Improved thermal energy storage unit

Abstract

A thermal energy storage unit includes a hollow conduit for allowing flow of a heat transfer fluid (HTF) through it. The conduit can hold a plurality of phase change material-filled (PCM-filled) containers arranged within the conduit to allow flow of HTF over the PCM- filled containers throughout the conduit. A major axis of at least a part of a container located along one side of the conduit is oriented at a first angle relative to a longitudinal axis of the conduit and a major axis of at least a part of a container located along an opposite side of the conduit is oriented at a second angle to the longitudinal axis, the second angle being a straight angle or having an opposite direction to the first angle, such that flow path of the HTF over the PCM-filled containers is spiral shaped.

Description

TITLEIMPROVED THERMAL ENERGY STORAGE UNITFIELD

[0001] The present invention relates to the field of thermal energy storage.BACKGROUND

[0002] Thermal energy storage (TES) is an important component of modern energy management. The use of thermal energy storage can optimize energy use, reduce energy costs, and enhance the reliability and sustainability of the power grid, thus facilitating the use of renewable energy sources. The use of TES can help smooth out energy demand curves by supplying stored thermal energy during peak demand periods, reducing the need for expensive peaker power plants thereby reducing carbon emissions and lowering electricity costs. TES systems can help deal with variability in heating and cooling loads in buildings and other facilities while minimizing the energy required for heating, ventilation and air conditioning (HVAC) systems.

[0003] One type of thermal energy storage technology known as “encapsulated ice”, includes the use of a plurality of containers or capsules containing a phase change material (PCM), such as water, for storing latent thermal energy and a heat transfer fluid (HTF), such as a glycol solution, for exchanging heat with the PCM (water / ice for example) inside the capsules.

[0004] “Encapsulated ice”-based systems are currently limited by poor heat transfer capabilities between the PCM and HTF, e.g., due to an imperfect design that provides a small heat exchange surface area, or uneven HTF flow passages between the capsules, thus reducing the efficiency of the thermal energy storage.SUMMARY

[0005] Embodiments of the invention provide a thermal energy storage unit having an improved design which provides a high ratio of phase change material (PCM) to heat transfer fluid (HTF) volume and an increased HTF flow path over PCM-filled containers, therebyexpanding the effective heat exchange surface area. The thermal energy storage unit design, according to embodiments of the invention, also produces multiple turbulent flows which increase heat exchange between the PCM and HTF thereby improving the efficiency of the thermal energy storage.

[0006] In one embodiment of the invention, a thermal energy storage unit includes a hollow conduit for allowing flow of HTF through it. The conduit is configured to hold a plurality of phase change material-filled (PCM-filled) containers arranged within the conduit to allow flow of the HTF over the PCM-filled containers throughout the conduit. Some of the containers are arranged adjacently along one wall or side of the conduit and are oriented at a first angle relative to a longitudinal axis of the conduit and other containers are arranged adjacently along an opposite wall or side of the conduit and are oriented at a second angle to the longitudinal axis of the conduit. The second angle is either a straight angle or has an opposite direction to the first angle. This arrangement of PCM-filled containers within the hollow conduit ensures that flow of the HTF over the PCM-filled containers is in a spiral path.

[0007] The first angle may include, for example, any angle between 5° to 80°, e.g., any angle between 10° to 80° or 5° to 60° or 30° to 60°, in relation to the longitudinal axis of the conduit and the second angle may be a 90° angle or, for example, any negative angle (relative to the longitudinal axis of the conduit) between 90 and 5 degrees.

[0008] In one embodiment, the arrangement of PCM-fdled containers within the conduit is at diverted angles in relation to a longitudinal axis of the conduit. For example, one set of adjacent containers is arranged at a positive 45° angle and an opposing set of adjacent containers is arranged at a negative 45° angle, all in relation to the longitudinal axis of the conduit.

[0009] The thermal energy storage unit, according to one embodiment, has adjacent PCM- filled containers arranged along parallel axes within a hollow conduit. In one example, the parallel axes of one group of containers arranged along a side of the conduit, are oriented at a positive angle of between 5° to 80° , e.g., 10° to 80°, 5° to 60° or 30° to 60° or, preferably of about 45°, in relation to a longitudinal axis of the conduit and the parallel axes of a another group of containers arranged along an opposing side of the conduit, are at a negative angleof, for example, between -60° to -30°, preferably of about -45° in relation to the longitudinal axis of the conduit, such that a fluid passage is provided between the adjacent PCM- filled containers in spiral and divided spiral paths. The properties of the PCM-filled containers and their arrangement within the conduit, enable a consistent flow of HTF throughout the conduit, which facilitates heat transfer between the HTF and PCM within the conduit.

[0010] The hollow conduit may be curvilinear shaped, for example, a cylinder tube. In other embodiments, the hollow conduit may be polygon (e.g., rectangular) shaped. The PCM-filled containers may be, for example, semi-ellipses (e.g., half or quarter ellipses) or semi- polygonal or rectangular, in correspondence with the shape of the hollow conduit. Several pairs of PCM-filled containers arranged along parallel axes within the conduit, form fluid passages which create multiple spiral flows of HTF through the conduit that divide into a plurality of spirals that can intertwine with each other. Flow of the HTF through the conduit also includes a plurality of spirals spanning the length of the inner perimeter of the conduit. The plurality of different and intertwining spiral flows of HTF enabled by embodiments of the invention, suggests an efficient arrangement of PCM-filled containers in a hollow conduit which greatly increases the turbulence of the HTF thereby enhancing heat exchange between the PCM and HTF and improving the efficiency of the thermal energy storage.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will now be described in relation to certain examples and embodiments with reference to the following illustrative figures so that it may be more fully understood. In the drawings:

[0012] Figs. 1A-1H schematically illustrate a thermal energy storage unit which includes a cylindrical conduit with PCM-filled containers arranged within, according to some embodiments of the invention;

[0013] Figs. 2A, 2B and 2C schematically illustrate a thermal energy storage unit which includes a rectangular conduit with rectangular PCM-filled containers arranged within, according to additional embodiments of the invention;

[0014] Fig. 3 schematically illustrates a thermal energy storage unit which includes a hexagonal conduit with semi-hexagonal PCM-filled containers arranged within, according to yet other embodiments of the invention;

[0015] Figs. 4A-4I schematically illustrate different PCM-filled containers, according to embodiments of the invention;

[0016] Figs. 5A, 5B and 5C schematically illustrate, correspondingly, exemplary PCM-filled containers, two adjacent containers and a plurality of adjacent containers in a conduit, according to embodiments of the invention;

[0017] Fig. 6A and 6B schematically illustrate, correspondingly, fluid passages formed by PCM-filled containers arranged within a conduit and the fluid flow enabled in the in the spaces formed by the container arrangement in the conduit, according to embodiments of the invention;

[0018] Figs. 7A and 7B schematically illustrate spiral fluid flows within the conduit, according to embodiments of the invention;

[0019] Fig. 8 schematically illustrates an array of connected energy storage units, according to an embodiment of the invention; and

[0020] Fig. 9 schematically illustrates a thermal energy storage system including a thermal storage energy unit, according to embodiments of the invention.DETAILED DESCRIPTION

[0021] Embodiments of the invention, some of which are exemplified in the description below, include a thermal energy storage unit which includes a hollow conduit, such as a tube, for allowing flow of a heat transfer fluid (HTF) through it and phase change material (PCM)- filled containers arranged within the conduit such that the HTF flows over heat exchanging surfaces of the containers.

[0022] Cooled HTF is typically flowed through the conduit to cause a phase change of PCM (e.g., solidifying or freezing) within the containers during an energy storing or charging stage. Warm HTF can be flowed through the conduit to melt frozen PCM within the containers during an energy harvesting or discharging stage. A charging stage is typically completed when all or most of the PCM within the containers is frozen and a discharging stage istypically completed when the warm HTF has reached a desired cold temperature, e.g., 5° Celsius.

[0023] The shape and arrangement of PCM-filled containers within the conduit, according to embodiments of the invention, creates a highly turbulent flow which increases heat exchange between the PCM and HTF, thereby improving the efficiency of the energy charging and discharging.

[0024] In one example, a thermal energy system (e.g., a HVAC system) which utilizes an energy storage unit or system according to embodiments of the invention, contains a fluid distribution system which may include one or more pumps, pipes, flow control mechanisms (such as valves) and monitoring components for monitoring, for example, temperatures and flow rates inside the thermal energy system. A chiller, which may be, e.g., an air-cooled or water-cooled chiller, is connected to the thermal energy system. During a charging stage, HTF is flowed through the chiller to cool the HTF and the cooled HTF is pumped from the chiller and is directed to flow through a conduit of an energy storage unit, to cause freezing of PCM within the PCM-filled containers located within the conduit. After the charging stage, the temperature of the HTF used for charging increases. The now warmed HTF is pumped out of the energy storage unit and can be directed back to the chiller to be cooled again.

[0025] During a discharging stage, water or another heat transfer fluid can be cooled by the frozen PCM, e.g., by using a storage unit or system according to embodiments of the invention as a heat exchanger. The cooled water or other fluid may then be directed to cool a load at an end-user, e.g., at a facility such as a building.

[0026] In one embodiment, HTF includes an antifreeze mixture designed to achieve a desired (low) temperature without freezing. Solutions that may be used as a HTF, include, for example, ethylene glycol or propylene glycol solutions with water. PCM is typically designed to freeze and / or stay frozen at a desired temperature to enable storing cool-type energy and discharging the energy per requirement (e.g., demands of a cooling system (e.g., HVAC) and / or facility using embodiments of the invention). The PCM may include, for example, paraffin, water or a mixture of water and eutectic solutions. In some embodiments, the PCM may include water mixed with an ice nucleation agent such as silver iodide or quartz.

[0027] Units and systems according to embodiments of the invention, are used to store energy and release it, e.g., during peak hours and / or upon demand. Units and systems according to embodiments of the invention can be installed in facilities such as office buildings, residential buildings, shopping malls, airport terminals, factories, server rooms, etc. Thus, embodiments of the invention can be used as a “behind the meter” system providing power on-site without passing through a meter.

[0028] In the following description, various aspects of the present invention will be described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of the present invention. However, it will also be apparent to one skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may be omitted or simplified in order not to obscure the present invention.

[0029] Figs. 1A-H, 2A-C and 3 schematically show thermal energy storage units according to embodiments of the invention. In the embodiments exemplified in Figs. 1A-H, thermal energy storage unit 100 includes a hollow conduit, such as tube 101, for allowing flow of HTF therethrough. In this example, tube 101 is curvilinear, e.g., cylinder shaped, however, in other embodiments the tube may be polygon or otherwise shaped. For example, unit 200 shown in Figs. 2A-2C includes a rectangular shaped tube 201 and thermal energy storage unit 300 shown in Fig. 3 includes a hexagonally shaped tube 301. Tubes 101, 201 and 301 may each include ports (such as port 15 shown in Fig. 1H) at opposing ends to enable inlet and outlet of HTF to the conduit and out of the conduit.

[0030] A conduit according to embodiments of the invention may be flexible. For example, a polyethylene pipe may be used as a hollow conduit according to embodiments of the invention. It should be noted that a curvilinear conduit, more than polygonal shaped conduits, can withstand high pressure from within, providing an especially robust conduit for an “encapsulated ice”-based thermal energy storage unit, where containers within the conduit go through many expansion / contraction cycles.

[0031] For example, a 315 millimeter (mm) diameter polyethylene pipe having a wall 12mm thick, which may serve as a conduit in embodiments of the invention, can withstand pressure of 6 bar.

[0032] The conduit is configured to hold a plurality of PCM-filled containers (also referred to herein as PCM-containing capsules).

[0033] Figs. 1 A-F are isometric views and Fig. 1G is a top view showing one or more pair(s) of semi-oval or semi-ellipse PCM-filled containers, such as capsules 102, 132 and 142 arranged within cylinder shaped tube 101 and capsules 152 and 162 (which are quarter-oval or quarter-ellipse PCM-filled containers, as shown in Fig. 1H), arranged within cylinder shaped tube 101.

[0034] In another example, Fig 2A depicts a cross section showing a pair of rectangular PCM-filled containers, such as rectangular capsules 202 arranged within rectangular-shaped tube 201. Fig. 2B depicts a cross section showing several pairs of rectangular capsules 202 arranged within tube 201 and Fig. 2C is an isometric view showing several pairs of rectangular capsules 202 arranged within tube 201. In yet another example, Fig. 3 is an isometric view showing several pairs of semi-hexagonal PCM-filled containers, such as semi-hexagonal capsules 302 arranged within a hexagonally shaped tube 301.

[0035] Typically, PCM-fdled containers are arranged within a conduit such that major axes of PCM-filled containers or of parts of containers located along one side of the conduit are oriented at a first angle relative to a longitudinal axis of the conduit and major axes of PCM- filled containers or of parts of containers which are located along an opposite side of the conduit, are oriented at a second angle to the longitudinal axis of the conduit. The second angle can be a straight angle or an angle having an opposite direction to the first angle.

[0036] In one embodiment, the first angle may be any angle between 5° to 80° in relation to the longitudinal axis of the conduit. In the examples illustrated in Figs. IB, 2B and 3 capsules 102’, 202’ and 302’ located along one side of tube 101, 201 and 301 (correspondingly) each have a major axis 11 that is oriented at a 45° angle to longitudinal axis X of the tube they are in , whereas capsules 102”, 202” and 302” located along an opposite side of tube 101, 201 and 301 (correspondingly) each have a major axis that is oriented at a -45° angle to the longitudinal axis X. The first and second angles need not be of the same absolute value. For example, as illustrated in Fig. 1C, capsules 102’ are positioned at a 45° angle relative to longitudinal axis X, whereas capsules 102”, which are located along an opposite side of tube 101, are positioned at a 90° angle relative to the longitudinal axis X.

[0037] In another example, which is illustrated in Fig. ID, part 112 of capsule 102 is located along one side of tube 101. A major axis 11’ of part 112 is positioned at a 90° angle relative to the longitudinal axis X, whereas a major axis of another part 122 of capsule 102, which is located along an opposite side of tube 101, is positioned at a 45° angle relative to the longitudinal axis X.

[0038] In yet another example, which is schematically illustrated in Fig. IE, part 112 is positioned at a first angle of between 5° to 80°, possibly between 10° to 80° or 5° to 60° or 30° to 60°, relative to the longitudinal axis X of tube 101, whereas another part 122 of capsule 102, which is located along an opposite side of tube 101, is positioned at a same or different angle relative to longitudinal axis X, but is diverted (e.g., is at an opposite direction) relative to the first angle.

[0039] The PCM- filled containers or parts of the containers located along one side of a conduit (e.g., tube 101, 201 or 301) may be of the same or similar or different dimensions than containers or parts of containers located along the opposite side of the conduit. For example, as schematically illustrated in Fig. IF, which is an isometric view of tube 101 and in Fig. 1G, which is a top view from one end of tube 101, PCM-containing capsules 132 are not the same size or volume as PCM-containing capsules 142. A minor axis M of one or more of capsules 132 that are located along one side of tube 101 is not the same as a minor axis M’ of one or more capsules 142 located along the opposite side of tube 101.

[0040] In some embodiments, at least some of the PCM-filled containers have a minor axis which is substantially equal to half of a nominal size (e.g., as detailed below) of the conduit (e.g., tubes 101, 201 or 301).

[0041] PCM-filled containers configured to be inserted into a hollow conduit (such as a curvilinear shaped conduit) may have a first edge configured to match the shape of the conduit (e.g., the first edge may be curved) and an opposing edge which does not match the shape of the conduit (e.g., the opposing edge may be straight). Between the two edges, the capsules typically have two surfaces (capsule walls) with a surface area that is larger than the other surfaces of the capsule. The surfaces of the capsule act as heat exchanging surfaces. The capsules are typically situated within a conduit such that the capsule edges face theconduit walls and the two larger surfaces face the conduit ends which include inlet and outlet ports.

[0042] For example, PCM- containing capsules (such as capsules 102, 202 and 302), according to some embodiments of the invention, each have a substantially straight edge along a major axis of the capsule and an opposing edge which is configured to match the contour of the tube in which they are placed. For example, PCM-containing capsules 102 typically each have a straight edge 103 along a major axis 11 of capsule 102 and a convex (e.g., curved or oval) opposing edge 113 to match the curve of the cylinder- shaped tube 101. Capsules 202 each have a straight edge 203 along a major axis of the capsule 202 and an opposing edge 213 which is straight, to match the contour of rectangular shaped tube 201. Capsules 302 each have a straight edge 303 along a major axis of the capsule 302 and an opposing edge 313 which is semi-hexagonal, to match the contour of hexagonally shaped tube 301. Other shaped tubes and capsules may be used.

[0043] Hollow conduits, according to embodiments of the invention, can be characterized by a nominal size which describes an inner dimension of the conduit, e.g., an inner diameter or inner height or width. Each of tubes 101, 201 and 301 has a nominal size and a longitudinal axis (X). In cylindrical tubes (such as tube 101) the nominal size is typically the inner diameter (d) of the tube. In polygonal shaped tubes (such as tubes 201 and 301) the nominal size is typically the inner height or the width (w) of the tube. In some embodiments, each of the PCM-containing capsules 102, 132, 142, 202 and 302 has a major axis which is substantially the same as or longer than the nominal size of the tube. For example, a major axis of a PCM-containing capsule may be 1.004 -5.75, possibly 1.15 -2, preferably, 1.4 times the length of the nominal size of the tube. Thus, PCM-containing capsules 102, 132, 142, 202 and 302 can fit into tubes 101, 201 and 301 (correspondingly) at an angle from 5° to 90°, preferably 45°, to the longitudinal axis (X) of the tube. Adjacent capsules can be arranged along parallel axes Al and A2 (shown in Fig. IB) within the conduit. Typically, axis Al is at a positive angle from 30° to 60°, preferably 45°, and A2 is at a negative angle from 30° to 60°, preferably 45°, relative to the longitudinal axis (X) such that the capsules are fixed in place and fluid passage is provided between the adjacent PCM-containing capsules or parts thereof.

[0044] In other embodiments, PCM-containing capsules or parts of the capsules have a major axis which is shorter than the nominal size of the tube, such that more than one capsule may be arranged (possibly one on top of each other) along each side or wall of the tube, e.g., as schematically illustrated in Fig. 1H. PCM-containing capsules 152 and 162 are both arranged along one side of tube 101, at an angle to a longitudinal axis of tube 101, as described herein. Having more than one capsule or capsule parts arranged along one side of a hollow conduit provides additional fluid passages 160 for HTF, between the capsules or capsule parts, which may increase the spiral flows of HTF through the conduit.

[0045] In some embodiments, one or more spacer(s) is located between adjacent PCM-filled containers located along one side and / or opposite side of the conduit. The spacer, may be any suitable block or wedge that can be placed between adjacent containers to provide a space between the adjacent containers or a spacer may be part of a construct that keeps containers apart to provide a space between the adjacent containers. In some embodiments, the spacer may be filled with PCM to provide additional heat exchanging surfaces within a conduit.

[0046] Figs. 4 A-I depict isometric views of some exemplary PCM-containing capsules, according to embodiments of the invention.

[0047] PCM-containing capsules 402A, 402B, 402C1, 402C2, 402D, 402E, 402F, 402G, 402H and 4021 are configured to be inserted into a hollow conduit having HTF flow through it. The capsules may be pre-filled with PCM via a filling inlet, e.g., inlet 443 shown in Fig. 4B and Fig. 4C.

[0048] A PCM-filled container such as the capsules described herein, typically has a first edge configured to match the shape of the hollow conduit (also referred to herein as a tube) and an opposing edge which does not match the shape of the conduit. For example, capsules 402A, 402B, 402C1, 402C2, 402D, 402E, 402H and 4021 are configured to be inserted into a curvilinear shaped hollow conduit and each have one edge that is curved to match the curve of a curvilinear shaped hollow conduit, and another edge that is not curved. Capsules 40 IF and 402G are similarly configured to be inserted into a polygon-shaped conduit. Having one edge that matches the shape of the conduit provides flexibility because it enables arranging PCM-filled containers in a hollow conduit along opposing sides or walls of the conduit, where the conduit may be of any desired curvature or shape. The other edge, which does notmatch the shape of the conduit, enables efficient fluid passage between capsules arranged along the opposing sides of the conduit, as further described herein.

[0049] The capsules exemplified herein each have an edge configured to match a contour of a conduit and an opposing edge which is a straight edge along a major axis of the capsule, however the opposing edge need not be straight. Other shaped edges may be used if they allow efficient fluid passage between capsules arranged along opposing sides of a conduit.

[0050] For example, the PCM-containing capsules 402A, 402B, 402C1, 402C2, 402D, 402E, 402H and 4021 have a straight edge 403 along a major axis of the capsule and a curved or circular opposing edge 413 to match the curve of a cylinder-shaped tube. Capsule 402F has a straight edge 403 along a major axis of the capsule 402F and an opposing edge 413F which is straight, to match the contour of a rectangular tube. Capsule 402G has a straight edge 403 along a major axis of the capsule 402G and an opposing edge 413G which is semi-hexagonal, to match the contour of a hexagonal shaped tube.

[0051] In one embodiment, a PCM-containing capsule includes two capsule-shaped bodies each capsule-shaped body having a straight edge along a major axis of the body (which is also a major axis of the capsule) and an opposing edge configured to match a contour of a tube, where the two capsule-shaped bodies are attached to each other at a center of their straight edge forming an X-like shape. For example, PCM-containing capsule 402E, which is schematically illustrated in Fig. 4E, includes two capsule-shaped bodies 46 and 48, each capsule-shaped body having a straight edge 403 along a major axis of the capsule and an opposing edge 413E configured to match a contour of a cylinder-shaped tube. The two capsule-shaped bodies 46 and 48 are attached to each other at the center C of their straight edge, forming an X-like shape.

[0052] The capsules have a major axis 41 and a minor axis 42, as shown in Fig. 4A. In some embodiments of the invention, the minor axis 42 is substantially equal to an inner radius of the tube, or to half of the nominal size of the tube. In polygonal shaped tubes half of the nominal size of the tube is essentially the apothem of the tube. The length of the major axis 41 may be substantially 1.4 times the length of the nominal size (e.g., inner diameter) of the tube, such that the capsules can be placed in the tube at an angle of substantially 45° to a longitudinal axis of the tube. In other embodiments, the length of the major axis 41 may be1.15 or 2 (or any number in the range between 1.15 and 2) times the length of the nominal size of the tube, such that the capsules can be placed in the tube at an angle of substantially 30° or 60° (or any angle within this range) to a longitudinal axis of the tube. In yet other embodiments, the length of the major axis 41 may be 1.004 or 5.75 (or any number in the range between 1.004 and 5.75) times the length of the nominal size of the tube, such that the capsules can be placed in the tube at an angle of substantially 5° or 80° (or any angle within this range) to a longitudinal axis of the tube. In some embodiments, capsules have a major axis that is substantially the same as the nominal size of the tube, such that the capsules can be placed in the tube at a 90° angle relative to the longitudinal axis of the tube. In some embodiments, as schematically exemplified in Fig. 4C, the length of the major axis 41 may be a fraction of the length of an inner diameter of the tube, however, more than one capsule may be located in tandem along a wall or side of the tube such that their major axes 41 when combined may be 1.004 or 5.75 (or any number in the range between 1.004 and 5.75) times the length of an inner diameter of the tube. For example, the combined length of capsules 402C1 and 402C2 when they are placed one on top of the other, may be higher than the length of an inner diameter of a tube. Capsules 402C1 and 402C2 may be positioned (one on top of another) along a wall or side of a tube at an angle (both capsules at the same angle) relative to a longitudinal axis of the tube.

[0053] Any of capsules 402A, 402B, 402C1, 402C2, 402D, 402E, 402F, 402G, 402H and 401 may be designed such that when two or more adjacent capsules are arranged along parallel axes within the tube (and possibly are in physical contact with each other), a space is formed between the adjacent capsules to enable HTF flow between the adjacent capsules. Typically, a space is also formed between the capsule perimeters and the inner boundary or perimeter of the tube.

[0054] In some embodiments, the capsules may include a protruding portion which enables the space between adjacent (and possibly touching) capsules to be formed. The protruding portion may be on an outer perimeter 410 of the capsule, for example protruding portion 411 as shown in Figs. 4A, 4C, 4F and 4G. In other embodiments, the protruding portion is on a wall of the capsule, for example, protruding portion on wall 420, as shown in Fig. 4B. In this example, the protruding portion includes a plurality of protrusions 421 which may bedistributed on the two larger surfaces of the capsule, e.g., on wall 420 and the opposing wall of the capsule (not shown). The protrusions 421 may be, for example, ellipse or dome shaped.

[0055] In the embodiment schematically shown in Fig. 4D, the walls 420 and 420’ (typically the two larger walls) of the capsule are concaved such that when adjacent capsules 402D, touch each other, a space is formed between the adjacent capsules due to the concaved walls.

[0056] In the embodiment shown in Figs. 4H and 41, the two larger surfaces of the capsule 402H and 4021 (namely walls 420 and 420’, correspondingly) include groves 415 which can provide a space in between adjacent capsules arranged in a tube, allowing HTF to flow over the capsules and in a spiral along the tube.

[0057] Fig. 5A depicts an isometric view of another exemplary PCM-containing capsule, according to an embodiment of the invention. Capsule 502 includes a protruding perimeter 511 and ellipsoid protrusions 521 on its possibly concaved walls 520 and 520’. Protrusions 521 may be otherwise shaped, e.g., protrusions 521 may be dome shaped. Walls 520 and 520’ are supported by enforcement elements 504 and 504’ located in a central part of the wall, to prevent collapse of the capsule. Enforcement elements 504 and 504’ may also protrude from the surface of the walls they support. In some embodiments, the enforcement element 504 on wall 520 of one capsule 502 is mis-aligned with enforcement element 504’ on wall 520’ of the same capsule 502. However, as shown in Figs. 5B and 5C, when capsules are arranged within a tube 501 at an angle to the longitudinal axis of the tube, the enforcement element 504 of one capsule is aligned with enforcement element 504’ of an adjacent capsule, and protrusions 521 of one capsule are aligned with protrusions 521 of an adjacent capsule to create a space 50 between adjacent capsules, as further described below.

[0058] Fig. 5B shows two adjacent capsules 502 arranged near each other, possibly in contact with each other. Protruding perimeter 511 and enforcement elements 504 and 504’ are first to come in contact with each other and do not allow the (possibly concaved) walls of the adjacent capsules touch each other, thereby creating a space 50 between the walls of the adjacent capsules. Thus, when adjacent PCM-containing capsules are arranged along parallel axes within a tube, a fluid passage is provided between the adjacent PCM-containing capsules, for flow of HTF through the tube. The space 50 may be partially obstructed byprotrusions 521 causing turbulence of the HTF flowing through the fluid passage provided by spaces 50.

[0059] Fig 6A shows a cross section of an arrangement of PCM-containing capsules within a tube having HTF flow through it. The cross section schematically illustrates fluid passages 60 formed by adjacent PCM-containing capsules 602b and 602f arranged within a tube. Due to the regular and repetitive arrangement of the capsules 602b and 602f, an uninterrupted fluid passage along the length of the tube is created by each space between the capsules such that HTF can flow through the fluid passages 60, thereby advantageously maintaining consistent flow of HTF from inlet to outlet.

[0060] As shown in the figures described above and with reference to Fig. 6A, PCM- containing capsules are arranged such that capsules or capsule parts or capsule bodies along one side of a tube, such as capsules 602f, are forward- leaning (e.g., leaning at a positive angle relative to a longitudinal axis of the tube) whereas capsules or capsule bodies arranged along the opposite side of the tube, such as capsules 602b, are backward-leaning (e.g., leaning at a negative angle relative to the longitudinal axis of the tube). This arrangement of capsules in angles of opposite directions, creates spiral shaped fluid passages, as illustrated by the arrows shown in Fig. 6 A.

[0061] Fig. 6B schematically shows the clearance for HTF to flow between capsules 602f and 602b. Fluid paths 61 are HTF streams enabled by spaces 60 between capsules 602f and 602b.

[0062] The arrangement of capsules 602f and 602b causes each space created between two adjacent forward-leaning capsules to be crossed by a space created by two adjacent backward-leaning capsules. Similarly, a space created between two adjacent forward leaning or backward leaning capsules would be crossed by a space created between two adjacent capsules arranged (on an opposite side) at a straight angle relative to a longitudinal axis of a conduit. Thus, one spiral fluid path divides into multiple intertwining spiral paths, as can be seen in Fig. 7A. HTF flowing through a space formed between PCM-containing capsules as described herein, flows in streams 71 that split and then join again, providing increased turbulence. In addition, as schematically shown in Fig. 7B, due to a space between the perimeter of the capsules arranged within the tube 701 and the inner perimeter or boundaryof the tube, a fluid passage is created through a larger spiral 75 which spans the length of the inner perimeter of the tube. This added spiral also contributes to efficient heat transfer.

[0063] Fig. 8 schematically illustrates a thermal energy storage system which includes a plurality of thermal energy storage units 800 in fluid communication. In this example, the energy storage units 800 include cylinder shaped conduits, such as, tubes 801.

[0064] The plurality of units 800 may be stacked one on top of another (and possibly secured to one another) for efficient space utilization at the location of installation of the system, for example in a building or other facility. The units 800 are in fluid communication, e.g., via HTF inlet 83 and HTF outlet 85, to enable cold or warm HTF to sequentially flow from one unit to another. Pipes 804 may lead HTF from one unit 800 to another and / or from a unit 800 to a load.

[0065] In one example of efficient space utilization, pipes 804 may be passed through a space 810 formed between the units 800 and / or between storage units 800 and a floor or other surface. Passing one or more of the pipes 804 through space 810 provides several possible benefits: saving floor space and producing a smaller footprint of a thermal storage system which includes thermal storage units and pipes connected to the thermal storage units; protecting the pipes from being damaged by equipment and / or people passing by the system; and providing a shaded passage for the pipes which potentially reduces heating of the pipes, may reduce losses in the thermal storage system and can increasing efficiency of the thermal storage system.

[0066] Fig. 9 schematically shows a thermal storage energy system 910 which can serve as a “behind the meter” solution, namely, a customer-sited storage system that is connected to the distribution system on the customer’s side of the electricity service meter.

[0067] In one embodiment, thermal energy storage system 910 includes one or more thermal energy storage unit 900 and a controller 912. The controller 912 may control, e.g., via pumps and / or valves 913, flow of warm or cold HTF through the conduit of at least one unit 900. Some or all of the units 900 of storage system 910 may be activated in parallel during each charging (freezing) and / or discharging (melting) cycle. Controller 912 may determine thenumber of units through which to flow cold HTF to produce charged units and / or the number of units through which to flow warm HTF, to discharge thermal energy from the units. The determination of the number of units to charge and / or discharge, may be based on a cooling demand 915 from the system.

[0068] Thermal energy storage units 900, according to embodiments of the invention, may include a conduit, e.g., tube, having almost any desired shape, which provides flexibility when installing a thermal energy storage system according to embodiments of the invention. Also, an existing pipe, such as a polyethylene pipe typically used in buildings and constructions, may be used as a conduit in a thermal energy storage unit, which enables easy retrofitting of thermal energy storage systems according to embodiments of the invention.

Claims

CLAIMS1. A thermal energy storage unit comprising: a hollow conduit for allowing flow of a heat transfer fluid (HTF) therethrough, the conduit configured to hold a plurality of phase change material-filled (PCM-filled) containers arranged within the conduit to allow flow of a heat transfer fluid (HTF) over the PCM-filled containers throughout the conduit, wherein a major axis of at least a part of a container located along one side of the conduit is oriented at a first angle relative to a longitudinal axis of the conduit and a major axis of at least a part of a container located along an opposite side of the conduit is oriented at a second angle to the longitudinal axis, the second angle being a straight angle or having an opposite direction to the first angle, such that flow of the HTF over the PCM-filled containers is in at least one spiral path.

2. The thermal energy storage unit of claim 1 wherein the first angle comprises any angle between 5° to 80° in relation to the longitudinal axis of the conduit.

3. The thermal energy storage unit of claim 1 wherein the first angle is a positive angle of approximately 45° relative to the longitudinal axis of the conduit and the second angle is a negative angle of approximately 45° relative to the longitudinal axis of the conduit.

4. The thermal energy storage unit of claim 1 wherein at least some of the PCM-filled containers have a major axis that is within a range of 1.004 - 5.75 times the length of a nominal size of the conduit.

5. The thermal energy storage unit of claim 1 wherein the major axis of the PCM-filled containers is substantially 1.4 times the length of the nominal size of the conduit.

6. The thermal energy storage unit of claim 1 wherein at least some of the PCM-filled containers have a minor axis which is substantially equal to half of the nominal size of the conduit.

7. The thermal energy storage unit of claim 1 wherein at least some of the PCM-filled containers located along the one side of the conduit are of similar or different dimensions than containers located along the opposite side of the conduit.

8. The thermal energy storage unit of claim 1 wherein a minor axis of at least some of the PCM-filled containers that are located along the one side of the conduit is different than a minor axis of PCM-fdled containers that are located along the opposite side of the conduit.

9. The thermal energy storage unit of claim 1 wherein the PCM- filled containers are configured to provide a space between adjacent containers when the adjacent containers are arranged along parallel axes within the conduit and are in physical contact with each other.

10. The thermal energy storage unit of claim 9 wherein the PCM-filled containers each have a protruding portion configured to provide the space between the adjacent containers.

11. The thermal energy storage unit of claim 10 wherein the protruding portion is on a perimeter of the container.

12. The thermal energy storage unit of claim 10 wherein the protruding portion is on a wall of the container.

13. The thermal energy storage unit of claim 1 comprising a spacer located between adjacent PCM-filled containers located along the one side and / or opposite side of the conduit, to provide a space between the adjacent containers.

14. The thermal energy storage unit of claim 1 wherein two larger walls of the PCM-filled containers are concaved.

15. The thermal energy storage unit of claim 1 wherein the conduit is curvilinear shaped.

16. The thermal energy storage unit of claim 1 wherein the conduit is polygonal shaped.

17. The thermal energy storage unit of claim 1 wherein the conduit comprises polyethylene.

18. The thermal energy storage unit of claim 1 wherein the conduit is configured to be in fluid communication with a conduit of another thermal energy storage unit.

19. The thermal energy storage unit of claim 1 wherein the spiral path is made to divide into a plurality of intertwining spiral paths.

20. A PCM-filled container configured to be inserted into a curvilinear shaped hollow conduit having a HTF flow therethrough, the PCM-filled container having a first edge configured to match the curvilinear shape of the conduit and an opposing edge which does not match the curvilinear shape of the conduit.

21. The PCM-filled container of claim 20 wherein the opposing edge is a straight edge.

22. The PCM-filled container of claim 20 comprising a protruding portion configured to provide a space between adjacent containers when arranged along a side of the conduit.

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