MULTI-CIRCUIT HVAC SYSTEMS AND METHODS

BACKGROUND

This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Heating, ventilation, and/or air conditioning (HVAC) systems may be used to thermally regulate an environment, such as a space within a building, home, or other structure. HVAC systems generally include a vapor compression system having heat exchangers, such as a condenser and an evaporator, which transfer thermal energy between the HVAC system and the environment. Typically, a compressor is fluidly coupled to a refrigerant circuit of the vapor compression system and is configured to circulate a working fluid (e.g., refrigerant) between the condenser and the evaporator. In this way, the compressor facilitates heat exchange between the refrigerant, the condenser, and the evaporator. In general, the working fluid should be contained within the refrigerant circuit of the vapor compression system, as working fluid migration to an enclosed space, such as the building, home, or other structure that may be serviced by the HVAC system, is undesirable. Unfortunately, existing HVAC systems may be susceptible to various shortcomings and/or may not provide a desired level of security against undesired working fluid migration to enclosed spaces.

SUMMARY

In one embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a primary heat transfer circuit having a first heat exchanger fluidly coupled to an ambient environment, an intermediate heat exchanger fluidly coupled to the first heat exchanger, and a compressor configured to circulate a refrigerant through the primary heat transfer circuit. The HVAC system also includes a secondary heat transfer circuit having a second heat exchanger fluidly coupled to a thermal load, the intermediate heat exchanger, where the intermediate heat exchanger is fluidly coupled to the second heat exchanger, and a pump configured to circulate a heat transfer fluid through the secondary heat transfer circuit. The HVAC system further includes a sensor configured to provide feedback indicative of an operational parameter of the heat transfer fluid and a controller communicatively coupled to the compressor and the pump, where the controller is configured to receive the feedback and adjust operation of the compressor, the pump, or both, based on the feedback.

In another embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a first primary heat transfer circuit having a first heat exchanger fluidly coupled to an ambient environment, an intermediate heat exchanger fluidly coupled to the first heat exchanger, and a first compressor configured to circulate a first refrigerant through the first heat exchanger and the intermediate heat exchanger. The HVAC system also includes a second primary heat transfer circuit having a second heat exchanger fluidly coupled to the ambient environment, the intermediate heat exchanger, and a second compressor, where the intermediate heat exchanger is fluidly coupled to the second heat exchanger, and the second compressor is configured to circulate a second refrigerant through the second heat exchanger and the intermediate heat exchanger. The HVAC system further includes a secondary heat transfer circuit having a third heat exchanger fluidly coupled to a thermal load, the intermediate heat exchanger, and a pump, where the intermediate heat exchanger is fluidly coupled to the third heat exchanger, and the pump is configured to circulate a heat transfer fluid through the third heat exchanger and the intermediate heat exchanger. The HVAC system additionally includes a controller communicatively coupled to the first compressor and the second compressor, where the controller is configured to operate the first compressor and block operation of the second compressor in a first operating mode of the HVAC system and to operate the second compressor and to block operation of the first compressor in a second operating mode of the HVAC system.

In a further embodiment, a heating, ventilation, and air conditioning (HVAC) system includes a primary heat transfer circuit having a first heat exchanger fluidly coupled to an ambient environment and a compressor fluidly coupled to the first heat exchanger and configured to circulate a refrigerant through the primary heat transfer circuit. The HVAC system also includes a secondary heat transfer circuit having a second heat exchanger fluidly coupled to a thermal load and a pump fluidly coupled to the second heat exchanger and configured to circulate a heat transfer fluid through the secondary heat transfer circuit, where the heat transfer fluid is a non-volatile or inert fluid. The HVAC system further includes an intermediate heat exchanger disposed along the primary heat transfer circuit and the secondary heat transfer circuit, where the intermediate heat exchanger is configured to transfer heat between the refrigerant and the heat transfer fluid, and the primary heat transfer circuit is entirely external to a perimeter of the thermal load.

BRIEF DESCRIPTION OF THE DRAWINGS

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;

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

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

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

FIG. 5 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 6 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 7 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 8 is a flow diagram of an embodiment of a process for operating a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 9 is a flow diagram of an embodiment of a process for operating a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 10 is a flow diagram of an embodiment of a process for operating a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 11 is a flow diagram of an embodiment of a process for operating a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 12 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure;

FIG. 13 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure; and

FIG. 14 is a schematic diagram of an embodiment of a portion of an HVAC system that includes a multi-circuit heat transfer system, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

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

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 loop or circuit (e.g., refrigerant circuit). A compressor may be used to circulate the working fluid (e.g., refrigerant) 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).

Additionally or alternatively, the HVAC system may include a heat pump (e.g., a heat pump system) having a first heat exchanger (e.g., a heating and/or cooling coil, an indoor coil, an evaporator) positioned within a building and/or the space to be conditioned, a second heat exchanger (e.g., a heating and/or cooling coil, an outdoor coil, a condenser) positioned in or otherwise fluidly coupled to an ambient environment (e.g., atmosphere), and a pump (e.g., a compressor) configured to circulate the working fluid (e.g., refrigerant) between the first and second heat exchangers to enable heat transfer between the thermal load (e.g., an air flow to be conditioned) and the ambient environment, for example. The heat pump system is operable to provide both cooling and heating to the space to be conditioned (e.g., a room, zone, or other region within a building) by adjusting a flow of the working fluid through the working fluid circuit (e.g., via a reversing valve). Further, the HVAC system may include a furnace system, a chiller system, and/or various other climate management components that may cooperate to regulate environmental parameters within the space to be conditioned. In some cases, it may be desirable to mitigate or avoid migration of working fluid (e.g., refrigerant) from the vapor compression system (e.g., working fluid circuit) into a space conditioned by the HVAC system (e.g., a room or zone within a building, home, or other structure).

Accordingly, embodiments of the present disclosure relate to an HVAC system that includes a plurality of heat transfer circuits that are configured to inhibit or substantially eliminate potential working fluid (e.g., refrigerant) migration from the vapor compression system and into the space conditioned by the HVAC system. For example, the HVAC system may include a primary heat transfer circuit (e.g., loop) configured to circulate a working fluid (e.g., refrigerant) and a secondary heat transfer circuit (e.g., loop) configured to circulate a non-volatile (e.g., inert) heat transfer fluid (e.g., a two-phase fluid, water, brine, glycol, a combination thereof). The primary heat transfer circuit may facilitate heat exchange between the working fluid and an ambient environment (e.g., the atmosphere), and the secondary heat transfer circuit may facilitate heat exchange between the heat transfer fluid and the space to be conditioned (e.g., with a supply air flow directed into or through the space). The primary heat transfer circuit may be in thermal communication with the secondary heat transfer circuit via an intermediate heat exchanger that is fluidly coupled between the primary and secondary heat transfer circuits. The intermediate heat exchanger facilitates heat exchange between the working fluid in the primary heat transfer circuit and the heat transfer fluid in the secondary heat transfer circuit (e.g., without mixing of the working fluid and the heat transfer fluid). Accordingly, the intermediate heat exchanger enables the primary and secondary heat transfer circuits to cooperatively facilitate heating or cooling of the space to be conditioned via heat exchange between the fluids circulating through the respective heat transfer circuits. The primary heat transfer circuit may be located fully or partially outside of the space to be conditioned by the HVAC system, whereas the secondary heat transfer circuit may be located fully or partially within the space to be conditioned. To this end, to the extent that migration of working fluid from the primary heat transfer circuit may occur, migration of working fluid into the space to be conditioned may be inhibited or substantially reduced. These and other features will be described below with reference to the drawings.

Turning now to the drawings, FIG. 1 illustrates an embodiment of a heating, ventilation, and/or air conditioning (HVAC) system for environmental management that 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.

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

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

A control device 16, one type of which may be a thermostat, may be used to designate the temperature of the conditioned air. The control device 16 also may be used to control the flow of air through the ductwork 14. For example, the control device 16 may be used to regulate operation of one or more components of the HVAC unit 12 or other components, such as dampers and fans, within the building 10 that may control flow of air through and/or from the ductwork 14. In some embodiments, other devices may be included in the system, such as pressure and/or temperature transducers or switches that sense the temperatures and pressures of the supply air, return air, and so forth. Moreover, the control device 16 may include computer systems that are integrated with or separate from other building control or monitoring systems, and even systems that are remote from the building 10.

FIG. 2 is a perspective view of an embodiment of the HVAC unit 12. In the illustrated embodiment, the HVAC unit 12 is a single package unit that may include one or more independent working fluid circuits and components that are tested, charged, wired, piped, and ready for installation. The HVAC unit 12 may provide a variety of heating and/or cooling functions, such as cooling only, heating only, cooling with electric heat, cooling with dehumidification, cooling with gas heat, or cooling with a heat pump. As described above, the HVAC unit 12 may directly cool and/or heat an air stream provided to the building 10 to condition a space in the building 10.

As shown in the illustrated embodiment of FIG. 2, a cabinet 24 encloses the HVAC unit 12 and provides structural support and protection to the internal components from environmental and other contaminants. In some embodiments, the cabinet 24 may be constructed of galvanized steel and insulated with aluminum foil faced insulation. Rails 26 may be joined to the bottom perimeter of the cabinet 24 and provide a foundation for the HVAC unit 12. In certain embodiments, the rails 26 may provide access for a forklift and/or overhead rigging to facilitate installation and/or removal of the HVAC unit 12. In some embodiments, the rails 26 may fit into “curbs” on the roof to enable the HVAC unit 12 to provide air to the ductwork 14 from the bottom of the HVAC unit 12 while blocking elements such as rain from leaking into the building 10.

The HVAC unit 12 includes heat exchangers 28 and 30 in fluid communication with one or more working fluid circuits. Tubes within the heat exchangers 28 and 30 may circulate working fluid (e.g., refrigerant, such as R-410A) through the heat exchangers 28 and 30. The tubes may be of various types, such as multichannel tubes, conventional copper or aluminum tubing, and so forth. Together, the heat exchangers 28 and 30 may implement a thermal cycle in which the working fluid undergoes phase changes and/or temperature changes as it flows through the heat exchangers 28 and 30 to produce heated and/or cooled air. For example, the heat exchanger 28 may function as a condenser where heat is released from the working fluid to ambient air, and the heat exchanger 30 may function as an evaporator where the working fluid absorbs heat to cool an air stream. In other embodiments, the HVAC unit 12 may operate in a heat pump mode where the roles of the heat exchangers 28 and 30 may be reversed. That is, the heat exchanger 28 may function as an evaporator and the heat exchanger 30 may function as a condenser. In further embodiments, the HVAC unit 12 may include a furnace for heating the air stream that is supplied to the building 10. While the illustrated embodiment of FIG. 2 shows the HVAC unit 12 having two of the heat exchangers 28 and 30, in other embodiments, the HVAC unit 12 may include one heat exchanger or more than two heat exchangers.

The heat exchanger 30 is located within a compartment 31 that separates the heat exchanger 30 from the heat exchanger 28. Fans 32 draw air from the environment through the heat exchanger 28. Air may be heated and/or cooled as the air flows through the heat exchanger 28 before being released back to the environment surrounding the HVAC unit 12. A blower assembly 34, powered by a motor 36, draws air through the heat exchanger 30 to heat or cool the air. The heated or cooled air may be directed to the building 10 by the ductwork 14, which may be connected to the HVAC unit 12. Before flowing through the heat exchanger 30, the conditioned air flows through one or more filters 38 that may remove particulates and contaminants from the air. In certain embodiments, the filters 38 may be disposed on the air intake side of the heat exchanger 30 to prevent contaminants from contacting the heat exchanger 30.

The HVAC unit 12 also may include other equipment for implementing the thermal cycle. Compressors 42 increase the pressure and temperature of the 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.

The HVAC unit 12 may receive power through a terminal block 46. For example, a high voltage power source may be connected to the terminal block 46 to power the equipment. The operation of the HVAC unit 12 may be governed or regulated by a control board 48. The control board 48 may include control circuitry connected to a thermostat, sensors, and alarms. One or more of these components may be referred to herein separately or collectively as the control device 16. The control circuitry may be configured to control operation of the equipment, provide alarms, and monitor safety switches. Wiring 49 may connect the control board 48 and the terminal block 46 to the equipment of the HVAC unit 12.

FIG. 3 illustrates a residential heating and cooling system 50, also in accordance with present techniques. The residential heating and cooling system 50 may provide heated and cooled air to a residential structure, as well as provide outside air for ventilation and provide improved indoor air quality (IAQ) through devices such as ultraviolet lights and air filters. In the illustrated embodiment, the residential heating and cooling system 50 is a split HVAC system. In general, a residence 52 conditioned by a split HVAC system may include 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.

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.

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. The outdoor unit 58 may include a reheat system in accordance with present embodiments.

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.

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 66 passes over the tubes or pipes and extracts heat from the combustion products. The heated air may then be routed from the furnace system 70 to the ductwork 68 for heating the residence 52.

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

In some embodiments, the vapor compression system 72 may use one or more of a variable speed drive (VSDs) 92, a motor 94, the compressor 74, the condenser 76, the expansion valve or device 78, and/or the evaporator 80. The motor 94 may drive the compressor 74 and may be powered by the variable speed drive (VSD) 92. The VSD 92 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 94. In other embodiments, the motor 94 may be powered directly from an AC or direct current (DC) power source. The motor 94 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 74 compresses a 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.

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.

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 80 relative to the supply air stream 98 and may reheat the supply air stream 98 when the supply air stream 98 is overcooled to remove humidity from the supply air stream 98 before the supply air stream 98 is directed to the building 10 or the residence 52.

It should be appreciated that any of the features described herein may be incorporated with the HVAC unit 12, the residential heating and cooling system 50, or other HVAC systems. Additionally, while the features disclosed herein are described in the context of embodiments that directly heat and cool a supply air stream provided to a building or other load, embodiments of the present disclosure may be applicable to other HVAC systems as well. For example, the features described herein may be applied to mechanical cooling systems, free cooling systems, chiller systems, or other heat pump or refrigeration applications.

As briefly discussed above, embodiments of the present disclosure are directed to an HVAC system having multiple heat transfer circuits that are configured to facilitate conditioning of a space serviced by the HVAC system, while inhibiting or substantially eliminating a possibility of working fluid (e.g., refrigerant) migration into the space (e.g., via escape from the HVAC system). To provide context for the following discussion, FIG. 5 is a schematic of an embodiment of a portion of an HVAC system 100 having a multi-circuit heat transfer system 102 configured to facilitate conditioning of a thermal load 104 (e.g., a building, home, or other suitable structure). In the illustrated embodiment, the HVAC system 100 includes a primary heat transfer circuit 106 (e.g., primary heat transfer loop) and a secondary heat transfer circuit 108 (e.g., secondary heat transfer loop) that are in thermal communication with one another via an intermediate heat exchanger 110. The primary heat transfer circuit 106 may include a first heat exchanger 112 (e.g., an outdoor heat exchanger, heat exchanger 60, condenser 76), an expansion device 114 (e.g., an electronic expansion valve [EEV], expansion device 78) and a compressor 116 (e.g., compressor 42) that are fluidly coupled to one another via one or more conduits of the primary heat transfer circuit 106. The first heat exchanger 112 may be positioned in an ambient environment 118 surrounding the primary heat transfer circuit 106 and/or to which the primary heat transfer circuit 106 is fluidly coupled or exposed. That is, the first heat exchanger 112 may be positioned external to (e.g., outside of) an interior of the thermal load 104. A first passage 120 (e.g., conduit, flow path) of the intermediate heat exchanger 110 may be fluidly coupled to and form at least a portion of the primary heat transfer circuit 106. The compressor 116 may be configured to circulate a working fluid 122 (e.g., a refrigerant) along the conduits of the primary heat transfer circuit 106 and through the first heat exchanger 112, the expansion device 114, and the first passage 120 of the intermediate heat exchanger 110. In this manner, the compressor 116 may facilitate heat exchange between the working fluid 122, the ambient environment 118, and a heat transfer fluid 124 within the secondary heat transfer circuit 108, as discussed in detail herein.

The secondary heat transfer circuit 108 may include a second heat exchanger 126 (e.g., an indoor heat exchanger, heat exchanger 62, evaporator 80) and a pump 128 (e.g., a compressor) that are fluidly coupled to one another via one or more conduits of the secondary heat transfer circuit 108. The second heat exchanger 126 may be positioned within an interior of the thermal load 104 and be configured to facilitate conditioning of the thermal load 104. That is, the second heat exchanger 126 may be configured to reject heat to and/or absorb heat from the thermal load 104. A second passage 130 (e.g., conduit, flow path) of the intermediate heat exchanger 110 may be fluidly coupled to and form at least a portion of the secondary heat transfer circuit 108. The second passage 130 may be fluidly isolated from the first passage 120 to inhibit mixing of working fluid 122 (e.g., refrigerant) from the primary heat transfer circuit 106 with the heat transfer fluid 124 of the secondary heat transfer circuit 108. The pump 128 may be configured to circulate the heat transfer fluid 124 (e.g., an inert fluid, a two-phase fluid) along the conduits of the secondary heat transfer circuit 108 and through the second heat exchanger 126 and the second passage 130 of the intermediate heat exchanger 110. In this manner, the pump 128 may facilitate heat exchange between the heat transfer fluid 124, the thermal load 104, and the working fluid 122 within the primary heat transfer circuit 106.

For example, in a cooling mode of the HVAC system 100, the compressor 116 may be configured to circulate the working fluid 122 along the primary heat transfer circuit 106 in a first direction 140. As such, the compressor 116 may delivered heated and compressed working fluid 122 to the first heat exchanger 112, such that the first heat exchanger 112 may reject heat from the working fluid 122 to the ambient environment 118. The expansion device 114 may expand the working fluid 122 received from the first heat exchanger 112 to cool the working fluid 122 and direct the cooled working fluid 122 through the first passage 120 of the intermediate heat exchanger 110. As such, the cooled working fluid 122 may absorb thermal energy from the heat transfer fluid 124 that may be directed through the second passage 130 of the intermediate heat exchanger 110 via the pump 128. In the cooling mode of the HVAC system 100, the pump 128 may direct the heat transfer fluid 124 in a second direction 142 along the secondary heat transfer circuit 108. As such, the pump 128 may direct cooled heat transfer fluid 124 received from the intermediate heat exchanger 110 to the second heat exchanger 126. Cooled heat transfer fluid 124 entering the second heat exchanger 126 may absorb thermal energy from the thermal load 104 (e.g., from a supply air flow directed to a conditioned space) and, thus, facilitate conditioning (e.g., cooling) of the thermal load 104.

In some embodiments, a flow direction of the working fluid 122 through the primary heat transfer circuit 106 may be reversible, such that the multi-circuit heat transfer system 102 may be operable as a heat pump configured to heat the thermal load 104. For example, the primary heat transfer circuit 106 may include one or more reversing valves, auxiliary expansion devices, and/or other components that may enable the compressor 116 to direct the working fluid 122 along the primary heat transfer circuit 106 in a manner that enables the first heat exchanger 112 to operate as an evaporator and enables the intermediate heat exchanger 110 to operate as a condenser. In this way, working fluid 122 circulating through the first heat exchanger 112 may absorb thermal energy from the ambient environment 118 and reject the absorbed thermal energy to the heat transfer fluid 124 of the secondary heat transfer circuit 108 (e.g., via the intermediate heat exchanger 110). The pump 128 may subsequently direct heated heat transfer fluid 124 from the intermediate heat exchanger 110 to the second heat exchanger 126 and, thus, enable the second heat exchanger 126 to reject heat to the thermal load 104 to heat the thermal load 104.

In the illustrated embodiment, the thermal load 104 includes a perimeter 150 that may define a boundary (e.g., outer boundary) of the thermal load 104. That is, the perimeter 150 may be indicative of one or more walls, partitions, windows, doors, roofs, floors, and/or other structures that may partially and/or fully separate (e.g., isolate, insulate) an interior 152 (e.g., an enclosed space, interior volume) of the thermal load 104 from the ambient environment 118. In certain embodiments, the primary heat transfer circuit 106 may be positioned fully and/or entirely outside of (e.g., external to) the perimeter 150, and the secondary heat transfer circuit 108 may be positioned fully and/or entirely within (e.g., internal to) the perimeter 150. The intermediate heat exchanger 110 may extend across or through the perimeter 150. Because the primary heat transfer circuit 106 is disposed external to (e.g., completely external to) the interior 152, to the extent that migration of working fluid 122 from the primary heat transfer circuit 106 may occur, working fluid 122 from the primary heat transfer circuit 106 may not migrate to the interior 152 of the thermal load 104.

In some embodiments, the primary heat transfer circuit 106 may be positioned fully outside of the perimeter 150, and the secondary heat transfer circuit 108 may be positioned at least partially within the perimeter 150. For example, to better illustrate, FIG. 6 is a schematic of an embodiment of a portion of the HVAC system 100, in which at least a portion 160 of the secondary heat transfer circuit 108 extends across or through the perimeter 150 and into the ambient environment 118. In other words, the portion 160 of the secondary heat transfer circuit 108 is positioned external to perimeter 150 and/or thermal load 104. In such embodiments, the intermediate heat exchanger 110 may be positioned outside of (e.g., fully outside of) the thermal load 104 (e.g., outside of the perimeter 150).

In certain embodiments, at least a portion of the primary heat transfer circuit 106 may be positioned within the thermal load 104 (e.g., within the perimeter 150). For example, to better illustrate, FIG. 7 is a schematic of an embodiment of a portion of the HVAC system 100, in which at least a portion 162 of the primary heat transfer circuit 106 extends across or through the perimeter 150 and into the interior 152 of the thermal load 104. In such embodiments, the intermediate heat exchanger 110 may be positioned within (e.g., fully within) the thermal load 104 (e.g., within the perimeter 150).

The following discussion continues with reference to FIG. 5. In some embodiments, the HVAC system 100 may include one or more first sensors 170 configured to monitor operational parameters or characteristics of the primary heat transfer circuit 106 and one or more second sensors 172 configured to monitor operational parameters or characteristics of the secondary heat transfer circuit 108. For example, the one or more first sensors 170 may be configured to provide feedback (e.g., data) indicative of a pressure of the working fluid 122 along one or more portions of the primary heat transfer circuit 106, a temperature of the working fluid 122 along one or more portions of the primary heat transfer circuit 106, a composition (e.g., material composition) of the working fluid 122, and/or other suitable parameters of or associated with the primary heat transfer circuit 106. The one or more second sensors 172 may be configured to provide feedback (e.g., data) indicative of a pressure of the heat transfer fluid 124 along one or more portions of the secondary heat transfer circuit 108, a temperature of the heat transfer fluid 124 along one or more portions of the secondary heat transfer circuit 108, a composition (e.g., material composition) of the heat transfer fluid 124, and/or other suitable parameters of or associated with the secondary heat transfer circuit 108.

The HVAC system 100 may include a controller 174 (e.g., a control system, a thermostat, a control panel, control circuitry) that is communicatively coupled to one or more components of the HVAC system 100 and is configured to monitor, adjust, and/or otherwise control operation of the components of the HVAC system 100. For example, one or more control transfer devices, such as wires, cables, wireless communication devices, and the like, may communicatively couple the compressor 116, the expansion device 114, the pump 128, the first sensors 170, the second sensors 172, and/or any other suitable components of the HVAC system 100 to the controller 174. That is, the compressor 116, the expansion device 114, the pump 128, the first sensors 170, and/or the second sensors 172 may each have one or more communication components that facilitate wired or wireless (e.g., via a network) communication with the controller 174. In some embodiments, the communication components may include a network interface that enables the components of the HVAC system 100 to communicate via various protocols such as EtherNet/IP, ControlNet, DeviceNet, or any other communication network protocol. Alternatively, the communication components may enable the components of the HVAC system 100 to communicate via mobile telecommunications technology, Bluetooth®, near-field communications technology, and the like. As such, the compressor 116, the expansion device 114, the pump 128, the first sensors 170, and/or the second sensors 172 may wirelessly communicate data and/or control signals between each other.

In some embodiments, the controller 174 may be a component of or may include the control panel 82. In other embodiments, the controller 174 may be a standalone controller, a dedicated controller, or another suitable controller included in the HVAC system 100. In any case, the controller 174 is configured to control components of the HVAC system 100 in accordance with the techniques discussed herein. The controller 174 includes processing circuitry 176, such as a microprocessor, which may execute software (e.g., executable instructions, code) for controlling the components of the HVAC system 100. The processing circuitry 176 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 176 may include one or more reduced instruction set (RISC) processors.

The controller 174 may also include a memory device 178 (e.g., a memory) that may store information, such as instructions, control software, look up tables, configuration data, code, etc. The memory device 178 may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory device 178 may store a variety of information and may be used for various purposes. For example, the memory device 178 may store processor-executable instructions including firmware or software for the processing circuitry 176 execute, such as instructions for controlling components of the HVAC system 100. In some embodiments, the memory device 178 is a tangible, non-transitory, machine-readable-medium that may store machine-readable instructions for the processing circuitry 176 to execute. The memory device 178 may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, or a combination thereof. The memory device 178 may store data, instructions, and any other suitable data.

In some embodiments, it may be desirable to operate the HVAC system 100 such that a temperature of the heat transfer fluid 124 along the secondary heat transfer circuit 108 does not fall below a lower threshold operating value (e.g., a lower operating temperature threshold). For example, in certain embodiments, the heat transfer fluid 124 may include a phase-change fluid (e.g., water) that may freeze (e.g., transition to a solid phase or state) at or near the lower threshold operating value. Freezing of the heat transfer fluid 124 along the secondary heat transfer circuit 108 may obstruct or block fluid flow along the conduits of the secondary heat transfer circuit 108 and, thus, inhibit operation of the secondary heat transfer circuit 108 and/or reduce an operational efficiency of the secondary heat transfer circuit 108. That is, obstruction of fluid flow along secondary heat transfer circuit 108 (e.g., due to freezing of the heat transfer fluid 124) may inhibit the pump 128 from circulating the heat transfer fluid 124 along the secondary heat transfer circuit 108 to facilitate heat exchange between the thermal load 104 and the second heat exchanger 126. Moreover, freezing (e.g., solidifying, coagulation) of the heat transfer fluid 124 within conduits or other components (e.g., the intermediate heat exchanger 110, the pump 128) of the secondary heat transfer circuit 108 may cause the heat transfer fluid 124 to expand, which may result in wear and/or performance degradation of the conduits and/or other components of the secondary heat transfer circuit 108. As such, the controller 174 may be configured (e.g., programmed) to monitor a temperature of the heat transfer fluid 124 within the secondary heat transfer circuit 108 and to perform a remedial action in response to a determination that a temperature of the heat transfer fluid 124 reaches or falls below the lower threshold operating value. In certain embodiments, the controller 174 may be configured (e.g., programmed) to monitor one or more alternate or additional operational parameters of the heat transfer fluid 124 within the secondary heat transfer circuit 108 and to perform a remedial action or operation in response to a determination that the one or more alternate or additional operational parameters deviate from corresponding target values by respective threshold amounts. For example, the controller 174 may be configured to monitor a flow rate, consistency, viscosity, and/or material composition of the heat transfer fluid 124 and to perform the remedial action or operation in response to a determination that any one of the aforementioned parameters deviates from a corresponding target value by a threshold amount.

To facilitate the following discussion, FIG. 8 is flow diagram of an embodiment of a process 180 for controlling the HVAC system 100 in accordance with the presently disclosed techniques to detect or inhibit freezing of heat transfer fluid 124 within the secondary heat transfer circuit 108. FIG. 8 will be referred to concurrently with FIG. 5 throughout the following discussion. It should be noted that the steps of the process 180 discussed below may be performed in any suitable order and are not limited to the order shown in the illustrated embodiment of FIG. 8. Moreover, it should be noted that additional steps of the process 180 may be performed, and certain steps of the process 180 may be omitted. In some embodiments, the process 180 may be executed by the processing circuitry 176 of the controller 174 and/or any other suitable processing circuitry of the HVAC system 100. The process 180 may be stored on, for example, the memory 88 and/or the memory device 178. Although the process 180 below is discussed with reference to monitoring a temperature of the heat transfer fluid 124, it should be understood that the process 180 and/or any other processes discussed herein may be implemented in accordance with the present techniques using any other suitable one or combination of operational parameters of the heat transfer fluid 124 (e.g., flow rate, viscosity, material composition).

The process 180 may begin with monitoring a temperature of the heat transfer fluid 124 in the secondary heat transfer circuit 108, as indicated by block 182. For example, the controller 174 may be configured to receive feedback (e.g., data) from the one or more second sensors 172 indicative of a temperature of the heat transfer fluid 124 along or at one or more sections and/or components of the secondary heat transfer circuit 108. The controller 174 may, based on the feedback from the one or more second sensors 172, determine whether the temperature of the heat transfer fluid 124 along any particular section of the secondary heat transfer circuit 108 is less than a lower threshold operating value, as indicated by block 184. In some embodiments, the lower threshold operating value may be stored on the memory device 178. The lower threshold operating value may be a user-selected value (e.g., a value stored on the memory device 178 in response to user input). As discussed below, in other embodiments, the controller 174 may be configured to determine the lower threshold operating value based on a composition (e.g., a measured material composition) of the heat transfer fluid 124. In any case, in response to a determination that the temperature of the heat transfer fluid 124 is greater than the lower threshold operating value, the controller 174 may return to block 182. In response to a determination that the temperature of the heat transfer fluid 124 is less that the lower threshold operating value, the controller 174 may perform a remedial action or operation, as indicated by block 186.

In some embodiments, to perform the remedial action at block 186, the controller 174 may deactivate the pump 128, the compressor 116, or both. In other embodiments, to perform the remedial action, the controller 174 may execute a temperature-increase control scheme that adjusts operation of the HVAC system 100 in a manner intended to increase a temperature of the heat transfer fluid 124, as indicated by block 188. The controller 174 may perform the temperature-increase control scheme for a predetermined time interval (e.g., ten seconds, one minute) or until the temperature of the heat transfer fluid 124 (e.g., as measured by the one or more second sensors 172) reaches or exceeds the lower threshold operating value.

In some embodiments, to perform the temperature-increase control scheme at block 188, the controller 174 may decrease an operational speed of the compressor 116. In this way, the controller 174 may reduce a rate of heat rejection from the working fluid 122 in the first heat exchanger 112 to the ambient environment 118, which may increase a temperature at which the working fluid 122 enters the first passage 120 of the intermediate heat exchanger 110. As such, the controller 174 may reduce a rate at which the working fluid 122 in the first passage 120 absorbs thermal energy from the heat transfer fluid 124 in the second passage 130 and, thus, cause an increase in the overall temperature of the heat transfer fluid 124 in the secondary heat transfer circuit 108.

Additionally or alternatively to reducing the speed of the compressor 116 at block 188, the controller 174 may adjust the expansion device 114 to reduce or inhibit expansion of working fluid 122 flowing across the expansion device 114, which may thereby increasing a relative temperature at which the working fluid 122 enters the intermediate heat exchanger 110.

In some embodiments, at block 188, the controller 174 may operate components (e.g., the compressor 116, a reversing valve) of the primary heat transfer circuit 106 to reverse a flow direction of the working fluid 122 along the primary heat transfer circuit 106. To this end, the controller 174 may operate the primary heat transfer circuit 106 as a heat pump in accordance with the techniques discussed above, such that the first heat exchanger 112 may absorb thermal energy from the ambient environment 118 and the intermediate heat exchanger 110 may reject the absorbed thermal energy to the heat transfer fluid 124 to heat the heat transfer fluid 124.

Additionally or alternatively, to perform the temperature-increase control scheme at block 188, the controller 174 may increase an operational speed of the pump 128. As such, the controller 174 may increase a rate at which the heat transfer fluid 124 absorbs thermal energy from the thermal load 104 (e.g., via the second heat exchanger 126), thereby causing an increase in the temperature of the heat transfer fluid 124.

In certain embodiments, the controller 174 may suspend execution of the temperature-increase control scheme and deactivate the pump 128, the compressor 116, or both, in response to a determination that the temperature of the heat transfer fluid 124 reaches or falls below an additional threshold value that may be less than the lower threshold operating value corresponding to block 184.

In some embodiments, the controller 174 may be configured to determine the lower threshold operating value the heat transfer fluid 124 based on a composition (e.g., a real-time composition) of the heat transfer fluid 124. For example, a magnitude of the lower threshold operating value may correspond to the composition of the heat transfer fluid 124. That is, a composition of the heat transfer fluid 124 may affect, for example, the temperature at which the heat transfer fluid freezes. In certain embodiments, the composition of the heat transfer fluid 124 within the secondary heat transfer circuit 108 may change over time. As an example, accumulation of impurities (e.g., non-condensable gases) within the secondary heat transfer circuit 108 may cause the composition of the heat transfer fluid 124 to vary over time. Accordingly, it may be advantageous to adjust a magnitude of the lower threshold operating value based on the actual (e.g., current, real-time) composition of the heat transfer fluid 124 in the secondary heat transfer circuit 108.

To facilitate the following discussion, FIG. 9 is flow diagram of an embodiment of a process 200 for controlling the HVAC system 100 in accordance with the presently disclosed techniques based on a measured composition of the heat transfer fluid 124. FIG. 9 will be referred to concurrently with FIG. 5 throughout the following discussion. It should be noted that the steps of the process 200 discussed below may be performed in any suitable order and are not limited to the order shown in the illustrated embodiment of FIG. 9. Moreover, it should be noted that additional steps of the process 200 may be performed, and certain steps of the process 200 may be omitted. In some embodiments, the process 200 may be executed by the processing circuitry 176 of the controller 174 and/or any other suitable processing circuitry of the HVAC system 100. The process 200 may be stored on, for example, the memory 88 and/or the memory device 178.

The process 200 may include determining a composition of the heat transfer fluid 124 in the secondary heat transfer circuit 108, as indicated by block 202. For example, the controller 174 may receive feedback (e.g., data) from the one or more second sensors 172 indicative of the composition of the heat transfer fluid 124 along a particular section of the secondary heat transfer circuit 108. The composition of the heat transfer fluid 124 may be indicative to relative amounts (e.g., percentages, ratios) of constituent components of the heat transfer fluid 124. In some embodiments, the controller 174 may receive feedback indicative of the composition of the heat transfer fluid 124 along a plurality of sections of the secondary heat transfer circuit 108 and/or may determine the composition based on an average of the various composition measurements acquired by the one or more second sensors 172.

In any case, as indicated by block 204, the controller 174 may determine the lower threshold operating value of the heat transfer fluid 124 based on the measured composition of the heat transfer fluid 124 (e.g., based on the feedback from the one or more second sensors 172). For example, the controller 174 may be configured to store (e.g., on the memory device 178) or otherwise access a look-up table or other database that correlates various compositions of the heat transfer fluid 124 to corresponding lower threshold operating values of the heat transfer fluid 124. As such, the controller 174 may utilize the look-up table or database to determine the lower threshold operating value for the heat transfer fluid 124 based on the current (e.g., real-time, actual, measured) composition of the heat transfer fluid 124. In certain embodiments, the controller 174 may be configured to calculate (e.g., using defined relationships or algorithms) the lower threshold operating value of the heat transfer fluid 124 based on the measured composition of the heat transfer fluid 124. The controller 174 may be configured to perform the steps of blocks 202 and 204 at predetermined time intervals (e.g., after lapse of a threshold number of days or weeks), upon start-up of the HVAC system 100, upon switching of the HVAC system 100 between different operating modes (e.g., cooling, heating), upon a predetermined quantity of operational cycles of the HVAC system 100, upon detection of reduced operational efficiency of the HVAC system 100 or a fault condition, in response to user input, in response to other suitable input, or any combination thereof. In any case, upon execution of block 204, the controller 174 may perform blocks 184 and 186 in accordance with the techniques discussed above with reference to FIG. 8.

In some embodiments, the controller 174 may utilize feedback from the one or more second sensors 172 (e.g., a composition sensor) to detect working fluid (e.g., refrigerant) that may be mixed and/or suspended within the heat transfer fluid 124, as indicated by block 210. Detection of working fluid within the heat transfer fluid 124 of the secondary heat transfer circuit 108 may be indicative of working fluid 122 migration from the intermediate heat exchanger 110 that may permit working fluid 122 from the primary heat transfer circuit 106 to enter (e.g., flow into) the secondary heat transfer circuit 108. As such, in response to detection of a threshold concentration of working fluid 122 in the secondary heat transfer circuit 108, the controller 174 may perform a corresponding remedial action or operation. For example, the controller 174 may suspend operation of the compressor 116, the pump 128, or both, and/or may transmit an alert message to a suitable electronic device (e.g., an electronic device of a user of the HVAC system 100 and/or an installer/service provider of the HVAC system 100).

In some embodiments, the controller 174 may be configured to perform a remedial action or operation in accordance with the techniques discussed above in response to a determination that a temperature of the heat transfer fluid 124 exceeds an upper threshold operating value. For example, to facilitate the following discussion, FIG. 10 is flow diagram of an embodiment of a process 220 for controlling the HVAC system 100 in accordance with the presently disclosed techniques. FIG. 10 will be referred to concurrently with FIG. 5 throughout the following discussion. It should be noted that the steps of the process 220 discussed below may be performed in any suitable order and are not limited to the order shown in the illustrated embodiment of FIG. 10. Moreover, it should be noted that additional steps of the process 220 may be performed, and certain steps of the process 220 may be omitted. In some embodiments, the process 220 may be executed by the processing circuitry 176 of the controller 174 and/or any other suitable processing circuitry of the HVAC system 100. The process 220 may be stored on, for example, the memory 88 and/or the memory device 178.

The process 220 may begin with monitoring a temperature of the heat transfer fluid 124 in the secondary heat transfer circuit 108, as indicated by block 222. The controller 174 may, based on feedback from the one or more second sensors 172, determine whether the temperature of the heat transfer fluid 124 along any particular section of the secondary heat transfer circuit 108 is greater than an upper threshold operating value, as indicated by block 224. In response to a determination that the temperature of the heat transfer fluid 124 is less than the upper threshold operating value, the controller 174 may return to block 222. In response to a determination that the temperature of the heat transfer fluid 124 is equal to or greater than the upper threshold operating value, the controller 174 may perform a remedial action or operation, as indicated by block 226.

In some embodiments, to perform the remedial action, the controller 174 may deactivate the pump 128, the compressor 116, or both. In other embodiments, to perform the remedial action, the controller 174 may perform a temperature-reduction control scheme, as indicated by block 228. As discussed below, execution of the temperature-reduction control scheme may enable the controller 174 to adjust operation of the HVAC system 100 in a manner that may decrease a temperature of the heat transfer fluid 124 along the secondary heat transfer circuit 108. The controller 174 may perform the temperature-reduction control scheme for a predetermined time interval (e.g., ten seconds, one minute) and/or until the temperature of the heat transfer fluid 124 (e.g., as measured by the one or more second sensors 172) falls below the upper threshold operating value.

In some embodiments, to perform the temperature-reduction control scheme at block 228, the controller 174 may increase an operational speed of the compressor 116. To this end, the controller 174 may increase a rate of heat rejection from the working fluid 122 in the first heat exchanger 112 to the ambient environment 118, which may decrease a temperature at which the working fluid 122 enters the first passage 120 of the intermediate heat exchanger 110. As such, the controller 174 may increase a rate at which the working fluid 122 in the first passage 120 may absorb thermal energy from the heat transfer fluid 124 in the second passage 130 and, thus, cause a decrease in the overall temperature of the heat transfer fluid 124 in the secondary heat transfer circuit 108.

Additionally or alternatively to increasing the speed of the compressor 116 at block 228, the controller 174 may adjust the expansion device 114 to increase expansion of working fluid 122 flowing across the expansion device 114, which may decrease the temperature at which the working fluid 122 enters the intermediate heat exchanger 110.

Additionally or alternatively, to perform the temperature-reduction control scheme at block 228, the controller 174 may decrease an operational speed of the pump 128. As such, the controller 174 may decrease a rate at which the heat transfer fluid 124 absorbs thermal energy from the thermal load 104 (e.g., via the second heat exchanger 126), thereby causing a decrease in the temperature of the heat transfer fluid 124.

In certain embodiments, the controller 174 may suspend execution of the temperature-reduction control scheme in response to a determination that the temperature of the heat transfer fluid 124 reaches or rises above an additional upper threshold operating value that may be greater than the upper threshold operating value corresponding to block 224.

In some embodiments, the controller 174 may be configured to perform a remedial action or operation or otherwise adjust operation of the HVAC system 100 based on a pressure of the working fluid 122 within the primary heat transfer circuit 106 and/or a pressure of the heat transfer fluid 124 within the secondary heat transfer circuit 108. FIG. 11 is flow diagram of an embodiment of a process 240 for controlling the HVAC system 100 in accordance with the presently disclosed techniques. FIG. 11 will be referred to concurrently with FIG. 5 throughout the following discussion. It should be noted that the steps of the process 240 discussed below may be performed in any suitable order and are not limited to the order shown in the illustrated embodiment of FIG. 11. Moreover, it should be noted that additional steps of the process 240 may be performed, and certain steps of the process 240 may be omitted. In some embodiments, the process 240 may be executed by the processing circuitry 176 of the controller 174 and/or any other suitable processing circuitry of the HVAC system 100. The process 240 may be stored on, for example, the memory 88 and/or the memory device 178.

The process 240 may begin with monitoring a pressure of the working fluid 122 within the primary heat transfer circuit 106 and/or monitoring a pressure of the heat transfer fluid 124 within the secondary heat transfer circuit 108, as indicated by block 242. For example, the controller 174 may, based on feedback from the one or more first sensors 170, determine the pressure of the working fluid 122 along a portion or portions of the primary heat transfer circuit 106. Additionally or alternatively, the controller 174 may, based on feedback from the one or more second sensors 172, determine the pressure of the heat transfer fluid 124 along a portion or portions of the secondary heat transfer circuit 108.

As indicated by block 244, the controller 174 may determine whether pressures of the working fluid 122 and/or the heat transfer fluid 124 deviate from corresponding target ranges (e.g., target operating pressure ranges), such as by a threshold amount. For example, the controller 174 may store (e.g., in the memory device 178) a target operating pressure range of the working fluid 122 and/or a target operating range of the heat transfer fluid 124. In response to a determination that the pressure of the working fluid 122 deviates from the corresponding target operating pressure range of the working fluid 122 by a respective threshold amount (e.g., a predetermined percentage) and/or in response to a determination that the pressure of the heat transfer fluid 124 deviates from the corresponding target operating pressure range by a respective threshold amount (e.g., a predetermined percentage), the controller 174 may perform a remedial action or operation, as indicated by block 246.

For example, in some embodiments, deviation of the pressure of the working fluid 122 below the target operation pressure range (e.g., by the threshold amount) may be indicative migration of the working fluid 122 from the primary heat transfer circuit 106 (e.g., in a conduit of the primary heat transfer circuit 106, in the first heat exchanger 112, in the intermediate heat exchanger 110). In response to a determination that the pressure of the working fluid 122 in the primary heat transfer circuit 106 is below the target operating pressure range (e.g., by the threshold amount), the controller 174 may suspend operation of the compressor 116, the pump 128, or both, and/or may transmit an alert message to a suitable electronic device (e.g., an electronic device of a user of the HVAC system 100 and/or of an installer/service provider of the HVAC system 100).

In certain embodiments, deviation of the pressure of the heat transfer fluid 124 below the target operation pressure range (e.g., by the threshold amount) may be indicative of migration of the heat transfer fluid 124 from the secondary heat transfer circuit 108 (e.g., in a conduit of the secondary heat transfer circuit 108, in the second heat exchanger 126, in the intermediate heat exchanger 110). In response to a determination that the pressure of the heat transfer fluid 124 in the secondary heat transfer circuit 108 is below the target operating pressure range (e.g., by the threshold amount), the controller 174 may suspend operation of the compressor 116, the pump 128, or both, and/or may transmit an alert message to a suitable electronic device (e.g., an electronic device of a user of the HVAC system 100 and/or of an installer/service provider of the HVAC system 100).

FIG. 12 is a schematic of an embodiment of a portion of the HVAC system 100, in which the intermediate heat exchanger 110 is omitted from the multi-circuit heat transfer system 102. In some embodiments, one or more conduits of the primary heat transfer circuit 106 may be intertwined with one or more conduits of the secondary heat transfer circuit 108 to form a conduit mesh 260. The conduit mesh 260 may place the conduits of the primary and secondary heat transfer circuits 106, 108 in thermal communication with one another to enable heat exchange between the working fluid 122 and the heat transfer fluid 124. That is, the conduit mesh 260 may facilitate conductive heat transfer between working fluid 122 circulating through the primary heat transfer circuit 106 and heat transfer fluid 124 circulating through the secondary heat transfer circuit 108. In certain embodiments, a heat conductive fluid or gel may be placed on and/or within the conduit mesh 260 (e.g., in interstitial spaces that may be formed between the conduits of the primary heat transfer circuit 106 and the conduits of the secondary heat transfer circuit 108) to further enhance a heat transfer effectiveness between the primary and secondary heat transfer circuits 106, 108 along the conduit mesh 260.

FIG. 13 is a schematic of an embodiment of a portion of the HVAC system 100, in which the multi-circuit heat transfer system 102 includes a tertiary heat transfer circuit 270. The tertiary heat transfer circuit 270 may include a third heat exchanger 272 (e.g., an outdoor heat exchanger, an evaporator), an additional expansion device 274 (e.g., an EEV) and an additional compressor 276 that are fluidly coupled to one another via one or more conduits of the tertiary heat transfer circuit 270. The third heat exchanger 272 may be positioned in the ambient environment 118 and be external to (e.g., outside of) the interior 152 of the thermal load 104. In some embodiments, the intermediate heat exchanger 110 may include a third passage 278 (e.g., conduit, flow path) that is fluidly coupled to and forms at least a portion of the tertiary heat transfer circuit 270. The additional compressor 276 may be configured to circulate an additional working fluid 280 (e.g., an additional refrigerant) along the conduits of the tertiary heat transfer circuit 270 and through the third heat exchanger 272, the additional expansion device 274, and the third passage 278 of the intermediate heat exchanger 110. In this manner, the additional compressor 276 may facilitate heat exchange between the additional working fluid 280, the ambient environment 118, and the heat transfer fluid 124 within the secondary heat transfer circuit 108.

As discussed above, the compressor 116 of the primary heat transfer circuit 106 may be configured to direct a flow of cooled working fluid 122 through the intermediate heat exchanger 110, such that the working fluid 122 flowing through the intermediate heat exchanger 110 may absorb thermal energy from the heat transfer fluid 124 in the second secondary heat transfer circuit 108. Conversely, the tertiary heat transfer circuit 270 may be configured to enable the additional compressor 276 to direct a flow of heated and compressed additional working fluid 280 to the intermediate heat exchanger 110, such that the intermediate heat exchanger 110 may reject heat from the additional working fluid 280 to the heat transfer fluid 124 in the secondary heat transfer circuit 108. In some embodiments, the controller 174 may be configured to selectively operate the compressor 116 of the primary heat transfer circuit 106 and/or the additional compressor 276 of the tertiary heat transfer circuit 270 to switch between operating the HVAC system 100 in a cooling mode or a heating mode, respectively.

For example, to operate the HVAC system 100 in the cooling mode, the controller 174 may activate the compressor 116 and stay (e.g., block) operation of the additional compressor 276. As such, the primary heat transfer circuit 106 may operate in accordance with the techniques discussed above to absorb thermal energy from the secondary heat transfer circuit 108 and, thus, enable the secondary heat transfer circuit 108 to absorb thermal energy from the thermal load 104 to cool the thermal load 104. Conversely, to operate the HVAC system 100 in the heating mode, the controller 174 may activate the additional compressor 276 and stay (e.g., block) operation of the compressor 116. As such, the tertiary heat transfer circuit 270 may operate to reject thermal energy to the secondary heat transfer circuit 108 and, thus, enable the secondary heat transfer circuit 108 to reject thermal energy to the thermal load 104 to heat the thermal load 104.

In some embodiments, a type or composition of the working fluid 122 and/or operational characteristics of the compressor 116 may be selected to facilitate and/or enhance operation of the HVAC system 100 in the cooling mode. Similarly, a type or composition of the additional working fluid 280 and/or operational characteristics of the additional compressor 276 may be selected to facilitate and/or enhance operation of the HVAC system 100 in the heating mode. That is, the primary and tertiary heat transfer circuits 106, 270 may employ different types of working fluids (e.g., refrigerants) and/or compressors. As used herein, the primary heat transfer circuit 106 may also be referred to as a first primary heat transfer circuit 106 and the tertiary heat transfer circuit 270 may also be referred to as a second primary heat transfer circuit 270.

FIG. 14 is a schematic of another embodiment of a portion of the HVAC system 100, in which the multi-circuit heat transfer system 102 includes the tertiary heat transfer circuit 270. In some embodiments, operation of the tertiary heat transfer circuit 270 may be configured to augment or supplement operation of the primary heat transfer circuit 106. For example, in some embodiments, the controller 174 may operate the primary heat transfer circuit 106, the tertiary heat transfer circuit 270, or both, based on a demand (e.g., a cooling demand) of the thermal load 104.

In some embodiments, a heat transfer capacity of the primary and tertiary heat transfer circuits 106, 270 may be different. As an example, a heat transfer capacity of the primary heat transfer circuit 106 may be less than a heat transfer capacity of the tertiary heat transfer circuit 270. The controller 174 may be configured to stage operation of the primary and tertiary heat transfer circuits 106, 270 based on a determined load or demand of the thermal load 104.

As an example, in response to a determination that the cooling and/or heating demand of the thermal load 104 is relatively low (e.g., a first demand level), the controller 174 may operate the compressor 116 of the primary heat transfer circuit 106 and stay operation of the additional compressor 276 of the tertiary heat transfer circuit 270. As such, the primary heat transfer circuit 106 may be operable to extract a relatively low amount of thermal energy from the heat transfer fluid 124 of the secondary heat transfer circuit 108.

In response to a determination that the cooling and/or heating demand of the thermal load 104 is moderate (e.g., a second demand level greater than the first demand level), the controller 174 may operate the additional compressor 276 of the tertiary heat transfer circuit 270 and stay operation of the compressor 116 of the primary heat transfer circuit 106. As such, the tertiary heat transfer circuit 270 may be operable to extract a moderate amount of thermal energy from the heat transfer fluid 124 of the secondary heat transfer circuit 108.

In response to a determination that the cooling and/or heating demand of the thermal load 104 is relatively high (e.g., a third demand level greater than the second demand level), the controller 174 may operate both the compressor 116 and the additional compressor 276. Accordingly, the primary and tertiary heat transfer circuits 106, 270 may cooperate to extract a relatively large amount of thermal energy from the heat transfer fluid 124 of the secondary heat transfer circuit 108.

Although the HVAC system 100 is shown as having three heat transfer circuits in the illustrated embodiment of FIG. 14, is should be understood that the HVAC system 100 may include any suitable quantity of heat transfer circuits. For example, the primary heat transfer circuit 106 may be replaced with two, three, four, five, or more than five discrete heat transfer circuits, and/or the secondary heat transfer circuit 108 may be replaced with two, three, four, five, or more than five discrete heat transfer circuits, where each of the heat transfer circuits is configured to operate in accordance with the techniques discussed herein.

It should be understood that features of any one or combination of the embodiments discussed above may be used individually or in combination with one another. That is, the multi-circuit heat transfer system 102 may include any one or combination of features shown in the illustrated embodiments of FIGS. 1-14 without materially departing from the novel teachings and advantages discussed herein.

As set forth above, embodiments of the present disclosure may provide one or more technical effects useful for inhibiting or substantially eliminating working fluid (e.g., refrigerant) migration into a space to be conditioned by an HVAC system. 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.

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.

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.

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).

MULTI-CIRCUIT HVAC SYSTEMS AND METHODS

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