WO2011062661A2

WO2011062661A2 - Collapsible hot water storage tank

Info

Publication number: WO2011062661A2
Application number: PCT/US2010/038162
Authority: WO
Inventors: Yan Kunczynski
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-11-23
Filing date: 2010-06-10
Publication date: 2011-05-26
Anticipated expiration: 2012-05-23
Also published as: WO2011062661A3

Abstract

A collapsible thermal storage tank appropriate for solar systems, addressing the need for large capacity at affordable cost, is provided in a modular design which can be easily transported and assembled. The modular design comprises laminated panels in a construction sandwiching an insulation core between thin metal sheets. The laminated panels, some of which fold walls and floor together for simplified assembly, are joined by an innovative clip and gasket design. The structure is liquid-tight without the need for a liner and surfaces are compatible for potable water. High insulation values of R-25 or greater are featured. The lightweight materials and the clip-together assembly make the tank appropriate for private as well as commercial use.

Description

TITLE: COLLAPSIBLE HOT WATER STORAGE TANK

CROSS-REFERENCE TO RELATED APPLICATIONS

This is an international application claiming priority to US Provisional Application 61/263,627, filed 11/23/2009, which is incorporated herein by reference in entirety.

FIELD OF THE INVENTION

This invention relates to thermal storage tanks, and more particularly to large-capacity tanks used in solar hot water installations.

BACKGROUND OF THE INVENTION

Thermal storage tanks have been generally used for residential domestic hot water (DHW). A particular type of hot water tank in increasing use is that forming a part of solar water heating systems. Depending on the amount of sun exposure a particular location receives, solar heating can represent a significant reduction in the cost of fossil-fuel heating. In such a system, a collector receives radiant heat from the sun and transfers it to a water storage tank by means of a heat exchanger, thereupon to be called for as demanded. The storage tank is sized to accommodate not only the heat exchanger, but also the required reservoir to hold the heat.

Solar water heating is one of the simplest and least expensive ways to harness renewable energy, and the potential for this technology lies far beyond DHW. The low energy cost is attractive for such residential uses as space heating and pool heating. Potential industrial uses include breweries, hospitals, Laundromats, and diary farms, to name a few. The energy stored in water in the form of heat can even be used to provide cooling by means of thermally-driven chillers. Buildings are thereby enabled to use solar energy for heating during the winter season and cooling during the summer. When scaled for large capacity, solar could displace significant amounts of non-renewable energy sources, such as natural gas, oil, and coal-derived electricity, while generating large savings in cost and carbon credits for bonus. Developments in low-pressure systems have made system components more affordable. The water system in the average installation operates with a pressure which delivers the water in a service flow when a valve or tap is turned on. The pressure comes from line pressure delivered to the installation, or, otherwise, from a pressurized bladder inside a storage tank. In some modern systems, however, some or all of the pressure can be eliminated by using an on-demand pump. This greatly simplifies a solar heating configuration, for example, wherein pressure-rated seals, fittings, and methods of joining can add appreciable cost. The reduced pressure in such a system need not be more than just enough to slowly circulate water. In such circumstances, the storage, or holding, tank is not required to be a pressure vessel, and can even be open on top to facilitate servicing.

Low pressure also simplifies the construction, and lowers the cost, of the solar collector component. Whereas copper tubing was once used to maintain integrity under pressure, channels can now be provided between two closely spaced metal plates to direct the flow of water in a serpentine path through a flat-plate collector with minimal pressure gradient. Efficiency gains are realized through the water being in direct contact with the irradiated surface and through the increase in the surface area of water-to-conductive-plate contact. The same construction can be used for the heat exchanger. In fact, in the case of the heat exchanger, heat transfer is facilitated by the exposure of both plates in submersion, in contrast to the directional exposure of the collector case.

Traditional system design sizes the collector array for the summer months, or the season of highest sun exposure, and then sizes the storage tank for the average daily requirement during that season. The rule of thumb is 40-80 liters of storage per square meter of collector. If the collector area is over-sized with respect to the storage volume, there is risk for damage to the equipment. The traditional design also requires a non-solar booster heater during the winter months, adding cost to the system and typically involving the use, directly or indirectly, of fossil fuels. Further, the water storage is frequently inappropriate for potable water since the temperature is typically maintained below that required for the prevention of contamination. Such species as the Legionella bacteria require the maintenance of temperature above 50°C, for example. In such circumstances, a secondary system is needed for potable water.

Design practice in the solar arts is driven by the costs of collectors, storage, and fossil fuel supplementation. The collector component has benefited from new

developments, as discussed above. The largest of these factors, however, is the cost of storage. One way to address storage cost is to allow more heat to be effectively collected and stored while finding more uses for this essentially free energy, such as space heating and cooling. Additional heat storage would eliminate the need for booster heating if the collector were sized for the winter season and matched with increased storage capacity for the summer season. The storage of more heat requires larger and better insulated storage tanks.

For large capacity, a single large tank, as opposed to a farm of smaller tanks, is preferred for the reduction in use of material and exposure of surface area, not to mention the heat retention capability of a massive body of water. A cylindrical tank shape would ordinarily be preferred because it minimizes the surface area to volume ratio. An integral cylindrical tank of any size, however, is difficult to transport and handle. One practical consideration is the narrow passageway represented by the standard thirty inch door frame.

What is needed is a collapsible, lightweight, storage tank solution which can be retrofitted to existing structures and easily assembled in place. The products presently available in the art all have certain deficiencies. STSS Co, for example, provides a cylindrical collapsible tank as large as 1242 liters, potentially serving up to five collectors, in a crate just 48cm in depth. This is achieved by laminating a thin metal sheet to an insulation backing to form a cylindrical sidewall and then folding the sidewall onto itself to form a flat configuration. The problem is, the insulation is limited in thickness by the need to fold it, and, consequently, high R- values cannot be attained.

A polygonal configuration with modular elements solves the problem of folding. In this case, the flat wall sections facilitate a compact configuration when disassembled for bundling. There is an additional advantage, also, of permitting thicker, and more insulative, panels. The branded tank, NovaMAX by Novan™ Solar Inc., for example, provides 300-plus gallon rectangular tanks that can be shipped in sections and bolted together. The sidewalls are faced with aluminum sheeting and backed with two inch insulation having an R-16 value. A liner is provided to seal the inside for water containment. A typical liner material, having good heat resistance, is EPDM

(ethylene-propylene-diene-monomer rubber). The liner, however, adds cost and places a limitation on storage temperature. An EPDM liner, for example, can cost as much as $32US/m² and must be used at 80°C or below.

It is anticipated that efficient installations will ultimately require 200-600 liters of storage capacity for each square meter of collector surface area. This, in turn, will require capacities exceeding 1500 liters and insulation values exceeding R-25. If safe potable water is to be included in the same installation, and if absorption chillers are also to be served, storage water temperatures exceeding 95 °C will be required.

Unitary tanks of this size and capability would be prohibitively large and costly for wide-spread use. As the representative products discussed above suggest, there is an unfulfilled need for easily- assembled, knocked-down, liner-less polygonal tanks which are inexpensive to construct and lightweight to handle and which additionally meet the above requirements for size, R- value and hold temperature.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to reduce costs by taking advantage of stock sizes in such building materials as insulation panels and sheet- metal coils.

It is a further object of the present invention to reduce costs by making a tank lightweight, foldable, and easy to install with hand tools.

It is a further object of the present invention to provide a modular construction facilitating knock-down for shipping and flexibility for capacity-scaling. It is a further object of the present invention to provide tank capacities in excess of 1500 liters, and preferably in the range of 3-34kl.

It is a further object of the present invention to provide tank insulation achieving values in the range of R-25 to R-75.

It is a further object of the present invention to provide a liner-less water-tight sealing means effective at temperatures of 95° C or greater.

It is a further object of the present invention to provide interior contact surfaces compatible with the storage of potable water.

It is a further object of the present invention to provide a storage capacity for at least the heat generated during the summer season by a collector array sized for the winter season at the intended installation location.

It is a further object of the present invention to provide sidewall construction that is sufficiently braced to withstand the hydrostatic pressure of a filled tank.

It is a further object of the present invention to provide spatial accommodation for heat exchangers of standard size in gang configuration.

These objects, and others to become hereinafter apparent, are embodied in a collapsible thermal storage tank for containment of a liquid medium comprising at least one foldable rectangular panel having a first configuration in the shape of a U, the U forming the tank side walls and bottom. The U has a second configuration in the form of flat fold, wherein the side walls are collapsed upon the bottom. The at least one rectangular panel includes three insulation cores, each having an inside face and an outside face. Each outside face is laminated to a first thin metal sheet. The three inside faces are joined to form a strip by lamination to a second thin metal sheet, the strip layout having spaces between insulation cores to accommodate the folds. The second thin metal sheet has flange extensions to form seams with adjoining panels. The collapsible thermal storage tank further comprises two rectangular end panels fitted to the first configuration to enclose the tank. Each end panel includes an insulation core having an inside face and an outside face. Each outside face is laminated to a first thin metal sheet. Each inside face is laminated to a second thin metal sheet, the second thin metal sheet having flange extensions to form seams with the flange extensions of the at least one foldable rectangular panel.

The collapsible thermal storage tank further comprises a plurality of U-shaped clips disposed around the pair of flanges meeting at each rectangular end panel side and bottom corner to seam- wise join each rectangular end panel to the at least one foldable rectangular panel. A plurality of resilient gaskets is disposed between each pair of flanges inside the U-shaped clips, whereby the resilience of the gaskets is sufficient to hold the U-shaped clips in place and to form a liquid-tight seal at each of the corners.

In the preferred embodiment, the collapsible thermal storage tank comprises a plurality of the foldable rectangular panels. The panels are sealingly joined at abutting flanges to modularly increase the volume of the tank. Additionally, the insulation cores are comprised of foam sheets laminated into a composite having an insulation value in the range of R-25 to R-75. Further, the first thin metal sheet is comprised of 0.51mm aluminum sheeting and the second thin metal sheet is comprised of 0.46mm 316L stainless steel.

As this is not intended to be an exhaustive recitation, other embodiments may be learned from practicing the invention or may otherwise become apparent to those skilled in the art.

DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood through the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: FIG. 1 is a perspective view of a collapsible thermal storage tank of the present invention;

FIG. 2 is an exploded view of the collapsible thermal storage tank;

FIG. 3 is a perspective view of the collapsed tank in shipping configuration;

FIG. 4 is a perspective view of a foldable rectangular panel component of the

collapsible thermal storage tank;

FIG. 5 is perspective view of an end panel component of the collapsible thermal

storage tank;

FIG. 6 is a sectional view along the lines 6-6 in Fig. 1;

FIG. 7 is a sectional view along the lines 7-7 in Fig. 1;

FIG. 8 is a partial sectional view showing detail A of Fig. 6;

FIG. 9 is a partial sectional view showing detail B of Fig. 6;

FIG. 10 is a partial sectional view showing detail C of Fig. 7;

FIG. 11 is a perspective view of a corner clamp component;

FIG. 12 is a partial perspective view of a tri-planar outside corner showing seam

detail;

FIG. 13 is a perspective view of a U-shaped clip component;

FIG. 14 is a cross-sectional view of the U-shaped clip compressing a resilient gasket; FIG. 15 is a partial perspective view of a tri-planar inside corner showing seam detail; and

FIG. 16 is a diagram of a solar water heating system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 16 shows a solar water heating system 1 comprised of one or more solar collectors 2 in fluid communication with a hot water storage tank 5 by means of an open loop circulatory pathway 4. The solar water heating system 1 may also include one or more heat exchangers 3 (not shown) in a closed loop configuration. In the preferred embodiment, the hot water tank 5 is a collapsible thermal storage tank 6.

The principal components of the collapsible thermal storage tank 6 are best shown in Fig's 1 and 2. The middle section of the tank is comprised of one or more foldable rectangular panels 7. The middle section is enclosed to form a rectangular vessel by two rectangular end panels 16. The vessel is covered by one or more top covers 19. The panels are joined by a means for sealingly joining 40. The means for sealingly joining 40 includes a means for sealing gaps 50. A means for reinforcing 60 girds the tank to withstand hydrostatic pressure when the tank is filled. Fig. 3 shows the various panels collapsed and stacked to form a shipping configuration.

Fig. 4 shows the foldable rectangular panel 7. The foldable rectangular panel 7 can take a first configuration 8, in which it is shaped in the form of a "U" 9, as the figure illustrates. It can also take a second configuration 10 in the form of a flat fold 11, in which side walls 12 are folded upon a bottom 13 (Fig. 3). In the preferred

embodiment, a folded corner 23 has a radius of approximately 16mm when folded at 90 degrees, corresponding to the first configuration 8, changing to a radius of approximately 8mm when folded at 180 degrees, corresponding to the second configuration 10. The stiffness of the preferred embodiment is such that there is a springy return to 90 degrees.

The foldable rectangular panel 7 is comprised of three insulation cores 20, each having an inside face 21 and an outside face 22. Each outside face 22 is laminated to a first thin metal sheet 30 serving to form a protective cover. The first thin metal sheet 30 is comprised of a second composition 35 in a configuration of a thin metal panel 31. The second composition 35 is preferably aluminum in 0.51mm thickness. The inside faces 21 are joined in a strip by lamination to a second thin metal sheet 32 serving to form a liquid-impermeable, corrosion-resistant, and potable- water- compatible interior surface. The second thin metal sheet 32 is comprised of a first composition 34 in a configuration of a thin metal strip 33. The first composition 34 is preferably 316L stainless steel in 0.46mm thickness. The second thin metal sheet 32 extends beyond the insulation cores 20 on the end-facing sides thereof to form flange extensions 17. The flange extensions 17 form seams 18 (Fig. 15) with adjoining panels. The three insulation cores 20 are arrayed along the strip with separations there between of approximately 2.54cm at the locations of the folded corners 23.

Fig. 5 shows the rectangular end panel 16. Essentially duplicating the laminate structure of the foldable rectangular panel 7, the rectangular end panel 16 is comprised of an insulation core 20 having an inside face 21 and an outside face 22. The outside face 22 is laminated to a first thin metal sheet 30 having the same composition and configuration as that of the foldable rectangular panel 7. The inside face 21 is laminated to a second thin metal sheet 32. The second thin metal sheet 32 has the same composition as that of the foldable rectangular panel 7, but the configuration, in this case, is that of a thin metal panel 31. The second thin metal sheet 32 of the rectangular end panel 16 also has flange extensions 17 extending outward from its two sides and bottom. The flange extensions 17 of the rectangular end panel 16 join with the flange extensions 17 of the foldable rectangular panel 7 to form spaced seams at sidewall corners 14 and bottom corner 15 (see also Fig. 15).

The insulation cores can be comprised of polyurethane, polystyrene, polyethylene, polyolefin, or a combination thereof, but are not limited to these materials. The insulation cores can be comprised of one or more foam sheets cut from standard 120cm X 240cm X 10cm stock sheets and laminated into a composite, but the composite, nevertheless, should not be limited to foam composition or to stock sheet configuration. The composite is anticipated to have insulation value of R-25 or greater, and preferably in the range of R-50 to R-75. In the preferred embodiment, the insulation core 20 is a composite of two 12.7cm foam sheets (20.3cm thickness is illustrated) and the insulation value is nominally R-50. In the preferred embodiment, the second thin metal sheet 32 is cut from a standard 4' wide coil. The first thin metal sheet 30 is rendered from 120cm X 240cm sheets, efficiently matching the layout of the foam sheets. All laminations are bonded with adhesive. The corners in the rectangular outline of the tank are filled-in with insulation plugs having aluminum sheet facings (the plugs are omitted in the drawings to reveal the flange detail). The plugs can be attached by riveting the plug facings to the adjoining panel facings.

The seams 18 are rendered liquid-tight by the means for sealingly joining 40, as illustrated in Fig's 6-15. The means for sealingly joining 40 is comprised of U- shaped clips 41 spanning the length of the side wall corners 14 and the bottom corner 15, as best shown in Fig's 13 and 14. The U-shaped clip 41 compresses, between its arms 42, a resilient gasket 46, placed between the mating flanges 17 in the side wall corners 14 and the bottom corner 15 to form a running length there through (Fig. 7). The arms 42 are angled inward to form narrow opening 43. The angle of arms 42 creates a wedge shape 44 in the resilient gasket 46 when pressed into and through the narrow opening 43 during forceful assembly with the clip. The wedge shape 44 effectively resists the removal of the U-shaped clip 41 while sealing off the joint formed by the flanges 17. The sealed joint is best shown in the cross-sectional view of Fig. 9. In the preferred embodiment, the U-shaped clip 41 is comprised of extruded aluminum. The resilient gasket 46 is comprised of an essentially rectangular silicone strip.

When the middle section of the collapsible thermal storage tank 6 is comprised of more than one foldable rectangular panel 7, whereby the collapsible thermal storage tank 6 is rendered expandable, the seam 18 resulting from abutting flanges 55 has a gap requiring the means for sealing gaps 50. The means for sealing gaps 50 also covers tri-planar corners 56, where gaps occur between runs of the U-shaped clip 41. Fig's 6 and 7 show sectional views through these gaps and provide keys to Detail's A and C, which are shown in Fig's 8 and 10, respectively. The means for sealing gaps 50 is comprised, in each individual case, with a contour-conforming means for clamping 51 and a compressible gasket 45.

In the case of the tri-planar corner 56, shown in Fig's 10-12, the compressible gasket 45 is the resilient gasket 46, which runs continuously through the corner. The contour-conforming means for clamping 51 is corner clamp 52. Corner clamp 52 has a moveable member and a stationary member biased by screws to compress the resilient gasket 46 there between. In the case of the abutting flanges 55, shown in Fig. 8, the compressible gasket 45 is a pair of elastic cords 54. The contour-conforming means for clamping 51, in this instance, is mid-seam batten clamp 53 (Fig. 15). Mid- seam batten clamp 53 is similarly comprised of a pair of members which run the length of the gap inside and outside. The pair of members is biased by a plurality of screws spaced at intervals to uniformly compress the pair of elastic cords nested within channels of the interior member. The corner clamp 52 is fabricated from steel plate. The interior member of the mid-seam batten clamp 53 is machined from 316L stainless steel flat bar. The exterior member is machined from aluminum flat bar. The elastic cord is comprised of approximately 4mm diameter silicone. The collective means for sealing gaps 50 renders the gaps leak-proof, even under hydrostatic pressure from a column of liquid inside the tank. Hydrostatic pressure bearing against the sidewall and end panels will bow them outward, unless the means for reinforcing 60 is applied thereto. The hydrostatic pressure is a function of the height of the stored water in the tank. A low aspect tank, one with a low ratio of height to floor area, will have a lower static resistance requirement, but may also have higher heat or evaporative losses due to higher surface area. Fig's 6 and 7 show a girding framework 61 encircling the tank at a floor level and at a mid- wall level. In the preferred embodiment, the girding framework 61 is comprised of the braces 62. The braces 62 may be comprised of metal, wood, or any material of sufficient modulus. In the preferred embodiment, the braces 62 are constructed with metal beams. The means for reinforcing 60 may additionally include cross-ties 63 (not shown) spanning from sidewall to sidewall. Further, the means for reinforcing 60 may be comprised of the insulation cores 20 themselves. Because the metal sheets are bonded to both sides of the cores, and because the sheets have high tensile strength, the composite structure is rendered thereby stiff and further stiffness is available by layering-up the composite. This has the effect of reducing the beam strength requirement for the braces 62, and may, in the simple module of a single folded rectangular panel 7, eliminate the need for any additional bracing. Lastly, the tank may be buried with the walls supported by backfill. The first thin metal sheet 31 and the corner plugs serve an important structural function, and this is particularly the case when the tank is buried.

In an alternate construction, the sidewalls and bottom can be prepared as separate panels and joined at flange ends by U-shaped clips 41 and resilient gaskets 46 to form two bottom seams. The foldable rectangular panel 7, however, eliminates these two seams and simplifies assembly by prefabricating the sidewalls and bottom. The modular construction with panels provides a convenient way to transport the knocked- down collapsible thermal storage tank 6. The modular panels will easily fit through a standard door frame. The use of foam insulation and thin metal sheets makes the construction lightweight and easily handled. Assembling the panels is a simple matter of pounding the U-shaped clips 41 with a mallet over the flange extensions 17 with the resilient gaskets 46 sandwiched in between, and finishing the sealing by applying the means for sealing gaps 50. It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the preceding description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. While the collapsible hot water tank herein has been discussed in the context of a solar water heating system, it will recognized that the present invention can be used in any water storage context, including that of chilled water. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.

Claims

CLAIMS What is claimed is:

1. A collapsible thermal storage tank for containment of a liquid medium,

characterized by comprising:

at least one foldable rectangular panel having a first configuration in the shape of a U, the U forming the tank side walls and bottom, and a second configuration in the form of flat fold, wherein the side walls are collapsed upon the bottom, the at least one rectangular panel including three insulation cores each having an inside face and an outside face, each outside face laminated to a first thin metal sheet, the three inside faces joined to form a strip by lamination to a second thin metal sheet, the layout of the strip having spaces between the insulation cores to accommodate the folds, the second thin metal sheet having flange extensions to form seams with adjoining panels; two rectangular end panels fitted to the first configuration to enclose the tank, each end panel including an insulation core having an inside face and an outside face, each outside face laminated to a first thin metal sheet, each inside face laminated to a second thin metal sheet, the second thin metal sheet having flange extensions to form seams with the flange extensions of the at least one foldable rectangular panel;

a plurality of U-shaped clips disposed around the pair of flanges meeting at each rectangular end panel side and bottom corner to seam-wise join each rectangular end panel to the at least one foldable rectangular panel; and

a plurality of resilient gaskets disposed between each pair of flanges inside the U-shaped clips, whereby the resilience of the gaskets is sufficient to hold the U- shaped clips in place and to form a liquid-tight seal at each of the corners.

2. The collapsible thermal storage tank of claim 1, wherein a plurality of foldable rectangular panels is sealingly joined at abutting flanges to modularly increase the volume of the tank.

3. The collapsible thermal storage tank of claim 1, wherein the insulation cores are comprised from one or more foam sheets of a standard 120cm X 240cm X 10cm size in a laminated composite.

4. The collapsible thermal storage tank of claim 3, wherein the laminated composite has an insulation value of at least R-25.

5. The collapsible thermal storage tank of claim 3, wherein the laminated composite preferably has an insulation value in the range of R-25 to R-75.

6. The collapsible thermal storage tank of claim 3, wherein the foam sheets are comprised of polyurethane, polystyrene, polyethylene, polyolefin or a combination thereof.

7. The collapsible thermal storage tank of claim 1, wherein the first thin metal sheet is comprised of 0.51mm aluminum sheeting.

8. The collapsible thermal storage tank of claim 1, wherein the second thin metal sheet is comprised of 0.46mm 316L stainless steel.

9. The collapsible thermal storage tank of claim 8, wherein the second thin metal sheet is cut to size from a standard coil of 120cm width.

10. The collapsible thermal storage tank of claim 1, further comprising a top cover having similar laminar construction to that used elsewhere in the tank.

11. The collapsible thermal storage tank of claim 1, wherein the lamination comprises adhesive bonding.

12. The collapsible thermal storage tank of claim 1, wherein the resilient gaskets are comprised of substantially rectangular silicone strips.

13. The collapsible thermal storage tank of claim 1, wherein each U-shaped clip has arms angled so as to form a narrowed opening, the U-shaped clip arms covering the resilient gasket along the length of the seam, the resilient gasket compressed between the arms to form a wedge shape which resists removal of the U-shaped clip from the seam.

14. The collapsible thermal storage tank of claim 1, wherein the gap between U- shaped clips at all tri-planar corners are provided with a means for sealing gaps.

15. The collapsible thermal storage tank of claim 14, wherein the means for sealing gaps is comprised of a compressible gasket and a contour-conforming means for clamping said gasket.

16. The collapsible thermal storage tank of claim 2, wherein the abutting flanges are provided with a means for sealing gaps.

17. The collapsible thermal storage tank of claim 16, wherein the means for sealing gaps is a compressible gasket and a contour-conforming means for clamping said gasket.

18. The collapsible thermal storage tank of claim 1, further comprising a means for reinforcing structure to withstand the hydrostatic pressure of a filled tank.

19. The collapsible thermal storage tank of claim 18, wherein the means for reinforcing is the stiffened structure resulting from the metal sheet lamination to the insulation core.

20. The collapsible thermal storage tank of claim 18, wherein the means for reinforcing is cross-ties spanning the tank at one or more mid-section locations of the walls.

21. The collapsible thermal storage tank of claim 18, wherein the means for reinforcing is girding framework positioned substantially at lower and middle elevations of the tank.

22. The collapsible thermal storage tank of claim 18, wherein the means for reinforcing comprises burying the tank and supporting the walls with fill.

23. A collapsible thermal storage tank for containment of a liquid medium, characterized by comprising: a thin metal strip of a first composition bent into a U-shape to form the tank sides and bottom, the thin metal strip inwardly collapsible to a flat form;

two thin metal panels of the first composition to form the ends of the tank; a means for sealingly joining the two thin metal panels and the thin metal strip to form a unitary container;

a plurality of foam sheets bonded to the exterior flat surfaces of the unitary container; and

whereas the thin metal strip in the flat form and the two thin metal panels are stackable, together with the plurality of foam sheets, to form a compact shipping configuration.

24. The collapsible thermal storage tank of claim 23, wherein the means for sealingly joining comprises flange extensions of the thin metal strip and the two thin metal panels which meet at corners and are joined by U-shaped clips compressing silicone strips positioned between the flange extensions.

25. The collapsible thermal storage tank of claim 23, further comprising thin metal panels of a second composition bonded to the exterior facings of the plurality of foam sheets, the thin metal panels of a second composition serving to provide protection there unto.

26. The collapsible thermal storage tank of claim 23, wherein the first composition is comprised of 316L stainless steel.

27. The collapsible thermal storage tank of claim 23, where in the second composition is comprised of aluminum.

28. The collapsible thermal storage tank of claim 23, wherein the foam sheets have an insulation value in the range of R-25 to R-75.