TECHNICAL FIELD

The present disclosure relates to an apparatus for storing and releasing thermal energy. BACKGROUND

Description of the Related Art

Thermal energy is used for space and water heating, among other things. Thermal energy may be generated or liberated through the combustion of biomass or hydrocarbon-based products such as wood, heating oil, propane, or natural gas, for example. Such products are fairly stable and can be stored for fairly long periods of time without degradation or loss of potential thermal energy release. Such products can also be fairly easily transported without significant degradation or loss of potential thermal energy release. These properties allow for combustion and release of thermal energy at a time and location selected for a particular requirement.

It is difficult however, to generate materials that store thermal energy from transient heat sources, such as solar power, for transport and later release of thermal energy. In an example, thermal energy may be collected by a solar thermal system, generated as electric or resistive heat from electricity supplied by photovoltaics or wind turbines, for example, from a ground source heat pump, or from waste heat sources, such as from effluent from a

manufacturing, or thermal power plant. Generating biomass or hydrocarbon materials from such sources is difficult and inefficient. Such thermal energy may be stored by heating water or other thermal masses, such as glycol, and may be transported or stored in insulated tanks, for example. However, such storage is only effective for short-term storage as the thermal energy will dissipate to the external environment through conduction or other means. Thus, a hot water tank, as an example, is not effective long term thermal energy storage mechanism, even with thermal insulation.

A useful long term thermal energy storage system is desired. In particular, a long term thermal energy storage system that has the ability to store thermal energy, to transport stored thermal energy from a source to a desired location, and to release such thermal energy at a desired time without significant loss of thermal energy over time, is desired. A solar thermal system with a transportable thermal energy storage system with minimal loss of thermal energy storage, over days or months, could allow for reduced area of solar collectors which could, in turn, reduce the associated cost of the solar collector.

It is known that thermal energy may be stored in certain phase change materials in a supercooled liquid state. Such a phase change material undergoes a phase transition from solid to liquid at an elevated temperature and when cooled, remains stable in a higher energy supercooled liquid state, below the phase transition temperature. Such a phase change material avoids spontaneously reverting to the lower energy solid state, and as such, can maintain thermal energy associated with the phase transition from the supercooled liquid state to the solid state. Salt hydrates with good solidification rates with respect to heat transfer, high latent heats of transition, and suitable transition temperatures exhibit strong supercooling behaviour and are good candidates for a phase change material based thermal energy storage apparatus. Sodium acetate trihydrate (NaCH3C02 ^» 3H20) is a safe and easily created material that can be supercooled to temperatures up to 108° Kelvin below the liquid-solid phase transition temperature and can be kept

supercooled for significant periods of time, exceeding one year, typically beyond the durations required of a stored thermal energy system.

Sodium acetate trihydrate has long been used as for supercooled liquid thermal energy storage in flexible heat packs for ready-to-use localized warming, for use as hand warmers, for example. In such instances, solid sodium acetate trihydrate in excess water is heated above the melting temperature, melted and fully dissolved, and then cooled and stored in a supercooled liquid state. The supercooled liquid sodium acetate trihydrate can then be triggered to solidify, releasing stored thermal energy at a desired time and location. The release of thermal energy in such flexible hard warmer heat packs is typically accomplished by manually flexing a pre-strained metallic flexible disc located inside the heat pack, immersed within the phase change material. The flexible metal disc is typically fitted with grooves that contain a trapped seed crystal of solid sodium acetate trihydrate. When the flexible disc is flexed, the grooves open and exposes the supercooled liquid sodium acetate trihydrate to the trapped seed crystal. The supercooled liquid sodium acetate trihydrate then crystalizes around the seed crystal, and in the process of solidifying, releases stored thermal energy.

Flexible hand warmer packs however, rely upon manual manipulation of the flexible disc to trigger the solidification process. To permit the manipulation of the flexible disc, the hand-warmer packs are typically made of a flexible translucent pouch which allows an operator to locate the flexible disc and then manipulate the flexible disc, through deformation of the flexible pouch. That is, to be manually manipulated, the flexible pouch must be sufficiently translucent, to locate the flexible disc, must be sufficiently small to allow for the external operator to be able to reach the flexible disc, and the pouch must be sufficiently flexible to allow for the flexion of the flexible disc.

Scaling a flexible heat pack to larger applications poses certain problems. The flexible disc typically moves freely within the supercooled sodium acetate trihydrate liquid. A pouch that is too large to allow for external manipulation of the flexible disc would frustrate the ability to manipulate the flexible disc to trigger nucleation and the release of thermal energy. That is, the pouch is limited in size. Secondly, locating the flexible disc within the supercooled liquid makes automation of the manipulation difficult. That is, an operator must visually locate the flexible disc for manipulation. Thirdly, the flexible nature of the pouch, required to allow for manipulation of the flexible disc, makes it difficult to incorporate within a heat exchange system. Fourthly, the pouch construction of flexible heat packs is a poor candidate for optimizing heat transfer rates with an external fluid medium.

BRIEF SUMMARY

A modular thermal energy storage apparatus can be summarized as having a housing defining a cavity; a phase change material located within the cavity; an extendable extension spring at least partially contained within the phase change material which may exist in a melted or solid state, wherein extension of the extendable extension spring triggers solidification of the phase change material and a release of thermal energy.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state, contained within the cavity; a first extendable extension spring at least partially contained within the phase change material; a first end plate positioned so as to cooperate with the first fluid flow plate to define a first fluid flow channel; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel and a first fluid outlet port in fluid communication with the first fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the first fluid flow plate from the phase change material to the heat exchange fluid in the first fluid flow channel.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate assembly comprising at least one fluid flow channel positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state, contained within the cavity; a first extendable extension spring at least partially contained within the phase change material; a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the fluid flow channel and a first fluid outlet port in fluid communication with the fluid flow channel for the egress of the heat exchange fluid from the fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the fluid flow plate from the phase change material to the heat exchange fluid in the fluid flow channel.

A thermal energy storage apparatus can be summarized as including: a base; a first fluid flow plate and a second fluid flow plate, the first and second fluid flow plates positioned so as to cooperate with the base to define a cavity; a phase change material which may exist in a melted or solid state contained within the cavity; at least one extendable extension spring at least partially contained within the phase change material; a first end plate positioned so as to cooperate with the first fluid flow plate to define a first fluid flow channel; a second end plate positioned so as to cooperate with the second fluid flow plate to define a second fluid flow channel, a first fluid inlet port in fluid communication with the first fluid flow channel for the ingress of a heat exchange fluid into the first fluid flow channel and a first fluid outlet port in fluid communication with the first fluid flow channel for the egress of the heat exchange fluid from the first fluid flow channel; a second fluid inlet port in fluid communication with the second fluid flow channel for the ingress of a heat exchange fluid into the second fluid flow channel and a second fluid outlet port in fluid communication with the second fluid flow channel for the egress of the heat exchange fluid from the second fluid flow channel; such that extension of the first extendable extension spring induces solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy from the phase change material across the first fluid flow plate and the second fluid flow plate to the heat exchange fluid in the first fluid flow channel and the second fluid flow channel.

A thermal energy storage apparatus can be summarized as including: at least one base; an at least one fluid flow plate positioned so as to cooperate with the base to define at least one cavity; a phase change material which may exist in a melted or solid state contained within at least one of the at least one cavity; an at least one extendable extension spring at least partially contained within the phase change material; an at least one end plate positioned so as to cooperate with the at least one fluid flow plate to define an at least one first fluid flow channel; an at least one fluid inlet port in fluid communication with the at least one fluid flow channel for the ingress of a heat exchange fluid into the at least one fluid flow channel, and an at least one fluid outlet port in fluid communication with the at least one fluid flow channel for the egress of the heat exchange fluid from the at least one fluid flow channel; such that extension the at least one extendable extension spring induces

solidification of at least a portion of the phase change material from a supercooled liquid state to a solid state, releasing thermal energy allowing for the transfer of thermal energy across the at least one fluid flow plate from the phase change material to the heat exchange fluid in the at least one fluid flow channel.

In any of the above implementations, the thermal energy storage apparatus can further include a baffle within the cavity which obstructs the sinking of solid phase change material.

In any of the above implementations, the thermal energy storage apparatus can include at least one baffle oriented substantially vertically in thermal communication with the phase change material and a fluid flow plate.

In any of the above implementations, the cavity can be substantially cylindrical. In any of the above implementations, the phase change material can comprise or consist of an organic material. In any of the above

implementations, the phase change material can comprise or consist of an inorganic material. In any of the above implementations, the phase change material can comprise a combination of both organic and inorganic materials. In any of the above implementations, the phase change material can comprise sodium acetate trihydrate. In any of the above implementations, the phase change material can comprise sodium acetate trihydrate with additional water.

In any of the above implementations, the thermal energy storage apparatus can further include a film disposed between the base and the first fluid flow plate, wherein the film chemically isolates the first fluid flow plate from the phase change material while maintaining thermal conductivity between the first fluid flow plate and the phase change material.

In any of the above implementations, a fluid flow plate can be comprised of aluminum bonded to stainless steel.

In any of the above implementations, a seal can be disposed between a fluid flow plate and the end plate, sealing the fluid flow channel. In any of the above implementations, a seal can be disposed between the fluid flow plate and the base, sealing the cavity.

In any of the above implementations, the base can further comprise at least one port to allow for the extension of extendable extension spring. In any of the above implementations, the base may further comprise at least one port to allow for filling the cavity with the phase change material.

In any of the above implementations, a fluid flow plate can be disposed with at least one flow director. In any of the above implementations, an end plate can be disposed with at least one flow director. In any of the above implementations, the fluid flow plate and the end plate cooperate to define at least one flow director.

In any of the above implementations, the fluid inlet port can traverse a portion of the base before being in fluid communication with the fluid flow channel. In any of the above implementations, the fluid outlet port can traverse a portion of the base after being in fluid communication with the fluid flow channel.

In any of the above implementations, the fluid inlet port can traverse a substantial portion of the base before being in fluid communication with the fluid flow channel.

In any of the above implementations, the first fluid inlet port and the second fluid inlet port can be in fluid communication with each other within the base. In any of the above implementations, the first fluid outlet port and the second fluid outlet port can be in fluid communication with each other within the base.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility.

Further, the particular shapes of the elements as drawn, are not necessarily intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings.

Figure 1 is a perspective view of a thermal energy storage apparatus according to at least one illustrated embodiment.

Figure 2 is a cross-section view of the thermal energy storage apparatus of Figure 1 from a front side thereof according to at least one illustrated embodiment.

Figure 3 is a cross-section view of the thermal energy storage apparatus of Figure 1 from the back side according to one embodiment. Figure 4 is a perspective view of a fluid flow plate of the thermal energy storage apparatus of Figure 1 according to at least one illustrated embodiment.

Figure 5 is a cross-section view of a thermal energy storage apparatus from a front side thereof according to at least one illustrated embodiment.

Figure 6A is a cross-section view of a cylindrical thermal energy storage apparatus taken along a longitudinal axis thereof according to at least one illustrated embodiment.

Figure 6B is a cross-section view of a cylindrical thermal energy storage apparatus taken along a longitudinal axis thereof according to at least another illustrated embodiment.

Figure 7A is a perspective view of base of a thermal energy storage apparatus, the base fitted with baffles according to at least one illustrated embodiment.

Figure 7B is a cross-section view of base fitted with baffles of Figure 7A, according to at least one illustrated embodiment.

Figure 8 is a cross-section view of a thermal energy storage apparatus from the front side according to at least one illustrated embodiment.

Figure 9 is a perspective view of a fluid flow plate of a thermal energy storage apparatus, the fluid flow plate having a number of vertically oriented baffles, according to one embodiment.

Figure 10 is a cross-section view of a stacked thermal energy storage apparatus from the front side according to at least one illustrated embodiment.

Figure 1 1 is a first perspective cross-section view of a thermal energy storage apparatus taken along a first plane, having housing composed of a unitary body and a cover plate, the cover plate fixable to the unitary body to seal an interior of the housing from an exterior thereof, and a finned plate heat exchanger positioned in the interior of the housing with a set of vertically extending fins, according to one embodiment.

Figure 12 is a top plane view of the thermal energy storage apparatus of Figure 1 1 with the cover illustrated as transparent to better illustrate an internal structure of the thermal energy storage apparatus.

Figure 13 is a second perspective cross-section view of the thermal energy storage apparatus of Figure 1 1 , taken along a second plane.

Figure 14 is a first perspective cross-section view of a thermal energy storage apparatus taken along a first plane, having housing composed of a unitary body and a cover plate, the cover plate fixable to the unitary body to seal an interior of the housing from an exterior thereof, and a finned tube heat exchanger positioned in the interior of the housing with a set of vertically extending fins, according to one embodiment.

Figure 15 is a top plane view of the thermal energy storage apparatus of Figure 14 with the cover illustrated as transparent to better illustrate an internal structure of the thermal energy storage apparatus.

Figure 16 is a second perspective cross-section view of the thermal energy storage apparatus of Figure 14, taken along a second plane.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments.

However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known materials, structures and methods associated with vehicles have not been shown or described in detail, to avoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification and claims which follow, the word "comprise" and variations thereof, such as, "comprises" and "comprising" are to be construed in an open, inclusive sense, that is as "including, but not limited to."

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singular forms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

The headings and Abstract provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

Figure 1 shows a perspective view of a thermal energy storage apparatus 10 according to at least one illustrated embodiment. Thermal energy storage apparatus 10 is shown with base 12. Moving outwardly from base 12, disposed on either side of base 12 may be film 24a and 24b. Film 24a and 24b may not be required depending on the particular structure and material of manufacture of fluid flow plates 16a and 16b, as is explained later in this disclosure. Base 12 and flow plates 16a and 16b collectively comprise a housing. Disposed on either side of optional film 24a and 24b, if incorporated, are fluid flow plates 16a and 16b. Disposed on either side of fluid flow plates 16a and 16b may be gaskets or seals 22a and 22b. Gaskets or seals 22a and 22b may not be required depending on the particular structure and material of manufacture of fluid flow plates 16a and 16b and end plates 18a and 18b, as is explained later in this disclosure. Disposed on either side of gaskets or seals 22a and 22b, if incorporated, are end plates 18a and 18b.

Figure 1 further shows heat exchange fluid inlets 30a and 30b to allow for the ingress of a heat exchange fluid into the thermal energy storage apparatus 10. Corresponding heat exchange fluid outlets are described later in this disclosure. Figure 1 further shows a seal 52 and a rod 46 extended through and sealed by seal 52. Figure 1 shows port 15 which may be a sealed cap or threated cap, for example, allowing for pouring in phase change material 14 or for the removal of phase change material 14 from cavity 13. Figure 1 further shows compression fastener(s) 50 which compresses the elements of base 12, film 22A and 22B, fluid flow plates 16A and 16B, gaskets or seals 22A and 22B, and end plates 18A and 18B, forming the basic structure of the thermal energy storage apparatus 10, according to this embodiment. The compression fastener(s) 50 can, for example, take the form of screws and matching threaded receptacles, threaded bolts and complementary nuts, clamps, and/or compression bands (e.g, spring steel bands).

Figure 2 shows a cross-sectional view of thermal energy storage apparatus 10 according to at least one illustrated embodiment. On either side of base 12 is disposed film 24A and 24B. On either side of film 24a and 24b are fluid flow plates 16a and 16b.

Base 12 cooperates with fluid flow plate 16a, with film 24a optimally disposed between base 12 and fluid flow plate 16a, and base 12 cooperates with fluid flow plate 16b, with film 24b optimally disposed between base 12 and fluid flow plate 16b, to collectively define cavity 13. Phase change material 14 is disposed in cavity 13. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13a above the phase change material 14, accommodating any thermal expansion of the phase change material.

Fluid flow plate 16a and end plate 18a cooperate to define a fluid flow channel 20a. Fluid flow plate 16a and end plate 18a may be optimally sealed by gasket or seal 22a to seal fluid flow channel 20a. Fluid flow plate 16b and end plate 18b cooperate to define fluid flow channel 20b on the other side of base 12. Fluid flow plate 16b and end plate 18b may be optimally sealed by gasket or seal 22b to seal fluid flow channel 20b.

Extendable extension spring 40 is located within cavity 13 and at least partially contained within phase change material 14. Extendable extension spring 40 is fixed to base 12 by mechanically engaging a tab 42. At the other end, extendable extension spring 40 engages rod 46. Rod 46 extends through spring port 44, located in the top of base 12, and is collared and otherwise sealed above base 12 by seal 52. Fluid flow plate 16A is in thermal communication with phase change material 14, via film 24a, where employed, allowing thermal energy to flow between fluid flow plate 16a and phase change material 14. Fluid flow plate 16b is in thermal communication with phase change material 14 via film 24b, where employed, allowing thermal energy to flow between fluid flow plate 16b and phase change material 14.

Heat exchange fluid inlet 30a is in fluid communication with fluid flow channel 20a via base 12 as shown by the dashed lines in Figure 2. Heat exchange fluid inlet 30b is in fluid communication with fluid flow channel 20b via base 12 as shown by the dashed lines in Figure 2. In another embodiment, heat exchange fluid inlet 30a may be in fluid communication with fluid flow channel 20a via end plate 18a, such that the heat exchange fluid inlet 30a is accessed from the side of thermal storage apparatus 10 and heat exchange fluid inlet 30b may be in fluid communication with fluid flow channel 20b via end plate 18b, such that the heat exchange fluid inlet 30b is accessed from the other side of thermal storage apparatus 10. Similarly, heat exchange fluid outlet 32a may be in fluid communication with fluid flow channel 20a via end plate 18a, such that the heat exchange fluid outlet 32a is accessed from the side of thermal storage apparatus 10 and heat exchange fluid outlet 32b may be in fluid communication with fluid flow channel 20b via end plate 18b, such that the heat exchange fluid outlet 32b is accessed from the other side of thermal storage apparatus 10.

Figure 3 is cross-sectional view of the backside of thermal energy storage apparatus 10 according to at least one illustrated embodiment. As was shown in Figure 2, Figure 3 shows on either side of base 12 is disposed optional film 24a and 24b. On either side of film 24a and 24b are fluid flow plates 16a and 16b. Base 12 cooperates with fluid flow plate 16a, with optional film 24a disposed between base 12 and fluid flow plate 16a, and base 12 cooperates with fluid flow plate 16b, with optional film 24b disposed between base 12 and fluid flow plate 16b, to collectively define cavity 13. Phase change material 14 is disposed in cavity 13. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13a above the phase change material 14. Fluid flow plate 16a and end plate 18a define a fluid flow channel 20a. Fluid flow plate 16a and end plate 18a may be sealed by gasket or seal 22a to seal fluid flow channel 20a. Fluid flow plate 16b and end plate 18b define fluid flow channel 20b on the other side of base 12. Fluid flow plate 16b and end plate 18b may be sealed by gasket or seal 22b to seal fluid flow channel 20b. Extendable extension spring 40 is located within cavity 13 and at least partially contained within phase change material 14. Extendable extension spring 40 is fixed to base 12 by mechanically engaging a tab 42. At the other end, extendable extension spring 40 engages rod 46. Rod 46 extends through spring port 44, located in the top of base 12, and collared above base 12 by seal 52. Spring port 44 is sealed by seal 52. Fluid flow plate 16a is in thermal communication (e.g., thermally conductive path) with phase change material 14 via film 24a, allowing thermal energy to conductively flow between fluid flow plate 16a and phase change material 14. Fluid flow plate 16a is in thermal communication (e.g., thermally conductive path) with phase change material 14 via film 24a, allowing thermal energy to conductively flow between fluid flow plate 16b and phase change material 14. Figure 3 shows heat exchange fluid outlet 32a. Heat exchange fluid outlet 32a is in fluid communication with fluid flow channel 20a via base 12 as shown by the dashed lines in Figure 3. Figure 3 also shows heat exchange fluid outlet 32b. Heat exchange fluid outlet 32b is in fluid communication with fluid flow channel 20b via base 12 as shown by the dashed lines in Figure 3.

Heat exchange fluid inlet 30a allows for the ingress of a heat exchange material 34 into fluid flow channel 20a. Heat exchange fluid outlet 32a allows for the egress of heat exchange material 34 out of fluid flow channel 20a. Heat exchange fluid inlet 30b allows for the ingress of a heat exchange material 34 into fluid flow channel 20b. Heat exchange fluid outlet 32b allows for the egress of heat exchange material 34 out of fluid flow channel 20b.

The relative locations of heat exchange fluid inlet 30a with respect to heat exchange fluid outlet 32a, and the relative locations of heat exchange fluid inlet 30b with respect to heat exchange fluid outlet 32b, may preferably be located diagonally from one another to promote the flow of heat exchange fluid across the bulk of the fluid flow plates 16a and 16b. Further, it may be preferable to locate the heat exchange fluid inlets 30a and 30b towards the top of thermal energy storage apparatus 10 and heat exchange fluid outlets 32a and 32b towards the bottom of thermal energy storage apparatus 10, as is explained later in this disclosure. However, the location of heat exchange fluid inlets and outlets may be positioned elsewhere and/or at other orientations.

Extendable extension spring 40 is configured to be in an unextended conformation or configuration at the resting unactuated or unextended state, for instance with the windings of extendable extension spring 40 in physical contact with one another. It is believed that extendable extension spring 40 in a conformation where the windings of extendable extension spring 40 are in physical contact with one another applies a local pressure that maintains phase change material 14 in the solid state, in isolation from the surrounding bulk phase change material 14, even when heated above the melting temperature. In such a conformation or configuration, extendable extension spring 40 spontaneously contains at least one seed crystal of phase change material 14 in the solid state.

Extendable extension spring 40 may be actuated from a relaxed state or configuration, e.g., in which the windings of extendable extension spring 40 are generally in physical contact with one another, to an extended state or configuration in which at least some of the windings of extendable extension spring 40 contained within phase change material 14 are separated from one another. Extendable extension spring 40 may be actuated manually, or may be actuated with a solenoid or other mechanical or electro-mechanical motor or servo or the like to extend extendable extension spring 40 upon demand.

Thermal energy storage apparatus 10 may be operated in particular states following initial set-up being: a charging state, a storage state, and a discharge state.

In set-up, cavity 13 is filled with phase change material 14 leaving a portion of cavity 13 unfilled so as to reduce the sealing pressure on seal ports, such as spring port 44, and to accommodate thermal expansion of the phase change material 14. Figure 1 shows port 15 which may be a sealed cap or threated cap, for example, allowing for pouring in phase change material 14 or for the removal of phase change material 14 from cavity 13. Partial filling of cavity 13 with phase change material 14 is not required and complete filling may be selected by a person of ordinary skill in the art, provided thermal storage apparatus 10 is fitted with a means to accommodate an increase in volume of phase change material 14 which may occur through a phase transition. Filling must however, at least partially immerse extendable extension spring 40 in phase change material 14. In set-up, phase change material 14 will be introduced into cavity 13, generally, in a liquid form, but may be introduced in a solid form.

In a charging state, heat exchange fluid inlets 30a and 30b are connected to an external source of heat exchange fluid. Heat exchange fluid outlets 32a and 32b may be connected to an external sink for heat exchange fluid or may be connected to the external source of heat exchange fluid to form a loop with heat exchange fluid circulating through thermal energy storage apparatus. In a charging state, heat exchange fluid is introduced into the heat exchange fluid inlets 30a and 30b which then flows via heat exchange fluid inlets 30A and 30B into fluid flow channels 20a and 20b and then out via heat exchange fluid outlets 32a and 32b back to the external source or reservoir, or to the external sink. In a charging state, heat exchange fluid is at a higher temperature than phase change material 14. As heat exchange fluid flows through fluid flow channels 20a and 20b, it imparts thermal energy to fluid flow plates 16a and 16b. As fluid flow plates 16a and 16b heat, they will in turn, thermally conductively impart thermal energy to phase change material 14, via film 24a and 24b, if such film is disposed between phase change material 14 and fluid flow plates 16a and 16b.

In a charging state, heat exchange fluid is at a temperature greater than the melting point of the phase change material 14 such that solid phase change material 14 melts or dissolves to become a liquid solution. Heat exchange fluid may receive its thermal energy from a solar thermal energy harvester, through a waste thermal energy recovery system or other means to heat the heat exchange fluid. Thus, when heated, heat exchange fluid then flows into fluid flow channels 20a and 20b, as described above, and, where heat exchange material is at a temperature greater than the temperature of the phase change material 14, thermal energy will flow across the fluid flow plates 16a and 16b, and film 24a and 24b, if used, to heat phase change material 14. Heat exchange fluid exits thermal storage apparatus 10 via the heat exchange fluid outlets 32a and 32b at a lower temperature than upon entering via heat exchange fluid inlets 30a and 30b, in a charging state. This process is continued until phase change material 14 is above the melting point of the phase change material 14, such that the phase change material 14 is liquefied, or dissolves, and at a temperature above the melting point of phase change material 14. At this point, flow of heat exchange fluid may be stopped and thermal energy storage apparatus 10 may enter the storage state.

In a charging state, it is preferable to have heat exchange fluid inlets 30a and 30b located towards the top of thermal energy storage apparatus 10 and to have heat exchange fluid outlets 32a and 32b located towards the bottom of thermal energy storage apparatus 10. Further, it is preferable to have heat exchange fluid inlets 30a and 30b located on one end of thermal energy storage apparatus 10 and to have heat exchange fluid outlets 32a and 32b located on the other end of thermal energy storage apparatus 10 such that heat exchange fluid enters towards the top front of the fluid flow plates 16a and 16b, and then travels generally diagonally downward towards the back of base 12 to achieve convective thermal transfer. However, other locations and/or orientations of heat exchange fluid inlets 30b and 30c and outlets 32a and 32b may be employed for a particular application. For example, heat exchange fluid inlets 30a and 30b may be located on the side of thermal energy storage apparatus 10 such that the heat exchange fluid inlets 30a and 30b run through end plates 18a and 18b. However, other locations and/or orientations of heat exchange fluid inlets 30a and 30b and outlets 32a and 32b may be employed for a particular application. Similarly, heat exchange fluid outlets 32a and 32b may be located on the side of thermal energy storage apparatus 10 such that the heat exchange fluid outlets 32a and 32b run through end plates 18a and 18b. With heat exchange fluid inlets 30a and 30b located towards the top and towards one side (front for example) of thermal energy storage apparatus 10 and heat exchange fluid outlets 32a and 32b located towards the opposite diagonal, towards the bottom and towards the back, for example, thermal energy from warmer heat exchange fluid entering heat exchange fluid inlets 30a and 30b at the top of thermal energy storage apparatus 10 will be imparted to the upper portion of phase change material 14. A convection current will be set up within phase change material 14 such that as colder, molten phase change material is heated, it will rise. The net effect is that there will; be a current of phase change material rising to the top, heating as it rises, and a current of heat exchange fluid flowing towards the bottom, cooling as it descends as it imparts thermal energy to the thermal energy storage apparatus 10. This countercurrent is desirable in heat exchange systems to created greater heat transfer.

When transitioning from the completion of the charging state to a storage state, phase change material 14 may then permitted to cool and, given its nature, phase change material 14 will enter a supercooled state, below the freezing point of phase change material 14. Once phase change material 14 is in a supercooled state, thermal energy storage apparatus 10 may be stored for extended periods of time exceeding one year and may be transported for discharge in a location different from the charging location, if desired.

In a storage state, thermal energy storage apparatus 10 may be disconnected from the external source of heated heat exchange fluid, and the heat exchange fluid inlets 30a and 30b and outlets 32a and 32b may be disconnected from the external source, if desired. Heat exchange fluid may also be evacuated from the fluid flow channels 20a and 20b, if desired, or may remain in fluid flow channels 20a and 20b.

The discharge state is initiated when it is desired that thermal energy storage apparatus 10 release stored thermal energy. The discharge of thermal energy occurs when phase change material 14, maintained in a supercooled liquid state, is triggered to enter a solid state. Before triggering phase change material 14 in a supercooled liquid state to enter a solid state, heat exchange fluid should be introduced into flow channels 20a and 20b, if previously empty, and heat exchange fluid inlets 30a and 30b should be connected to a source of heat exchange fluid, and heat exchange fluid outlets 32a and 32b should be connected to a sink of heat exchange fluid, such that heat exchange fluid can impart thermal energy to the thermal mass sought to be heated. The discharge of thermal energy occurs when phase change material 14, in a supercooled liquid state, is triggered to enter a solid state. At a discharge time, extendable extension spring 40 is extended either by manually pulling on extendable extension spring 40 to extend it, through seal 52 directly, or via rod 46 or by having extended extendable extension spring 40 by operation of solenoid or other mechanical/electromechanical means. It has been found that when extendable extension spring 40 located within phase change material 14, in a supercooled liquid state, is extended phase change material 14 is triggered to enter a solid state. It is believed that the local environment contained between the windings of extendable extension spring 40 in an unextended conformation maintains or contains phase change material 14 in a solid state. When extendable extension spring 40 is extended, the phase change material 14 in a solid state contained between the windings of extendable extension spring 40 is open to the bulk phase change material 14 in the supercooled liquid state and presents as a seed crystal upon which phase change material 14 in the supercooled liquid state crystalizes and solidifies. As phase change material 14 transitions from the supercooled liquid state to a solid state, thermal energy is released. Heat exchange fluid in fluid flow channels 20a and 20b, at a temperature below the temperature of phase change material 14 which releases thermal energy through solidification will receive thermal energy by thermal conduction from phase change material 14 across fluid flow plates 16a and 16b and film 24a and 24b, if used. Heat exchange fluid may then be pumped or fed or otherwise motivated from fluid flow channels 20a and 20b out of thermal energy storage apparatus 10 via heat exchange fluid outlets 32a and 32b to an external sink desired to be heated. Heat exchange fluid may be reintroduced into fluid flow channels 20a and 20b via heat exchange fluid inlets 30a and 30b to replace heat exchange fluid pumped or fed or otherwise motivated out of fluid flow channels 20a and 20b. A loop of heat exchange fluid may be used to feed into fluid flow channels 20a and 20b via heat exchange fluid inlets 30a and 30b and out of fluid flow channels 20a and 20b via heat exchange fluid outlets 32a and 32b. This process may continue until thermal equilibrium is reached. Thermal energy storage apparatus 10 may then be placed back into a charging state, or may be stored in the discharged state, if desired.

The system can be operated in reverse if desired and the direction of flow of heat exchange fluid may be switched based on whether the system is in a charging state or discharge state. For example, in a charging state, heat exchange fluid may enter at heat exchange fluid inlets 30a and 30b and may exit at heat exchange fluid outlets 32A and 32B. If desired, external plumbing may be manipulated or a flow direction valve or pump may be switched so that in a discharge state, heat exchange fluid may enter at heat exchange fluid outlets 32a and 32b and may exit at heat exchange fluid inlets 30a and 30b.

Materials and method of manufacture of thermal energy storage apparatus 10 can be selected by a person of ordinary skill in the art for a particular size, volume, type of phase change material, type of heat exchange fluid, and other aspects of a particular application.

In one embodiment, phase change material 14 is comprised of sodium acetate trihydrate, with or without additional water, which has some corrosive properties as against steel or other materials. Sodium acetate trihydrate may itself not be properly classified as organic or inorganic but may be classified as comprised of organic and inorganic materials. Other possible phase change materials include organic or inorganic materials that melt in the operational temperature range and supercool or can be made to supercool and include salt hydrate inorganic phase change materials and sugar alcohol phase change material, such as xylotol, erithritol, for example. An appropriate phase change material may only be selected by a person of ordinary skill in the art.

Base 12 may be constructed from a material that has sufficient mechanical properties to ensure the structural integrity of base 12 and thermal storage apparatus 10 as a whole. Base 12 may also be manufactured from a material that has desired thermal properties and desired chemical properties. Base 12 may be manufactured from plastic such as cast and machined polypropylene. Plastic, such as polypropylene, has good mechanical properties that allows for rigid construction, when sufficiently thick, and has good chemical properties to avoid corrosion when exposed to phase change material 14.

Polypropylene also has low thermal conductivity which may be preferable as it is preferentially desired for thermal energy to flow between phase change material 14 and heat exchange material located in fluid flow channels 20a and 20b, across fluid flow plates 16A and 16B. Base 12 may be made of more than one material, such steel which has good mechanical properties, partially or fully encased in polypropylene, for example, to achieve the net desired properties of base 12 as a whole. The materials and method of manufacture base 12 may be selected by the person of ordinary skill in the art for a particular application.

When used, in a particular embodiment, film 24a and 24b may be a metalized film, such as a film composed of mylar/aluminum/polyethylene. A metalized mylar film 24 provides a chemical barrier between phase change material 14 and fluid flow plates 16b and 16b while maintaining thermal conductivity between phase change material 14 and fluid flow plates 16a and 16b. Film 24a and 24b and may also serve as a gasket or seal to seal cavity 13 between base 12 and fluid flow plates 16a and 16b. The materials and method of manufacture for film 24a and 24b may be selected by the person of ordinary skill in the art for a particular application.

Fluid flow plates 16a and 16b may be constructed out of materials which have good thermal conductivity and good mechanical rigidity. Fluid flow plates 16a and 16b may be constructed from cast or machined aluminum alloy, such as a 6061 alloy. Fluid flow plates 16a and 16b may also be constructed from cast or machined steel or stainless steel, for example. As noted above, film 24a and 24b provides a chemical barrier between phase change material 14 and fluid flow plates 16a and 16b. However, where phase change material 14 is not corrosive to fluid flow plates 16a and 16b, film 24a and 24b may not be required. Alternatively, where phase change material 14 is corrosive to fluid flow plates 16a and 16b, film 24a and 24b may not be required, if fluid flow plates 16a and 16b are coated with a thermally conductive coating which renders fluid flow plates 16a and 16b chemically resistant to corrosion caused by phase change material 14. Fluid flow plates 16a and 16b may otherwise be bonded or laminated with a film to seal fluid flow plates 16a and 16b from phase change material 14. If a film 24a or 24b is not used, a gasket or seal may still be required to ensure cavity 13 does not leak to the external environment. Fluid flow plates 16a and 16b may be manufactured from a bonded aluminum and 302/304 stainless steel plate, for example, with the stainless steel side exposed to the phase change material 14. A thin layer of stainless steel provides corrosion resistance and thermal conductivity to the aluminum layer. Further, aluminium is less expensive than stainless steel, and a bonded aluminum stainless steel fluid flow plate may be desirable over a full stainless steel plate. Bonding of metals may be produced in a manner as is known by a person of ordinary skill in the art, including processes in the art used in the manufacture of metal stovetop cookware. The materials and method of manufacture for fluid flow plates 16a and 16b can be selected by the person of ordinary skill in the art for a particular application.

End plates 18a and 18b may be constructed out of materials which have good mechanical rigidity and low thermal conductivity, so as to avoid conduction of thermal energy to the surrounding environment. End plates 18a and 18b may be constructed from polypropylene, for example. To increase the mechanical properties of the polypropylene, for a given thickness, end plates 18a and 18b may be made of plastic encased or coated steel, or aluminum, for example, or may be constructed in a layered manner, such as a sandwich or laminate of plastic and steel. Such a combination would allow for the polypropylene side to face fluid flow channels 20a and 20b, which would allow the low thermal conductively of the plastic to avoid thermal conduction to a steel or other metal back layer which has good mechanical properties, to achieve the net desired properties of the end plates 18a and 18b as a whole. End plates 18a and 18b may be made of the same metals as disclosed in respect of the fluid flow plates 16a and 16b above, but to reduce thermal leakage to the surrounding environment, should preferably be insulated on the outside using insulation such as ethylene propylene diene monomer foam, as an example. The materials and method of manufacture of end plates 18a and 18b may be selected by the person of ordinary skill in the art for a particular application.

Extendable extension spring 40 is configured to be in an unextended conformation at the resting unactuated state such that the windings of extendable extension spring 40 are in physical contact with one another. The material for extendable extension spring 40 may selected from materials that have appropriate spring constant and minimum load (pre-stressed) to be actuatable by a solenoid or servo selected for thermal energy storage apparatus 10, and have appropriate windings, diameter, and pre-stressing to allow for retention of a seed crystal of phase change material 14 in an unextended state. Extendable extension spring 40 with elevated minimum load and elevated spring constant is preferred for applications involving the transportation of the thermal energy storage apparatus 10, giving the extendable extension spring 40 resistance to flexure caused by transportation shock and therefore resistance to risks of unintended solidification trigger during transport. For example, extendable extension spring 40 may

constructed from 300 grade stainless steel, and may be commercially purchased as item # 94135K36 from McMaster-Carr, Aurora, Ohio. A person of ordinary skill in the art may select the material for extendable extension spring 40 for a particular application, but suitable materials include type 300 series stainless steels and corrosion resistant nickel alloys including incoloy, hastaloy, for example.

The combination of end plate 18a, gasket or sealant 22b, fluid flow plate 16b, film 24b, and base 12 on one side, and on the other side, base 12, film 24a, fluid flow plate 16a, gasket or sealant 22a, and end plate 18a are held together under compression through one or more compression fasteners 50. Compression fasteners 50 may be a series of through bolts which engage or penetrate the perimeter of base 12, fluid flow plates 16a and 16b, and end plate 18a and 18b, and other elements, as may be required, which are then secured with nuts to apply a general compression force across the elements, as shown in Figure 1 (where only one instance of compression fastener 50 is called out for clarity). Alternatively, bands (e.g., metal band, spring steel band) may circumscribe thermal energy storage apparatus 10 to apply a general compression force across the respective elements of thermal storage apparatus 10. As another example, in another example, guiding rods or other means may be employed to line up the various elements of thermal storage apparatus 10 and thermal storage apparatus 10 may be compressed and secured by an external bolted end-plate assembly as is used for commercial plate-and-frame heat exchangers, for example. The materials and method of manufacture of compression fastener(s) 50 may be selected by the person of ordinary skill in the art for a particular application.

Figure 4 shows a fluid flow plate 16a according to at least one illustrated embodiment. Figure 4 shows fluid flow plate 16a with fluid outlet 54 and fluid inlet 58 with flow directors 34 machined, molded or cast, or set by any suitable means, into the surface of fluid flow channel 20a. Fluid flow channel 20a is defined by the cooperation of fluid flow plate 16a and end plate 18a (not shown in Figure 4). Fluid flow plate 16b, in one embodiment, as shown in Figures 1 , 2, and 3 may be a mirror image of fluid flow plate 16a, shown in Figure 4. As shown in Figure 1 , compression fastener(s) 50 can include a series of through bolts. To allow for such through bolts, fluid flow plate 16a has a series of perimeter positioned holes 56 drilled or otherwise disposed in fluid flow plate 16a, such that the threaded action of nuts on one or more end of such through bolts will apply a compression force to the particular elements of the thermal energy storage apparatus 10. The nuts and ends of through bolts are depicted in Figure 1 as compression fastener(s) 50. Flow directors 34 (Figure 4) within fluid flow channel 20a (and fluid flow channel 20b, not shown) redirect the flow of heat exchange fluid as it flows across the fluid flow plates, 16a and 16b, respectively, as heat exchange fluid passes from heat exchange inlet 30a to heat exchange fluid outlet 32a or from heat exchange inlet 30b to heat exchange fluid outlet 32b (or vice-versa if the system is operated in reverse, if desired) in the case of fluid flow channel 20b. The flow directors 34 assist in ensuring heat exchange fluid engages with the available surface of fluid flow plate 16a (and 16b not shown), enhanced by the additional surface area available on the face or faces of flow directors 34, within fluid flow channels 20a and 20b to increase the conduction of thermal energy between phase change material 14 and heat exchange fluid. Flow directors 34 may be diamond-shaped features, as shown in the embodiment in Figure 4, but may also be selected by a person of ordinary skill in the art given the particular conditions or requirements of a particular system. For example, flow directors 34 may contact end plates 18a or 18b such that the heat exchange fluid must pass around flow directors 34. As another example, flow directors 34 may not contact end plates 18a or 18b such that the heat exchange fluid may pass around and over flow directors 34. As another example, fluid flow plates 16a and 16v may have flow one or more directors that is a channel, are channels, or are channel like which may be continuous or interrupted. A person of ordinary skill in the art may select the nature of any given the particular conditions or requirements of a particular system, including whether laminar flow or turbulent flow is desired, the location of heat exchange fluid inlets 30a and 30b, heat exchange fluid outlets 32a and 32b, other factors, including the general shape of the thermal energy storage apparatus 10 as a whole. Such flow directors 34 may be features of fluid flow plates 16a and 16b, or end plates 20a and 20b, or both fluid flow plates 16a and 16b and end plates 20a and 20b such that the cooperation of fluid flow plates 16a and 16b and end plates 20a and 20b define flow directors 34. Rod 46 may be constructed of a simply solid circular cylinder of material with machined or inserted eye hooks, for example, for engaging with extendable extension spring 40 on one end, and with solenoid or actuator on the other end. Rod 46 may preferably be made of material to withstand the chemical or corrosive effects of the phase change 14, although rod 46 may not contact phase change material 14 directly in ordinary operation. The materials and method of manufacture of rod 46 may be selected by the person of ordinary skill in the art for a particular application.

Tab 42 may be constructed of a machined part of base 12 or as an inserted eye hook into base 12, for example, for engaging with extendable extension spring 40 on the bottom end. The materials and method of manufacture of tab 42 may be selected by the person of ordinary skill in the art for a particular application.

Seal 52 may be constructed of a rubber or similar pliable material that may be adhered or otherwise fixed to base 12 on one end, and may be adhered or otherwise fixed to rod 46 on the other end. Seal 52 is preferred to be selected for integrity under pressure (from thermal expansion of phase change material 14) and at elevated temperature, as well as chemical resistance to phase change material 14 vapour and vapour condensate. Seal 52 may be form of a static or moving shaft seals, or a bellows seal such as may be commercially purchased from McMaster-Carr of Aurora, Ohio as SKU 5298K79, and cut to size, as needed, for example. The materials and method of manufacture of seal 52 may be selected by the person of ordinary skill in the art for a particular application.

Optionally, heat exchange fluid inlets 30a and 30b may be located in base 12 and may traverse a portion of base 12 before turning and entering fluid flow channels 20a and 20v. Similarly, heat exchange fluid outlets 32a and 32b may be located in base 12 such that heat exchange fluid exits fluid flow channels 20a and 20b and then traverses a portion of base 12 before exiting the thermal energy storage apparatus 10 at heat exchange fluid outlets 32a and 32b. As phase change material 14 solidifies, it condenses and becomes denser, as compared to phase change material 14 in the liquid state. In a charging state, thermal energy is supplied to phase change material 14 from heat exchange fluid in fluid flow channels 20a and 20b. As phase change material 14 transitions from a solid state to a liquid state, any remaining solid phase change material 14 may sink to the bottom of cavity 13. As such, it may be preferable to apply more thermal energy to the bottom of cavity 13 to liquefy any sinking solid phase change material 14 although such a configuration may lead to concentration of phase change material solute towards the bottom of cavity 13, which may lead to the creation of an inhomogeneous solid phase change material 14, such as anhydrous/hydrous sodium acetate, which may lead to auto-nucleation, which is not desired. To avoid undesirable levels of concentration of solute, a mechanical mixer may be employed, such as a rotating paddle wheel, which may be extant within cavity 13 and operated via a port, for example. As such, configuring base 12 to house heat exchange fluid inlets 30a and 30b and heat exchange fluid outlets 32a and 32b and configuring base 12 such that heat exchange fluid inlets 30a and 30b or heat exchange fluid outlets 32a and 32b traverse a lower portion of base 12 before turning to or turning from fluid flow channels 20a or 20a would provide additional thermal energy to the bottom of base 12 and the bottom of cavity 13 to heat sunken solid phase change material 14. As such, it may be preferential to configure base 12 so as to have a more thermally conductive bottom portion to allow for the conduction of thermal energy as described above, or that such elements may be positioned towards the upper surface of the bottom of base 12 to improve heat transfer, provided there is sufficient material between such channels and the upper surface of the bottom of base 12 to prevent a leak or rupture at all operating temperatures of thermal storage apparatus 10. It is advantageous for base 12 to be otherwise insulated or insulating to minimize thermal losses to the external environment. Base 12 may be generally circular, square, rectangular, or other shape, selected by a person of ordinary skill in the art.

In one embodiment, thermal energy storage apparatus 10 may be generally configured to remain in the upright orientation shown in Figure 1 . With this orientation, spring ports 44 located on the upper surface of base 12 may only need to be configured to prevent the egress of vapour of phase change material 14, as compared to being configured to prevent the egress of liquid phase change material 14. However, if phase change material 14 substantially fills cavity 13, thermal expansion of phase change material 14 at elevated temperatures may cause phase change material 14 to expand into port 15 or spring ports 44 and seal 52, and such ports may require sealing against pressure from liquid phase change material 14.

Optimally, in at least one embodiment, extendable extension spring 40 may be extended to outside of base 12 by the top portion of extendable extension spring 40 extending through a sealed spring port 44, located in the top of base 12, such that the top of extendable extension spring is engaged and activated to trigger solidification of phase change material 14, removing the need for rod 46.

In at least one embodiment, flow channel 20A may be sealed through a gasket or sealant 22a such that the fluid flow channel 20a is sealed from the external environment. Flow channel 20b may be sealed through a gasket or sealant 22b such that the fluid flow channel 20b is sealed from the external environment. In another embodiment, gasket or sealant 22a and 22b may not be required if tolerances of fluid flow plate and end plate allow for a leak free joint, or where fluid flow plate is otherwise sealed to end plate or by an adhesive, or by brazing or welding, for example. Suitable materials for gasket or sealant 22a and 22b for a particular application may, for example, include silicone rubber, nitril rubber, latex rubber (depending on use with glycol or not), and butyl rubber. Thermal energy storage apparatus 10 is shown in Figures 1 , 2, and 3 as a two sided apparatus with a general bilateral symmetry. In another illustrated embodiment, thermal energy storage apparatus 10 may be a one sided apparatus, with fluid flow channel on one side only. Figure 5 shows a one-sided apparatus in cross section, according to at least one illustrated embodiment. As shown in Figure 5, base 12 cooperates with fluid flow plate 16a to define cavity 13 in which phase change material 14 is located. Phase change material 14 may not fill the entirety of cavity 13 leaving a vapour space 13a above the phase change material 14. Fluid flow plate 16a and an end plate 18a define a fluid flow channel 20a, where fluid flow plate 16a has sufficient thermal conductivity to be in thermal communication with phase change material 14 and to allow thermal energy to flow between fluid flow plate 16A and phase change material 14. As shown in Figure 5, fluid flow plate 16a and end plate 18a, which define fluid flow channel 20a, may be sealed through a gasket or sealant 22a such that the fluid flow channel 20a is sealed from the external environment. Gasket or sealant 22a may not be required if tolerances of fluid flow plate 16a and end plate 18a allow for a leak free joint. In this embodiment, film 24a may be optimally disposed between fluid flow plate 16a and base 12.

The shape of thermal energy storage apparatus 10 may be configured by a person of ordinary skill in the art however, it has been found that a greater surface area of fluid flow plates to volume of cavity ratio allows for greater conduction of thermal energy between phase change material and heat exchange fluid. In at least one illustrated embodiment, thermal energy storage apparatus 10 may be generally cylindrical in shape, including for example, a circular cylinder shape. A cross-section of a circular cylindrical shaped thermal energy storage apparatus 10 is depicted in Figure 6A. Figure 6A shows the cylindrical thermal energy storage apparatus 10 with cavity 13, extendable extension spring 40, phase change material 14 within cavity 13, a cylindrical fluid flow plate 16c and a cylindrical end plate 18c. The cylindrical fluid flow plate 16c and a cylindrical end plate 18c define the cylindrical fluid flow channel 20c. In this embodiment, base 12 may be comprised of end caps that secure and further cooperate with the above elements to define cavity 13 and fluid flow channel 20c. Inlets and outlets may be included within such end caps. For example, a base 12 end cap component may be a machined cylindrical block with machined cylindrical channels into which cylindrical fluid flow plate 16c and a cylindrical end plate 18c sit or may be cylindrical ridges which abut cylindrical fluid flow plate 16c and a cylindrical end plate 18c. The end caps and fluid flow plate 16c are collectively a housing. Seals may be employed as required.

Figure 6B shows a cross-section of a thermal energy storage apparatus 10 according to another embodiment. In this embodiment, the cavity is defined by the cylindrical wall fluid flow plate 16c and the end caps, not shown. In this embodiment, the thermal storage apparatus sits within a bath of heat exchange fluid, such as may be found in a shell and tube heat exchanger.

Thermal storage apparatus 10 may optionally include more than one extendable extension spring 40 placed within cavity 13, each at least partially immersed within phase change material 14. Generally, the more windings of extendable extension springs, which are increased with the number of extendable extension springs within cavity 13, the greater probability that the extension of an extendable extension spring will release a seed crystal of phase change material 14 triggering the solidification of phase change material 14. Further, with more than one extendable extension spring 40 placed within cavity 13, each at least partially submerged within phase change material 14, where each is extended at or near the same time, the greater the speed with which phase change material 14 may release thermal energy as it transitions from a supercooled liquid to a solid.

A thermocouple or thermocouples or other temperature sensors may be introduced into cavity 13, or may be extant within cavity 13 to inform operational systems as to when either thermal equilibrium or supercooling is reached, or when other thresholds are reached, which may trigger the start or cessation of a pump or other mechanism motivating heat transfer material, or may trigger the start or cessation of a mixing element, or for other aspects of operation such as solidification triggering. Such temperature sensors may enter the cavity 13 through base 12, for example, and may be sealed by compression fittings or by other means described herein.

Cavity 13 may be a single cavity, may be comprised of a number of subcavities, or may be a single cavity fitted with baffles. Figure 7A depicts a perspective view of base 12 fitted with baffles 60 (only one called out for clarity of the figure), without phase change material 14 filled within cavity 13. Figure 7A shows port 15. Figure 7A shows holes drilled or otherwise located within base 12 as part of compression fastener(s) or fittings 50, or to permit the passage of bolts, for example. Figure 7A also shows spring port 44, in this embodiment showing two spring ports 44 for two extendable extension springs (extendable extension springs not shown). Baffles 60 also have ports to allow for the passage of extendable extension spring, not shown, through cavity 13 to engage with tab 42. Figure 7A also shows base 12, and baffles 60 configured with additional ports or passages 68 to allow for the addition of thermocouples, if desired. Figure 7A also shows heat exchange fluid inlet 30a, which then turns within base 12 and is configured to enter the fluid flow channel (not shown) via port 62. Similarly, heat exchange fluid would exit the fluid flow channel via port 64 which would then turn and exit the fluid flow outlet 32a (not sown in Figure 7A). In at least one embodiment, the fluid flow inlet may split within base 12 and turn and feed fluid flow channels on both sides of base 12.

Figure 7B shows a cross sectional view of base 12 fitted with baffles 60 (only one called out for clarity of the figure), without phase change material 14 filled within cavity 13. Figure 7B shows port 15. Figure 7B shows holes drilled or otherwise located within base 12 as part of compression fastener(s) or fittings 50, or to permit the passage of bolts, for example. Figure 7B also shows spring port 44, in this illustrated embodiment showing two spring ports 44 for two extendable extension springs, (extendable extension springs not shown). Baffles 60 also have ports to allow for the passage of extendable extension spring, not shown, through cavity 13 to engage with tab 42. Figure 7B also shows base 12, and baffles 60 configured with additional ports or passages to allow for the addition of thermocouples, if desired. Figure 7B also shows heat exchange fluid inlet 30a, which then turns within base 12 and is configured to enter the fluid flow channel (not shown) via port 62. Similarly, heat exchange fluid would exit the fluid flow channel via port 64 which would then turn and exit the fluid flow outlet 32a. In at least one embodiment, the fluid flow inlet may split within base 12 and turn and feed fluid flow channels on both sides of base 12. As can be seen in Figure 7B, baffles 60 do not traverse the entirety of cavity 13, so as to allow for filling of cavity 13 with phase change material via the single port 15. In another embodiment, baffles 60 may traverse cavity 13, but may have holes or apertures to for filling of cavity 13 with phase change material via the single port 15. In another embodiment, baffles 60 may traverse cavity 13 such that cavity 13 effectively becomes a plurality of cavities, each requiring a port for filling, if filling occurs after assembly.

Baffles 60 may be in any conformation, as selected by a person of ordinary skill in the art, provided they have some horizontal component, as compared to the direction of gravity to combat stratification of the phase change material 14 by preventing much of the solid phase change material 14 from sinking to the bottom of the cavity 13 during melting. When arranged vertically, baffles 60 may assist in the transfer of heat from phase change material 14 to fluid flow plates 16a and 16a. Baffles 60 may or may not transverse the entirety of cavity 13, but to permit the filling of the entirety of cavity 13 from a single filling port, baffles should not traverse the entirety of cavity 13, or should be fitted with apertures to permit the flow of phase change material 14 around or through baffles 60. Further, baffles 60 may be fitted with apertures to permit the passage of extendable extension spring 40 through the bulk of phase change material 14. Baffles 60 may also assist heat transfer from the phase change material 14 to fluid flow plates as baffles 60 may be constructed of thermally conductive materials, and sealed or coated as described herein Phase change material 14 may be any material capable of being in a liquid or solid state and capable of being supercooled in a liquid state. Phase change material 14 may be sodium acetate trihydrate with or without additional water, for example, provided the phase transition temperatures and other properties of the phase change material 14 do not exceed the operating temperature limits of the materials of construction of the other elements of the thermal energy storage apparatus 10. The preferable phase change material may be selected by a person of ordinary skill in the art for a particular application based on the teachings herein.

Figure 8 shows baffles 60 that are in thermal communication with fluid flow plates 16a or 16b and with phase change material 14. Only one baffle 60 is called out in Figure 8, for clarity, and baffles 60 are only shown on one portion of fluid flow plate 16a, for clarity. However, baffles 60 may be arranged on any part of fluid flow plate 16a or 16B and may be generally uniformly distributed across such fluid flow plates. Baffles 60 may be arranged generally horizontally, or generally vertically, or at an angle selected by a person of ordinary skill in the art. Generally vertically arranged fins may be preferable as they may be able to be infiltrate the cavity 13 without interfering with extendable extension spring 40 as baffles 60 shown as generally horizontal fins may have to be shorter or have ports to allow for the passage of extendable extension spring 40, or other elements such as a thermocouple, if employed. Baffles 60, for example in the form of thermally conductive fins or pins may be fixed to the cavity-facing sides of the fluid flow plates 16a or 16b or may be machined integral elements of fluid flow plates 16a or 16b. However, the use of such baffles 62 may make the use of film 24a or 24b more difficult to implement. As such, the coated fluid flow plates, as described above, or corrosion resistant fluid flow plates (e.g., stainless steel) sealed to base 12 without the use of film 24a or 24b, may be preferable. In another embodiment, thermally conductive material may be distributed throughout cavity 13 such that it is in thermal communication with both phase change material 14 and fluid flow plates fluid flow plate 16a or 16b, to enhance the thermal transfer between phase change material and fluid flow plates 16a or 16b. Such thermally conductive material may include metallic packing, material, metallic foam or wool, or a graphite composite, for example. Such material may be fixed or abutted to a fluid flow plate to ensure thermal communication, and where loose packing material is selected, for example, then the conductivity is generally determined by the orientation and packing of the material such that there may be at least one pathway of thermal communication from the material to a fluid flow plates, such that the majority of the material is in some manner in thermal communication with the fluid flow plates.

Figure 9 shows a perspective view of a fluid flow plate 16a with baffles 60 as vertically oriented fins. Figure 9 shows the side of fluid flow plate 16a facing cavity 13. Only one instance if baffles 60 is called out in Figure 9, for clarity.

Figure 10 is a cross-section view of a stacked thermal energy storage apparatus from the front side according to one embodiment. Figure 10 shows a stack configuration of a thermal energy storage apparatus 10, comprised of a plurality of bases (three shown in Figure 10) with associated fluid flow plates and end plates, to complete a stacked arrangement of unit cells to comprise a stacked thermal energy storage apparatus 10D. Going from left to right, the stacked thermal energy storage apparatus 10D shows end plate 18a, a fluid flow plate 16b and base 12. On the right hand side of the left hand base 12, is disposed a fluid flow plate 16a, a central end plate 18d and then fluid flow plate 16b. Continuing on, is another base 12, a fluid flow plate 16a, a central end plate 18d, fluid flow plate 16B, base 12, fluid flow plate 16a and end plate 18a. The stacked thermal energy storage apparatus 10d is configured such that the base units share the central end plates 18d. Also in this configuration, but not shown, compression fastener(s) or fittings 50 may compress the entire stacked thermal energy storage apparatus 10d with one such compression fastener or fitting. For example, compression fastener or fitting comprised of through bolts would run through the elements listed above and compress the thermal energy storage apparatus 10d stack. Also shown in Figure 10 is a single heat exchange inlet port 30d for each base 12 where heat exchange fluid enters base 12 via heat exchange inlet port 30d which then traverses a portion of base 12 before turning and entering the fluid flow plates 16a and 16b on either side of the particular base 12. Seals and films may be employed in such a stacked thermal energy storage apparatus 10d, as is described above, but are not shown for clarity. Further, the number of bases within a single stacked thermal energy storage apparatus may be selected by a person of ordinary skill in the art for a particular application. Stacked thermal energy storage apparatus may be configured such that each base unit cell operates independently, where it is preferable that central end plates 18d are thermally insulating to thermally isolate the adjoining base unit cells or stacked thermal energy storage apparatus may be configured such that the base unit cells operate collectively, where it is not required that central end plates 18d are thermally insulating.

Figures 1 1 , 12 and 13 show a thermal energy storage apparatus 100, according to at least one illustrated embodiment.

The thermal energy storage apparatus 100 comprises a housing

102, one or more actuators 104, and a heat exchanger 106. The housing 102 is composed of a unitary body 108 and a cover plate 1 10.

The unitary body 108, which can be denominated as a bucket, is preferably a unitary (i.e., single piece construction), including a number of walls that delineate an interior or cavity 1 12 from an exterior 1 14 of the unitary body 108. The unitary body 108 preferably comprises a non-reactive material, for example a plastic, for instance a thermoplastic (e.g., polypropylene, high density polyethylene (HDPE)) or a thermosetting plastic, which may or may not take the form of a reinforced plastic material, for instance a resin reinforced with fibrous material (e.g., carbon fiber, fiberglass). The unitary body 108 can be formed via various molding techniques, for example injection molding, reaction injection molding, cast molding, therm oforming, or compression molding.

Alternatively, the unitary body 108 can comprise other materials, for example various metals.

The unitary body 108 is preferably completely sealed at a bottom

1 16 thereof, and along any side edges 1 18 (only one called out) thereof.

Preferably, the unitary body 108 has only a single opening 120, located at a top 122 thereof, to provide access to the interior or cavity 1 12 during manufacture or assembly of the thermal energy storage apparatus 100. The unitary body 108 may include a peripheral flange 124 about the top 122 thereof, to facilitate mechanical coupling of the cover plate 1 10 thereto.

The cover plate 1 10 is positioned over the opening 120 of the unitary body 108 and secured thereto under compression via one or more compression fasteners 126 (only one called out for clarity). Compression fasteners 126 may be a set of through bolts which engage or penetrate the cover plate 1 10 and the peripheral flange 124 of the unitary body 108 via through-holes, which compression fasteners 126 are then secured with nuts 128 (only one called out for clarity) to apply a general compression force across the elements, as shown in Figure 1 1 . Alternatively, bands (e.g. , metal band, spring steel band) may circumscribe the cover plate 1 10 and the unitary body 108 to apply a general compression force across the respective elements of thermal storage apparatus 100.

Alternatively or additionally, the cover plate 1 10 can be either adhesively joined or fusion bonded (e.g., welded, brazed, soldered) to the unitary body 108. These bonds would also act as inherent seals, therefore a gasket or O-ring may be omitted.

One or more gaskets or seals 130 (Figure 1 1 ) may be positioned between the cover plate 1 10 and the peripheral flange 124 of the unitary body 108. For example, an annular or generally closed-loop gasket may be positioned between the cover plate 1 10 and the peripheral flange 124 of the unitary body 108. The seal 130 can be substantially flat, even when uncompressed. Alternatively, the seal 130 may have a generally circular or oval cross-section (e.g., O-ring), particularly where one or both of the cover plate 1 10 and, or the peripheral flange 124 of the unitary body 108 have a recess 132 (Figure 1 1 ) sized and dimensioned to partially receive the seal therein,

The cover plate 1 10 may include a port 134 which may be a sealed cap or threaded cap, for example, allowing for pouring in phase change material (not illustrated in Figures 1 1 or 12) or for the removal of phase change material from cavity 1 12. In use, phase change material is disposed in cavity 1 12. Phase change material may not fill the entirety of cavity 1 12, but rather may leave a vapour space 136 above the phase change material, as illustrated in other implementations described herein.

The cover plate 1 10 includes a heat exchange fluid inlet 138a in fluid communication with heat exchanger 106. The cover plate 1 10 includes a heat exchange fluid outlet 138b in fluid communication with heat exchanger 106. The heat exchange fluid inlet 138a and heat exchange fluid outlet 138b may both be conveniently accessible from a top of the thermal storage apparatus 100.

The cover plate 1 10 may include a fitting 142 to fluidly couple to a pressure balance reservoir (not shown), for example via a flexible hose (not shown). The pressure balance reservoir can be employed to pressure balance the air/vapour space 136 in the cavity 1 12. The source of pressure may be the result of thermal expansion of the phase change material and, or, due to increased vapour pressure of the liquid phase change material at elevated temperature.

The cover plate 1 10 may include a fitting 140 to thermally or fluidly couple a temperature sensor (not shown) thereto to determine a temperature of a phase change material contained inside cavity 1 12. The cover plate 1 10 includes an aperture, denominated as spring port 144, from which a portion of the actuator 104 extends from the interior of cavity 1 12 to the exterior 1 14 of the thermal storage apparatus 100.

When assembled, the heat exchanger 106 is positioned in the interior of cavity 1 12 of the housing 102, sealed therein by the cover plate 1 10, and typically submerged in the phase change material when in operation. The heat exchanger 106 preferably has a large surface area relative to a volume thereof, for example employing a plurality of heat exchange structures 146 (only one called out for clarity), for example fins or pins, that have a large surface area relative to a volume of the respective heat exchange structures. The heat exchanger 106 may take a variety of forms, for example, the outward facing finned plates heat exchanger illustrated in Figures 1 1 -13, the finned tubing heat exchanger illustrated in Figures 14-15, inward facing finned plates (either double or single sided with fins), pinned plates, or the flat channel plates illustrated, for instance in Figure 1 . As illustrated, the heat exchanger 106 preferably has a body (e.g., opposed plates 148a, 148b (Figure 12) secured to one another via fusion bonding (e.g., welding, brazing, soldering), adhesive, fasteners, and, or compression bands) 148 that forms a fluid flow path 149 (Figure 13) for heat exchange fluid therethrough. The fluid flow path 149 is preferably a circuitous fluid flow path 149, extending from one portion of the body 148 to another portion of the body 148 and traversing at least a majority of the body 148 of the heat exchanger 106. The body 148 of the heat exchanger 106 can be similar or even identical to the flow plates previously described, however positioned as a structure within the cavity 1 12 and spaced from the walls thereof.

The heat exchange structures (e.g., fins) 146 may extend laterally outward from the body 148 of the heat exchanger 106, and may be aligned vertically in the cavity 1 12. That is, the heat exchange structures (e.g., fins) 146 may extend at least partially from at least proximate the bottom 1 16 of the unitary body 108 toward the cover plate 1 10. The heat exchange structures (e.g., fins) 146 may extend only partially laterally across the cavity 1 12, to prevent forming isolated pockets therebetween.

The actuator 104 includes an extendable extension spring 150 and a rod 152. The extendable extension spring 150 is located within cavity 1 12 and at least partially contained within phase change material. Extendable extension spring 150 is fixed to body 108 by mechanical engagement of a tab 154. At the other end, extendable extension spring 150 engages rod 152. Rod 152 extends through spring port 144, located in the cover plate 1 10, and is collared and otherwise sealed above cover plate 1 10 by seal 156 (Figure 12). While only a single actuator 104 is illustrated, some implementations may include two or more actuators.

Extendable extension spring 150 is moveable between an unextended conformation or configuration at the resting unactuated or unextended state, for instance with the windings of extendable extension spring 150 in physical contact with one another. It is believed that extendable extension spring 150 in a conformation where the windings of extendable extension spring 150 are in physical contact with one another applies a local pressure that maintains phase change material in the solid state, in isolation from the surrounding bulk phase change material, even when heated above the melting temperature. In such a conformation or configuration, extendable extension spring 150 spontaneously contains at least one seed crystal of phase change material in the solid state.

Extendable extension spring 150 may be actuated from a relaxed state or configuration, e.g., in which the windings of extendable extension spring 150 are generally in physical contact with one another, to an extended state or configuration in which at least some of the windings of extendable extension spring 150 contained within phase change material are separated from one another. Extendable extension spring 150 may be actuated manually, or may be actuated with a solenoid or other mechanical or electro-mechanical motor or servo or the like to extend extendable extension spring 150 upon demand.

The thermal storage apparatus 100 advantageously provides a structure that allows "drop in" assembly.

For example, the thermal storage apparatus 100 may be assembled by positioning the heat exchanger 106 and actuator 104 in the unitary body 108 via the opening 120 therein, then positioning the cover plate 1 10 over the opening 120, and fastening the cover plate 1 10 to the unitary body 108, either with or without a gasket therebetween. Phase change material may be added to the cavity 1 12 either via the opening 102, before positioning the cover plate 1 10, or can be added via the port 134 after fixing the cover plate 1 10 to the unitary body. A temperature sensor may be coupled to the corresponding fixture either before the cover plate 1 10 is positioned, or after the cover plate 1 10 is positioned. Coupling to the heat exchange fluid inlet 138a and heat exchange fluid outlet 138b may be made after assembly, as can a coupling to a pressure reservoir.

Even more advantageously, the heat exchanger 106 and, or, the actuator 104 may be first be secured to the cover plate 1 10. For instance, the heat exchanger 106 may be physically coupled to the cover plate 1 10 via one or more fixtures that form the fluid inlet and outlet 138a, 138b. Also for instance, one or more bearings may be carried by the cover plate 1 10 and closely slideably receive the rod 152 of the actuator 104, either with or without stops that limit axial travel thereof to a defined amount. The heat exchanger 106 and, or, the actuator 104 are then dropped into the cavity as the cover plate is positioned over the opening 120. The cover plate 1 10 is then fastened to the unitary body 108, either with or without a gasket therebetween. Coupling to the heat exchange fluid inlet 138a and heat exchange fluid outlet 138b may be made after assembly. Phase change material may be added to the cavity 1 12 either via the opening 102, before positioning the cover plate 1 10, or can be added via the port 134 after fixing the cover plate 1 10 to the unitary body. A temperature sensor may be coupled to the corresponding fixture either before the cover plate 1 10 is positioned, or after the cover plate 1 10 is positioned. Coupling to the heat exchange fluid inlet 138a and heat exchange fluid outlet 138b may be made after assembly, as can a coupling to a pressure reservoir.

In operation, the thermal storage apparatus 100 may function in a similar fashion to the various other implementations described herein.

Figures 14, 15 and 16 show a thermal energy storage apparatus 200, according to at least one illustrated embodiment.

The thermal energy storage apparatus 200 comprises a housing 202, one or more actuators 204, and a heat exchanger 206. The housing 202 is composed of a unitary body 208 and a cover plate 210.

The unitary body 208, which can be denominated as a bucket, is preferably a unitary (i.e., single piece construction), including a number of walls that delineate an interior or cavity 212 from an exterior 214 of the unitary body 208. The unitary body 208 preferably comprises a non-reactive material, for example a plastic, for instance a thermoplastic (e.g., polypropylene, high density polyethylene (HDPE)) or a thermosetting plastic, which may or may not take the form of a reinforced plastic material, for instance a resin reinforced with fibrous material (e.g., carbon fiber, fiberglass). The unitary body 208 can be formed via various molding techniques, for example injection molding, reaction injection molding, cast molding, thermoforming, or compression molding.

Alternatively, the unitary body 208 can comprise other materials, for example various metals.

The unitary body 208 is preferably completely sealed at a bottom 216 thereof, and along any side edges 218 (only one called out) thereof.

Preferably, the unitary body 208 has only a single opening 220, located at a top 222 thereof, to provide access to the interior or cavity 212 during manufacture or assembly of the thermal energy storage apparatus 200. The unitary body 208 may include a peripheral flange 224 about the top 222 thereof, to facilitate mechanical coupling of the cover plate 210 thereto. The cover plate 210 is positioned over the opening 220 of the unitary body 208 and secured thereto under compression via one or more compression fasteners 226 (only one called out for clarity). Compression fasteners 226 may be a set of through bolts which engage or penetrate the cover plate 210 and the peripheral flange 224 of the unitary body 208 via through-holes, which compression fasteners 226 are then secured with nuts 228 (Figure 16, only one called out for clarity) to apply a general compression force across the elements, as shown in Figure 14. Alternatively, bands (e.g., metal band, spring steel band) may circumscribe the cover plate 210 and the unitary body 208 to apply a general compression force across the respective elements of thermal storage apparatus 100.

Alternatively or additionally, the cover plate 210 can be either adhesively joined or fusion bonded (e.g., welded, brazed, soldered) to the unitary body 208. These bonds would also act as inherent seals, therefore a gasket or O-ring may be omitted.

One or more gaskets or seals 230 (Figure 14) may be positioned between the cover plate 210 and the peripheral flange 224 of the unitary body 208. For example, an annular or generally closed-loop gasket may be positioned between the cover plate 210 and the peripheral flange 224 of the unitary body 208. The seal 230 can be substantially flat, even when uncompressed. Alternatively, the seal 230 may have a generally circular or oval cross-section (e.g., O-ring), particularly where one or both of the cover plate 210 and, or the peripheral flange 224 of the unitary body 208 have a recess 232 (Figure 14) sized and dimensioned to partially receive the seal therein,

The cover plate 210 may include a port 234 which may be a sealed cap or threaded cap, for example, allowing for pouring in phase change material (not illustrated in Figures 14 or 15) or for the removal of phase change material from cavity 212. In use, phase change material is disposed in cavity 212. Phase change material may not fill the entirety of cavity 212, but rather may leave a vapour space 236 above the phase change material, as illustrated in other implementations described herein.

The cover plate 210 includes a heat exchange fluid inlet 238a in fluid communication with heat exchanger 206. The cover plate 210 includes a heat exchange fluid outlet 238b in fluid communication with heat exchanger 206. The heat exchange fluid inlet 238a and heat exchange fluid outlet 238b may both be conveniently accessible from a top of the thermal storage apparatus 200.

The cover plate 210 may include a fitting 242 to fluidly couple to a pressure balance reservoir (not shown), for example via a flexible hose (not shown). The pressure balance reservoir can be employed to pressure balance the air/vapour space 236 in the cavity 212. The source of pressure may be the result of thermal expansion of the phase change material and, or, due to increased vapour pressure of the liquid phase change material at elevated temperature.

The cover plate 210 may include a fitting 240 to thermally or fluidly couple a temperature sensor (not shown) thereto to determine a temperature of a phase change material contained inside cavity 212.

The cover plate 210 includes an aperture, denominated as spring port 244, from which a portion of the actuator 104 extends from the interior of cavity 212 to the exterior 214 of the thermal storage apparatus 200.

When assembled, the heat exchanger 206 is positioned in the interior of cavity 212 of the housing 202, sealed therein by the cover plate 210, and typically submerged in the phase change material when in operation. The heat exchanger 206 preferably has a large surface area relative to a volume thereof, for example employing a plurality of heat exchange structures 246 (only one called out for clarity), for example fins or pins, that have a large surface area relative to a volume of the respective heat exchange structures. The heat exchanger 206 may take a variety of forms, for example, the finned tubing heat exchanger illustrated in Figures 14-15, the outward facing finned plates heat exchanger illustrated in Figures 1 1 -13, inward facing finned plates (either double or single sided with fins), pinned plates, or the flat channel plates illustrated, for instance in Figure 1 . As illustrated, the heat exchanger 206 preferably has a serpentine conduit 248 that provides a circuitous a fluid flow path 249 (Figure 15) for heat exchange fluid therethrough.

The heat exchange structures (e.g., fins) 246 may extend laterally outward from the serpentine conduit 248 of the heat exchanger 206, and may be array in the cavity 212. The heat exchange structures (e.g. , fins) 246 may extend at least partially from at least proximate the bottom 216 of the unitary body 208 toward the cover plate 210. The heat exchange structures (e.g., fins) 246 may extend only partially laterally across the cavity 212, to prevent forming isolated pockets therebetween.

The actuator 204 includes an extendable extension spring (not visible and a rod 252. The extendable extension spring is located within cavity 212 and at least partially contained within phase change material. Extendable extension spring is fixed to body 208 by mechanical engagement of a tab (not visible). At the other end, extendable extension spring engages rod 252. Rod 252 extends through spring port 244, located in the cover plate 210, and is collared and otherwise sealed above cover plate 210 by seal 256 (Figure 15). While only a single actuator 204 is illustrated, some implementations may include two or more actuators.

Extendable extension spring is moveable between an unextended conformation or configuration at the resting unactuated or unextended state, for instance with the windings of extendable extension spring in physical contact with one another. It is believed that extendable extension spring in a

conformation where the windings of extendable extension spring are in physical contact with one another applies a local pressure that maintains phase change material in the solid state, in isolation from the surrounding bulk phase change material, even when heated above the melting temperature. In such a conformation or configuration, extendable extension spring spontaneously contains at least one seed crystal of phase change material in the solid state.

Extendable extension spring may be actuated from a relaxed state or configuration, e.g., in which the windings of extendable extension spring are generally in physical contact with one another, to an extended state or configuration in which at least some of the windings of extendable extension spring contained within phase change material are separated from one another. Extendable extension spring may be actuated manually, or may be actuated with a solenoid or other mechanical or electro-mechanical motor or servo or the like to extend extendable extension spring upon demand.

The thermal storage apparatus 200 advantageously provides a structure that allows "drop in" assembly.

For example, the thermal storage apparatus 200 may be assembled by positioning the heat exchanger 206 and actuator 204 in the unitary body 208 via the opening 220 therein, then positioning the cover plate 210 over the opening 220, and fastening the cover plate 210 to the unitary body 208, either with or without a gasket therebetween. Phase change material may be added to the cavity 212 either via the opening 202, before positioning the cover plate 210, or can be added via the port 234 after fixing the cover plate 210 to the unitary body. A temperature sensor may be coupled to the corresponding fixture either before the cover plate 210 is positioned, or after the cover plate 210 is positioned. Coupling to the heat exchange fluid inlet 238a and heat exchange fluid outlet 238b may be made after assembly, as can a coupling to a pressure reservoir.

Even more advantageously, the heat exchanger 206 and, or, the actuator 204 may be first be secured to the cover plate 210. For instance, the heat exchanger 206 may be physically coupled to the cover plate 210 via one or more fixtures that form the fluid inlet and outlet 238a, 238b. Also for instance, one or more bearings may be carried by the cover plate 210 and closely slideably receive the rod 252 of the actuator 204, either with or without stops that limit axial travel thereof to a defined amount. The heat exchanger 206 and, or, the actuator 204 are then dropped into the cavity as the cover plate is positioned over the opening 220. The cover plate 210 is then fastened to the unitary body 208, either with or without a gasket therebetween. Coupling to the heat exchange fluid inlet 238a and heat exchange fluid outlet 238b may be made after assembly. Phase change material may be added to the cavity 212 either via the opening 202, before positioning the cover plate 210, or can be added via the port 234 after fixing the cover plate 210 to the unitary body. A temperature sensor may be coupled to the corresponding fixture either before the cover plate 210 is positioned, or after the cover plate 210 is positioned. Coupling to the heat exchange fluid inlet 238a and heat exchange fluid outlet 238b may be made after assembly, as can a coupling to a pressure reservoir.

In operation, the thermal storage apparatus 200 may function in a similar fashion to the various other implementations described herein.

The above description of illustrated examples, implementations, and embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed.

Although specific examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art.

Many of the methods described herein can be performed with variations. For example, many of the methods may include additional acts, omit some acts, and/or perform acts in a different order than as illustrated or described.

The various examples, implementations, and embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary, to employ systems, circuits, devices, methods, and concepts in various patents, applications, and

publications to provide yet further embodiments. U.S. Patent Application Serial No. 15/21 1 ,878, filed July 15, 2016, is incorporated herein by reference in its entirety.

These and other changes can be made to the examples, implementations, and embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.

Accordingly, the claims are not limited by the disclosure.