Heat pump protection against high pressure trips in defrost cycle

Abstract

A HVAC&R system includes a heat pump configured to selectively circulate a working fluid. The heat pump includes an outdoor heat exchanger, an indoor heat exchanger, a compressor, a reversing valve configured to direct the working fluid from the compressor to the outdoor heat exchanger or to the indoor heat exchanger, and a controller. The controller is configured to determine whether a pressure of the working fluid exiting the compressor exceeds a pressure threshold, and, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, control the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of India Provisional Patent Application No. 202421045310, entitled “HEAT PUMP PROTECTION AGAINST HIGH PRESSURE TRIPS IN DEFROST CYCLE,” filed Jun. 12, 2024, which is herein incorporated by reference in its entirety for all purposes.BACKGROUND

[0002] 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 and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0003] Embodiments of the present disclosure are generally directed to a heat pump of a heating, ventilation, and / or air conditioning (HVAC) system, and, more specifically, to features of the heat pump that are configured to reduce, negate, or mitigate adverse effects associated with tripping (e.g., compressor tripping of the heat pump).

[0004] An HVAC system provides proper ventilation and maintains air quality in a confined space, such as a commercial or household building. For example, the HVAC system circulates a refrigerant through a closed circuit (e.g., a refrigerant loop or circuit, vapor compression loop or circuit) including a compressor, a condenser, an expansion device, and an evaporator. During operation, the system components are subject to various pressure, temperature, and load conditions that may fluctuate depending on ambient temperature, system demand, and operating mode. Certain operating conditions, such as excessively high working fluid pressure, may trigger tripping. While necessary for equipment safety, such tripping may interrupt operation and reduce overall system efficiency and reliability. Accordingly, it is now recognized that improved HVAC systems and / or associated control methods are desired.SUMMARY

[0005] 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.

[0006] In an embodiment, a heat pump configured to selectively circulate a working fluid includes an outdoor heat exchanger, an indoor heat exchanger, a compressor, a reversing valve configured to direct the working fluid from the compressor to the outdoor heat exchanger or to the indoor heat exchanger, and a controller. The controller is configured to determine whether a pressure of the working fluid exiting the compressor exceeds a pressure threshold, and, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, control the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

[0007] In another embodiment, a method of operating a heat pump includes determining that a pressure of a working fluid exiting a compressor of the heat pump exceeds a pressure threshold, and, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, controlling the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

[0008] In a further embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a heat pump configured to circulate a working fluid through two or more circuits. The heat pump includes a first outdoor heat exchanger in a first circuit, a second outdoor heat exchanger in a second circuit, an indoor heat exchanger, a compressor, a pressure sensor disposed downstream of the compressor to measure a pressure of the working fluid exiting the compressor, a first temperature sensor configured to measure a first temperature of the working fluid within the first outdoor heat exchanger, a reversing valve configured to direct the working fluid from the compressor to the first outdoor heat exchanger, the second outdoor heat exchanger, or the indoor heat exchanger, and a controller. The controller configured to determine whether the pressure exceeds a pressure threshold, determine whether the first temperature exceeds a temperature threshold, and, in response to determining that the pressure exceeds the pressure threshold or the first temperature exceeds the temperature threshold, control the reversing valve to direct the working fluid to flow from the compressor through the reversing valve to the indoor heat exchanger.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0010] FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and / or air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0011] FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

[0012] FIG. 3 is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

[0013] 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;

[0014] FIG. 5 is a block diagram of an embodiment of a portion of an HVAC system including a heat pump, in accordance with an aspect of the present disclosure;

[0015] FIG. 6 is a block diagram of an embodiment of the portion of the HVAC system in FIG. 5 where the heat pump is operating in heating mode, in accordance with an aspect of the present disclosure; and

[0016] FIG. 7 is a block diagram of an embodiment of the portion of the HVAC system in FIG. 5 where the heat pump is operating in cooling mode or defrost mode, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0017] One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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,”“having,” and “based on” 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] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, to one skilled in the art that embodiments of the present disclosure may be practiced without some of these specific details.

[0020] As briefly discussed above, a heating, ventilation, and / or 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 transfers 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 (e.g., a refrigerant) 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] Generally, the compressor receives low-pressure working fluid vapor from the evaporator and compresses it before delivering high-pressure vapor to the condenser, thereby enabling thermal energy transfer for heating or cooling a confined space. Specifically, in a heat pump system, the indoor and outdoor heat exchangers therein alternate between functioning as an evaporator and a condenser depending on the operation mode (e.g., heating mode, cooling mode, and defrost mode). The system may include a reversing valve that operates to reverse the flow of working fluid within the system to facilitate these mode-dependent role changes. In heating mode, the outdoor heat exchanger functions as the evaporator, absorbing heat from the ambient air, while the indoor heat exchanger functions as the condenser, releasing heat to condition the confined space. Conversely, in cooling mode, the roles are reversed: the indoor heat exchanger acts as the evaporator, absorbing heat from the confined space, and the outdoor heat exchanger acts as the condenser, rejecting heat to the ambient environment. During defrost mode, which is typically initiated during heating operation to remove accumulated frost from the outdoor heat exchanger, the system temporarily reverses the working fluid flow from its heating mode configuration, causing the outdoor heat exchanger to operate as a condenser instead of an evaporator. This reversal of the working fluid flow allows the outdoor coil to be heated, thereby melting the accumulated frost and restoring heat transfer efficiency.

[0022] However, such reversal may cause an elevated discharge pressure of the working fluid exiting the compressor, potentially triggering high-pressure tripping. While tripping is a protective function initiated by safety controls to prevent damage to the compressor or other system components, frequent or premature tripping can interrupt system operation and reduce overall efficiency. For example, because termination of the defrost mode typically requires the compressor to be operating, a compressor trip during defrost may prevent the heat pump from exiting the defrost mode. As a result, the system may continue operating in defrost mode unintentionally when the compressor subsequently restarts. Accordingly, improvements in heat pump systems and associated control methods are desirable to reduce the occurrence of premature tripping and its adverse effects on system performance.

[0023] Present embodiments may monitor the discharge pressure of the working fluid exiting the compressor and terminate the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. The predetermined pressure threshold is set below the discharge pressure level at which the compressor may trip. In accordance with the present disclosure, a heat pump system includes a controller configured to determine whether the discharge pressure of the working fluid exiting the compressor exceeds the predetermined pressure threshold. When the discharge pressure is equal to or exceeds the predetermined threshold, the controller may terminate defrost mode operation by blocking the working fluid flow from flowing from the compressor to the outdoor heat exchanger. In some embodiments, the controller may be further configured to monitor additional operating conditions (e.g., temperature of the working fluid in the outdoor heat exchanger) and determine whether those operation conditions warrant termination of the defrost mode (e.g., a temperature exceeds a predetermined temperature threshold). In some embodiments, the controller may terminate the defrost mode by controlling operation of the reversing valve. In some embodiments, the controller may further control the reversing valve to operate the heat pump in the heating mode. In some embodiments, the controller may continue with the heating mode operation until frosting is detected at the outdoor heat exchanger. These and other aspects of the present disclosure are described in greater detail below with reference to the drawings.

[0024] Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and / or 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.

[0025] In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12. The building 10 may be a commercial structure or a residential structure. As shown, the HVAC unit 12 is disposed on the roof of the building 10; however, the HVAC unit 12 may be located in other equipment rooms or areas adjacent the building 10. The HVAC unit 12 may be a single package unit containing other equipment, such as a blower, integrated air handler, and / or auxiliary heating unit. In other embodiments, the HVAC unit 12 may be part of a split HVAC system, such as the system shown in FIG. 3, which includes an outdoor HVAC unit 58 and an indoor HVAC unit 56.

[0026] The HVAC unit 12 is an air-cooled device that implements a refrigeration cycle to provide conditioned air to the building 10. Specifically, the HVAC unit 12 may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit 12 is a rooftop unit (RTU) that conditions a supply air stream, such as environmental air and / or a return air flow from the building 10. After the HVAC unit 12 conditions the air, the air is supplied to the building 10 via ductwork 14 extending throughout the building 10 from the HVAC unit 12. For example, the ductwork 14 may extend to various individual floors or other sections of the building 10. In certain embodiments, the HVAC unit 12 may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes. In other embodiments, the HVAC unit 12 may include one or more refrigeration circuits for cooling an air stream and a furnace for heating the air stream.

[0027] 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.

[0028] 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 vapor compression 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.

[0029] 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.

[0030] The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more vapor compression circuits. Tubes within the heat exchangers 28 and 30 may circulate a working fluid (e.g., a refrigerant), such as R-410A, R-407, R-134a, R-1234ze, R1233zd, R-32, hydrofluoro olefin (HFO), “natural” refrigerants like ammonia (NH3), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable working fluid through the heat exchangers 28 and 30. As will be appreciated, different working fluid may include different saturation properties depending on chemical composition and mixture composition. 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 stream. In other embodiments, the HVAC unit 12 may operate in a heat pump mode where the roles of the heat exchangers 28 and 30 may be reversed. That is, the heat exchanger 28 may function as an evaporator and the heat exchanger 30 may function as a condenser. In further embodiments, the HVAC unit 12 may include a furnace for heating the air stream that is supplied to the building 10. While the illustrated embodiment of FIG. 2 shows the HVAC unit 12 having two of the heat exchangers 28 and 30, in other embodiments, the HVAC unit 12 may include one heat exchanger or more than two heat exchangers.

[0031] 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.

[0032] 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 configuration 44. However, in other embodiments, any number of the compressors 42 may be provided to achieve various stages of heating and / or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit 12, such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other things.

[0033] 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.

[0034] FIG. 3 illustrates a residential heating and cooling system 50, also in accordance with present techniques. The residential heating and cooling system 50 may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system 50 is a split HVAC system. In general, a residence 52 conditioned by a split HVAC system may include working fluid conduits 54 that operatively couple the indoor unit 56 to the outdoor unit 58. The indoor unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit 58 is typically situated adjacent to a side of residence 52 and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The working fluid conduits 54 transfer working fluid between the indoor unit 56 and the outdoor unit 58, typically transferring primarily liquid working fluid in one direction and primarily vaporized working fluid in an opposite direction.

[0035] When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor unit 58 serves as a condenser for re-condensing vaporized working fluid flowing from the indoor unit 56 to the outdoor 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 unit 58.

[0036] The outdoor unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor unit 58 and exits the unit at a temperature higher than it entered. The indoor unit 56 includes a blower or fan 66 that directs air through or across the indoor heat exchanger 62, where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork 68 that directs the air to the residence 52. The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence 52 is higher than the set point on the thermostat, or 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.

[0037] The residential heating and cooling system 50 may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers 60 and 62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58 will serve as an evaporator to evaporate working fluid and thereby cool air entering the outdoor unit 58 as the air passes over the outdoor heat exchanger 60. The indoor heat exchanger 62 will receive a stream of air blown over it and will heat the air by condensing the working fluid.

[0038] In some embodiments, the indoor unit 56 may include a furnace system 70. For example, the indoor unit 56 may include the furnace system 70 when the residential heating and cooling system 50 is not configured to operate as a heat pump. The furnace system 70 may include a burner assembly and heat exchanger, among other components, inside the indoor unit 56. Fuel is provided to the burner assembly of the furnace 70 where it is mixed with air and combusted to form combustion products. The combustion products may pass through tubes or piping in a heat exchanger, separate from heat exchanger 62, such that air directed by the blower or fan 66 passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system 70 to the ductwork 68 for heating the residence 52.

[0039] FIG. 4 is an embodiment of a vapor compression system 72 that can be used in any of the systems described above. The vapor compression system 72 may circulate a working fluid 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.

[0040] 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.

[0041] 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 passing 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.

[0042] The liquid working fluid delivered to the evaporator 80 may absorb heat from another air stream, such as a supply air stream 98 provided to the building 10 or the residence 52. For example, the supply air stream 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid 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 stream 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.

[0043] In some embodiments, the vapor compression system 72 may further include a reheat coil. In the illustrated embodiment, the reheat coil is represented as part of the evaporator 80. The reheat coil is positioned downstream of the evaporator heat exchanger relative to the supply air stream 98 and may reheat the supply air stream 98 when the supply air stream 98 is overcooled to remove humidity from the supply air stream 98 before the supply air stream 98 is directed to the building 10 or the residence 52.

[0044] It should be appreciated that any of the features described herein may be incorporated with the HVAC unit 12, the residential heating and cooling system 50, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications. Further, a heat pump in any of the HVAC systems illustrated in FIGS. 1-4 and / or any other suitable HVAC system may include, as described in greater detail with reference to later drawings below, a controller configured to block tripping (e.g., tripping caused by elevated working fluid pressure) during defrost mode by terminating the defrost mode upon detecting certain operating conditions of the heat pump. For example, the controller may be configured to monitor, via a pressure sensor, the discharge pressure of the working fluid exiting the compressor and terminate, via control of a reversing valve, the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. Detailed aspects of the heat exchanger, including detailed aspects of the controller, the pressure sensor, and the reversing valve, are described below with reference to later drawings.

[0045] FIG. 5 is a block diagram of an embodiment of a portion of an HVAC system 100 including a heat pump 102, in accordance with an aspect of the present disclosure. A vapor compression system 104 (e.g., vapor compression system 72 of FIG. 3) is incorporated into the heat pump 102 to circulate a working fluid through a circuit starting with a compressor 106 (e.g., compressor 42 of FIG. 2 and compressor 74 of FIG. 4). The circuit may also include a reversing valve 108, an outdoor heat exchanger 110 (e.g., outdoor heat exchanger 60), an expansion device (e.g., expansion valve) 112, and an indoor heat exchanger 114 (e.g., indoor heat exchanger 62).

[0046] In some embodiments, the compressor 106, the reversing valve 108, the outdoor heat exchanger 110, and the expansion device 112 may be housed in an outdoor unit (e.g., outdoor unit 58 of FIG. 3) disposed outside the building (e.g., building 10 of FIG. 1) that contains the space conditioned by the heat pump 102. A piping system may be provided between the components within the outdoor unit to facilitate the flow of the working fluid. In some embodiments, the outdoor unit may include one or more outdoor fans (e.g., fan 64 of FIG. 3) configured to generate airflow across the outdoor heat exchanger 110.

[0047] The indoor heat exchanger 114 may be housed within an indoor unit (e.g., indoor unit 56) located inside of the building, such as in a utility room, an attic, a basement, and so forth. The indoor unit may include an indoor fan (e.g., fan 66 of FIG. 3) configured to direct supply air across the heat exchanger coils of the indoor heat exchanger 114, thereby heating or cooling the air depending on the operating mode. The conditioned supply air may then be distributed to the interior space of the building through a ductwork system (e.g., ductwork 14 of FIG. 1 and ductwork 68 of FIG. 3) or other air distribution system. The indoor unit and the outdoor unit may be fluidly coupled via one or more working fluid conduits (e.g., working fluid conduits 54 of FIG. 3) to form a working fluid circuit (e.g., loop).

[0048] The outdoor heat exchanger 110 may be configured to facilitate thermal exchange between the working fluid and ambient air, and the indoor heat exchanger 114 may be configured to facilitate thermal exchange between the working fluid and the air within the conditioned space. The outdoor heat exchanger 110 and the indoor heat exchanger 114 may, respectively, include one or more heat exchanger coils for circulating the working fluid. As such, the heat pump 102 may operate to heat or cool the space by selectively transferring thermal energy between the indoor air and the ambient air.

[0049] To heat the space, thermal energy may be absorbed from the ambient air by the outdoor heat exchanger 110 and transferred via the working fluid to the indoor heat exchanger 114 for delivery into the conditioned space. Conversely, to cool the space, thermal energy may be absorbed from the indoor air by the indoor heat exchanger 114 and transferred via the working fluid to the outdoor heat exchanger 110 for discharge to the ambient air. The direction of heat transfer may be controlled by the reversing valve 108, and the expansion device 112 may facilitate pressure and temperature regulation of the working fluid to support efficient heating or cooling operations.

[0050] The heat pump 102 may be configured to switch among multiple operating modes, such as heating mode, cooling mode, and defrost mode, by using the reversing valve 108 to control the direction of working fluid flow within the vapor compression circuit. In heating mode, the reversing valve 108 directs high-pressure working fluid from the compressor 106 to the indoor heat exchanger 114. In cooling mode, the reversing valve 108 reverses the flow, routing the high-pressure working fluid from the compressor 106 to the outdoor heat exchanger 110. In defrost mode, which typically initiates from the heating mode during cold weather conditions, the heat pump 102 may temporarily operate in a cooling configuration to melt frost that has accumulated on the outdoor heat exchanger 110. During defrost mode, the reversing valve 108 redirects the heated working fluid to the outdoor heat exchanger 110, raising its temperature and causing the frost to melt. In some embodiment, the system 100 may disable the indoor fan (e.g., fan 66 of FIG. 3) and / or activate auxiliary heating elements during the defrost cycle to maintain comfort within the conditioned space. Once the outdoor heat exchanger 110 has been sufficiently defrosted, the heat pump 102 may automatically return to heating mode and resume normal operation.

[0051] Specifically, the reversing valve 108 may selectively route the discharge of the compressor 106 to either the outdoor heat exchanger 110 or the indoor heat exchanger 114, while routing the return flow from the other heat exchanger back to the compressor 106 to complete the circuit. For example, in heating mode, the reversing valve 108 may route the high-pressure discharge from the compressor 106 to the indoor heat exchanger 114 and route the low-pressure return flow from the outdoor heat exchanger 110 back to the compressor 106. Conversely, in cooling mode, the reversing valve 108 may route the discharge from the compressor 106 to the outdoor heat exchanger 110 and route the return flow from the indoor heat exchanger 114 back to the compressor 106.

[0052] In some embodiments, the reversing valve 108 may have a first port 116 in fluid communication with a discharge port 118 of the compressor 106 and a second port 120 in fluid communication with an inlet port 122 of the compressor 108. Further, the reversing valve 108 may have a third port 124 in fluid communication with the outdoor heat exchanger 110 (e.g., an inlet port 126 thereof) and a fourth port 128 in fluid communication with the indoor heat exchanger 114 (e.g., an inlet port 130 thereof). The reversing valve 108 selectively establishes communication between the ports 116, 120, 124, and 128 depending upon mode of operation of the heat pump 102.

[0053] For example, referring to FIG. 6, a block diagram of an embodiment of the portion of the HVAC system 100 in FIG. 5 where the heat pump 102 is operating in heating mode is illustrated, in accordance with an aspect of the present disclosure. In heating mode, the outdoor heat exchanger 110 functions as an evaporator and the indoor heat exchanger 114 functions as a condenser. The reversing valve 108 connects the first port 116 to the fourth port 128, thereby routing the high-pressure discharge from the compressor 106 to the indoor heat exchanger 114 (e.g., via the inlet port 130). Simultaneously, the reversing valve 108 connects the third port 124 to the second port 120, thereby routing the low-pressure return flow from the outdoor heat exchanger 110 back to the compressor 106 (e.g., via the inlet port 122).

[0054] Thus, in heating mode, the vapor compression circuit may operate as follows: low-pressure, low-temperature working fluid enters the compressor 106, where it is compressed into a high-pressure, high-temperature working fluid (e.g., vapor). The high-pressure, high-temperature working fluid is then discharged from the compressor 106 and directed by the reversing valve 108 to the indoor heat exchanger 114, which functions as a condenser and exchanges heat with an environment (e.g., a building interior). Within the indoor heat exchanger 114, the working fluid releases thermal energy to the indoor air and condenses into a high-pressure liquid. The condensed working fluid then flows through the expansion device 112, where the working fluid is depressurized. The resulting low-pressure working fluid flows into the outdoor heat exchanger 110, which functions as an evaporator. There, the working fluid absorbs heat from the ambient air and evaporates into a low-pressure vapor, which then returns to the compressor 106 to complete the cycle.

[0055] As another example, referring to FIG. 7, a block diagram of an embodiment of the portion of the HVAC system 100 in FIG. 5 where the heat pump 102 is operating in cooling mode or defrost mode is illustrated, in accordance with an aspect of the present disclosure. In cooling mode or defrost mode, the indoor heat exchanger 114 functions as an evaporator and the outdoor heat exchanger 110 functions as a condenser. The reversing valve 108 connects the first port 116 to the third port 124, thereby routing the high-pressure discharge from the compressor 106 to the outdoor heat exchanger 110 (e.g., via the inlet port 126). Simultaneously, the reversing valve 108 connects the fourth port 128 to the second port 120, thereby routing the low-pressure return flow from the indoor heat exchanger 114 back to the compressor 106 (e.g., via the inlet port 122).

[0056] Thus, in cooling mode, the vapor compression circuit may operate as follows: low-pressure, low-temperature working fluid enters the compressor 106, where it is compressed into a high-pressure, high-temperature working fluid (e.g., vapor). The high-pressure, high-temperature working fluid is then discharged from the compressor 106 and directed by the reversing valve 108 to the outdoor heat exchanger 110, which functions as a condenser and exchanges heat with an outdoor environment. Within the outdoor heat exchanger 110, the working fluid releases thermal energy to the ambient air and condenses into a high-pressure liquid. The condensed working fluid then flows through the expansion device 112, where the working fluid is depressurized. The resulting low-pressure working fluid flows into indoor heat exchanger 114, which functions as an evaporator. There, the working fluid absorbs heat from the indoor air, cooling the conditioned space, and evaporates into a low-pressure vapor, which then returns to the compressor 106 to complete the cycle.

[0057] Similarly, in defrost mode, the heat pump 102 may temporarily operate in a configuration similar to cooling mode in order to remove frost or ice accumulation on the outdoor heat exchanger 110. The reversing valve 108 may redirect the high-pressure, high-temperature working fluid from the compressor 106 to the outdoor heat exchanger 110, which functions as a condenser. As such, thermal energy may be released to the outdoor coil to melt any accumulated frost.

[0058] Returning to FIG. 5, the heat pump 102 may further include a controller 132 (e.g., an automation control system, a programmable logic controller) configured to manage operation of the vapor compression circuit. The controller 132 may include processing circuitry 134 (e.g., a processor system including one or more processors). The processing circuitry 134 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 134 may include one or more reduced instruction set (RISC) processors.

[0059] The controller 132 may also include memory 136 (e.g., one or more memory devices) that may store information, such as instructions, control software, look up tables, configuration data, etc. The memory 136 may include a volatile memory, such as random access memory (RAM), and / or a nonvolatile memory, such as read-only memory (ROM). The memory 136 may store a variety of information and may be used for various purposes. For example, the memory 136 may store processor-executable instructions including firmware or software for the processing circuitry 134 to execute, such as instructions for controlling components of the HVAC system 100. In some embodiments, the memory 136 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 134 to execute. The memory 136 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 136 may store data, instructions, and any other suitable data.

[0060] The controller 132 may further include communication circuitry 138. The communication circuitry 138 may be configured to facilitate communications among components of the controller 132 and enable the controller 132 to communicate with other components of the HVAC system 100. The communication circuitry 138 may support wired communication protocols (e.g., RS-485, Ethernet, CAN bus) and / or wireless communication protocols (e.g., Wi-Fi, Bluetooth, Zigbee, Z-Wave, cellular). The communication circuitry 138 may include transceivers, network interfaces, modems, or other communication hardware as needed to support these functions.

[0061] The controller 132 may be configured to manage the overall operation of the heat pump 102 by coordinating the functions of various components within the vapor compression circuit. In particular, the controller 132 may control the activation and deactivation of the compressor 106, the configuration of the reversing valve 108 to switch among heating, cooling, and defrost modes, and the operation of expansion device 112 and system fans to regulate heat exchange processes. Based on inputs received from system sensors 139 (e.g., pressure sensor, temperature sensor, flow sensor), the controller 132 may evaluate current operating conditions and determine the appropriate mode of operation. The sensors may be disposed at any suitable location within the HVAC system 100 to obtain sensor data pertaining to operating conditions. For example, the controller 132 may monitor operating conditions and initiate or terminate defrost cycles when certain predefined criteria are satisfied. In some embodiments, the controller 132 may be configured to determine occurrence of frosting in the outdoor heat exchanger 110 based on one or more operating parameters (e.g., collected via the sensors 139, estimated based on sensor data collected via the sensors 139), such as ambient air temperature, and to initiate defrost cycles accordingly. The controller 132 may further be configured to determine whether the accumulated frost has been sufficiently melted by monitoring one or more operating parameters (e.g., collected via the sensors 139, estimated based on sensor data collected via the sensors 139), such as the temperature of the working fluid within the outdoor heat exchanger 110 and terminate the defrost cycles when predetermined conditions are satisfied. As another example, the controller 132 may detect fault conditions, such as abnormal pressure or temperature levels, based on sensor data collected via the sensors 139 and implement protective actions to maintain system reliability and performance. Such protective actions may include initiating a compressor shutdown (e.g., compressor trip), adjusting fan speeds, or modifying the operation of the reversing valve 108 or expansion device 112 to reduce system stress and prevent damage.

[0062] During defrost mode, the heat pump 102 may reverse the flow of the working fluid to direct hot refrigerant through the outdoor heat exchanger 110 in order to melt accumulated frost or ice. This reversal of flow may reduce heat rejection efficiency at the outdoor coil, particularly under low ambient temperature conditions or when airflow is restricted due to ice buildup. As a result, the pressure of the working fluid at the discharge side of the compressor 106 may become elevated. In some instances, the elevated discharge pressure may trigger a protective response, such as a compressor trip, to prevent damage or operational failure.

[0063] However, a compressor trip during defrost mode may prevent the heat pump 102 from exiting the defrost mode, because termination of the defrost mode typically requires the compressor 106 to be operating. As a result, the heat pump 102 may continue operating in defrost mode unintentionally when the compressor 106 subsequently restarts, leading to unnecessary energy consumption and reduced operational reliability and efficiency.

[0064] To avoid a compressor trip while the heat pump 102 is operating in defrost mode, present embodiments may include a pressure sensor 140 configured to monitor the discharge pressure of the working fluid exiting the compressor 106. In some embodiments, the pressure sensor 140 may be disposed along a discharge line connecting the discharge port 118 of the compressor 106 and the first port 116 of the reversing valve 108. The pressure sensor 140 may be operatively coupled to the controller 132 to transmit pressure measurements, such that the controller 132 may analyze the measurements and terminate defrost mode before the compressor 106 shuts down due to tripping. Specifically, the controller 132 may determine whether the discharge pressure exceeds a predetermined pressure threshold, which is set below the discharge pressure value at which the compressor may trip. In some embodiments, the predetermined pressure threshold may be determined based on the discharge pressure value at which the compressor may trip. In some embodiments, the predetermined pressure threshold may be determined based on the geographical location of the HVAC system 100. For example, the pressure threshold may be determined based on the climate of the geographical location of the HVAC system 100, including temperature, humidity, and atmospheric pressure. When the discharge pressure is equal to or exceeds the predetermined pressure threshold, the controller 132 may terminate defrost mode. In some embodiments, the controller 132 may generate instructions to block the working fluid flow from flowing from the compressor 106 to the outdoor heat exchanger 110. For example, the controller 132 may generate instructions to control the reversing valve 108 such that the reversing valve 108 transitions from defrost mode to heating mode by disconnecting the connection between the first port 116 and the third port 124 and the connection between the fourth port 128 and the second port 120, and establishing a connection between the first port 116 and the fourth port 128 and a connection between the third port 124 and the second port 120. Thus, the working fluid may be directed from the compressor 106 to the indoor heat exchanger 114 and the defrost mode may be terminated.

[0065] In some embodiments, the controller 132 may utilize any other suitable operating parameters to determine discharge pressure of the working fluid. For example, the controller 132 may measure the temperature of the working fluid and apply a mathematical formula to estimate the discharge pressure of the working fluid based on the measured temperature and / or other relevant parameters.

[0066] In some embodiments, the heat pump 102 may further include a temperature sensor 142 configured to monitor (directly or indirectly) the temperature of the working fluid within the outdoor heat exchanger 110. In some embodiments, the temperature sensor 142 may be disposed at an end (e.g., discharge end) of the outdoor heat exchanger 130 or any other suitable location relative to flow through the outdoor heat exchanger 110 to collect temperature measurements for evaluating heat exchanger performance and / or operating conditions. For example, the temperature sensors 142 may be positioned such that it is in thermal communication with a bottom (e.g., relative to gravity) internal portion of the outdoor heat exchanger 110 to facilitate readings from a relatively cooler area of the outdoor heat exchanger 110. The temperature sensor 142 may be operatively coupled to the controller 132 to transmit the temperature measurements. In some embodiments, the controller 132 may use the temperature measurements to determine when to initiate or terminate defrost mode. For example, the controller 132 may monitor the temperature of the working fluid within the outdoor heat exchanger 110 and determine whether the temperature exceeds a predetermined temperature threshold. In some embodiments, the predetermined temperature threshold corresponds to a temperature value of the working fluid within the outdoor heat exchanger 110 during normal cooling mode operation in the absence of frosting. In some embodiments, the predetermined temperature threshold may be determined based on the geographical location of the HVAC system 100. For example, the temperature threshold may be determined based on the climate of the geographical location of the HVAC system 100, including temperature, humidity, and atmospheric pressure. When the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold, the controller 132 may terminate defrost mode.

[0067] In some embodiments, the controller 132 may be configured to terminate defrost mode when either the discharge pressure is equal to or exceeds the predetermined pressure threshold or the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold. In other embodiments, the controller 132 may be configured to terminate defrost mode only when both the discharge pressure is equal to or exceeds the predetermined pressure threshold and the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold. In some embodiments, the pressure sensor 140 and / or the temperature sensor 142 may be configured to sense and transmit measurements exclusively during defrost mode, thereby allowing the controller 132 to monitor and control relevant operating conditions specific to the defrost cycles. For example, the controller 132 may establish communication with the pressure sensor 140 and / or the temperature sensor 142 during defrost mode.

[0068] In some embodiments, the controller 132 may include a timer configured to determine a total time elapsed since the start of defrost mode operation. The controller 220 may compare the total elapsed time with a predetermined time threshold periodically or intermittently and terminate defrost mode when the total elapsed time is equal to or exceeds the predetermined time threshold.

[0069] In some embodiments, the controller 132 may be configured to evaluate the discharge pressure of the working fluid exiting the compressor 106, the temperature of the working fluid within the outdoor heat exchanger 110, and the total time elapsed since the start of defrost mode operation, independently or in combination with others, to determine whether to terminate the defrost mode. Based on this evaluation, the controller 132 may determine that one or more termination conditions have been satisfied. Once the controller 132 determines that the defrost mode should be terminated, it may generate control signals to operate the reversing valve 108 to return the system to heating mode. For example, the controller 132 may cause the reversing valve 108 to disconnect the flow paths corresponding to defrost mode and establish flow paths corresponding to heating mode, thereby resuming normal heating operation. Specifically, and as previously discussed, the controller 132 may generate instructions to control the reversing valve 108 to disconnect the connection between the first port 116 and the third port 124, and the connection between the fourth port 128 and the second port 120, and to establish a connection between the first port 116 and the fourth port 128, and a connection between the third port 124 and the second port 120. Thus, the working fluid may be blocked from flowing from the compressor 106 to the outdoor heat exchanger 110; instead, the working fluid may be directed from the compressor 106 to the indoor heat exchanger 114.

[0070] In some aspects, the heat pump of the present disclosure may include two or more refrigeration circuits. For example, the heat pump may include two or more circuits that share a common indoor heat exchanger. Each circuit may include a compressor, a reversing valve, and an outdoor heat exchanger, all operatively coupled to the common indoor heat exchanger. The heat pump may also include a controller configured to manage the operation of all circuits. In certain embodiments, the heat pump may further include two or more temperature sensors, each configured to measure the temperature of the working fluid in the respective outdoor heat exchanger of the circuits. The controller may be configured to determine that the temperature-based condition is satisfied when the measured temperature of the working fluid in one of the outdoor heat exchangers exceeds a predetermined temperature threshold.

[0071] As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for improving the reliability and efficiency of defrost operations in heat pump systems. Specifically, present embodiments are provided to enable the heat pump systems to monitor the discharge pressure of the working fluid exiting the compressor and terminate the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. As such, the heat pump systems may avoid restarting in defrost mode after a protective interruption, such as a compressor trip, thereby enhancing operational reliability and preventing unnecessary energy consumption. 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.

[0072] 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.

[0073] 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.

[0074] 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 will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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....

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of India Provisional Patent Application No. 202421045310, entitled “HEAT PUMP PROTECTION AGAINST HIGH PRESSURE TRIPS IN DEFROST CYCLE,” filed Jun. 12, 2024, which is herein incorporated by reference in its entirety for all purposes.BACKGROUND

[0002] 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 and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0003] Embodiments of the present disclosure are generally directed to a heat pump of a heating, ventilation, and / or air conditioning (HVAC) system, and, more specifically, to features of the heat pump that are configured to reduce, negate, or mitigate adverse effects associated with tripping (e.g., compressor tripping of the heat pump).

[0004] An HVAC system provides proper ventilation and maintains air quality in a confined space, such as a commercial or household building. For example, the HVAC system circulates a refrigerant through a closed circuit (e.g., a refrigerant loop or circuit, vapor compression loop or circuit) including a compressor, a condenser, an expansion device, and an evaporator. During operation, the system components are subject to various pressure, temperature, and load conditions that may fluctuate depending on ambient temperature, system demand, and operating mode. Certain operating conditions, such as excessively high working fluid pressure, may trigger tripping. While necessary for equipment safety, such tripping may interrupt operation and reduce overall system efficiency and reliability. Accordingly, it is now recognized that improved HVAC systems and / or associated control methods are desired.SUMMARY

[0005] 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.

[0006] In an embodiment, a heat pump configured to selectively circulate a working fluid includes an outdoor heat exchanger, an indoor heat exchanger, a compressor, a reversing valve configured to direct the working fluid from the compressor to the outdoor heat exchanger or to the indoor heat exchanger, and a controller. The controller is configured to determine whether a pressure of the working fluid exiting the compressor exceeds a pressure threshold, and, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, control the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

[0007] In another embodiment, a method of operating a heat pump includes determining that a pressure of a working fluid exiting a compressor of the heat pump exceeds a pressure threshold, and, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, controlling the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

[0008] In a further embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a heat pump configured to circulate a working fluid through two or more circuits. The heat pump includes a first outdoor heat exchanger in a first circuit, a second outdoor heat exchanger in a second circuit, an indoor heat exchanger, a compressor, a pressure sensor disposed downstream of the compressor to measure a pressure of the working fluid exiting the compressor, a first temperature sensor configured to measure a first temperature of the working fluid within the first outdoor heat exchanger, a reversing valve configured to direct the working fluid from the compressor to the first outdoor heat exchanger, the second outdoor heat exchanger, or the indoor heat exchanger, and a controller. The controller configured to determine whether the pressure exceeds a pressure threshold, determine whether the first temperature exceeds a temperature threshold, and, in response to determining that the pressure exceeds the pressure threshold or the first temperature exceeds the temperature threshold, control the reversing valve to direct the working fluid to flow from the compressor through the reversing valve to the indoor heat exchanger.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0010] FIG. 1 is a perspective view of an embodiment of a building incorporating a heating, ventilation, and / or air conditioning (HVAC) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0011] FIG. 2 is a perspective view of an embodiment of a packaged HVAC unit, in accordance with an aspect of the present disclosure;

[0012] FIG. 3 is a perspective view of an embodiment of a split, residential HVAC system, in accordance with an aspect of the present disclosure;

[0013] 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;

[0014] FIG. 5 is a block diagram of an embodiment of a portion of an HVAC system including a heat pump, in accordance with an aspect of the present disclosure;

[0015] FIG. 6 is a block diagram of an embodiment of the portion of the HVAC system in FIG. 5 where the heat pump is operating in heating mode, in accordance with an aspect of the present disclosure; and

[0016] FIG. 7 is a block diagram of an embodiment of the portion of the HVAC system in FIG. 5 where the heat pump is operating in cooling mode or defrost mode, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0017] One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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,”“having,” and “based on” 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] In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, to one skilled in the art that embodiments of the present disclosure may be practiced without some of these specific details.

[0020] As briefly discussed above, a heating, ventilation, and / or 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 transfers 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 (e.g., a refrigerant) 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] Generally, the compressor receives low-pressure working fluid vapor from the evaporator and compresses it before delivering high-pressure vapor to the condenser, thereby enabling thermal energy transfer for heating or cooling a confined space. Specifically, in a heat pump system, the indoor and outdoor heat exchangers therein alternate between functioning as an evaporator and a condenser depending on the operation mode (e.g., heating mode, cooling mode, and defrost mode). The system may include a reversing valve that operates to reverse the flow of working fluid within the system to facilitate these mode-dependent role changes. In heating mode, the outdoor heat exchanger functions as the evaporator, absorbing heat from the ambient air, while the indoor heat exchanger functions as the condenser, releasing heat to condition the confined space. Conversely, in cooling mode, the roles are reversed: the indoor heat exchanger acts as the evaporator, absorbing heat from the confined space, and the outdoor heat exchanger acts as the condenser, rejecting heat to the ambient environment. During defrost mode, which is typically initiated during heating operation to remove accumulated frost from the outdoor heat exchanger, the system temporarily reverses the working fluid flow from its heating mode configuration, causing the outdoor heat exchanger to operate as a condenser instead of an evaporator. This reversal of the working fluid flow allows the outdoor coil to be heated, thereby melting the accumulated frost and restoring heat transfer efficiency.

[0022] However, such reversal may cause an elevated discharge pressure of the working fluid exiting the compressor, potentially triggering high-pressure tripping. While tripping is a protective function initiated by safety controls to prevent damage to the compressor or other system components, frequent or premature tripping can interrupt system operation and reduce overall efficiency. For example, because termination of the defrost mode typically requires the compressor to be operating, a compressor trip during defrost may prevent the heat pump from exiting the defrost mode. As a result, the system may continue operating in defrost mode unintentionally when the compressor subsequently restarts. Accordingly, improvements in heat pump systems and associated control methods are desirable to reduce the occurrence of premature tripping and its adverse effects on system performance.

[0023] Present embodiments may monitor the discharge pressure of the working fluid exiting the compressor and terminate the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. The predetermined pressure threshold is set below the discharge pressure level at which the compressor may trip. In accordance with the present disclosure, a heat pump system includes a controller configured to determine whether the discharge pressure of the working fluid exiting the compressor exceeds the predetermined pressure threshold. When the discharge pressure is equal to or exceeds the predetermined threshold, the controller may terminate defrost mode operation by blocking the working fluid flow from flowing from the compressor to the outdoor heat exchanger. In some embodiments, the controller may be further configured to monitor additional operating conditions (e.g., temperature of the working fluid in the outdoor heat exchanger) and determine whether those operation conditions warrant termination of the defrost mode (e.g., a temperature exceeds a predetermined temperature threshold). In some embodiments, the controller may terminate the defrost mode by controlling operation of the reversing valve. In some embodiments, the controller may further control the reversing valve to operate the heat pump in the heating mode. In some embodiments, the controller may continue with the heating mode operation until frosting is detected at the outdoor heat exchanger. These and other aspects of the present disclosure are described in greater detail below with reference to the drawings.

[0024] Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and / or 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.

[0025] In the illustrated embodiment, a building 10 is air conditioned by a system that includes an HVAC unit 12. The building 10 may be a commercial structure or a residential structure. As shown, the HVAC unit 12 is disposed on the roof of the building 10; however, the HVAC unit 12 may be located in other equipment rooms or areas adjacent the building 10. The HVAC unit 12 may be a single package unit containing other equipment, such as a blower, integrated air handler, and / or auxiliary heating unit. In other embodiments, the HVAC unit 12 may be part of a split HVAC system, such as the system shown in FIG. 3, which includes an outdoor HVAC unit 58 and an indoor HVAC unit 56.

[0026] The HVAC unit 12 is an air-cooled device that implements a refrigeration cycle to provide conditioned air to the building 10. Specifically, the HVAC unit 12 may include one or more heat exchangers across which an air flow is passed to condition the air flow before the air flow is supplied to the building. In the illustrated embodiment, the HVAC unit 12 is a rooftop unit (RTU) that conditions a supply air stream, such as environmental air and / or a return air flow from the building 10. After the HVAC unit 12 conditions the air, the air is supplied to the building 10 via ductwork 14 extending throughout the building 10 from the HVAC unit 12. For example, the ductwork 14 may extend to various individual floors or other sections of the building 10. In certain embodiments, the HVAC unit 12 may be a heat pump that provides both heating and cooling to the building with one refrigeration circuit configured to operate in different modes. In other embodiments, the HVAC unit 12 may include one or more refrigeration circuits for cooling an air stream and a furnace for heating the air stream.

[0027] 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.

[0028] 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 vapor compression 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.

[0029] 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.

[0030] The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more vapor compression circuits. Tubes within the heat exchangers 28 and 30 may circulate a working fluid (e.g., a refrigerant), such as R-410A, R-407, R-134a, R-1234ze, R1233zd, R-32, hydrofluoro olefin (HFO), “natural” refrigerants like ammonia (NH3), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable working fluid through the heat exchangers 28 and 30. As will be appreciated, different working fluid may include different saturation properties depending on chemical composition and mixture composition. 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 stream. In other embodiments, the HVAC unit 12 may operate in a heat pump mode where the roles of the heat exchangers 28 and 30 may be reversed. That is, the heat exchanger 28 may function as an evaporator and the heat exchanger 30 may function as a condenser. In further embodiments, the HVAC unit 12 may include a furnace for heating the air stream that is supplied to the building 10. While the illustrated embodiment of FIG. 2 shows the HVAC unit 12 having two of the heat exchangers 28 and 30, in other embodiments, the HVAC unit 12 may include one heat exchanger or more than two heat exchangers.

[0031] 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.

[0032] 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 configuration 44. However, in other embodiments, any number of the compressors 42 may be provided to achieve various stages of heating and / or cooling. As may be appreciated, additional equipment and devices may be included in the HVAC unit 12, such as a solid-core filter drier, a drain pan, a disconnect switch, an economizer, pressure switches, phase monitors, and humidity sensors, among other things.

[0033] 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.

[0034] FIG. 3 illustrates a residential heating and cooling system 50, also in accordance with present techniques. The residential heating and cooling system 50 may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system 50 is a split HVAC system. In general, a residence 52 conditioned by a split HVAC system may include working fluid conduits 54 that operatively couple the indoor unit 56 to the outdoor unit 58. The indoor unit 56 may be positioned in a utility room, an attic, a basement, and so forth. The outdoor unit 58 is typically situated adjacent to a side of residence 52 and is covered by a shroud to protect the system components and to prevent leaves and other debris or contaminants from entering the unit. The working fluid conduits 54 transfer working fluid between the indoor unit 56 and the outdoor unit 58, typically transferring primarily liquid working fluid in one direction and primarily vaporized working fluid in an opposite direction.

[0035] When the system shown in FIG. 3 is operating as an air conditioner, a heat exchanger 60 in the outdoor unit 58 serves as a condenser for re-condensing vaporized working fluid flowing from the indoor unit 56 to the outdoor 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 unit 58.

[0036] The outdoor unit 58 draws environmental air through the heat exchanger 60 using a fan 64 and expels the air above the outdoor unit 58. When operating as an air conditioner, the air is heated by the heat exchanger 60 within the outdoor unit 58 and exits the unit at a temperature higher than it entered. The indoor unit 56 includes a blower or fan 66 that directs air through or across the indoor heat exchanger 62, where the air is cooled when the system is operating in air conditioning mode. Thereafter, the air is passed through ductwork 68 that directs the air to the residence 52. The overall system operates to maintain a desired temperature as set by a system controller. When the temperature sensed inside the residence 52 is higher than the set point on the thermostat, or 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.

[0037] The residential heating and cooling system 50 may also operate as a heat pump. When operating as a heat pump, the roles of heat exchangers 60 and 62 are reversed. That is, the heat exchanger 60 of the outdoor unit 58 will serve as an evaporator to evaporate working fluid and thereby cool air entering the outdoor unit 58 as the air passes over the outdoor heat exchanger 60. The indoor heat exchanger 62 will receive a stream of air blown over it and will heat the air by condensing the working fluid.

[0038] In some embodiments, the indoor unit 56 may include a furnace system 70. For example, the indoor unit 56 may include the furnace system 70 when the residential heating and cooling system 50 is not configured to operate as a heat pump. The furnace system 70 may include a burner assembly and heat exchanger, among other components, inside the indoor unit 56. Fuel is provided to the burner assembly of the furnace 70 where it is mixed with air and combusted to form combustion products. The combustion products may pass through tubes or piping in a heat exchanger, separate from heat exchanger 62, such that air directed by the blower or fan 66 passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system 70 to the ductwork 68 for heating the residence 52.

[0039] FIG. 4 is an embodiment of a vapor compression system 72 that can be used in any of the systems described above. The vapor compression system 72 may circulate a working fluid 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.

[0040] 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.

[0041] 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 passing 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.

[0042] The liquid working fluid delivered to the evaporator 80 may absorb heat from another air stream, such as a supply air stream 98 provided to the building 10 or the residence 52. For example, the supply air stream 98 may include ambient or environmental air, return air from a building, or a combination of the two. The liquid 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 stream 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.

[0043] In some embodiments, the vapor compression system 72 may further include a reheat coil. In the illustrated embodiment, the reheat coil is represented as part of the evaporator 80. The reheat coil is positioned downstream of the evaporator heat exchanger relative to the supply air stream 98 and may reheat the supply air stream 98 when the supply air stream 98 is overcooled to remove humidity from the supply air stream 98 before the supply air stream 98 is directed to the building 10 or the residence 52.

[0044] It should be appreciated that any of the features described herein may be incorporated with the HVAC unit 12, the residential heating and cooling system 50, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications. Further, a heat pump in any of the HVAC systems illustrated in FIGS. 1-4 and / or any other suitable HVAC system may include, as described in greater detail with reference to later drawings below, a controller configured to block tripping (e.g., tripping caused by elevated working fluid pressure) during defrost mode by terminating the defrost mode upon detecting certain operating conditions of the heat pump. For example, the controller may be configured to monitor, via a pressure sensor, the discharge pressure of the working fluid exiting the compressor and terminate, via control of a reversing valve, the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. Detailed aspects of the heat exchanger, including detailed aspects of the controller, the pressure sensor, and the reversing valve, are described below with reference to later drawings.

[0045] FIG. 5 is a block diagram of an embodiment of a portion of an HVAC system 100 including a heat pump 102, in accordance with an aspect of the present disclosure. A vapor compression system 104 (e.g., vapor compression system 72 of FIG. 3) is incorporated into the heat pump 102 to circulate a working fluid through a circuit starting with a compressor 106 (e.g., compressor 42 of FIG. 2 and compressor 74 of FIG. 4). The circuit may also include a reversing valve 108, an outdoor heat exchanger 110 (e.g., outdoor heat exchanger 60), an expansion device (e.g., expansion valve) 112, and an indoor heat exchanger 114 (e.g., indoor heat exchanger 62).

[0046] In some embodiments, the compressor 106, the reversing valve 108, the outdoor heat exchanger 110, and the expansion device 112 may be housed in an outdoor unit (e.g., outdoor unit 58 of FIG. 3) disposed outside the building (e.g., building 10 of FIG. 1) that contains the space conditioned by the heat pump 102. A piping system may be provided between the components within the outdoor unit to facilitate the flow of the working fluid. In some embodiments, the outdoor unit may include one or more outdoor fans (e.g., fan 64 of FIG. 3) configured to generate airflow across the outdoor heat exchanger 110.

[0047] The indoor heat exchanger 114 may be housed within an indoor unit (e.g., indoor unit 56) located inside of the building, such as in a utility room, an attic, a basement, and so forth. The indoor unit may include an indoor fan (e.g., fan 66 of FIG. 3) configured to direct supply air across the heat exchanger coils of the indoor heat exchanger 114, thereby heating or cooling the air depending on the operating mode. The conditioned supply air may then be distributed to the interior space of the building through a ductwork system (e.g., ductwork 14 of FIG. 1 and ductwork 68 of FIG. 3) or other air distribution system. The indoor unit and the outdoor unit may be fluidly coupled via one or more working fluid conduits (e.g., working fluid conduits 54 of FIG. 3) to form a working fluid circuit (e.g., loop).

[0048] The outdoor heat exchanger 110 may be configured to facilitate thermal exchange between the working fluid and ambient air, and the indoor heat exchanger 114 may be configured to facilitate thermal exchange between the working fluid and the air within the conditioned space. The outdoor heat exchanger 110 and the indoor heat exchanger 114 may, respectively, include one or more heat exchanger coils for circulating the working fluid. As such, the heat pump 102 may operate to heat or cool the space by selectively transferring thermal energy between the indoor air and the ambient air.

[0049] To heat the space, thermal energy may be absorbed from the ambient air by the outdoor heat exchanger 110 and transferred via the working fluid to the indoor heat exchanger 114 for delivery into the conditioned space. Conversely, to cool the space, thermal energy may be absorbed from the indoor air by the indoor heat exchanger 114 and transferred via the working fluid to the outdoor heat exchanger 110 for discharge to the ambient air. The direction of heat transfer may be controlled by the reversing valve 108, and the expansion device 112 may facilitate pressure and temperature regulation of the working fluid to support efficient heating or cooling operations.

[0050] The heat pump 102 may be configured to switch among multiple operating modes, such as heating mode, cooling mode, and defrost mode, by using the reversing valve 108 to control the direction of working fluid flow within the vapor compression circuit. In heating mode, the reversing valve 108 directs high-pressure working fluid from the compressor 106 to the indoor heat exchanger 114. In cooling mode, the reversing valve 108 reverses the flow, routing the high-pressure working fluid from the compressor 106 to the outdoor heat exchanger 110. In defrost mode, which typically initiates from the heating mode during cold weather conditions, the heat pump 102 may temporarily operate in a cooling configuration to melt frost that has accumulated on the outdoor heat exchanger 110. During defrost mode, the reversing valve 108 redirects the heated working fluid to the outdoor heat exchanger 110, raising its temperature and causing the frost to melt. In some embodiment, the system 100 may disable the indoor fan (e.g., fan 66 of FIG. 3) and / or activate auxiliary heating elements during the defrost cycle to maintain comfort within the conditioned space. Once the outdoor heat exchanger 110 has been sufficiently defrosted, the heat pump 102 may automatically return to heating mode and resume normal operation.

[0051] Specifically, the reversing valve 108 may selectively route the discharge of the compressor 106 to either the outdoor heat exchanger 110 or the indoor heat exchanger 114, while routing the return flow from the other heat exchanger back to the compressor 106 to complete the circuit. For example, in heating mode, the reversing valve 108 may route the high-pressure discharge from the compressor 106 to the indoor heat exchanger 114 and route the low-pressure return flow from the outdoor heat exchanger 110 back to the compressor 106. Conversely, in cooling mode, the reversing valve 108 may route the discharge from the compressor 106 to the outdoor heat exchanger 110 and route the return flow from the indoor heat exchanger 114 back to the compressor 106.

[0052] In some embodiments, the reversing valve 108 may have a first port 116 in fluid communication with a discharge port 118 of the compressor 106 and a second port 120 in fluid communication with an inlet port 122 of the compressor 108. Further, the reversing valve 108 may have a third port 124 in fluid communication with the outdoor heat exchanger 110 (e.g., an inlet port 126 thereof) and a fourth port 128 in fluid communication with the indoor heat exchanger 114 (e.g., an inlet port 130 thereof). The reversing valve 108 selectively establishes communication between the ports 116, 120, 124, and 128 depending upon mode of operation of the heat pump 102.

[0053] For example, referring to FIG. 6, a block diagram of an embodiment of the portion of the HVAC system 100 in FIG. 5 where the heat pump 102 is operating in heating mode is illustrated, in accordance with an aspect of the present disclosure. In heating mode, the outdoor heat exchanger 110 functions as an evaporator and the indoor heat exchanger 114 functions as a condenser. The reversing valve 108 connects the first port 116 to the fourth port 128, thereby routing the high-pressure discharge from the compressor 106 to the indoor heat exchanger 114 (e.g., via the inlet port 130). Simultaneously, the reversing valve 108 connects the third port 124 to the second port 120, thereby routing the low-pressure return flow from the outdoor heat exchanger 110 back to the compressor 106 (e.g., via the inlet port 122).

[0054] Thus, in heating mode, the vapor compression circuit may operate as follows: low-pressure, low-temperature working fluid enters the compressor 106, where it is compressed into a high-pressure, high-temperature working fluid (e.g., vapor). The high-pressure, high-temperature working fluid is then discharged from the compressor 106 and directed by the reversing valve 108 to the indoor heat exchanger 114, which functions as a condenser and exchanges heat with an environment (e.g., a building interior). Within the indoor heat exchanger 114, the working fluid releases thermal energy to the indoor air and condenses into a high-pressure liquid. The condensed working fluid then flows through the expansion device 112, where the working fluid is depressurized. The resulting low-pressure working fluid flows into the outdoor heat exchanger 110, which functions as an evaporator. There, the working fluid absorbs heat from the ambient air and evaporates into a low-pressure vapor, which then returns to the compressor 106 to complete the cycle.

[0055] As another example, referring to FIG. 7, a block diagram of an embodiment of the portion of the HVAC system 100 in FIG. 5 where the heat pump 102 is operating in cooling mode or defrost mode is illustrated, in accordance with an aspect of the present disclosure. In cooling mode or defrost mode, the indoor heat exchanger 114 functions as an evaporator and the outdoor heat exchanger 110 functions as a condenser. The reversing valve 108 connects the first port 116 to the third port 124, thereby routing the high-pressure discharge from the compressor 106 to the outdoor heat exchanger 110 (e.g., via the inlet port 126). Simultaneously, the reversing valve 108 connects the fourth port 128 to the second port 120, thereby routing the low-pressure return flow from the indoor heat exchanger 114 back to the compressor 106 (e.g., via the inlet port 122).

[0056] Thus, in cooling mode, the vapor compression circuit may operate as follows: low-pressure, low-temperature working fluid enters the compressor 106, where it is compressed into a high-pressure, high-temperature working fluid (e.g., vapor). The high-pressure, high-temperature working fluid is then discharged from the compressor 106 and directed by the reversing valve 108 to the outdoor heat exchanger 110, which functions as a condenser and exchanges heat with an outdoor environment. Within the outdoor heat exchanger 110, the working fluid releases thermal energy to the ambient air and condenses into a high-pressure liquid. The condensed working fluid then flows through the expansion device 112, where the working fluid is depressurized. The resulting low-pressure working fluid flows into indoor heat exchanger 114, which functions as an evaporator. There, the working fluid absorbs heat from the indoor air, cooling the conditioned space, and evaporates into a low-pressure vapor, which then returns to the compressor 106 to complete the cycle.

[0057] Similarly, in defrost mode, the heat pump 102 may temporarily operate in a configuration similar to cooling mode in order to remove frost or ice accumulation on the outdoor heat exchanger 110. The reversing valve 108 may redirect the high-pressure, high-temperature working fluid from the compressor 106 to the outdoor heat exchanger 110, which functions as a condenser. As such, thermal energy may be released to the outdoor coil to melt any accumulated frost.

[0058] Returning to FIG. 5, the heat pump 102 may further include a controller 132 (e.g., an automation control system, a programmable logic controller) configured to manage operation of the vapor compression circuit. The controller 132 may include processing circuitry 134 (e.g., a processor system including one or more processors). The processing circuitry 134 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 134 may include one or more reduced instruction set (RISC) processors.

[0059] The controller 132 may also include memory 136 (e.g., one or more memory devices) that may store information, such as instructions, control software, look up tables, configuration data, etc. The memory 136 may include a volatile memory, such as random access memory (RAM), and / or a nonvolatile memory, such as read-only memory (ROM). The memory 136 may store a variety of information and may be used for various purposes. For example, the memory 136 may store processor-executable instructions including firmware or software for the processing circuitry 134 to execute, such as instructions for controlling components of the HVAC system 100. In some embodiments, the memory 136 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 134 to execute. The memory 136 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 136 may store data, instructions, and any other suitable data.

[0060] The controller 132 may further include communication circuitry 138. The communication circuitry 138 may be configured to facilitate communications among components of the controller 132 and enable the controller 132 to communicate with other components of the HVAC system 100. The communication circuitry 138 may support wired communication protocols (e.g., RS-485, Ethernet, CAN bus) and / or wireless communication protocols (e.g., Wi-Fi, Bluetooth, Zigbee, Z-Wave, cellular). The communication circuitry 138 may include transceivers, network interfaces, modems, or other communication hardware as needed to support these functions.

[0061] The controller 132 may be configured to manage the overall operation of the heat pump 102 by coordinating the functions of various components within the vapor compression circuit. In particular, the controller 132 may control the activation and deactivation of the compressor 106, the configuration of the reversing valve 108 to switch among heating, cooling, and defrost modes, and the operation of expansion device 112 and system fans to regulate heat exchange processes. Based on inputs received from system sensors 139 (e.g., pressure sensor, temperature sensor, flow sensor), the controller 132 may evaluate current operating conditions and determine the appropriate mode of operation. The sensors may be disposed at any suitable location within the HVAC system 100 to obtain sensor data pertaining to operating conditions. For example, the controller 132 may monitor operating conditions and initiate or terminate defrost cycles when certain predefined criteria are satisfied. In some embodiments, the controller 132 may be configured to determine occurrence of frosting in the outdoor heat exchanger 110 based on one or more operating parameters (e.g., collected via the sensors 139, estimated based on sensor data collected via the sensors 139), such as ambient air temperature, and to initiate defrost cycles accordingly. The controller 132 may further be configured to determine whether the accumulated frost has been sufficiently melted by monitoring one or more operating parameters (e.g., collected via the sensors 139, estimated based on sensor data collected via the sensors 139), such as the temperature of the working fluid within the outdoor heat exchanger 110 and terminate the defrost cycles when predetermined conditions are satisfied. As another example, the controller 132 may detect fault conditions, such as abnormal pressure or temperature levels, based on sensor data collected via the sensors 139 and implement protective actions to maintain system reliability and performance. Such protective actions may include initiating a compressor shutdown (e.g., compressor trip), adjusting fan speeds, or modifying the operation of the reversing valve 108 or expansion device 112 to reduce system stress and prevent damage.

[0062] During defrost mode, the heat pump 102 may reverse the flow of the working fluid to direct hot refrigerant through the outdoor heat exchanger 110 in order to melt accumulated frost or ice. This reversal of flow may reduce heat rejection efficiency at the outdoor coil, particularly under low ambient temperature conditions or when airflow is restricted due to ice buildup. As a result, the pressure of the working fluid at the discharge side of the compressor 106 may become elevated. In some instances, the elevated discharge pressure may trigger a protective response, such as a compressor trip, to prevent damage or operational failure.

[0063] However, a compressor trip during defrost mode may prevent the heat pump 102 from exiting the defrost mode, because termination of the defrost mode typically requires the compressor 106 to be operating. As a result, the heat pump 102 may continue operating in defrost mode unintentionally when the compressor 106 subsequently restarts, leading to unnecessary energy consumption and reduced operational reliability and efficiency.

[0064] To avoid a compressor trip while the heat pump 102 is operating in defrost mode, present embodiments may include a pressure sensor 140 configured to monitor the discharge pressure of the working fluid exiting the compressor 106. In some embodiments, the pressure sensor 140 may be disposed along a discharge line connecting the discharge port 118 of the compressor 106 and the first port 116 of the reversing valve 108. The pressure sensor 140 may be operatively coupled to the controller 132 to transmit pressure measurements, such that the controller 132 may analyze the measurements and terminate defrost mode before the compressor 106 shuts down due to tripping. Specifically, the controller 132 may determine whether the discharge pressure exceeds a predetermined pressure threshold, which is set below the discharge pressure value at which the compressor may trip. In some embodiments, the predetermined pressure threshold may be determined based on the discharge pressure value at which the compressor may trip. In some embodiments, the predetermined pressure threshold may be determined based on the geographical location of the HVAC system 100. For example, the pressure threshold may be determined based on the climate of the geographical location of the HVAC system 100, including temperature, humidity, and atmospheric pressure. When the discharge pressure is equal to or exceeds the predetermined pressure threshold, the controller 132 may terminate defrost mode. In some embodiments, the controller 132 may generate instructions to block the working fluid flow from flowing from the compressor 106 to the outdoor heat exchanger 110. For example, the controller 132 may generate instructions to control the reversing valve 108 such that the reversing valve 108 transitions from defrost mode to heating mode by disconnecting the connection between the first port 116 and the third port 124 and the connection between the fourth port 128 and the second port 120, and establishing a connection between the first port 116 and the fourth port 128 and a connection between the third port 124 and the second port 120. Thus, the working fluid may be directed from the compressor 106 to the indoor heat exchanger 114 and the defrost mode may be terminated.

[0065] In some embodiments, the controller 132 may utilize any other suitable operating parameters to determine discharge pressure of the working fluid. For example, the controller 132 may measure the temperature of the working fluid and apply a mathematical formula to estimate the discharge pressure of the working fluid based on the measured temperature and / or other relevant parameters.

[0066] In some embodiments, the heat pump 102 may further include a temperature sensor 142 configured to monitor (directly or indirectly) the temperature of the working fluid within the outdoor heat exchanger 110. In some embodiments, the temperature sensor 142 may be disposed at an end (e.g., discharge end) of the outdoor heat exchanger 130 or any other suitable location relative to flow through the outdoor heat exchanger 110 to collect temperature measurements for evaluating heat exchanger performance and / or operating conditions. For example, the temperature sensors 142 may be positioned such that it is in thermal communication with a bottom (e.g., relative to gravity) internal portion of the outdoor heat exchanger 110 to facilitate readings from a relatively cooler area of the outdoor heat exchanger 110. The temperature sensor 142 may be operatively coupled to the controller 132 to transmit the temperature measurements. In some embodiments, the controller 132 may use the temperature measurements to determine when to initiate or terminate defrost mode. For example, the controller 132 may monitor the temperature of the working fluid within the outdoor heat exchanger 110 and determine whether the temperature exceeds a predetermined temperature threshold. In some embodiments, the predetermined temperature threshold corresponds to a temperature value of the working fluid within the outdoor heat exchanger 110 during normal cooling mode operation in the absence of frosting. In some embodiments, the predetermined temperature threshold may be determined based on the geographical location of the HVAC system 100. For example, the temperature threshold may be determined based on the climate of the geographical location of the HVAC system 100, including temperature, humidity, and atmospheric pressure. When the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold, the controller 132 may terminate defrost mode.

[0067] In some embodiments, the controller 132 may be configured to terminate defrost mode when either the discharge pressure is equal to or exceeds the predetermined pressure threshold or the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold. In other embodiments, the controller 132 may be configured to terminate defrost mode only when both the discharge pressure is equal to or exceeds the predetermined pressure threshold and the temperature of the working fluid within the outdoor heat exchanger 110 is equal to or exceeds the predetermined temperature threshold. In some embodiments, the pressure sensor 140 and / or the temperature sensor 142 may be configured to sense and transmit measurements exclusively during defrost mode, thereby allowing the controller 132 to monitor and control relevant operating conditions specific to the defrost cycles. For example, the controller 132 may establish communication with the pressure sensor 140 and / or the temperature sensor 142 during defrost mode.

[0068] In some embodiments, the controller 132 may include a timer configured to determine a total time elapsed since the start of defrost mode operation. The controller 220 may compare the total elapsed time with a predetermined time threshold periodically or intermittently and terminate defrost mode when the total elapsed time is equal to or exceeds the predetermined time threshold.

[0069] In some embodiments, the controller 132 may be configured to evaluate the discharge pressure of the working fluid exiting the compressor 106, the temperature of the working fluid within the outdoor heat exchanger 110, and the total time elapsed since the start of defrost mode operation, independently or in combination with others, to determine whether to terminate the defrost mode. Based on this evaluation, the controller 132 may determine that one or more termination conditions have been satisfied. Once the controller 132 determines that the defrost mode should be terminated, it may generate control signals to operate the reversing valve 108 to return the system to heating mode. For example, the controller 132 may cause the reversing valve 108 to disconnect the flow paths corresponding to defrost mode and establish flow paths corresponding to heating mode, thereby resuming normal heating operation. Specifically, and as previously discussed, the controller 132 may generate instructions to control the reversing valve 108 to disconnect the connection between the first port 116 and the third port 124, and the connection between the fourth port 128 and the second port 120, and to establish a connection between the first port 116 and the fourth port 128, and a connection between the third port 124 and the second port 120. Thus, the working fluid may be blocked from flowing from the compressor 106 to the outdoor heat exchanger 110; instead, the working fluid may be directed from the compressor 106 to the indoor heat exchanger 114.

[0070] In some aspects, the heat pump of the present disclosure may include two or more refrigeration circuits. For example, the heat pump may include two or more circuits that share a common indoor heat exchanger. Each circuit may include a compressor, a reversing valve, and an outdoor heat exchanger, all operatively coupled to the common indoor heat exchanger. The heat pump may also include a controller configured to manage the operation of all circuits. In certain embodiments, the heat pump may further include two or more temperature sensors, each configured to measure the temperature of the working fluid in the respective outdoor heat exchanger of the circuits. The controller may be configured to determine that the temperature-based condition is satisfied when the measured temperature of the working fluid in one of the outdoor heat exchangers exceeds a predetermined temperature threshold.

[0071] As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for improving the reliability and efficiency of defrost operations in heat pump systems. Specifically, present embodiments are provided to enable the heat pump systems to monitor the discharge pressure of the working fluid exiting the compressor and terminate the defrost mode operation upon detecting that the discharge pressure exceeds a predetermined pressure threshold. As such, the heat pump systems may avoid restarting in defrost mode after a protective interruption, such as a compressor trip, thereby enhancing operational reliability and preventing unnecessary energy consumption. 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.

[0072] 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.

[0073] 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.

[0074] 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 will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are 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....

Claims

1. A heat pump configured to selectively circulate a working fluid, the heat pump comprising:an outdoor heat exchanger;an indoor heat exchanger;a compressor;a reversing valve configured to direct the working fluid from the compressor to the outdoor heat exchanger or to the indoor heat exchanger; anda controller configured to:determine whether a pressure of the working fluid exiting the compressor exceeds a pressure threshold; andin response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, control the reversing valve to block the working fluid from flowing from the compressor through the reversing valve to the outdoor heat exchanger.

2. The heat pump of claim 1, wherein the pressure threshold is lower than a trip pressure value of the compressor.

3. The heat pump of claim 1, wherein the controller is configured to, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, control the reversing valve to disconnect a first flow path from the compressor to the outdoor heat exchanger and establish a second flow path from the compressor to the indoor heat exchanger.

4. The heat pump of claim 1, comprising a pressure sensor disposed at a discharge side of the compressor, wherein the pressure of the working fluid exiting the compressor is determined based on a pressure measurement of the pressure sensor.

5. The heat pump of claim 4, wherein the pressure sensor is disposed along a working fluid flow path between the compressor and the reversing valve.

6. The heat pump of claim 1, comprising a temperature sensor configured to measure a temperature of the working fluid, wherein the pressure of the working fluid exiting the compressor is determined based on a temperature measurement of the temperature sensor.

7. The heat pump of claim 1, wherein the controller is configured to:control the reversing valve to enable the working fluid to flow from the compressor to the indoor heat exchanger;determine whether to defrost the outdoor heat exchanger based on measured parameters of the heat pump;in response to determining to defrost the outdoor heat exchanger:control the reversing valve to enable the working fluid to flow from the compressor to the outdoor heat exchanger via the reversing valve;determine whether a pressure measurement of a pressure sensor exceeds the pressure threshold; andin response to determining that the pressure measurement of the pressure sensor exceeds the pressure threshold, control the reversing valve to block the working fluid from flowing from the compressor to the outdoor heat exchanger via the reversing valve.

8. The heat pump of claim 1, wherein the controller is configured to determine whether to defrost the outdoor heat exchanger based on an outdoor temperature measure.

9. The heat pump of claim 1, comprising a temperature sensor configured to measure a temperature of the working fluid within the outdoor heat exchanger, wherein the controller is configured to:determine whether the pressure of the working fluid exiting the compressor exceeds the pressure threshold or the temperature of the working fluid within the outdoor heat exchanger exceeds a temperature threshold; andin response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold or the temperature of the working fluid within the outdoor heat exchanger exceeds the temperature threshold, control the reversing valve to block the working fluid from flowing from the compressor to the outdoor heat exchanger.

10. The heat pump of claim 9, wherein the controller is configured to:determine whether the pressure of the working fluid exiting the compressor exceeds the pressure threshold and the temperature of the working fluid within the outdoor heat exchanger exceeds the temperature threshold; andin response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold and the temperature of the working fluid within the outdoor heat exchanger exceeds the temperature threshold, control the reversing valve to block the working fluid from flowing from the compressor to the outdoor heat exchanger.

11. The heat pump of claim 9, wherein the temperature sensor is disposed at a discharge end of the outdoor heat exchanger.

12. The heat pump of claim 9, wherein:the temperature threshold corresponds to a temperature value of the working fluid within the outdoor heat exchanger during cooling mode operation in absence of frosting, andthe controller is configured to direct the working fluid, via control of the reversing valve, from the compressor to the outdoor heat exchanger during the cooling mode operation.

13. The heat pump of claim 1, wherein the heat pump comprises an expansion device configured to create a pressure drop in the working fluid as the working fluid passes through the expansion device.

14. The heat pump of claim 1, wherein the compressor, the reversing valve, and the outdoor heat exchanger are housed in an outdoor unit.

15. A method of operating a heat pump, comprising:determining that a pressure of a working fluid exiting a compressor of the heat pump exceeds a pressure threshold; andin response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, controlling a reversing valve to block the working fluid from flowing from the compressor through the reversing valve to an outdoor heat exchanger.

16. The method of claim 15, comprising, in response to determining that the pressure of the working fluid exiting the compressor exceeds the pressure threshold, controlling the reversing valve to enable the working fluid to flow from the compressor through the reversing valve to an indoor heat exchanger.

17. The method of claim 16, comprising:controlling the reversing valve to enable the working fluid to flow from the compressor to the outdoor heat exchanger;determining a total time elapsed since the working fluid is enabled to flow from the compressor to the outdoor heat exchanger;determining whether the pressure of the working fluid exiting the compressor of the heat pump exceeds the pressure threshold; andin response to determining that the total time elapsed since the working fluid is enabled to flow from the compressor to the outdoor heat exchanger exceeds a time threshold or the pressure of a working fluid exiting the compressor of the heat pump exceeds the pressure threshold, controlling the reversing valve to block the working fluid from flowing from the compressor to the outdoor heat exchanger via the reversing valve.

18. The method of claim 17, comprising, in response to determining that the total time elapsed since the working fluid is enabled to flow from the compressor to the outdoor heat exchanger exceeds a time threshold and the pressure of the working fluid exiting the compressor of the heat pump exceeds the pressure threshold, controlling the reversing valve to block the working fluid from flowing from the compressor to the outdoor heat exchanger.

19. A heating, ventilation, and air conditioning (HVAC) system, comprising:a heat pump configured to circulate a working fluid through two or more circuits, comprising:a first outdoor heat exchanger in a first circuit;a second outdoor heat exchanger in a second circuit;an indoor heat exchanger;a compressor;a pressure sensor disposed downstream of the compressor to measure a pressure of the working fluid exiting the compressor;a first temperature sensor configured to measure a first temperature of the working fluid within the first outdoor heat exchanger;a reversing valve configured to direct the working fluid from the compressor to the first outdoor heat exchanger, the second outdoor heat exchanger, or the indoor heat exchanger; anda controller configured to:determine whether the pressure exceeds a pressure threshold;determine whether the first temperature exceeds a temperature threshold; andin response to determining that the pressure exceeds the pressure threshold or the first temperature exceeds the temperature threshold, control the reversing valve to direct the working fluid to flow from the compressor through the reversing valve to the indoor heat exchanger.

20. The heating, ventilation, and air conditioning (HVAC) system of claim 19, comprising a second temperature sensor configured to measure a second temperature of the working fluid within the second outdoor heat exchanger, wherein the controller is configured to:determine whether the second temperature exceeds a temperature threshold; andin response to determining that the pressure exceeds the pressure threshold or one of the first temperature and the second temperature exceeds the temperature threshold, control the reversing valve to direct the working fluid to flow from the compressor through the reversing valve to the indoor heat exchanger.

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