Field of the Invention

The invention relates to a heat store in the form of a canister which accommodates a phase change material and which can be located within a reservoir to be in heat exchange relationship with a heat transfer liquid.

Background

The use of a phase change medium for the purpose of heating or cooling is well known. The present invention relates to a heat exchange reservoir which accommodates a phase change material for the purpose of heating a heat transfer liquid. One such application comprises a heat exchange reservoir which can be used to heat water. A difficulty that has been experienced in the past with such heat exchange reservoirs is their weight. Because of their weight they present a problem when it comes to installation since they may require specialised lifting equipment, including cranes, when being installed.

A solution to this problem is to provide the reservoir in an unassembled form in order that it can be installed on site. However, because of their nature the assembly of a reservoir on site requires specialised personnel and can be labour intensive.

Disclosure of the Invention

Throughout this specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. According to one aspect, the invention resides in a canister which is intended in use to be accommodated within a reservoir of a heat store, the reservoir defines a substantially closed space having an inlet and an outlet, the space intended in use to receive a heat exchange liquid which is to be delivered into the space through the inlet, and from the space though the outlet, wherein in use the space accommodates a plurality of canisters, each canister being sealingly closed and accommodating a phase change medium, each canister being formed of a thermally conductive material which does not react with either the heat exchange liquid or the phase change medium, each canister being arranged and configured to be able to withstand the pressures created by the phase change material as a result of both the change in temperature of the phase change material and the change in phase of the phase change material.

Preferably the phase change medium has a melting temperature within the range of temperatures to which the heat exchange liquid is to be heated.

Preferably the canister is cylindrical in shape.

According to a preferred feature of the invention each canister incorporates a diffusion means to diffuse temperature between the central portion of the canister and the walls of the canister. Preferably the diffusion means is in the form of at least one thermally conductive element. Preferably the interior of the canister supports the at least one thermally conductive element which extends between the walls of the canister and the central portion of the canister and wherein the thermally conductive element is formed of a thermally conductive material which does not react to the phase change medium. According to a preferred feature of the invention the conductive element comprises a set of vanes which extend radially from a central support. According to a preferred feature of the invention the central support is in the form of a hollow tube, said vanes extending radially from the outer face of the tube. According to a preferred feature of the invention the conductive element extends for substantially the full length of the interior of the canister. According to a preferred feature of the invention an end of the canister is removable to open the interior of the canister, said conductive element being dimensioned to be capable of being inserted into the canister through the end. According to a preferred feature of the invention the conductive element is formed of the same material as the canister.

A significant problem associated with utilising the heat generated during the exothermic stage of a phase change is associated with maximising the heat transfer from the central region of the phase change medium to the outer region. The present invention overcomes this issue by incorporating a diffusion means to assist in diffusing the heat generated from the central portion of the phase change medium to the outer region. The diffusion means would also reduce the time taken for the endothermic stage of the phase change.

According to a preferred feature of the invention the quantity of phase change material is sufficient to substantially fill the canister when the phase change material is in its liquid form. According to a preferred feature of the invention the quantity of phase change material is sufficient to substantially fill the canister when the phase change material is in its liquid form and is at the maximum anticipated operating temperature of the reservoir.

According to a preferred feature of the invention the canister is formed of aluminium.

According to a preferred feature of the invention the canister is formed of stainless steel.

According to another aspect, the invention resides in a heat store comprising a reservoir defining a closed space, the reservoir having an inlet and an outlet, the space intended in use to receive a heat exchange liquid which is to be delivered into the space through the inlet and from the space though the outlet, the space accommodating a plurality of canisters of the form as described above. According to a preferred feature of the invention the wall of the reservoir is provided with an opening associated with a closure, whereby said canisters can be introduced into the reservoir and withdrawn from the reservoir though said opening.

According to a preferred feature of the invention said canisters are all of the same configuration and substantially similar internal volume.

According to a preferred feature of the invention the canisters are randomly supported within the reservoir.

According to a preferred feature of the invention the canisters are contained within an enclosure which is removably received in the reservoir, said enclosure having openings in its walls, said openings dimensioned sufficiently to permit a free flow of said heat exchange fluid through the walls whilst preventing the movement of said canisters from the enclosure. According to a preferred feature of the invention the enclosure is formed of a porous or perforate fabric material. According to a preferred feature of the invention the enclosure is formed of a net or mesh-like material.

According to one embodiment of the above aspect of the invention the canisters are cylindrical in shape.

According to a preferred feature of the invention said canisters are supported within the reservoir in a fixed array. The array may comprise at least one set of canisters supported within the reservoir by a support element which is non-fixedly supported within the reservoir.

According to a preferred feature of the invention a first end of each canister is formed to be receivable in an opening in the support element so as to be grippingly engaged thereby. According to a preferred feature of the invention the first end is formed with an axially directed, generally annular, rib having a radially and outwardly directed flange thereon wherein the flange is receivable though the opening with resilient deformation of the opening to enable the canister to be retained by the support element. According to a preferred feature of the embodiment the rib is circumferentially continuous. According to a preferred feature of the embodiment the opening is formed with radial protrusions which are engagable with the rib axially inward of the flange.

According to a preferred feature of the invention the support element comprises a planar element formed with said openings.

According to preferred feature of the embodiment the second end of the canister is concave. According to an alternative preferred feature of the embodiment the second end of the canister is convex.

According to a preferred feature of the invention the reservoir accommodates a number of sets of canisters. According to a preferred feature of the invention the sets are stacked one upon the other. According to a preferred feature of the invention the reservoir has opposed ends interconnected by a side wall wherein the cross-section of the reservoir is substantially constant between the ends, wherein one end can be removed, said support element having a configuration substantially conforming to the cross sectional configuration of the reservoir, said sets being received in the reservoir in a longitudinal array between the ends. According to a preferred feature of the invention the inlet delivers said liquid into one end portion of the reservoir and the outlet receives liquid from the other end portion of the reservoir.

According to a preferred feature of the invention the reservoir is pressurised. According to an alternative feature of the invention the reservoir is not pressurised.

According to a preferred feature of the invention the heat exchange liquid comprises potable water and the canisters are formed of stainless steel. According to a preferred feature of the invention the heat exchange liquid comprises a secondary heat exchange liquid and the reservoir is associated with a secondary heat exchanger having a first exchange circuit for the secondary heat exchange liquid and a second heat exchange circuit for potable water

According to one aspect, the invention resides in a canister which is intended in use to be accommodated within a reservoir of a heat store, each canister being sealingly closed and accommodating a phase change medium, each canister being formed of a thermally conductive material which does not react with either the heat exchange liquid or the phase change medium, each canister being arranged and configured to be able to withstand the pressures created by the phase change material as a result of both the change in temperature of the phase change material and the change in phase of the phase change material, each canister incorporating a diffusion means to diffuse heat between a central portion of the canister and an outer portion of the canister.

According to one aspect, the invention resides in a canister adapted to accommodate a phase change medium, the canister incorporating a diffusion means to diffuse heat between a central portion of the canister and an outer portion of the canister.

According to one aspect, the invention resides in a canister adapted to accommodate a phase change medium, the canister incorporating a diffusion means to diffuse heat between a central portion of the canister and an outer portion of the canister, the canister being charged with the phase change material sufficient to substantially fill the canister when the phase change material is in its liquid form and is at the desired operating temperature of the reservoir.

According to one aspect, the invention resides in a heat store reservoir comprising a plurality of canisters as herein before described. The invention will be more fully understood in the light of the following description of several specific embodiments.

Brief Description of the Drawings

The description is made with reference to the accompanying drawings of which:

Figure 1 is a schematic sectional side elevation of a heat exchange reservoir according to a first embodiment of the invention;

Figure 2 is a schematic sectional side elevation of a heat exchange reservoir according to a second embodiment of the invention;

Figure 3 is an upper partial isometric view of a heat exchange reservoir according to a third embodiment showing a portion of a side wall removed and an closure at one end in an exploded position;

Figure 4 is a partial lower isometric view of the reservoir of the third embodiment showing the side wall and base of the reservoir in a cut away form;

Figure 5 is a sectional isometric view of a canister for use in the reservoir according to the third embodiment;

Figure 6 is an isometric view of a set of canisters supported from a support element according to the third embodiment;

Figure 7 is an enlarged view of a first end of the canister as it is received in the support element according to the third embodiment

Figure 8 is a sectional isometric view of the canister which can be used in each of the embodiments; and

Figure 9 is a partial isometric exploded view of the canister of Figure 8. Detailed Description of Specific Embodiments

The embodiments described below relate to a heat store reservoir whereby the heat store may be used to heat a heat exchange liquid that may pass through the reservoir. Obviously the reservoir is only able to store a quantity of heat energy. Once this quantity has been depleted, the heat energy in the reservoir may be replenished. One way in which the heat energy may be replenished is by heating the heat exchange liquid and passing the heated heat exchange liquid through the reservoir so as to 'recharge' the heat store reservoir.

Each of the reservoirs described in the embodiments comprise a plurality of canisters, each filled with a phase change material. The canisters are accommodated within the reservoir which is adapted to have a heat exchange medium, such as water, flow therethrough. The water is in heat exchange relationship with the phase change material in the canisters, for reasons which will be discussed below.

To facilitate the introduction of heat into the canisters to recharge the reservoir heated heat exchange medium flows through the reservoir. The heated exchange medium is carried by a heat exchange circuit which is in heat exchange relationship with a heat source such as a solar collector or heat pump to heat the water.. The heat source may be provided external the reservoir (e.g. solar) or within the reservoir (e.g. heat coil located near the reservoir inlet).

The heat from the heat exchange medium is absorbed by the phase change material. With the absorption of sufficient heat the phase change material will melt into a liquid. Whilst in the liquid phase the phase change material stores both the sensible heat which has been applied to it as well as the latent heat. The reservoir then acts as a heat store, providing a convenient means to store the heat energy until heat is required. To extract the heat (e.g. for the purpose of heating another source of water) the heat exchange medium is accommodated within another circuit which is in heat exchange relationship with a water reservoir.

In the case of the first embodiment as shown at figure 1 the reservoir 11 defines a closed space and has an inlet 19 and an outlet 21. The space defined by the reservoir is intended to receive a large number of sealed canisters 23.

Each canister is filled with a phase change medium such as sodium acetate tri- hydrate, which has a crystallisation temperature of the order of 58°C. When filling the canisters with the phase change material the canister and the phase change material is heated to generally the maximum temperature anticipated for the application before the canister is sealed.

The canisters are formed of an aluminium alloy which is substantially un-reactive to the heat exchange liquid within the reservoir and the phase change material. Each canister is configured such that it will be able to withstand the pressures exerted upon it as a result of the temperature changes likely to occur within the reservoir and the phase changes of the material. Each canister is of an identical form and has a cylindrical shape with a concave lower end wall 25 and cap 26 which is applied to the first end to sealingly close the canister.

In addition as shown at figures 8 and 9 the interior of each canister accommodates a diffuser means in the form of a thermally conductive element 41.

The purpose of the conductive element is to at least partially overcome the difficulties associated with the low coefficient of thermal conductivity of the phase change material, both in the liquid and solid phases. The conductive element 41 is formed of aluminium and comprises a central tube 43 having a set of radially extending vanes 45 formed on its outer face. The diameter of the conductive element is such that it can be inserted into the first end of the open canister before the cap 26 is applied. The conductive element is formed of aluminium. The reservoir also comprises an inlet 19, which opens into the lower end of the reservoir, and an outlet 21 which opens into the upper end of the reservoir.

The canisters are accommodated within the reservoir in random manner as shown. Such an arrangement serves to induce a turbulent flow through the reservoir and maximise the exchange of heat between the heat exchange fluid and the canisters. Once the canisters are located within the reservoir the reservoir is sealed and the reservoir is such that the interior can be pressurised.

The second embodiment shown in figure 2 is similar to the first embodiment with the exception that in use the reservoir is not pressurised and an upper end of the reservoir can be removed to facilitate access to the canisters.

According to a variation of the first and second embodiments the canisters are accommodated within one or more bag-like enclosures which are formed of a mesh or net like material. The use of such enclosures facilitates the introduction and possible later removal of the canisters into and from the reservoir.

The third embodiment of the invention, as shown in figures 3, 4, 6 and 7, is directed to a heat store which can be readily installed on site without the need of specialised lifting equipment and specialised personnel.

The third embodiment comprises a reservoir 11 which is of a generally cubic form having an upper end wall 13 and a lower end wall 15 and side walls 17, defining a space having a generally square cross section. The upper end wall is removable to facilitate access into the interior of the reservoir and is associated with suitable fixing means and seals to enable it to close the reservoir to define a sealed space within the reservoir.

The upper portion of one side wall accommodates an inlet pipe 19 and an outlet pipe 21. The inlet and outlet pipes are intended to be removably mounted into the side wall. The space defined by the reservoir is intended to receive a large number of sealed canisters 23.

As shown in figure 7, once the cap is applied to the first end the upper end face of the closed canister defines an annular rib 27 which extends axially from the first end. The outer end of the rib is formed with a radially outwardly directed flange 29.

The canisters are arranged in sets where each set is supported from a planar support element 31 which has a configuration generally complementary to the cross sectional shape of the reservoir. In addition the support element 31 is formed with a set of openings 33 which have a diameter corresponding or greater than the outer diameter of the flanges 29 on the canisters. The inner edge of each opening is formed with a set of angularly spaced protrusions 35 which are resiliently deformable to permit the rib 27 of the canister to be pushed through the aperture. The protrusions then engage underneath the flange to resist disengagement of the canister from the support element 31.

The openings are arranged in an array to enable a number of canisters to be supported from the support element to depend there from in closely spaced relationship. The support provided by the support element enables a space to be provided between the sides of the canister to enable the heat exchange liquid to readily flow between the canisters. As shown particularly in figure 7, once the canisters are in place, the openings of the support element 31 are not completely blocked. This facilitates the flow of the heat exchange liquid through the space and serves to restrict fluid flow past the support elements 31. This promotes thermal stratification between the sets of canisters during the heating phase, and minimises channelling of the flow of heat exchange fluid through the reservoir.

The depth of the space of the reservoir is sufficient to accommodate several sets of said canisters in a stacked arrangement as shown in Figures 3 and 4. The inlet pipe 19 is formed with an inner axial extension 37 which extends from the upper end of the reservoir to the lower end. As best shown in figure 3 the extension 37 is received in aligned openings in the support elements which are not associated with canisters.

In addition the lower end of the space supports a heater coil 39 to heat the incoming heat exchange medium when recharging the heat store. The heating coil can be electrically powered or can comprise a heat pump or can be heated by a flow of heated fluid through the coil.

According to an alternative embodiment of the invention the canisters are formed of stainless steel and the heat exchange medium comprises potable water.

Each embodiment provides a heat store which (if required) can be readily installed on site without the need for specialised personnel or lifting equipment. For example the third embodiment can be provided as a kit of parts comprising:

• a reservoir with the upper end ready to be removed;

• inlet and outlet pipes;

• support elements; and

• canisters.

Once the kit has been delivered to the site of installation, the canisters can be inserted into the support elements to form the sets of canisters. In so doing the corresponding opening of the support elements which is to receive the inlet pipe is left vacant. The upper wall of the reservoir is removed and the sets of canisters are stacked into the reservoir with the vacant openings of the support elements aligned. The inlet pipe is then installed by having its inner extension inserted into the vacant openings before being sealingly fixed to the side wall. The outlet pipe is also sealingly fixed into the side wall. The upper wall is then sealingly fixed to the upper end of the reservoir and the assembly is complete.

According to an alternative embodiment which is a variation of the third embodiment the reservoir, support elements and canisters can have any desired configuration.

According to an alternative embodiment which is a variation of the third embodiment the inlet and outlet can be fixed into position in the upper portion wall of the reservoir without the inner extensions of the first embodiment and the extensions can be located in position on site.

According to an alternative embodiment which is a variation of the third embodiment the inlet and outlet can be fixed into position in the wall of the reservoir at opposite ends to avoid the necessity to install them into the reservoir on site.

The present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent products, formulations and methods are clearly within the scope of the invention as described herein. In addition the shape of the canisters and the reservoir need not be restricted to the particular shape of the canisters or reservoir of the embodiment.