Priority Application

[0001] The present application claims priority to U.S. Provisional Patent Application Serial No. 62/088,362, filed on December 5, 2014, entitled "HIGH- EFFICIENCY HYBRID HEAT REMOVAL SYSTEM," which is incorporated herein by reference in its entirety.

Field of Disclosure

[0002] The field of the disclosure relates generally to heat removal systems, and particularly to a hybrid heat transfer system.

Background

[0003] The demand for energy conservation has grown substantially due to concerns over limited resources and the environment. This has led to advances in energy efficient appliances. For example, current energy efficient refrigerators use almost 40 percent less energy compared to models from over fifteen years ago. The ability to further improve the efficiency of energy efficient refrigerators is limited by a need for versatile performance. For example, consumers require refrigerators that operate in broad temperature ranges and adapt to rapid changes all while maintaining accurate temperature control.

[0004] Existing refrigeration techniques use either passive or active cooling techniques. As used herein, the term "passive" when used in the context of heating or cooling refers to thermal transfer that occurs without requiring additional energy, e.g., via natural processes such as conduction, convection, radiation, etc. As used herein, the term "active" when used in the context of heating or cooling refers to thermal transfer that requires additional energy (e.g., electricity) to occur, e.g., via the use of power-consuming devices such as compressors, heat pumps, Peltier junctions, etc. As such, an active cooling system is one that involves the consumption of energy to cool something, as opposed to passive cooling that does not consume energy. [0005] The most common type of energy efficient refrigerators use vapor compression systems. In these systems, mechanical components consume energy to actively transport heat. These components may include a compressor, a condenser, a thermal expansion valve, an evaporator, plumbing that circulates a working fluid (e.g., refrigerant), and a thermostat. The components circulate the refrigerant, which undergoes forced phase changes to transport heat from a cooling chamber to an external environment. Less common refrigeration systems include thermoelectric cooling systems. In these systems, a

thermoelectric heat pump consumes energy to actively transport heat from a passive subsystem that accepts heat from a cooling chamber to another passive subsystem that rejects heat to an external environment.

[0006] Because refrigeration systems are usually heavily insulated, there is by design no thermally conductive path through which heat can be transferred from the cooling chamber to an external environment by passive transmission alone. For this reason, these refrigeration systems have no means to reject heat from the cooling chamber should the active component fail.

[0007] This problem also plagues active systems that are designed to maintain an internal chamber at a set temperature regardless of the temperature of the external environment: should the active components fail, there is no thermally conductive path through which heat can be transferred to heat or cool the internal chamber as needed. In addition, the lack of an alternative, passive path means that external environmental conditions cannot be taken advantage of in order to reduce power consumption. For example, if a chamber needs to be warmed up slightly and the external environment is warmer than the chamber, the existence of an alternative, passive path would allow the chamber to be warmed up via passive thermal transfer instead of via the active device, thus obviating the need to consume (and pay for) the energy that the active device would have used. The same would apply to a chamber that needs to be cooled down slightly where the external environment is colder than the chamber: a passive path could be used to transfer heat from the chamber to the external environment without the need to consume additional energy to run a heat pump, compressor, or the like. [0008] As such, there remains a need for systems and methods for heat transfer that provides higher energy efficiency at lower costs while maintaining versatility of performance. Summary

[0009] Systems and methods for a hybrid heat transfer system are disclosed.

[0010] According to one aspect, a hybrid heat transfer system includes a first thermally conductive path configured to passively transfer heat between a load having a load temperature T _L and an ambient environment having an ambient temperature T _A , and a second thermally conductive path configured to actively transfer heat between the load and the ambient environment, the second path comprising a heat pump.

[0011] According to one aspect, the heat pump is either in an activated state or a deactivated state, and when the heat pump is in the activated state, heat is actively transferred through the second thermally conductive path, and when the heat pump is in the deactivated state, heat is not actively transferred through the second thermally conductive path.

[0012] According to another aspect, when the heat pump is in the deactivated state, heat is transferred passively through the second thermally conductive path.

[0013] According to one aspect, each of the first and second paths comprises its own separate heat exchange component for transferring heat to or from the load. According to another aspect, the first and second paths share a common heat exchange component for transferring heat to or from the load.

[0014] According to one aspect, each of the first and second paths includes its own separate heat exchange component for transferring heat to or from the ambient environment. According to another aspect, the first and second paths share a common heat exchange component for transferring heat to or from the ambient environment.

[0015] According to one aspect, the first thermally conductive path comprises a thermal diode in series between the load and the ambient environment.

According to one aspect, the thermal diode allows heat transfer from the load to the ambient environment and blocks heat transfer from the ambient environment to the load. According to one aspect, the thermal diode comprises a

thermosiphon.

[0016] According to one aspect, the second thermally conductive path includes a thermal diode in series between the load and the ambient

environment. According to one aspect, the thermal diode is in series between the load and the heat pump.

[0017] According to one aspect, the second thermally conductive path includes a thermal capacitor in series between the load and the ambient environment. According to one aspect, the second thermally conductive path includes a thermal capacitor in series between the load and the heat pump. According to one aspect, the thermal capacitor comprises a phase change material and/or a thermal mass.

[0018] According to one aspect, the second thermally conductive path includes a thermal diode, a thermal capacitor, and a heat pump in series between the load and the ambient environment. According to one aspect, the second thermally conductive path includes a thermal diode and a thermal capacitor in series between the load and the heat pump.

[0019] According to one aspect, the first thermally conductive path also includes a heat pump.

[0020] According to another aspect, a hybrid heat transfer system includes a thermally conductive path for transferring heat from a load having a load temperature T _L to an ambient environment having an ambient temperature T _A , where the thermally conductive path includes a thermal capacitor having a storage temperature T _s , a heat pump having an activated state, during which heat is actively transferred by the heat pump, and a deactivated state during which heat is not actively transferred by the heat pump, and a thermal diode, connected in series between the load and the ambient environment.

[0021] According to one aspect, the thermal capacitor comprises a phase change material and/or a thermal mass. [0022] According to one aspect, a first side of the thermal capacitor is in contact with the load, a first side of the heat pump is in contact with a second side of the thermal capacitor, a first side of the thermal diode is in contact with a second side of the heat pump, and a second side of the thermal diode transfers heat to the ambient environment.

[0023] According to yet another aspect, a hybrid heat transfer system includes a first component for active heating and/or cooling of a load, the operation of the first component being controlled by at least one control input, and a control system configured for controlling the operation of the first component via the at least one control input according an algorithm.

[0024] According to one aspect, the control system includes at least one temperature sensor and a controller having hardware and configured to receive temperature information from the at least one temperature sensor, to process that information according to the algorithm to determine a desired operation of the first component, and to control the operation of the first component.

[0025] According to one aspect, the controller controls the operation of the first component via activating and switching circuitry between the controller and the first component.

[0026] According to yet another aspect, a method for controlling a hybrid heat transfer system having a first thermally conductive path for passively transferring heat between a load having a load temperature T _L and an ambient environment having an ambient temperature T _A and having a second thermally conductive path for actively transferring heat between the load and the ambient environment where the second path includes a heat pump, includes: monitoring the values of T _L and T _A . Upon a determination that T _L is greater than a first threshold T _L H, if T _A is greater than or equal to T _L , the heat pump is activated such that heat is actively transferred from the load to the ambient environment via the second path; if T _A is less than T _L , however, the heat pump is deactivated such that heat is not actively transferred from the load to the ambient environment via the second path (e.g., heat is passively transferred from the load to the ambient environment via the first path). Upon a determination that T _L is less than a second threshold T _L L, if T _A is less than or equal to T _L , the heat pump is activated such that heat is actively transferred from the ambient environment to the load via the second path; if T _A is greater than T _L , however, the heat pump is deactivated such that heat is not actively transferred from the ambient environment to the load via the second path (e.g., heat is passively transferred from the ambient environment to the load via the first path). Upon a

determination that T _L L≤ T _L ≤ T _L H, the current operating state of the heat pump (either activated or deactivated) is unchanged.

[0027] The methods and systems described herein provide improved higher efficiency at lower costs while improving versatility of performance such as operating at broad temperature ranges and speed of cooling while maintaining accurate control of temperature.

[0028] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

Brief Description of the Drawing Figures

[0029] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0030] Figure 1 A illustrates an exemplary structure of a hybrid heat transfer system according to an embodiment of the present disclosure, where the system includes first and second thermally conductive paths for transferring heat between a load and an ambient environment, the second path including a heat pump;

[0031 ] Figure 1 B illustrates a orthogonal view of an exemplary hybrid heat transfer system according to an embodiment of the present disclosure, in which the first path is upwind from the second path, so that the heat from the active second path does not affect the performance of the passive first path; [0032] Figure 1 C illustrates a functional description of the system in Figure 1 A according to an embodiment of the present disclosure;

[0033] Figure 1 D illustrates a flow chart for an exemplary method for a hybrid heat transfer system according to an embodiment of the present disclosure;

[0034] Figures 2A and 2B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first and second thermally conductive paths share a common heat exchanger for transferring heat to or from the load;

[0035] Figures 2C and 2D illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first and second thermally conductive paths share a common heat exchanger for transferring heat to or from the ambient environment;

[0036] Figures 3A and 3B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first thermally conductive path is thermally connected to the load through a thermal diode;

[0037] Figures 4A and 4B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first thermally conductive path is thermally connected to the load through a thermal diode and where the first and second paths share a common heat exchanger for transferring heat to or from the ambient environment;

[0038] Figures 5A and 5B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the second thermally conductive path is thermally connected to the load through a thermal diode;

[0039] Figures 6A and 6B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the second thermally conductive path is thermally connected to the load through a thermal capacitor;

[0040] Figures 7 A and 7B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the second thermally conductive path is thermally connected to the load through a thermal diode and a thermal capacitor;

[0041] Figures 8A and 8B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the second thermally conductive path is thermally connected to the load through a thermal diode and a thermal capacitor and in which the first thermally conductive path also includes a heat pump;

[0042] Figures 9A and 9B illustrate an exemplary structure and a functional description, respectively, of a hybrid heat transfer system according to yet another embodiment of the present disclosure, in which a thermally conductive path between a load and an ambient environment includes a thermal capacitor, a heat pump, and a thermal diode connected in series; and

[0043] Figure 10 illustrates a block diagram of an exemplary hybrid heat transfer system according to another embodiment of the present disclosure.

Detailed Description

[0044] Systems and methods for a hybrid heat transfer system are disclosed. The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. [0045] It should be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish between elements. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure.

[0046] It should also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0047] It should also be understood that the singular forms "a," "an," and "the" include the plural forms, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "includes," and/or "including," when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Moreover, the term "and/or" includes any and all combinations of one or more of the associated listed items.

[0048] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having meanings that are consistent with their meanings in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0049] A heat transfer path includes one or more components that may be thermally coupled in series to provide heat flow along the path. For example, heat may be removed from an enclosure (e.g., refrigerator cabinet) and moved along a heat transfer path for subsequent release to an external environment (i.e., ambient environment). A heat transfer path may be part of and/or thermally coupled to an "accept side" and/or a "reject side" of the heat removal system. The accept side accepts heat from a thermal load (e.g., removes heat from the load). The reject side rejects heat to an external/ambient environment.

[0050] A heat transfer path may be "active" and/or "passive" depending on whether the heat transfer path provides active and/or passive heat flow. For example, component(s) of a heat transfer path may cause the heat transfer path to provide "active" heat transfer when consuming energy. On the other hand, the same heat transfer path may provide "passive" heat transfer when the same component(s) are not consuming energy. As such, the distinction between an active heat transfer path and a passive heat transfer path depends on whether an appreciable amount of heat can be transferred actively and/or passively by the path. More specifically, a heat transfer path may include at least one active heat exchange component and one or more passive components. Yet whether or not the heat transfer path is said to be an "active heat transfer path" or a "passive heat transfer path" depends on whether the heat transfer path is configured to transfer an appreciable amount of heat actively and/or passively.

[0051] An active heat transfer path includes at least one component that causes heat transfer by consuming energy. As such, an active heat transfer path transfers an appreciable amount of heat when the at least one component is consuming energy. Such components are referred to herein generally as "active heat exchange components." Examples of active heat exchange components include heat pumps such as vapor-compressors, Stirling coolers, thermoelectrics, and any structure, apparatus, and/or material that transfers or modulates heat by consuming energy. Thus, an active heat transfer path transfers an appreciable amount of heat when at least one of its active heat exchange components is consuming energy.

[0052] A passive heat transfer path includes one or more passive components that enhance the effectiveness of the natural cooling process without consuming energy. Examples of passive components include heat sinks, thermosiphons, heat pipes, heat exchangers, phase-change materials, or any structure, apparatus, and/or material that rely on natural process of heat dissipation or modulation without consuming energy. Thus, a passive heat transfer path transfers an appreciable amount of heat without consuming energy.

[0053] Accordingly, a heat transfer path that includes an active heat exchange component is an active heat transfer path while it is consuming energy to actively transfer heat and may be a passive heat transfer path if the active heat transfer path transfers an appreciable amount of heat passively while the active heat exchange component is not consuming energy. Conversely, a passive heat transfer path may include an active heat exchange component that is not consuming energy while the passive heat transfer path is passively transferring an appreciable amount of heat.

[0054] The embodiments disclosed herein for a heat removal system utilize combinations of active and/or passive components that form one or more active and/or passive heat transfer paths. These combinations achieve one or more of higher efficiency, broad temperature ranges, speed of cooling, accurate control of temperature, and lower costs.

[0055] Before continuing the description of embodiments of the present disclosure, it is beneficial to define some terms as follows:

[0056] As used herein, a "component" refers to a part or element of a larger whole. A component may include any apparatus, material, and/or system. For example, a component of a heat transfer path is a part or element of the heat transfer path. A "path" is formed from a plurality of components connected in series configured to provide a direction for transferring heat.

[0057] As used herein, the term "active heat exchange" refers to the operation of any component to actively move heat by consuming energy. The heat is moved from one location of the path (i.e., the "source") at a lower temperature to another location of the path (i.e., the "sink") at a higher temperature. An example of an active heat exchange component is a heat pump. A heat pump only moves an appreciable amount of heat when consuming energy. While not being limited thereto, in some embodiments, a heat pump is a solid-state heat pump including one or more thermoelectric modules, where each thermoelectric module includes multiple thermoelectric devices (see, for example, U.S. Patent No. 8,216,871 , entitled METHOD FOR THIN FILM THERMOELECTRIC MODULE FABRICATION, which is hereby incorporated herein by reference for its teachings of a thermoelectric module). Other examples of a heat pump include a vapor compression heat pump and a Stirling Cycle heat pump. Because an active heat exchange component actively moves heat, it can be modeled by analogy to a current source of an electrical circuit that actively moves current.

[0058] As used herein, the term "passive component" refers to a component that passively moves or modulates heat without consuming energy. The heat may be naturally accepted, transferred, and rejected by a passive component as a result of a temperature differential across the passive component. Examples of passive components include heat sinks/heat exchangers, thermosiphons, heat pipes, Phase-Change Materials (PCMs), and the like.

[0059] Figure 1 A illustrates an exemplary structure of a hybrid heat transfer system according to an embodiment of the present disclosure, where the system includes first and second thermally conductive paths for transferring heat between a load and an ambient environment, the second path including a heat pump.

[0060] In the embodiment illustrated in Figure 1 A, a hybrid heat transfer system 10, also referred to herein as "the system 10," includes a first thermally conductive path 12, also referred to herein as "the first path 12," and a second thermally conductive path 14, also referred to herein as "the second path 14," both of which operate to transfer heat between a load 16 having a load

temperature (T _L ) and an ambient environment 18 having an ambient temperature (T _A ). Examples of loads include, but are not limited to, electrical or electronic circuits, printed circuit boards (PCBs), electrical machines, environmentally controlled spaces, e.g., refrigerators, storage units, homes and office buildings, etc. The first path 12 is configured to passively transfer heat. The second thermally conductive path 14 is configured to actively transfer heat and includes a heat pump 20 for that purpose.

[0061] In the embodiment illustrated in Figure 1 A, the first path 12 includes a heat exchanger 22 for transferring heat to or from the load 16 and a heat exchanger 24 for transferring heat to or from the ambient environment 18. The second path 14 likewise includes a heat exchanger 26 for transferring heat to or from the load 16 and a heat exchanger 28 for transferring heat to or from the ambient environment 18. In this illustrated example, the heat exchangers 22, 24, 26, and 28 are finned metal heat exchangers/heat sinks, but are not limited thereto. Other types of heat exchangers/sinks may be used. Examples of heat exchangers include, but are not limited to, air-cooled heat exchangers, water cooled heat exchangers, etc.

[0062] In one embodiment, the heat pump 20 may be in either an activated state, in which heat is actively transferred between the load 16 and the ambient environment 18, or a deactivated state, in which heat is not actively transferred between the load 16 and the ambient environment 18. For example, a controller or control system (not illustrated) may control the heat pump 20 such that the heat pump 20 is selectively controlled to be in the activated state or the

deactivated state depending on a desired control algorithm. In some

embodiments, the heat pump 20 may still transfer heat passively even when it is in the deactivated state. In other embodiments, the heat pump 20 may prevent such heat transfer when it is in the deactivated state, e.g., acting as a thermal insulator between the load 16 and the ambient environment 18.

[0063] In the embodiment illustrated in Figure 1 A, the first path 12 is separated from the second path 14 by a gap. The gap decouples the paths to prevent heat from leaking, or at least mitigate heat leakage, from the second path 14 to the first path 12 and back to the enclosed environment through the heat exchanger 22. In some embodiments, the gap may include an insulator to further prevent leak-back. In some embodiments, as described below, the gap may be omitted altogether.

[0064] In one embodiment, the load 16 may be located within its own environment separate from the ambient environment 18. In the embodiment illustrated in Figure 1 A, for example, the load 16 may be located within a structure 30 that provides a local environment for the load 16. In one

embodiment, the structure 30 may be a climate- or temperature-controlled space, such as a refrigerator, a freezer, an environmentally controlled enclosure, such as one with an Ingress Protection (IP) rating, and the like. Likewise, the heat exchangers 24 and 28 may also be located within a structure or in a location which provides additional conditions. For example, the heat exchangers 24 and 28 may be located in a case, chassis, frame, or other environment that provides a continual flow of air (or water) over the heat exchangers. These environments may provide additional benefits, as will be described below in reference to Figure 1 B.

[0065] Figure 1 B illustrates an orthogonal view of the hybrid heat transfer system 10 according to an embodiment of the present disclosure. In the embodiment illustrated in Figure 1 B, each of the first path 12 and the second path 14, both represented by dotted arrows, includes finned heat exchangers 24 and 28, respectively, which, in some embodiments, benefit from airflow 32 provided by one or more fans 34, which may, in some embodiments, be mounted within an enclosing structure 36.

[0066] In the embodiment illustrated in Figure 1 B, the heat exchangers 22 and 26 are, e.g., thermally conductive plates (e.g., metal plates) that provide a thermal interface between the load 16 and the first and second paths 12 and 14, respectively, but in alternative embodiments these structures may be absent. For example, the load 16 may be mated to the heat exchanger 24 and the heat pump 20 directly, e.g., through direct contact and held in position via clamps, bolts, or other fasteners. A thermal paste may be present at the mating surfaces to more efficiently effect the transfer for heat between these and other mated structures. Alternatively, the load 16 may be coupled to a heat exchanger indirectly (e.g., via an intervening structure) or even remotely (e.g., by radiation of heat across an air gap). Other interfacing methods are also contemplated.

[0067] In the embodiment illustrated in Figure 1 B, the heat Q _c from the load 16 is drawn into the first path 12 via the heat exchanger 22 and dissipated into the ambient environment 18 via the heat exchanger 24. The heat from the load 16 is also drawn into the second path 14 via the heat exchanger 26 to the heat pump 20, which, if active, will transfer heat into the heat exchanger 28. [0068] Figure 1 B illustrates a configuration where the heat exchanger 24 from the first path 12 is upwind from the heat exchanger 28 from the second path 14. Since an active heat pump may transfer more heat than may be transferred passively, the heat exchanger 28 is likely to be hotter than the heat exchanger 24; by placing the heat exchanger 28 downwind of the heat exchanger 24, the first path 12 is less likely to be affected by the heat being produced by the second path 14, and thus more efficient than if the heat exchanger 24 were downwind from the heat exchanger 28. In other words, by placing the heat exchanger 28 downwind from the heat exchanger 24, heat leakage from the second path 14 into the first path 12 is mitigated.

[0069] The operation of exemplary hybrid heat transfer systems, such as the systems illustrated in Figures 1 A and 1 B, for example, may be described using a graphic representation that is analogous to an electrical circuit schematic. This type of representation is referred to herein as a thermal circuit schematic. For example, a structure that passively conducts thermal energy is analogous to a resistor and is therefore referred to herein as a thermal resistor. As used herein, the term "thermal resistor" refers to a component that passively accepts heat from a higher temperature environment and rejects heat to a lower temperature environment. An example of a thermal resistor includes a heat exchanger. A heat exchanger commonly transfers heat with a fluid medium. The fluid medium is frequently air, but may also be water or a refrigerant. Thermal resistance is a property of a particular heat exchanger. As such, a heat exchanger can be modeled by analogy to a resistor of an electrical circuit.

[0070] A structure that conducts heat in only one direction is analogous to a diode and is therefore referred to herein as a thermal diode. As used herein, the term "thermal diode" refers to a component that causes heat to passively flow preferentially in one direction of a path. Conversely, a thermal diode prevents heat from leaking back in the direction opposite of the preferred direction of the path. Examples of a thermal diode include a thermosiphon. A thermosiphon uses passive two-phase heat exchange for transporting heat based on natural convection. A thermosiphon transports heat between an evaporator and a condenser via a working fluid using buoyancy and gravitational and/or centripetal forces, without the need of a mechanical pump. In particular, as the working fluid is heated in the evaporator, the heated working fluid (e.g., gas) naturally rises up through the thermosiphon to the condenser via buoyancy forces due to the decreased density of the heated working fluid. When the working fluid is cooled in the condenser, the cooled working fluid (e.g., liquid) naturally sinks down through the thermosiphon to the evaporator via gravitational and/or centripetal forces due to the increased density of the cooled working fluid.

[0071] Unlike heat pipes that contain a wicking medium to induce capillary forces that facilitate movement of a working fluid to transport heat, a

thermosiphon does not rely on capillary forces to move the working fluid.

Consequently, this allows heat flow from an evaporator to a condenser region and prevents heat from leaking back to the evaporator. As such, a thermosiphon can be modeled by analogy to a diode of an electrical circuit.

[0072] A structure that stores thermal energy or a thermal energy deficit (e.g., as in the case of a PCM in its frozen state) is analogous to a capacitor and is therefore referred to herein as a thermal capacitor. As used herein, the term "thermal capacitor" refers to a component that passively stores heat. An example of a thermal capacitor is a PCM. A PCM is a material that changes from one phase to another at specific temperatures. As a result, a PCM is capable of passively storing and releasing large amounts of heat. Heat is absorbed when the material changes to a higher energy state (e.g., solid to liquid) and releases heat when the material changes to a lower energy state (e.g., liquid to solid). As such, a PCM can be modeled by analogy to a capacitor of an electrical circuit.

[0073] A structure that actively conducts thermal energy is analogous to a current source and is therefore referred to herein as a thermal source. It is noted that a thermal source may operate to supply heat, may operate to remove heat, or may be configurable to do either.

[0074] Thus, a thermal system can be represented by the equivalent symbols used in electrical circuit schematics, i.e., to create a thermal circuit schematic. An example of a thermal circuit schematic for the embodiment illustrated in Figure 1 A is shown in Figure 1 C.

[0075] Figure 1 C illustrates a functional description of the system 10 in Figure 1 A according to an embodiment of the present disclosure. In the embodiment illustrated in Figure 1 C, the system 10 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the first path 12 and the second path 14 from the load 16 having a load temperature T _L to the ambient environment 18 having an ambient temperature T _A . In the first path 12, the heat exchanger 22 is represented as thermal resistor Rth _, u and the heat exchanger 24 is represented as thermal resistor R _t h,Ai - In the second path, the heat exchanger 26 is represented as thermal resistor R _t h,L2, the heat exchanger 28 is represented as thermal resistor R _t h,A2, and the heat pump 20 is represented as a thermal source. In one embodiment, the heat pump 20 may be a Thermoelectric (TEC) device which may be provided with power, shown as arrow P _T EC in Figure 1 C.

[0076] The structure represented by the thermal circuit schematic illustrated in Figure 1 C may not be the same temperature throughout, but may have different temperatures in different locations. In the embodiment illustrated in Figure 1 C, the nodes labeled T _L represent thermal contacts with the load 16, which has a load temperature T _L; the nodes labeled T _A represent thermal contacts with the ambient environment 18, which has an ambient temperature T _A . Other labeled nodes represent locations within the first or second paths 12 and 14 where the temperature at the respective locations may be different than T _L or T _A . In the embodiment illustrated in Figure 1 C, for example, T _LA is the temperature at a point in the first path 12 between the load 16 and the ambient environment 18, TI_HP is the temperature at a point in the second path 14 between the load 16 and the heat pump 20, and T _H p _A is the temperature at a point in the second path 14 between the heat pump 20 and the ambient environment 18. An example operation of system 10 will now be illustrated using Figure 1 D.

[0077] Figure 1 D illustrates a flow chart for an exemplary method for a hybrid heat transfer system (e.g., the hybrid heat transfer system 10 of Figure 1 A or 1 B) according to an embodiment of the present disclosure. Figure 1 D illustrates the concept that the hybrid heat transfer system 10 may operate in various modes and that these modes may be selected or entered into based on trigger conditions. The method will be described with reference to Figure 1 C.

[0078] In the embodiment illustrated in Figure 1 D, one or more temperatures, such as T _L and T _A (and, optionally, other temperatures, such as ΤΊ, T ₂ , etc.) are monitored (step 100). As will be described in more detail below, the detection of certain trigger conditions can cause the system to enter an active cooling mode, a passive cooling (or heating) mode, or an active heating mode.

[0079] For the purposes of illustration only, it is assumed that, in the

embodiment illustrated in Figure 1 D, the load 16 has a desired operating range of temperatures from a load low temperature T _L L to a load high temperature T _L H- In this example, T _L L < T _L H, and it is desired that T _L L < T _L < T _L H- [0080] In this embodiment, the process checks whether T _L is higher than T _L H (step 102), which would indicate that the load 16 needs to be cooled, in which case the process then checks whether T _A is less than T _L (step 104). If so, passive cooling alone may be sufficient to lower T _L , and thus active cooling is turned off (or remains off) (step 106), and the process returns to step 100. If, at step 104, T _A is greater than T _L , then active cooling is needed, since passive cooling requires T _A to be less than T _L for heat to be transferred from the load 16 to the ambient environment 18. In this case, active cooling is turned on (or remains on) (step 108), and the process returns to step 100.

[0081 ] In this embodiment, if, at step 102, T _L is not above the upper limit T _L H, then the process checks whether T _L is below the lower limit T _L i_ (step 1 10), which would indicate that the load needs to be heated, in which case the process then checks whether T _A is greater than T _L (step 1 12). If so, passive heating alone may be sufficient to raise T _L , and thus active heating is turned off (or remains off) (step 1 14), and the process returns to step 100. If, at step 1 12, T _A is less than T _L , then active heating is needed, since passive heating requires T _A to be greater than T _L . In this case, active heating is turned on (or remains on) (step 1 16), and the process returns to step 100. [0082] In this embodiment, if, at step 1 10, T _L is not less than T _L L, then the load 16 is within the desired temperature range and thus the process makes no change (step 1 18) before returning to step 100. In one embodiment, "no change" means maintaining whatever mode (e.g., active cooling, passive cooling, active heating, or passive heating) in which the system is currently operating. For example, if the system detects that active cooling is needed (i.e., the process moves from step 102 to step 104 and then to step 106), then at some

subsequent point in time the active cooling should successfully lower T _L to where it is between T _L L and T _L H (i.e., the process moves from step 102 to step 1 10 to step 1 18.) It may be necessary to continue operating in active cooling mode in order to maintain T _L within the desired temperature range,

[0083] Figure 1 D illustrates an embodiment in which the second path 14 can actively heat as well as actively cool. For example, in one embodiment, the operation of the heat pump 20 may be reversed, i.e., it may transfer heat in either direction by, e.g., reversing the direction of current flow through the heat pump 20. In this embodiment, the heat pump 20 may be used to warm up the load 16. Alternatively, other devices, such as resistive heaters, for example, may be employed to provide heat to the load 16 and/or to supplement the operation of the heat pump 20. In alternative embodiments, however, the heat pump 20 may operate in only one direction, e.g., to actively cool. In these embodiments, steps 1 10, 1 12, 1 14, and 1 16 may be omitted. Likewise, It will be understood that the process illustrated in Figure 1 D may include additional steps not shown.

[0084] In general, Figure 1 D illustrates the principle that in some

embodiments, a first path 12 and a second path 14 provide parallel heat flow paths to remove Q _c at temperature T _L . In some embodiments, the operation of the system 10 is a function of differences between T _A and the temperatures of any nodes upstream of the heat exchangers 24 and 28. A temperature differential between T _L HP and T _A may determine whether the heat pump 20 is activated to remove Q _C via the second path 14. For example, when T _L HP is equal to or less than T _A , the heat pump 20 may be activated to remove Q _c via the second path 14. When T _L HP is greater than T _A , the heat pump 20 may be deactivated such that Q _c passively flows through the first path 12 due to natural dissipation caused by the temperature differential. Accordingly, the first path 12 may reduce costs and improve energy efficiency and/or the second path 14 may provide broader temperature ranges of operation. However, the operation of the system 10 is not limited thereto.

[0085] In some embodiments, the heat pump 20 may activate while T _L HP is greater T _A to provide rapid cooling. In other words, the heat pump 20 may activate even though T _L HP is greater T _A when rapid cooling is required. In some embodiments, the first path 12 may be used only as a backup path when the second path 14 fails. Accordingly, the system 10 can provide cost-effective operations to improve efficiency and performance compared to systems that only use active or passive cooling techniques.

[0086] The method illustrated in Figure 1 D is intended to be illustrative and not limiting. For example, rather than just one value of T _L H, a system may have a pair of temperature thresholds that are designed to provide a form of hysteresis, e.g., a different upper limit depending on whether TJs currently rising (T _L HR) or falling (T _L HF)- In one embodiment, T _L HR is several degrees higher than T _L HF SO if T _L is rising, the heat pump 20 does not turn on to cool the load 16 until T _L is above T _L HR, but if T _L is falling, heat pump 20 does not turn off until T _L is below TLHF _. This may result in energy savings when compared to having the heat pump 20 enable or disable active cooling based on a single threshold T _L H- [0087] Figures 2A and 2B illustrate an exemplary structure and functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first and second thermally conductive paths share a common heat exchanger (which may also be referred to as a "shared" heat exchanger) for transferring heat to or from the load. In one embodiment illustrated in Figure 2A, the first thermally conductive path 12 and the second thermally conductive path 14 are thermally connected to the load 16 via a common heat exchanger 38. The descriptions of elements 18, 20, 24, 28, TLA, TLHP, and T _H PA are the same as for Figure 1 A and therefore will not be repeated here. [0088] Referring now to Figure 2B, the system 10 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the first path 12 and the second path 14 from the load 16 having a load temperature T _L to the ambient environment 18 having an ambient temperature T _A . The common heat exchanger 38 is represented as thermal resistor R _t h,i_. The descriptions of elements 20, 24, 28, PTEC, T _L A, T _L HP, and T _H PA are the same as for Figure 1 C and therefore will not be repeated here.

[0089] Figures 2C and 2D illustrate an exemplary structure and functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first and second thermally conductive paths share a common heat exchanger for transferring heat to or from the ambient environment. In the embodiment illustrated in Figure 2C, the first path 12 and the second path 14 not only share the common heat exchanger 38, but also share the common heat exchanger 40. The descriptions of elements 16, 18, 20, and 30 are the same as for Figure 1 A and therefore will not be repeated here.

[0090] Referring now to Figure 2D, the system 10 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the first path 12 and the second path 14 from the load 16 (not shown) having a load temperature T _L to the ambient environment 18 (not shown) having an ambient temperature T _A . The common heat exchanger 38 is represented as thermal resistor R _t h,i_, and the common heat exchanger 40 is represented as thermal resistor R _t h _, A- The descriptions of elements 20, P _T EC, T _L HP, and T _H PA are the same as for Figure 1 C and therefore will not be repeated here.

[0091 ] Figures 3A and 3B illustrate an exemplary structure and functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first thermally conductive path is thermally connected to the load in series through a thermal diode. In the embodiment illustrated in Figure 3A, a thermal diode 42 connects the common heat exchanger 38 to the heat exchanger 24 of the first path 12. The descriptions of elements 16, 18, 20, 28, and 30 are the same as previously described and therefore will not be repeated here.

[0092] A characteristic of a thermal diode is that it passively transfers heat efficiently in one direction only. In some embodiments, the thermal diode 42 is a thermosiphon. A typical thermosiphon is a tube that contains coolant that changes from a liquid state that to a gas state in the presence of heat. In operation, when the coolant is heated, the resulting gas rises through the tube via buoyancy forces to a cooler region of the tube, where the gas condenses back to liquid and flows back to the hotter region of the tube via gravitational forces. The change of state from liquid to gas extracts heat and the

condensation from gas to liquid releases that heat. In this manner, heat is extracted from one end of the thermosiphon (e.g., at the load end) and released at the other end of the thermosiphon (e.g., into the ambient environment). In other words, the thermosiphon provides passive, two-phase heat transfer in one direction, namely, from an evaporator region of the thermosiphon (which in this example is connected to the common heat exchanger 38) to a condenser region of the thermosiphon (which in this example is connected to the heat exchanger 24).

[0093] The presence of thermal diode 42 provides the benefit that heat can flow efficiently through the first path 12 from the load 16 to the ambient environment 18 but not in the opposite direction, which protects the load 16 from receiving unwanted heat via the first path 12, e.g., in conditions where the ambient temperature T _A is high relative to the load temperature T _L . Another advantage to this configuration is that the heat exchanger 24 of the first path 12 may be positioned or located at some distance away from the heat exchanger 28 of the second path 14, which, during active operation of the heat pump 20, may get quite hot. Separating the heat exchanger 24 from the heat exchanger 28 by some distance may thermally isolate the heat exchanger 24 from the heat exchanger 28, with the result that any heat produced by the heat exchanger 28 is less likely to have an effect on the heat exchanger 24 itself (e.g., via conduction or radiation of heat) or on the environment proximate to the heat exchanger 24 (e.g., via convection).

[0094] In one embodiment, one or more thermosiphons may be connected in series between the common heat exchanger 38 and the heat exchanger 24. An evaporator region of the thermosiphons may be thermally coupled to the common heat exchanger 38, and a condenser region of the thermosiphons may be coupled to the separate heat exchanger 24. As such, the thermosiphons operate as a thermal diode such that the thermal diode combined with any thermal insulation prevents heat from leaking back into the structure 30, which is an enclosed environment, from the external environment.

[0095] Referring now to Figure 3B, the system 10 is illustrated as a thermal circuit schematic showing the flow of heat Q _c through the first path 12 and the second path 14 from the load 16 (not shown) having a load temperature T _L to the ambient environment 18 (not shown) having an ambient temperature T _A . T _D A is the temperature of a point in path 12 between the thermal diode 42 and the ambient environment 18. The descriptions of elements 20, 24, 28, 38, P _T EC, TLHP, and T _H PA are the same as previously described and therefore will not be repeated here. In the embodiment illustrated in Figure 3B, it can be seen that the first path 12 includes the thermal diode 42.

[0096] Figures 4A and 4B illustrate an exemplary structure and functional description, respectively, of a hybrid heat transfer system according to another embodiment of the present disclosure, in which the first thermally conductive path is thermally connected to the load through a thermal diode and where the first and second paths share a common heat exchanger for transferring heat to or from the ambient environment. The embodiment of the system 10 illustrated in Figure 4A may be considered to be a variation on the system 10 illustrated in Figure 3A, with the difference that both the first path 12 and the second path 14 share the common heat exchanger 40. The descriptions of elements 16, 18, 20, 30, 38, and 42 are the same as previously described and therefore will not be repeated here. [0097] Referring now to Figure 4B, the system 1 0 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the first path 1 2 and the second path 1 4 from a load having a load temperature T _L to an ambient environment having an ambient temperature T _A . The first path 1 2 includes a thermal diode 42 and the second path 1 4 includes a heat pump 20. The common, ambient-side heat exchange is represented as thermal resistor F _A - The descriptions of elements 38, 40, P _TEC , T _LHP , and T _HPA are the same as previously described and therefore will not be repeated here.

[0098] The embodiments described above and illustrated in Figures 3A, 3B, 4A, and 4B include a thermal diode in the first thermally conductive path 1 2. In alternative embodiments, a thermal diode may be included in the second thermally conductive path 1 4, as illustrated in Figures 5A and 5B.

[0099] Figures 5A and 5B illustrate an exemplary structure and functional description, respectively, of hybrid heat transfer system 1 0 according to another embodiment of the present disclosure, in which the second thermally conductive path 1 4 is thermally connected to the load 1 6 through the thermal diode 42. The embodiment illustrated in Figure 5A may be considered a variation on the system 1 0 illustrated in Figure 2A, with the difference that the second path 14 includes the thermal diode 42 in series between the common heat exchanger 38 and the heat pump 20. The descriptions of elements 1 6, 1 8, 24, 28, and 30 are the same as previously described and therefore will not be repeated here.

[00100] In this configuration, the heat pump 20 can actively draw heat away from the top of thermal diode 42. For example, where the thermal diode 42 is a thermosiphon, the heat pump 20 can cool the top of the thermal diode 42 to encourage condensation of the gas that collects there and thus increase the performance of the thermal diode 42.

[00101] Referring now to Figure 5B, the system 1 0 is illustrated as a thermal circuit schematic showing the flow of heat Q _c through the first path 1 2 and the second path 1 4 from the load 1 6 (not shown) having a load temperature T _L to the ambient environment 1 8 (not shown) having an ambient temperature T _A . In this embodiment, the second path 1 4 includes both the thermal diode 42 and the heat pump 20 in series. T _L D is the temperature of a point in the second path 1 4 between the load 1 6 and the thermal diode 42. T _D HP is the temperature of a point in the second path 14 between the thermal diode 42 and the heat pump 20. The descriptions of elements 24, 28, 38, P _T EC, T _H PA, and T _L A are the same as previously described and therefore will not be repeated here.

[00102] The following embodiments illustrate configurations that include a thermal capacitor. Examples of thermal capacitors include, but are not limited to, devices that include or contain a phase change material and/or a thermal mass. For example, a thermal capacitor may include a reservoir of water that can be actively cooled until the water becomes ice, which is then used to passively cool (or at least absorb heat from) the load 1 6. Likewise, a thermal capacitor may be actively heated and then used to passively heat (or at least provide heat to) the load 1 6. A thermal capacitor may simply be a component having a large thermal mass that is used to absorb heat from or provide heat to the load.

[00103] Figures 6A and 6B illustrate an exemplary structure and functional description, respectively, of the hybrid heat transfer system 1 0 according to another embodiment of the present disclosure, in which the second thermally conductive path 1 4 is thermally connected to the load through the thermal capacitor. The embodiment illustrated in Figure 6A may be considered a variation on the system 1 0 illustrated in Figure 2A, with the difference that the second path 1 4 includes a thermal capacitor 44 in series between the common heat exchanger 38 and the heat pump 20. The thermal capacitor 44 is, in some embodiments, a PCM. In cooling applications, the thermal capacitor 44 is charged by the heat pump 20 such that the thermal capacitor 44 stores a thermal energy deficit (e.g., a PCM is frozen). However, in heating applications, the thermal capacitor 44 is charged by the heat pump 20 (configured to heat rather than cool) such that the thermal capacitor 44 stores thermal energy (e.g., a PCM is unfrozen or in a liquid state). The descriptions of elements 1 2, 1 6, 1 8, 24, 28, and 30 are the same as previously described and therefore will not be repeated here. [00104] In one embodiment, when the heat pump 20 is consuming energy, heat is extracted from the thermal capacitor 44. As a result, the heat pump 20 charges the thermal capacitor 44. After the thermal capacitor 44 is fully charged, the heat pump 20 may continue extracting heat from the thermal capacitor 44 at the same rate as the thermal capacitor 44 removes heat from the load.

[00105] When the heat pump 20 is not consuming energy, the thermal capacitor 44 may passively remove heat from the load until the thermal capacitor 44 is completely discharged. The thermal capacitor 44 can be recharged when the heat pump 20 is again consuming energy. Accordingly, the thermal capacitor 44 allows the second path 14 to remove heat actively or passively.

[00106] In some embodiments, the thermal capacitor 44 operates as a clamp to regulate the temperature of the load 16. For example, the thermal capacitor 44 may comprise a PCM. As the PCM absorbs heat, it may change states (e.g., from a solid to a liquid, from a liquid to a gas, or from a solid to a gas) during which the temperature of the PCM - and the load 16 - is clamped at its melting point temperature. Meanwhile, the first path 12 provides a failsafe heat flow path from the common heat exchanger 38 to the ambient environment 18 in the event that the load 16 overwhelms the thermal capacitor 44.

[00107] Referring now to Figure 6B, system 10 is illustrated as a thermal circuit schematic showing the flow of heat Q _c through first path 12 and second path 14 from a load having a load temperature T _L to an ambient environment having an ambient temperature T _A . In this embodiment, the second path 14 includes a thermal capacitor 44 in series with a heat pump 20. T _L c is the temperature at a point in the second path 14 between the load 16 and the thermal capacitor 44. TCHP is the temperature at a point in the second path 14 between the thermal capacitor 44 and the heat pump 20. The descriptions of elements 24, 28, 38, PTEC, THPA, and T _L A are the same as previously described and therefore will not be repeated here.

[00108] The presence of the thermal capacitor 44 in the system 10 has several potential advantages. One such advantage is that the thermal capacitor 44 may be "charged" (i.e., actively cooled or heated, e.g., to a target temperature) by operating the heat pump 20 in its active state while external power is available, so that the thermal capacitor 44 can cool or heat the load 16 in conditions where, e.g., external power is unavailable or the heat pump 20 is otherwise deactivated. This capability is useful, for example, in a scenario in which a package containing food or other items must be shipped to a distant location: prior to shipping, the thermal capacitor 44 may be actively charged (cooled) by the heat pump 20 that is plugged into a wall outlet or otherwise connected to an external power source. Once the thermal capacitor 44 is fully charged, the heat pump 20 is disconnected from the external power source and the now-cooled package is shipped. The thermal capacitor 44 may then continue to keep the contents of the package acceptably cool while the package is in transit and cannot be connected to a power source.

[00109] Another advantage of including the thermal capacitor 44 is that in environments where external power is continually available, a power company commonly charges a surcharge for power that is consumed during peak demand periods. In this scenario, the system 10 that includes the thermal capacitor 44 may be configured such that external power is used to charge the thermal capacitor 44 (and possibly actively cool the load 16) late at night or during other low-demand periods to avoid having to pay the higher rates charged during peak demand periods. The thermal capacitor 44 may then be used to cool the load 16 during (at least a portion of) the peak hours. Furthermore, power companies often charge businesses based on their peak instantaneous power usage. The use of the thermal capacitor 44 allows a business to stagger the times during which the heat pump 20 (or possibly the times at which multiple heat pumps 20 of the system 10) is active so that the overall peak power usage is reduced. In this manner, a business entity may dramatically reduce power costs.

[00110] Figures 7A and 7B illustrate an exemplary structure and functional description, respectively, of the hybrid heat transfer system 10 according to another embodiment of the present disclosure, in which the second thermally conductive path 14 is thermally connected to the load 16 through the thermal diode 42 and the thermal capacitor 44. The embodiment illustrated in Figure 7A may be considered a variation on the system illustrated in Figure 5A, with the difference that the second path 14 includes the thermal capacitor 44 in series between the thermal diode 42 and the heat exchanger 28. The descriptions of elements 1 2, 1 6, 1 8, 24, 30, and 38 are the same as previously described and therefore will not be repeated here.

[00111] Referring now to Figure 7B, the system 1 0 is illustrated as a thermal circuit schematic showing the flow of heat Q _c through the first path 1 2 and the second path 1 4 from the load 1 6 (not shown) having a load temperature T _L to the ambient environment 1 8 (not shown) having an ambient temperature T _A . In this embodiment, the second path 1 4 includes the thermal diode 42 and the thermal capacitor 44 in series with the heat pump 20. T _L D is the temperature at a point in the second path 1 4 between the load 1 6 and the thermal diode 42. T _D c is the temperature at a point in the second path 14 between the thermal diode 42 and the thermal capacitor 44. The descriptions of elements 24, 28, 38, PTEC, T _L A, TCHP, and T _H PA are the same as previously described and therefore will not be repeated here. The temperature T _L D at the load side of the thermal diode 42 may be different from the temperature T _D c at the ambient side of thermal diode 42. Likewise, the temperature T _D c at the load side of the thermal capacitor 44 may be different from the temperature T _C HP on the opposite side of the thermal capacitor 44.

[00112] The presence of thermal capacitor 44 may provide some or all of the benefits described above. For example, the heat pump 20 may actively charge the thermal capacitor 44 so that it can increase the efficiency of the thermal diode 42 to extract heat from the load 1 6 even during times when the heat pump 20 is not activated or is inoperable due to unavailability of external power.

[00113] Figures 8A and 8B illustrate an exemplary structure and functional description, respectively, of the hybrid heat transfer system 1 0 according to another embodiment of the present disclosure, in which the second thermally conductive path 1 4 is thermally connected to the load 1 6 through the thermal diode 42 and the thermal capacitor 44 and in which the first thermally conductive path 1 2 also includes the heat pump 20. The embodiment illustrated in Figure 8A may be considered a variation on the system 1 0 illustrated in Figure 7A, with the difference that the formerly passive first path 1 2 now includes its own heat pump 46. The descriptions of elements 1 2, 1 6, 1 8, 20, 24, 28, 30, 38, 42, and 44 are the same as previously described and therefore will not be repeated here.

[00114] Referring now to Figure 8B, the system 1 0 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the first path 1 2 and the second path 1 4 from the load 1 6 (not shown) having a load temperature T _L to the ambient environment 1 8 (not shown) having an ambient temperature T _A . In this embodiment, the first path 1 2 also includes the heat pump 46. T _C HP2 is the temperature at a point in the second path 14 between the thermal capacitor 44 and the heat pump 20. T _H P2 is the temperature at a point in the second path 14 between the heat pump 20 and the ambient environment 1 8. T|_HPI is the temperature at a point in the first path 1 2 between the load 1 6 and the heat pump 46. THP-IA is the temperature at a point in the first path 1 2 between the heat pump 46 and the ambient environment 1 8. The temperature T _L HPI at the load side of the heat pump 46 may be different from the temperature T _H PIA- In the

embodiment illustrated in Figure 8B, each of the two heat pumps 20 and 46 can be controlled independently of the other; the power provided to heat pump 46 is shown as arrow P _T ECI and the power provided to heat pump 20 is shown as arrow PTEC2- The descriptions of elements 20, 24, 28, 38, 42, and 44 are the same as previously described and therefore will not be repeated here.

[00115] Figures 9A and 9B illustrate an exemplary structure and functional description, respectively, of a hybrid heat transfer system 48, also referred to herein as "the system 48," according to yet another embodiment of the present disclosure, in which a thermally conductive path 50, also referred to herein as "the path 50," between the load 1 6 and the ambient environment 1 8 includes the thermal capacitor 44, the heat pump 20, and the thermal diode 42 connected in series. In the embodiment illustrated in Figure 9A, the system 48 includes a thermally conductive path 50 between the load 1 6 having a load temperature T _L and the ambient environment 1 8 having an ambient temperature T _A , the path 50 including the thermal capacitor 44, the heat pump 20, and the thermal diode 42. In the embodiment illustrated in Figure 9A, the heat exchanger 26 provides a thermal interface between the load 16 and the path 50, and the heat exchanger 28 provides a thermal interface between the path 50 and the ambient

environment 18.

[001 16] Referring now to Figure 9B, the system 48 is illustrated as a thermal circuit schematic showing the flow of heat Qc through the thermally conductive path 50 from the load 16 (not shown) having a load temperature T _L to the ambient environment 18 (not shown) having an ambient temperature T _A . In the embodiment illustrated in Figure 9B, the heat exchanger 26 is represented as a thermal resistor R _t h,i_, and the heat exchanger 28 is represented as thermal resistor R _thiA . The path 50 also includes the thermal capacitor 44, the heat pump 46, and the thermal diode 42. T _H PD is the temperature at a point on the path 50 between the heat pump 20 and the thermal diode 42. T _D A is the temperature at a point on path 50 between the thermal diode 42 and the ambient environment 18. The descriptions of elements 20, 24, 28, 38, 42, 44, P _T EC, T _L C, and T _C HP are the same as previously described and therefore will not be repeated here. The temperature T _C HP at the load side of the heat pump 46 may be different from the temperature T _H PD-

[001 17] Figure 10 illustrates a block diagram of an exemplary hybrid heat transfer system 52, also referred to herein as "the system 52," according to another embodiment of the present disclosure. In the embodiment illustrated in Figure 10, the system 52 includes active heating and/or cooling components 54, also referred to herein as "active components 54," and a control system 56. In some embodiments, the system 52 may optionally include passive heating and/or cooling components 58, also referred to herein as "passive components 58." In the embodiment illustrated in Figure 10, the control system 56 includes one or more temperature sensors 60, which provide temperature data and optionally other types of data as well, to a controller 62. In one embodiment, the controller 62, which may be implemented as one or more Central Processing Units (CPUs), Application-Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or the like or any combination thereof, processes the data provided by sensors 60 according to an algorithm. The controller 62 controls the operation of active components 54 via activating and switching circuitry 64. The system 52 may optionally include a computer memory 66 for storing computer programs and/or data.

[00118] In one embodiment, for example, the control system 56 may implement the process described above and illustrated in Figure 1 D to determine whether to cause the one or more active components 54 to change from an activated state to a deactivated state or vice versa.

[00119] In one embodiment, for example, the system 52 includes both the active components 54 and the passive components 58. In one such

embodiment, the passive components 58 may passively transfer heat continually, and the system 52 activates the active components 54 only when the passive components 58 cannot transfer enough heat, such as when the ambient environment 18 is hotter than the target load temperature T _L . In another embodiment, the passive components 58 act as a backup system to transfer heat if the active components 54 are inoperative, either due to lack of an external power source or due to component failure.

[00120] In one embodiment, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the controller 62 according to any one of the embodiments described herein is provided. In one embodiment, a carrier containing the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as a computer memory 66).

[00121] It should be noted that the embodiments described above are not limited thereto. For example, the systems may add or omit any components and arrange the components in any order to form any number of paths without departing from the scope of the invention.

[00122] As described above, some embodiments of the present disclosure include a heat removal system that utilizes a plurality of components that form one or more heat transfer paths. The plurality of components may include active components and passive components. In some embodiments, the hybrid heat removal system includes a plurality of components that form a plurality of heat transfer paths including at least one active heat transfer path and at least one passive heat transfer path. The active heat transfer path includes an active heat exchange component and is configured to provide active heat removal from a load when the active heat exchange component is active. The passive heat transfer path is configured to provide passive heat removal from the load. The passive heat transfer path is in parallel with the active heat transfer path.

[00123] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.