Hvac Cascade Heat Pump

This application claims the benefit of U.S. provisional patent application Ser. No. 63/569,947, filed Mar. 26, 2024, the entire contents of which are incorporated herein by reference.

Embodiments of the present disclosure pertain to the art of heating, ventilation, and air-conditioning (HVAC) systems.

Heat pumps are used in a variety of settings, for example, in heating, ventilation, and air fluid conditioning (HVAC) systems that provide a desired air temperature in a facility. Such heat pumps commonly include a compressor, evaporator, expansion device, and condenser. The heat pumps input work to the refrigerant, e.g., by driving the compressor, thereby enabling the refrigerant to move heat from a colder heat reservoir to a warmer heat sink.

Some heat pumps are provided as “split” systems, having a first heat exchanger arranged inside of the building to be conditioned and a second heat exchanger located outside of the building to be conditioned. When such a heat pump is used in areas having very cold outdoor temperatures, the heat pump is forced to operate at a high-pressure ratio which results in increased power consumption. In addition the density of the refrigerant is lower at colder outdoor and a decreased refrigerant mass flow. Further, as the temperature outdoors drops, the building load increases so the heating capacity output of the heat pump is critical. There is therefore a need to improve the performance of a heat pump that operates at lower outdoor air temperatures.

According to an embodiment, an assembly includes a heat pump and a cascade module fluidly couplable to the heat pump. The cascade module is fluidly connected to the heat pump during a first mode of operation to increase a capacity of the heat pump and the cascade module is not fluidly connected to the heat pump during a second mode of operation.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the heat pump includes an indoor unit and an outdoor unit.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the cascade module is a separate module, removably mounted at the outdoor unit.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the cascade module is a separate module, removably mounted at the indoor unit.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the cascade module is a separate module, positioned remotely from both the indoor unit and the outdoor unit.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the cascade module is integral with the heat pump.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the heat pump includes a compressor, a first heat exchanger, at least one expansion device, and a second heat exchanger and the cascade module includes a second compressor and a cascade heat exchanger.

In addition to one or more of the features described herein, or as an alternative, in further embodiments when the cascade module is fluidly connected to the heat pump during the first mode of operation, the assembly includes a first vapor compression loop associated with the compressor and a second vapor compression loop associated with the second compressor and the first vapor compression loop and the second vapor compression loop are thermally coupled at the cascade heat exchanger.

In addition to one or more of the features described herein, or as an alternative, in further embodiments in the first mode of operation, the compressor, the cascade heat exchanger, the at least one expansion device and the second heat exchanger are fluidly connected and in combination form the first vapor compression loop.

In addition to one or more of the features described herein, or as an alternative, in further embodiments in the first mode of operation, the second compressor, the first heat exchanger, the at least one expansion device, and the cascade heat exchanger are fluidly connected and in combination form the second vapor compression loop.

In addition to one or more of the features described herein, or as an alternative, in further embodiments during the second mode of operation, the assembly includes a single vapor compression loop defined by the heat pump.

In addition to one or more of the features described herein, or as an alternative, in further embodiments a controller is operably coupled to the compressor, the second compressor, and at least one valve. The controller is configured to identify a mode of operation associated with a demand on the fluid conditioning system and operate the at least one valve to initiate operation in the identified mode.

In addition to one or more of the features described herein, or as an alternative, in further embodiments including at least one sensor operably coupled to the controller, the at least one sensor being configured to monitor at least one parameter or operating condition associated with the heat pump.

According to an embodiment, a method of operating a heat pump includes receiving a demand on the heat pump, determining a mode of operation in response to the demand by comparing the demand with a heating capacity of the heat pump, and if the demand is greater than the heating capacity of the heat pump, fluidly connecting a cascade module to the heat pump.

In addition to one or more of the features described herein, or as an alternative, in further embodiments fluidly connecting the cascade module to the heat pump further comprises operating at least one valve to control a flow of refrigerant to the cascade module.

In addition to one or more of the features described herein, or as an alternative, in further embodiments if the demand is less than the heating capacity of the heat pump, fluidly isolating the cascade module from the heat pump.

In addition to one or more of the features described herein, or as an alternative, in further embodiments fluidly disconnecting the cascade module from the heat pump further comprises operating at least one valve to direct a flow of refrigerant away from the cascade module.

In addition to one or more of the features described herein, or as an alternative, in further embodiments monitoring the heating capacity of a heat exchanger of the fluid conditioning system and initiating a defrost mode when the heating capacity of the heat exchanger is less than or equal to a threshold.

In addition to one or more of the features described herein, or as an alternative, in further embodiments initiating the defrost mode includes fluidly connecting the cascade module to the heat pump and transforming at least one reversing valve from a first position to a second position.

In addition to one or more of the features described herein, or as an alternative, in further embodiments monitoring the heating capacity of the heat exchanger further comprises monitoring at least one parameter or operating condition of the heat pump associated with the heating capacity.

In addition to one or more of the features described herein, or as an alternative, in further embodiments the at least one parameter or operating condition of the heat pump is at least one of temperature, pressure, and refrigerant mass flow.

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

With reference now to, a schematic diagram of an example of a basic vapor compression cycle of a fluid conditioning system, such as an air conditioning system for example, is illustrated. The vapor compression cycle includes one or more compressors, a first heat exchanger, an expansion device, and a second heat exchanger. A fluid, such as a refrigerant for example, is configured to circulate through the vapor compression cycle, such as in a counterclockwise direction for example.

In operation, the compressorreceives a refrigerant vapor from the second heat exchangerand compresses it to a high temperature and pressure. The relatively hot refrigerant vapor is then delivered to the first heat exchangerwhere it is cooled and condensed to a liquid state via heat exchange relationship with a cooling medium C, such as air or water. Accordingly, when the first heat exchangerreceives the refrigerant output from the compressor, the first heat exchanger functions as a condenser. The cooled liquid refrigerant flows from the first heat exchangerto the expansion device, such as an expansion valve for example, in which the refrigerant is expanded to a lower pressure where the temperature is reduced and the refrigerant may exist in a two-phase liquid/vapor state. From the expansion device, the refrigerant is provided to the second heat exchanger. Because heat is transferred from a secondary medium, such as air for example, to the refrigerant within the second heat exchanger, causing any refrigerant in the liquid phase to vaporize, the second heat exchangerfunctions as an evaporator. From the second heat exchanger, the low-pressure vapor refrigerant returns to the compressorso that the cycle may be repeated.

In embodiments where the fluid conditioning systemis a heat pump, the flow of refrigerant within the vapor compressor cycle may be reversed. In such embodiments, the refrigerant may flow clockwise from the compressorto the second heat exchanger, the expansion device, and the first heat exchangersequentially. In such instances, the refrigerant within the second heat exchangeris cooled and condensed to a liquid state and the refrigerant within the first heat exchanger is heated to form a low-pressure vapor. Accordingly, when operating in this reverse flow direction, the second heat exchangerfunctions as the condenser and the first heat exchangerfunctions as the evaporator of the vapor compression cycle.

With reference now to, a schematic diagram of a heat pumpis shown. In the illustrated, non-limiting embodiment, the heat pumpincludes a first, indoor unit or portionpositioned inside a building to be conditioned and a second outdoor unit or portionpositioned outside of the building. It should be understood that embodiments where the fluid conditioning systemis installed in a single casing located partially or completely inside or outside of the building are also within the scope of the disclosure.

As shown, at least one compressoris located within the outdoor unit. The one or more compressorsmay be any suitable single or multistage compressor, including, but not limited to a screw compressor, reciprocating compressor, centrifugal compressor, scroll compressor, rotary compressor, or axial-flow compressor. The compressor(s)may be fixed speed or variable speed and may be driven by an electrically powered motor, or another suitable energy source.

The first heat exchangeris arranged within the indoor unitand is directly or indirectly fluidly coupled to the one or more compressors. The first heat exchangermay be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium. For example, the first heat exchangermay include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, or combinations thereof. In other embodiments, the first heat exchangermay be a round-tube plate fin, microchannel, shell- and tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, or any combination thereof. In the illustrated, non-limiting embodiment, the air or other medium is moved (drawn, blown, or pumped) over the first heat exchangervia a first movement mechanism, such as a axial or centrifugal fan for example.

The fluid conditioning systemincludes at least one expansion device. Although a single expansion deviceis illustrated, it should be understood that embodiments having a separate indoor expansion device positioned within the indoor portion and an outdoor expansion device positioned within the outdoor portion are also contemplated herein. The first heat exchangeris fluidly coupled to the expansion device.

The second heat exchangeris arranged within the outdoor unitof the fluid conditioning systemand is also fluidly coupled to the expansion device. In embodiments including a separate indoor expansion device and outdoor expansion device, the first heat exchangeris fluidly coupled to a first (indoor) expansion device and the second heat exchangeris fluidly coupled to a second (outdoor) expansion device. In some embodiments, refrigerant is only configured to flow through one of the expansion devices in each direction of flow through the refrigeration circuit. In other embodiments, the refrigerant may be configured to flow through both expansion devices,in series, regardless of a direction of flow; however, the refrigerant will only be expanded in one of the expansion devices, such as the downstream expansion device relative to the direction of flow, and the flow will be unrestricted in the other expansion device.

Similar to the first heat exchanger, the second heat exchangermay be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium. In the illustrated, non-limiting embodiment, the second heat exchangeris disposed about the outer extent of the outdoor unit. However, embodiments where the second heat exchangeris arranged at another location, such as within or proximal to the outdoor unitare also contemplated herein.

The second heat exchangermay have any suitable configuration. For example, the second heat exchangermay include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, or combinations thereof. In other embodiments, the second heat exchangermay be a round-tube plate fin heat exchanger, microchannel heat exchanger, shell- and tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, or any combination thereof.

In the illustrated, non-limiting embodiment, the outdoor unitincludes a second movement mechanism, such as a fan assembly for example, to move air or another medium over the second heat exchanger. The second movement mechanismmay be arranged adjacent a topof the outdoor unit, as shown, or may be positioned near a bottomof the outdoor portion, or at any point between the topand the bottomto push or pull air through the outdoor portion.

The fluid conditioning systemadditionally includes a reversing valveconfigured to redirect the flow of refrigerant R therein. In the illustrated embodiment, the reversing valveis arranged within the outdoor unitand includes a fluidly separate first flow path and second flow path. In a first state, as shown in, the first flow path fluidly connects an outlet of the one or more compressorsto the first heat exchanger, and the second flow path fluidly connects the second heat exchangerto an inlet of the one or more compressors. In a second state, the first flow path fluid connects the outlet of the one or more compressorsto the second heat exchangerand the second flow path fluidly connects the first heat exchangerto the inlet of the one or more compressors(). It should be understood that the fluid conditioning systemillustrated and described herein is intended as an example only and that a fluid conditioning system having another configuration and/or additional components arranged along the fluid flow path are also within the scope of the disclosure.

The fluid conditioning system may be operable in a “heating” mode, as shown in. When the reversing valveis in the first state, refrigerant is configured to flow through the closed refrigeration circuit from the compressorto the first heat exchangeracting as a condenser. Within the first heat exchanger, heat is transferred from the refrigerant to the air moving across the first heat exchangerby the first movement mechanism. This warmed air may be used to heat one or more areas to be conditioned within the building. The partially or fully condensed liquid refrigerant is provided from the first heat exchangerto the expansion devicewhere the pressure is reduced causing the refrigerant to be expanded and cooled to a temperature below the ambient temperature. Within the second heat exchanger, heat is transferred to the refrigerant from the air moving across the second heat exchangerby the second movement mechanism. This heat causes the liquid portions of the refrigerant to evaporate to a gaseous phase. From the second heat exchanger, the refrigerant is returned to the compressorvia the reversing valve.

During normal operation of the fluid conditioning system in a heating mode, frost can accumulate on the second heat exchanger. When frost accumulates on the second heat exchanger, the frost diminishes heat transfer from the air to the heat exchanger and therefore provides undesirable insulating properties to the heat exchanger. The undesirable insulating properties result in an increase in the temperature difference between the temperature of the air and the temperature of the heat exchanger. As the extent and thickness of frost increases, the degree of insulating properties of the frost increases. Accordingly, the temperature of the second heat exchangerwill continue to decrease indefinitely as frost continues to accumulate.

As frost accumulates on the second heat exchangerand the operating temperature of the second heat exchangerdecreases, the operating temperature of the refrigerant within the second heat exchangerdecreases as a result. Given a fixed amount of superheat, the density of the refrigerant vapor leaving the second heat exchangerdecreases as the temperature of the vapor decreases. Decreasing vapor density for a given volume flow results in decreasing mass flow, and the heating capacity of the refrigerant system decreases. Therefore, the extent and thickness of the presence of frost will directly relate to a decrease in mass flow and heating capacity.

To eliminate, or at least mitigate, this frost, the fluid conditioning systemmay transition to a defrost mode, such as by switching the reversing valveto the second state. In the second state, shown inthe direction of flow of refrigerant through the closed refrigerant circuit is reversed. Accordingly, the warm, high pressure refrigerant output from the at least one compressoris routed to the second heat exchangersuch that the second heat exchangerfunctions as a condenser rather than as an evaporator. As the second heat exchanger, heat is rejected from the fluid, thereby melting the frost to prepare the second heat exchangerfor operation as an evaporator once the system transforms back to a heating mode. In the defrost mode, the second movement mechanismmay be disabled to prevent air movement through the second heat exchangerthus enabling the temperature of the second heat exchangerto increase.

From the second heat exchanger, the refrigerant is expanded in an expansion device, such as the indoor expansion device (not shown), and then is delivered to the first heat exchanger, which is configured to operate as an evaporator. Within the first heat exchanger, the refrigerant can absorb heat from the medium moving across the first heat exchangervia the first movement mechanism. In an embodiment, the fluid conditioning systemincludes an auxiliary heaterconfigured to heat the cool air output from the first heat exchangerduring a defrost cycle to meet the heating demands of the area being conditioned. From the first heat exchanger, the refrigerant is returned to the compressorvia the reversing valve.

With reference now to, another fluid conditioning systemaccording to an embodiment is illustrated. In an embodiment, the fluid conditioning systemis similar to the heat pump described above with respect to; however, the fluid conditioning systemmay additionally include or be connected to a cascade moduleselectively operable to extend the operating conditions of the fluid conditioning system. In some embodiments, the cascade moduleis an integral portion of the fluid conditioning system. In such embodiments, the indoor unit, outdoor unit, and cascade modulemay be packaged as a single unit. In other embodiments, the cascade moduleis separate module that can be attached to and removed from both new and existing fluid conditioning systems.

When installed, the cascade modulemay be fluidly coupled to at least a portion of the fluid conditioning system. For example, the cascade modulemay be fluidly coupled to the outdoor unit, to the indoor unit, or both. Further, the cascade modulemay be continuously fluidly connected to the fluid conditioning system, or alternatively, may be selectively fluidly connected to the fluid conditioning system. In embodiments where the cascade moduleis selectively fluidly connected to the fluid conditioning system, one or more valves V are operable to control the flow of refrigerant in response to a desired mode of operation of the fluid conditioning system. For example, the at least one valve may be operated to direct a flow of refrigerant to the cascade moduleor may be operated to direct a flow of refrigerant away from the cascade module.

The cascade modulemay include a plurality of components. In the illustrated, non-limiting embodiment, the components include a compressor, and a heat exchanger(see). In an embodiment, the cascade modulemay additionally include a reversing valve. However, embodiments including only a portion of these components, additional components, and/or alternative components are also within the scope of the disclosure. It should be appreciated that the cascade modulemay additionally include one or more conduits operable to fluidly connect components of the cascade moduleto one another or to another portion of the heat pump. Further, these conduits may cooperate with or may form conduits that define a direct flow path between the indoor unitto the outdoor unit.

In some embodiments, the plurality of components is integrated or packaged within a single housing or unit, illustrated schematically atin. In such embodiments, the housingis located at, and in some embodiments is mechanically affixed to, a portion of the outdoor unitor a portion of the indoor unit. Further, in other embodiments, the components associated with the cascade modulemay be separated into a plurality of packages or units. In such embodiments, the units may be mounted at the same location about the fluid conditioning system, such as the outdoor unitor the indoor unitfor example, or may be split between the indoor unitand the outdoor unit. Further, embodiments where a unit including at least a portion of the cascade module, and in some embodiments the entirety of the cascade module, is mounted at another location remote from both the indoor unitand outdoor unitare also contemplated herein. For example, the fluid conditioning systemmay be associated with a building, and the cascade modulemay be positioned at a different location about the building than the indoor unit.

When the cascade moduleis fluidly connected to the fluid conditioning system, the overall capacity of the heat pumpis increased. As used herein, the term “fluidly connected” when used relative to the cascade moduleis intended to describe embodiments where at least one of the compressorand the heat exchangerof the cascade moduleis configured to receive a flow of refrigerant. In an embodiment, such as shown infor example, when the cascade moduleis fluidly connected to the heat pump, the heat pumpis transformed from a single vapor compression loop to a plurality of fluidly separate vapor compression loops. For example, the fluid conditioning systemmay include two fluidly separate compression loops, identified at VCand VCrespectively, thermally coupled to one another. The vapor compression loops VC, VCmay be thermally coupled at a component of the cascade module. As will be described in more detail below, in an embodiment, the two vapor compression loops VC, VCare thermally coupled to one another at the heat exchangerof the cascade moduleduring one or more modes of operation.

The heat pumpis operable in a plurality of modes. For example, the modes of operation may include but are not limited a full load heating mode, a partial load heating mode, a full load cooling mode, a partial load cooling mode, and a turbo defrost mode. With reference to, a schematic diagram of the fluid conditioning systemin a full load heating mode is illustrated. In the full load heating mode, the cascade moduleis fluidly connected to the remainder of the fluid conditioning system. The reversing valveis in a first position or state such that the refrigerant within the first vapor compression loop VCis configured to flow from the compressorof the outdoor unitto a first passof the cascade heat exchangerof the cascade module. The first passof the cascade heat exchangerfunctions as a condenser causing the refrigerant of the first vapor compression loop VCto be cooled therein. The resulting cool liquid refrigerant is then provided to an expansion device, such as within the outdoor unit, and to the second heat exchangerof the outdoor unitoperable as an evaporator in series. The refrigerant vapor output from the evaporatoris then returned to the inlet of the compressorto repeat the cycle.

Similarly, the reversing valveof the cascade moduleis in a first position such that the refrigerant within the second vapor compressor loop VCis configured to flow from the outlet of the compressorof the cascade moduleto the first heat exchanger. In the full load heating mode, the first heat exchangerfunctions as a condenser, thereby cooling the refrigerant to a liquid. From the first heat exchanger, the refrigerant of the second vapor compression loop VCflows to an expansion device, such as the expansion devicearranged within the indoor unitor an expansion device within the cascade module, and then to a second passof the cascade heat exchanger. The second passof the cascade heat exchangeris configured as an evaporator such that heat from the refrigerant within the first pass(from the first compression loop VC) of the cascade heat exchangeris transferred to the refrigerant within the second pass, thereby causing the refrigerant within the second pass to vaporize. The refrigerant output from the second passhas a higher vapor quality and enthalpy than the refrigerant provided to the second pass, and is returned to the inlet of the compressorof the cascade module.