the fan 126, the condenser 108, and so forth. The HVAC system 100 also includes a pressure transducer 180 (e.g., pressure sensor) configured to detect a pressure of the working fluid within the conduit 122 and / or at the inlet 164 of the compressor 110. In some embodiments, the HVAC system 100 may also include the second pressure switch 162 discussed above in addition to the pressure transducer 180.

[0067] The HVAC system 100 also includes a variable speed drive (VSD) 182 (e.g., variable frequency drive) associated with the fan 126. As will be appreciated, the VSD 182 is configured to enable operation of the fan 126 at variable speeds. In this way, the fan 126 may operate to draw variable amounts (e.g., flow rates) of the air flow 128 across the condenser 108. The pressure transducer 180 may be communicatively coupled to the controller 150, the VSD 182, or both. In some embodiments, the pressure transducer 180 may be communicatively coupled to the controller 150, and the controller 150 may be communicatively coupled to the VSD 182 and configured to transmit control signals to the VSD 182. In any case, the HVAC system 100 is configured to adjust operation of the fan 126 in response to a pressure of the working fluid at the inlet 164 of the compressor 110 detected by the pressure transducer 180. For example, the pressure transducer 180 and / or the controller 150 may control the VSD 182 to decrease a speed of the fan 126 in response to detection of a reduction in the pressure of the working fluid at the inlet 164 of the compressor 110. In some embodiments, as the pressure of the working fluid at the inlet 164 continues to reduce or fall (e.g., below a threshold value, below the second pressure threshold), the pressure transducer 180 and / or the controller 150 may further decrease the speed of the fan 126 via control of the VSD 182. In this way, reductions in the pressure of the working fluid at the inlet 164 may result in a corresponding reduction in the speed of the fan 126 to enable a reduced an amount of the air flow 128 directed across the condenser 108. As similarly discussed above, a reduction in the amount of air flow 128 directed across the condenser 108 may result in less cooling of the working fluid in the condenser 108, which may cause an increase in the overall pressure of the working fluid within the working fluid circuit 104 and the reheat circuit 102. In some embodiments, the HVAC system 100 may instruct the VSD 182 to suspend operation of the fan 126 in response to detection of the second threshold pressure at the inlet 164 of the compressor 110 by the pressure transducer 180 and / or by the second pressure switch 162. In this way, actuation or tripping of the first pressure switch 160 (e.g., low-pressure switch) may be avoided, and the HVAC system 100 may continue to operate in the reheat mode without undesired interruption in operation of the HVAC system 100 to condition the air flow 118.

[0068] FIG. 7 is a schematic of another embodiment of the HVAC system 100, in accordance with present techniques. In the illustrated embodiment, the HVAC system 100 includes a heat pump 200 (e.g., heat pump system). The heat pump 200 may include a portion of or all of the components of the vapor compression system 72 discussed above. The heat pump 200 includes a first heat exchanger 202 (e.g., indoor heat exchanger) and a second heat exchanger 204 (e.g., outdoor heat exchanger) that are fluidly coupled to one another via a working fluid circuit 206 (e.g., one or more conduits, refrigerant circuit). The first heat exchanger 202 may be in thermal communication with (e.g., fluidly coupled to) a thermal load 208 (e.g., a room, space, and / or device) serviced by the heat pump 200, and the second heat exchanger 204 may be in thermal communication with an ambient environment 210 (e.g., the atmosphere) surrounding the HVAC system 100.

[0069] In some embodiments, a blower 212 (e.g., indoor fan) may direct a first air flow (e.g., supply air flow) across the first heat exchanger 202 to facilitate heat exchange between working fluid within the first heat exchanger 202 and the thermal load 208, while a fan 214 may direct a second air flow (e.g., ambient air flow) across the second heat exchanger 204 to facilitate heat exchange between working fluid within the second heat exchanger 204 and the ambient environment 210. An expansion device 216 (e.g., an electronic expansion valve) may be disposed along the working fluid circuit 206 between the first heat exchanger 202 and the second heat exchanger 204 and may be configured to regulate (e.g., throttle) a working fluid flow and / or a working fluid pressure differential between the first and second heat exchangers 202, 204.

[0070] The heat pump 200 also includes a compressor 218 disposed along the working fluid circuit 206. The compressor 218 is configured to direct working fluid flow through the first heat exchanger 202, the second heat exchanger 204, and remaining components (e.g., the expansion device 216) that may be fluidly coupled to the working fluid circuit 206. The working fluid circuit 206 includes a suction conduit 220 and a discharge conduit 222, and the compressor 218 is fluidly coupled to the suction conduit 220 and the discharge conduit 222. Thus, the compressor 218 may draw (e.g., intake) a working fluid flow from the suction conduit 220 and discharge (e.g., output) the working fluid flow through the discharge conduit 222.

[0071] The compressor 218 is fluidly coupled to a remainder of the working fluid circuit 206 via a reversing valve 224 (e.g., switch-over valve). In particular, the reversing valve 224 may include a first port 226 that is fluidly coupled to the suction conduit 220, a second port 228 that is fluidly coupled to the discharge conduit 222, a third port 230 that is fluidly coupled to a first conduit portion 232 of the working fluid circuit 206 extending to the first heat exchanger 202, and a fourth port 234 that is fluidly coupled to a second conduit portion 236 of the working fluid circuit 206 extending to the second heat exchanger 204.

[0072] In the illustrated embodiment, the reversing valve 224 is shown in a first configuration (e.g., heating mode configuration), in which the reversing valve 224 fluidly couples the first port 226 and the fourth port 234 and fluidly couples the second port 228 and the third port 230. The reversing valve 224 is also configured to transition to a second configuration (e.g., cooling mode configuration), in which the reversing valve 224 fluidly couples the first port 226 and the third port 230 and fluidly couples the second port 228 and the fourth port 234. In the first configuration, the reversing valve 224 enables the compressor 218 to receive a flow of working fluid from the second heat exchanger 204 and to discharge a flow of working fluid to the first heat exchanger 202. In the second configuration, the reversing valve 224 enables the compressor 218 to receive a flow of working from the first heat exchanger 202 and to discharge a flow of working fluid to the second heat exchanger 204. In this way, while in the first configuration, the reversing valve 224 enables the heat pump 200 to operate in a heating mode, in which the second heat exchanger 204 absorbs thermal energy from the ambient environment 210, and the first heat exchanger 202 rejects the absorbed thermal energy (e.g., absorbed from the ambient environment 210) to the thermal load 208 (e.g., supply air flow directed across the first heat exchanger 202) to heat the thermal load 208. In the second configuration, the reversing valve 224 enables the heat pump 200 to operate in a cooling mode, the first heat exchanger 202 absorbs thermal energy from the thermal load 208 to cool the thermal load 208 (e.g., cool the supply air flow), and the second heat exchanger 204 rejects the absorbed thermal energy (e.g., absorbed from the thermal load 208) to the ambient environment 210 (e.g., ambient air flow).

[0073] In accordance with present techniques, the HVAC system 100 may further include one or more pressure switches (e.g., pressure sensors) configured to detect a pressure of the working fluid circulated through the HVAC system 100 (e.g., heat pump 200). As similarly described above, the heat pump 200 includes a first pressure switch 250 (e.g., low-pressure switch, first pressure sensor) and a second pressure switch 252 (e.g., defrost pressure switch, second pressure sensor). The first and second pressure switches 250 and 252 are configured to detect a pressure of the working fluid within the suction conduit 220. For example, the first and second pressure switches 250 and 252 may be configured to detect a pressure of the working fluid at the first port 226 of the reversing valve 224 and / or at an inlet (e.g., suction inlet) of the compressor 218. The first and second pressure switches 250 and 252 are also configured to be actuated or “tripped” in response to detection of a pressure of the working fluid that falls below a respective threshold pressure (e.g., trip pressure) of the first and second pressure switches 250 and 252. That, the first pressure switch 250 (e.g., low-pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a first threshold pressure (e.g., trip pressure), and the second pressure switch 252 (e.g., defrost pressure switch) may be configured to trip or actuate (e.g., open) in response to the working fluid pressure falling below a second threshold pressure (e.g., trip pressure). The second threshold pressure may be greater than the first threshold pressure. For example, the second threshold pressure may be greater than the first threshold pressure by approximately 5 pounds per square inch (psi), 10 psi, 15 psi, 20 psi, 25 psi, or any other suitable pressure value. In some embodiments, the first threshold pressure is approximately 50 to 60 psi, and the second threshold pressure is approximately 70 to 80 psi.

[0074] In some circumstances, the pressure of the working fluid within the suction conduit 220 may decrease below the first threshold pressure and / or the second threshold pressure, such as in certain operating modes of the heat pump 200 and / or due to operational conditions of the HVAC system 100. For example, operation of the heat pump 200 in the heating mode and in low ambient temperatures (e.g., low temperatures of ambient air directed across the second heat exchanger 204, low temperatures of the ambient environment 210) may cause the pressure of the working fluid within the working fluid circuit 206 to decrease. That is, ambient air flow at low temperatures that is drawn across the second heat exchanger 204 may reduce the temperature and / or pressure of the working fluid directed through the second heat exchanger 204, which may result in an overall pressure decrease of the working fluid circulated through the working fluid circuit 206. In some instances, the temperature of the second heat exchanger 204 may decrease such that the second heat exchanger 204 is susceptible to formation of frost or other frozen fluid on the second heat exchanger 204. Accordingly, actuation of the first pressure switch 250 or the second pressure switch 252 may induce an operational adjustment in the heat pump 200. For example, upon detection of a pressure of the working fluid in the suction conduit 220 below the first threshold pressure, the first pressure switch 250 may be actuated. In some embodiments, the first pressure switch 250 (e.g., low pressure switch) may transmit data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 250. To this end, the heat pump 200 may include an embodiment of the controller 150 (e.g., including processing circuitry 152 and memory device 154) discussed above with reference to FIGS. 5 and 6, and the first pressure switch 250 may be communicatively coupled to the controller 150.

[0075] In response to receipt of data or feedback indicative of the working fluid pressure and / or indicative of actuation of the first pressure switch 250, the controller 150 may adjust operation of the heat pump, such as by suspending operation of the compressor 218 and / or otherwise interrupting operation of the heat pump 200. As will be appreciated, during operation in the heating mode, the second heat exchanger 204 may operate as an evaporator and may reject heat from the working fluid to the ambient environment 210. Thus, in low ambient temperatures, the second heat exchanger 204 may be susceptible to formation of frost or other froze liquid, such as on a surface of the second heat exchanger 204, which may be indicated by particular low pressures of the working fluid discharged by the second heat exchanger 204 and entering the compressor 218 via the reversing valve 224 and the suction conduit 220. Accordingly, embodiments of the present disclosure include the second pressure switch 252 configured to be actuated or tripped in response to detection of a working fluid pressure below the second threshold pressure that is greater than the first threshold pressure of the first pressure switch 250. In the illustrated embodiment, the second pressure switch 252 (e.g., defrost pressure switch) is configured to interrupt supply of power to the blower 212 (e.g., indoor fan) configured to force an air flow (e.g., supply air flow) across the first heat exchanger 202. For example, the second pressure switch 252 may be disposed along a power conduit 254 (e.g., power line, power supply connection, signal line, 24 volt [V] power wire) configured to direct supply of power to the blower 212. In some embodiments, the power conduit 254 may be configured to direct supply of power from the controller 150 to the blower 212, as shown. Alternatively, the power conduit 254 may be configured to direct supply of power from another power source or another component of the heat pump 200 to the blower 212.

[0076] In any case, upon (e.g., in response to) detection of a working fluid pressure below the second threshold pressure, the second pressure switch 250 may open and interrupt supply of power to the blower 212 via the power conduit 254. Operation of the blower 212 may therefore be suspended, which may reduce, substantially reduce, or suspend flow of air (e.g., supply air) across the first heat exchanger 202. In this way, heat transfer between the supply air and the working fluid within the first heat exchanger 202 may be reduced, which may result in an increase in the temperature and / or pressure of the working fluid directed through the first heat exchanger 202 (e.g., less cooling of the working fluid) and thereby result in an increase in the overall pressure and temperature of the working fluid circulated through the working fluid circuit 206. Indeed, the pressure and temperature of the working fluid circulated through the second heat exchanger 204 may also be increased as a result, which may increase the temperature of the second heat exchanger 204 above a dew point temperature and / or maintain a temperature of the second heat exchanger 204 above the dew point temperature. In this way, frost accumulated on the second heat exchanger 204 may be melted and / or formation of frost on the second heat exchanger 204 may be avoided. As the second threshold pressure is greater than the first threshold pressure of the first pressure switch 250, actuation or tripping of the first pressure switch 250 (e.g., low-pressure switch) may thereby be avoided. In this way, the heat pump 200 may continue to operate in the heating mode without undesired interruption and / or inefficient operation of the heat pump 200 due to frost formation on the second heat exchanger 204.

[0077] In some embodiments, subsequent to actuation or tripping of the second pressure switch 252, the second pressure switch 252 may be reset or “closed” upon detection of a working fluid pressure at the suction conduit 220 that is greater than a second additional threshold pressure. For example, the second additional threshold pressure may be greater than the second threshold pressure (e.g., trip pressure) by approximately 25 psi, 30 psi, 35 psi, 40 psi, 45 psi, or another suitable pressure value. Upon reset of the second pressure switch 250, supply of power to the blower 212 via the power conduit 254 may resume, and operation of the blower 212 to draw the supply air flow across the first heat exchanger 202 may resume.

[0078] FIG. 8 is a schematic of another embodiment of the HVAC system 100 that includes the heat pump 200, in accordance with present techniques. The embodiment of FIG. 8 includes certain elements and element numbers similar to those of the embodiment described above with reference to FIG. 7, including the first heat exchanger 202, the second heat exchanger 204, the working fluid circuit 206, the reversing valve 224, the first pressure switch 250 (e.g., low pressure switch, first pressure sensor), the blower 212, and so forth. The heat pump 200 also includes a pressure transducer 260 (e.g., second pressure sensor) configured to detect a pressure of the working fluid within the suction conduit 220, at the first port 226, and / or at the inlet of the compressor 218. In some embodiments, the heat pump 200 may also include the second pressure switch 252 discussed above in addition to the pressure transducer 260.

[0079] The heat pump 200 also includes a variable speed drive (VSD) 262 (e.g., variable frequency drive) associated with the blower 212. As will be appreciated, the VSD 262 is configured to enable operation of the blower 212 at variable speeds. In this way, the blower 212 may operate to draw variable amounts (e.g., flow rates) of the supply air flow across the first heat exchanger 202. The pressure transducer 260 may be communicatively coupled to the controller 150, the VSD 262, or both. In some embodiments, the pressure transducer 260 may be communicatively coupled to the controller 150, and the controller 150 may be communicatively coupled to the VSD 262 and configured to transmit control signals to the VSD 262. In any case, the heat pump 200 is configured to adjust operation of the blower 212 in response to a pressure of the working fluid within the suction conduit 220 detected by the pressure transducer 260. For example, the pressure transducer 260 and / or the controller 150 may control the VSD 262 to decrease a speed of the blower 212 in response to detection of a reduction in the pressure of the working fluid within the suction conduit 220. In some embodiments, as the pressure of the working fluid within the suction conduit 220 continues to reduce or fall (e.g., below a threshold value, below the second pressure threshold), the pressure transducer 260 and / or the controller 150 may further decrease the speed of the blower 212 via control of the VSD 262.

[0080] In this way, reductions in the pressure of the working fluid within the suction conduit 220 may result in a corresponding reduction in the speed of the blower 212 to enable a reduction an amount of the supply air flow directed across the first heat exchanger 202. As similarly discussed above, a reduction in the amount of supply air flow directed across the first heat exchanger 202 may result in less cooling of the working fluid in the first heat exchanger 202, which may cause an increase in the overall pressure of the working fluid within the working fluid circuit 206, as well as an increase in the temperature of the second heat exchanger 204. Thus, formation of frost on the second heat exchanger 204 may be avoided and / or frost formed on the second heat exchanger 204 may be melted. In some embodiments, the heat pump 200 may instruct the VSD 262 to suspend operation of the blower 212 in response to detection of the second threshold pressure within the suction conduit 220 by the pressure transducer 260 and / or by the second pressure switch 252. In this way, actuation or tripping of the first pressure switch 250 (e.g., low-pressure switch) may be avoided, and the heat pump 200 may continue to operate in the heating mode without undesired interruption and / or inefficient operation of the heat pump 200 due to frost formation on the second heat exchanger 204.

[0081] Additionally or alternatively, in some embodiments the controller 150 may be configured to control operation of the VSD 182 based on data (e.g., feedback) from one or more sensors 264. For example, the sensors 264 may include a first sensor 266 (e.g., first temperature sensor) configured to detect an operating parameter of the second heat exchanger 204 (e.g., outdoor heat exchanger), such as a temperature of the working fluid within and / or discharged from the second heat exchanger 204, a surface temperature (e.g., coil temperature) of the second heat exchanger 204, or another suitable parameter. The sensors 264 may also include a second sensor 268 (e.g., second temperature sensor) configured to detect an operating parameter of the ambient environment 210. For example, the second sensor 268 may detect a temperature (e.g., dew point temperature) of the ambient environment 210. The sensors 264 may be communicatively coupled to the controller 264 and be configured to transmit data and / or feedback indicative of the respective parameters detected or measured by the sensors 264. Based on the data, the controller 150 may adjust operation of the heat pump 200, such as operation of the VSD 262 to adjust operation of the blower 212. In accordance with the present techniques, the controller 150 may adjust operation of the VSD 262 to control (e.g., reduce) a speed of the blower 212 based on a comparison to a detected temperature of the working fluid at the second heat exchanger 204 and / or a detected temperature of the second heat exchanger 204 relative to a detected temperature, such as a dew point temperature, of the ambient environment 210. For example, the controller 150 may operate to reduce a speed of the blower 212 in order to maintain a temperature of the second heat exchanger 204 above a dew point temperature of the ambient environment 210 and mitigate formation of frost (e.g., freezing of moisture) on the second heat exchanger 204. In some embodiments, an amount of a speed reduction of the blower 212 implemented by the controller 150 may be based on (e.g., associated with, correspond to, proportional to) a difference value between the detected temperature associated with the second heat exchanger 204 and the detected temperature (e.g., dew point temperature) of the ambient environment 210.

[0082] FIG. 9 is a schematic of an embodiment of a control system 300 that may be implemented with an embodiment of the HVAC system 100 to enable one or more of the operations described herein. The control system 300 may include one or more components similar to those described above. For example, the control system 300 may include an embodiment of the controller 150 (e.g., control board, thermostat, HVAC unit controller, transformer) and a pressure switch 302 (e.g., pressure sensor, pressure transducer, HGRH pressure switch, defrost pressure switch). For example, the pressure switch 302 may be an embodiment of the second pressure switch 162 or the second pressure switch 252 described above. It should be appreciated that the control system 300 may be implemented with any of the embodiments of the HVAC system 100 described above to enable functionalities in accordance with the present techniques.

[0083] The control system 300 also includes a contactor 304 (e.g., relay) including a coil 306 (e.g., contactor coil) and a switch 308 (e.g., contactor switch, contacts). The coil 306 is configured to receive a signal 310 (e.g., 24V signal) from the controller 150 and to be energized based on receipt of the signal 310. Energization of the coil 304 causes the switch 308 to close, which enables supply of power (e.g., 120V power, 240V power) from a power source 312 to a fan motor 314 via the switch 308 and via a power line 316 (e.g., high voltage wiring, one or more power wires). For example, upon energization, the coil 306 may cause (e.g., magnetically cause, physically cause) contacts of the switch 308 to close and establish a flow path (e.g., electrical current path) to enable supply of power from the power source 312 to the fan motor 314 via the contactor 304. The fan motor 314 may be configured to drive operation (e.g., rotation) of an embodiment of the fan 126 or an embodiment of the blower 212. In some embodiments, the power line 316 may enable transmission of power to a variable speed drive (e.g., VSD 182, VSD 262) configured to enable operation of the fan motor 314 at variable speeds.

[0084] As described above, the pressure switch 302 is configured to detect a pressure of working fluid along the conduit 122 of the working fluid circuit 104 and / or at the inlet 164 of the compressor 110. The pressure switch 302 may be a pressure switch configured to transition from a closed configuration to an open configuration (e.g., trip) in response to detection of a pressure of the working fluid below a threshold pressure (e.g., second threshold pressure value, pressure value, threshold value). In the open configuration, the pressure switch 302 may block transmission of the signal 310 from the controller 150 to the contactor 304. Thus, the coil 306 may not receive the signal 310 and may not be energized, which causes the switch 308 to remain in an open configuration or to transition from a closed configuration to the open configuration. In the open configuration, the switch 308 may block transmission of power to the fan motor 314, which suspends operation of the fan motor 314 and the fan or blower associated with the fan motor 314.

[0085] As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for operating HVAC systems, such as HVAC systems having a reheat circuit and / or HVAC systems having a heat pump system, during operational conditions and / or modes that may induce low pressures of working fluid within the HVAC system. In particular, present embodiments enable adjustment to operation of one or more fans of the HVAC system in response to detection of a pressure of a working fluid directed to an inlet of a compressor that is below a threshold pressure and without causing operational interruptions of the HVAC system typically incurred in response to detections of working fluid pressures below a certain limit. It should be understood that the technical effects and technical problems in the specification are examples and are not limiting. Indeed, it should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems.

[0086] While only certain features and embodiments 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 disclosure.

[0087] 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, or those unrelated to enablement. 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.

[0088] The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Examples

Embodiment Construction

[0017]One or more specific embodiments of the present disclosure will be described below. These described embodiments are 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'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.

[0018]When introducing elements of various embodiments of...

Claims

1. A heating, ventilation, and air conditioning (HVAC) system, comprising:a working fluid circuit comprising a compressor configured to circulate a working fluid along the working fluid circuit and a suction conduit configured to direct the working fluid to the compressor;a first pressure sensor configured to detect a first pressure of the working fluid along the suction conduit; anda second pressure sensor configured to detect a second pressure of the working fluid along the suction conduit,wherein the HVAC system is configured to adjust operation of the compressor in response to detection of the first pressure of the working fluid below a first threshold value, and the HVAC system is configured to adjust operation of a fan of the HVAC system in response to detection of the second pressure of the working fluid below a second threshold value.

2. The HVAC system of claim 1, wherein the second threshold value is greater than the first threshold value.

3. The HVAC system of claim 2, wherein the working fluid circuit comprises:a reheat heat exchanger configured to transfer heat from the working fluid to a supply air flow;an outdoor heat exchanger configured to transfer heat from the working fluid to an ambient air flow; anda valve configured to receive the working fluid from the compressor, wherein the value is configured to direct a first portion of the working fluid to the reheat heat exchanger and a second portion of the working fluid to the outdoor heat exchanger.

4. The HVAC system of claim 3, comprising the fan, wherein the fan is configured to force the ambient air flow across the outdoor heat exchanger.

5. The HVAC system of claim 4, wherein the second pressure sensor is a pressure switch, the pressure switch is configured to transition from a closed configuration to an open configuration in response to detection of the second pressure of the working fluid below the second threshold value, and the pressure switch is configured to interrupt supply of power to the fan in the open configuration.

6. The HVAC system of claim 2, wherein the HVAC system comprises a heat pump comprising the working fluid circuit, the heat pump is configured to operate in a heating mode and in a cooling mode, and the working fluid circuit comprises:an indoor heat exchanger configured to transfer heat from the working fluid to a supply air flow in the heating mode; andan outdoor heat exchanger configured to transfer heat from an ambient air flow to the working fluid in the heating mode.

7. The HVAC system of claim 6, comprising the fan, wherein the fan is configured to force the supply air flow across the indoor heat exchanger.

8. The HVAC system of claim 7, wherein the second pressure sensor is a pressure switch, the pressure switch is configured to transition from a closed configuration to an open configuration in response to detection of the second pressure of the working fluid below the second threshold value, and the pressure switch is configured to interrupt supply of power to the fan in the open configuration.

9. The HVAC system of claim 6, wherein the second pressure sensor is a pressure transducer, and the heat pump comprises:the fan, wherein the fan is configured to force the supply air flow across the indoor heat exchanger;a variable speed drive configured to adjust a speed of the fan; anda controller communicatively coupled to the pressure transducer, the fan, and the variable speed drive, wherein the controller is configured to regulate operation of the variable speed drive.

10. The HVAC system of claim 9, wherein the controller is configured to adjust operation of the variable speed drive to reduce a speed of the fan in response to detection of the second pressure of the working fluid below the second threshold value via the pressure transducer.

11. The HVAC system of claim 1, wherein the first pressure sensor is a pressure switch, the pressure switch is configured to transition from a closed configuration to an open configuration in response to detection of the first pressure of the working fluid below the first threshold value, and the pressure switch is configured to interrupt supply of power to the compressor in the open configuration.

12. A heating, ventilation, and air conditioning (HVAC) system, comprising:a working fluid circuit comprising a compressor, a suction conduit configured to direct a working fluid to the compressor, and a heat exchanger configured to place the working fluid in a heat exchange relationship with an air flow;a fan configured to force the air flow across the heat exchanger;a pressure switch configured to detect a first pressure of the working fluid along the suction conduit, wherein the pressure switch is configured to actuate in response to detection of the first pressure below a first threshold value; anda pressure sensor configured to detect a second pressure of the working fluid along the suction conduit,wherein the HVAC system is configured to adjust operation of the fan in response to detection of the second pressure of the working fluid below a second threshold value, and the second threshold value is greater than the first threshold value.

13. The HVAC system of claim 12, wherein the air flow is a supply air flow, the heat exchanger is a reheat heat exchanger configured to transfer heat from the working fluid to the supply air flow, and the fan is an outdoor fan configured to force an ambient air flow across an additional heat exchanger of the working fluid circuit.

14. The HVAC system of claim 13, wherein the pressure sensor is an additional pressure switch, the additional pressure switch is configured to transition from a closed configuration to an open configuration in response to detection of the second pressure of the working fluid below the second threshold value, and the additional pressure switch is configured to interrupt supply of power to the outdoor fan in the open configuration.

15. The HVAC system of claim 12, wherein the HVAC system is a heat pump configured to operate in a heating mode and in a cooling mode, the air flow is a supply air flow, the heat exchanger is an indoor heat exchanger configured to transfer heat from the working fluid to the supply air flow in the heating mode, and the fan is an indoor fan configured to force the supply air flow across the indoor heat exchanger.

16. The HVAC system of claim 15, wherein the pressure sensor is an additional pressure switch is configured to interrupt supply of power to the indoor fan in response to detection of the second pressure of the working fluid below the second threshold value.

17. The HVAC system of claim 15, wherein the pressure sensor is a pressure transducer, and the HVAC system comprises:a variable speed drive configured to adjust a speed of the indoor fan; anda controller communicatively coupled to the pressure transducer, the indoor fan, and the variable speed drive,wherein the controller is configured to control the variable speed drive to reduce the speed of the indoor fan in response to detection of the second pressure of the working fluid below the second threshold value.

18. The HVAC system of claim 17, wherein the controller is configured to suspend operation of the indoor fan in response to a determination that a temperature of an outdoor heat exchanger of the working fluid circuit is within a threshold difference value of a dew point temperature of an ambient environment of the outdoor heat exchanger.

19. The HVAC system of claim 12, wherein the pressure switch is configured to actuate from a closed configuration to an open configuration in response to detection of the first pressure of the working fluid below the first threshold value, and the pressure switch is configured to interrupt supply of power to the compressor in the open configuration.

20. A heating, ventilation, and air conditioning (HVAC) system, comprising:a compressor configured to circulate a working fluid along a working fluid circuit;a suction conduit of the working fluid circuit configured to direct the working fluid to the compressor;a heat exchanger of the working fluid circuit configured to place the working fluid in a heat exchange relationship with an air flow;a fan configured to force the air flow across the heat exchanger;a first pressure switch configured to detect a first pressure of the working fluid along the suction conduit, wherein the first pressure switch is configured to interrupt supply of power to the compressor in response to detection of the first pressure below a first threshold value; anda second pressure switch configured to detect a second pressure of the working fluid along the suction conduit, wherein the second pressure switch is configured to interrupt supply of power to the fan in response to detection of the second pressure below a second threshold value, and wherein the second threshold value is greater than the first threshold value.

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