WO2013030360A2

WO2013030360A2 - A modular phase change material system

Info

Publication number: WO2013030360A2
Application number: PCT/EP2012/067002
Authority: WO
Inventors: Mick MCKEEVER
Original assignee: Dublin Institute Of Technology
Priority date: 2011-09-02
Filing date: 2012-08-31
Publication date: 2013-03-07
Also published as: WO2013030360A3; GB201115174D0; GB2494181A; EP2761235A2

Abstract

The present application provides a modular phase change material system which is suitable for retrofitting to hot water cylinders to improve the energy storage capacity of the cylinder.

Description

TITLE

A MODULAR PHASE CHANGE MATERIAL SYSTEM

FIELD

The present application relates to water heating cylinders and methods of improving their cost efficiency.

BACKGROUND

With an increasing green agenda, there has been a general move towards improving the energy efficiency of buildings.

One problem that has been identified in the energy efficiency of older homes is the age of the space and water heating systems. Homes typically have a hot water cylinder tank to store hot water, and these are normally placed at the centre of the home in the "airing cupboard". The space and water heating systems are coupled and the practice is to heat water with the auxiliary electric heater, termed the Immersion heater, in the months when space heating is not required (April - October). This is generally considered easier to operate by the occupant especially when the heating system is oil fired.

Natural gas fired heating systems tend to be more modern with decoupled space and water heating loops and due to the unlimited availability of gas, these systems may be operated all year round. In older housing stock, cylinder tanks were never insulated and an insulation jacket is retro-fitted by the occupant to combat this problem. Standard insulation jackets are only tied to the tank and are often difficult to fit but go in some way to improve the energy efficiency of the dwelling.

An initiative to improve the energy consumption in the domestic sector by the Irish government is Time of Use (TOU) tariffs for both domestic electricity and domestic gas which is replicated in similar forms in other countries. Whilst TOU tariffs are currently only at a trial stage, it is envisaged that in the future the cost of using electrical energy and natural gas will vary over a 24 hour period. The objective of TOU tariffs is to shift the energy demand profile of the user to times when energy supply exceeds demand, such as at night time when electricity demand is low. One way to achieve this demand shift is to heat the cylinder tank at off-peak times and extract the stored hot water in the cylinder tank for use over the day. Much work has been conducted on solar powered storage tanks and one of the challenges is to keep the tank temperature profile stratified in order to get good heat transfer from the working fluid at the bottom to the tank fluid. One advantage of an electrical heater is that the temperature of the heating element is always above the temperature of the water surrounding it.

When large quantities of hot water are required for a dwelling, the standard procedure is to use a 200-300 litre tank to capture a higher solar fraction. In dwellings in the British Isles, living space is at a premium and accordingly dwellings may not have space for the tank. In contrast, in other countries, for example Germany, all houses must have a basement by law in which the hot water tank may be located.

The central space in the traditional British "Airing Cupboard" is tight and was only designed for tanks up to 150 litres. One technique to reduce the volume to energy ratio, or energy density, is to include PCM within the tank structure. Unfortunately, these systems are generally only applicable when a tank is being retrofitted or a new collector system is being installed. During low season periods, solar collector systems require complimentary heating from an auxiliary heater or space heating system.

The present application is directed at improving the storage efficiency of hot water tanks.

Summary

The present application improves the storage efficiency of hot water tanks providing a Phase Change Material (PCM) system which may be retro fitted to an existing hot water cylinder to improve the thermal storage capacity of the cylinder. More specifically, a module, system and kit employing same are provided in accordance with the claims which follow. A method of retrofitting a phase change material system to a hot water cylinder is also provided.

In a first embodiment, a module is provided for use in a modular phase change material system for fitting to a tank. The module comprises a plurality of reservoirs, each reservoir storing an amount of phase change material and having a heat transfer surface for transferring heat between the reservoir and the tank, wherein each reservoir is articulably connected to adjacent reservoirs so that in use the module may accommodate its shape to the underlying tank so that each heat transfer surface is in contact with the underlying tank. Suitably, the heat transfer surface is triangular in shape. An articulable connection may be provided along the sides of the triangular shape. Suitably, the heat transfer surfaces of each of the reservoirs combine to provide an overall heat transfer surface for the module. In which case, the overall heat transfer surface may be triangular in shape.

The heat transfer surface suitably defines a base of each reservoir and each reservoir extends a height in a direction transverse to the base. Suitably, the length of an edge of the base is in the range 20mm to 45mm. In one exemplary implementation, the length of an edge of the base is 31 mm.

Suitably, the height of the reservoir is between 60 and 90 mm. In one exemplary implementation, the height of the module is approximately 75mm.

A fixing means may be provided for fixing the module to an adjacent module or other feature. Suitably, the phase change material is a paraffin or salt hydrate based phase change material.

A modular phase change material system suitably comprises a plurality of these modules.

In a further embodiment, a modular phase change material system is provided for fitting to a tank. The system suitably comprises a plurality of modules, each module having a surface for abutting with the surface of a tank and each module containing a phase change material, wherein each of the modules are shaped to co-operate with adjoining modules in use so as to cover an upper region of the tank.

The surface for abutting the tank may be substantially triangular in shape.

Each module suitably comprises a plurality of segments with each segment containing a phase change material and each module having a surface for abutting with the surface of a tank. The surface of the module abutting the hot water cylinder may be substantially triangular in shape. A fixing means may be positioned at each corner of the modules to allow fixing with an adjacent module.

In a further embodiment, a kit is provideed for retrofitting a phase change material system to a hot water cylinder. Suitably, the kit comprises a) a plurality of phase change modules, each module storing an amount of phase change material; and b) a bridle for placing about a water outlet of the hot water cylinder to provide a fixing means for the phase change modules.

In a further embodiment, a method is provided for fitting a phase change material system to a hot water cylinder having a water outlet fitting at the top of the cylinder, the method comprising the steps of: a) placing a bridle around the water outlet fitting and closing the bridle to form a loop about the water outlet; b) connecting a PCM module storing an amount of PCM material to the bridle; and c) repeating step b) for one or more PCM modules.

Other advantages and features will become apparent from the description which follows.

DESCRIPTION OF DRAWINGS

A more complete and better understanding of the application will be appreciated from the detailed description which follows and from the accompanying drawings in which:

Fig. 1 is a side view of a conventional hot water cylinder known in the art;

Fig. 2 illustrates how the system of the present application may be employed to provide a reservoir of phase change material about the upper part of a cylinder of the type shown in Fig. 1 ;

Fig. 3 illustrates the placement of a plurality of modules of the present application onto the top surface of a hot water cylinder of the type shown in Fig. 1 ;

Fig. 4 illustrates the placement of a plurality of modules onto the upper side wall of the hot water cylinder of the type shown in Fig. 1 ;

Fig. 5 is a top view of an exemplary module suitable for use in the arrangement of Fig. 3 or 4 made up of a plurality of segments;

Fig. 6 is a side view of the exemplary module of Fig. 5;

Fig. 7 is a side profile view of an exemplary segment from the exemplary module of Fig. 6;

Fig. 7A is a top view of the exemplary segment of Fig. 7;

Fig. 8 is a top view of a frame provided about the exemplary module of Fig. 5;

Fig. 9 is a side view of an exemplary segment incorporating the frame about a section A-A' in Fig. 8;

DETAILED DESCRIPTION OF DRAWINGS

The present application is directed at a solution suitable for retro fitting to existing hot water cylinders of the type in which the cylinder and insulation are not integrally formed together so that the external wall of the cylinder is accessible. It may also be employed where it is possible to remove the insulation in the area to which the present system will be fitted.

A conventional hot water heating cylinder 1 , as shown in Fig. 1 , is substantially cylindrical in shape with a flat bottom surface and a curved top surface. The curved top surface is shaped like a saucer dome. In the exemplary cylinder shown, a pipe fitting 2 is provided in the side wall of the cylinder near the bottom for connecting to a corresponding feed pipe 4, which provides cold water to the cylinder. A further pipe fitting 6 is provided at or near the top from which hot water is drawn off the cylinder through another pipe 8. The water in the cylinder may be heated by an electrical element extending into the cylinder with a mounting 10 on the outside of the cylinder to facilitate the making of electrical connections between the element and a main supply. The cylinder may have other piped connections (not shown), e.g. for connecting water flow from a boiler or solar collector. The cylinder may be covered by an insulation jacket (not shown), sometimes referred to as a lagging jacket, to reduce hear losses.

The present application provides a modular phase change material system 12, which as shown in Fig. 2, in use extends to substantially cover an upper region of the cylinder including the top surface and upper section of the side wall. It will be appreciated from the description that follows that the system does not completely cover the upper region of the cylinder and may leave several areas of the cylinder exposed. Where there is an insulation jacket the modular phase change material system is positioned between the cylinder and the insulation jacket. The effectiveness of the system is significantly reduced if there is no insulation jacket or alternative means of insulation present. It will be appreciated that the system does not necessarily extend beyond half way down the cylinder. The reason for this is that hot water is generally drawn from the top of the cylinder and thus the most efficient use of the a phase change material is towards the top of the cylinder.

The modular phase change material system is used to retain a phase change material in which heat from the cylinder may be stored and returned to the cylinder as the temperature of the water in the cylinder drops.

A wide variety of different phase change materials (PCM) are known and may be employed including for example, organic hydro-carbon based wax such as a paraffin based material. An example of a paraffin based phase change material is that of RT58 sold under the RUBITHERM ® trade mark available from Rubitherm

Technologies GmbH of Berlin, Germany. An alternative PCM material is a salt hydrate such as for example sodium acetate tri-hydrate. It will be appreciated that other PCM materials may also be employed. In use, the system effectively surrounds the upper part of the cylinder. The system has a heat transfer surface which abuts the surface of the cylinder and allows for the transfer of heat between the phase change material and the water in the cylinder through the cylinder wall which is typically a metal such as copper or steel.

As the water in the cylinder is heated above the melting point of the PCM material, energy from the cylinder causes the PCM to melt. This energy may be re-released to the cylinder as the temperature of the cylinder falls below the melting point of the PCM.

It will be appreciated that the present application does not improve the efficiency of the hot water system. However, it can significantly reduce the operating cost of the cylinder by allowing for heating of the cylinder to be shifted from a peak electricity tariff time to an off peak electricity tariff.

Conventionally, heating of water for domestic use can be achieved in a number of ways, through electrical heating, carbon based fuel systems and solar powered renewable technologies.

It has been determined that where solar power is employed, the use of the auxiliary (electrical or gas) heater during low tariff night time is often avoided due to fear that the next day may be sunny. However, where this is not the case then auxiliary power is used at a higher tariff.

The inventor of the present application has determined that by using PCM, the energy storage capacity of an existing domestic water (e.g.136 litre) tank can be increased. In no way is the system envisaged to be more energy efficient than the cylinder alone, rather the present system takes the same energy or possibly slightly more but does so at a cheaper cost to the end user.

Specifically, the present system provides a low cost solution to allow the electrical immersion heater to transfer energy to the tank and PCM at night, which may then be extracted from the tank during the day. This retrofitting solution would be a far cheaper proposal than the costs associated with replacing the tank with a larger new tank including the replacement cost of the cylinder and the cost of labour and disruption or indeed the costs associated with replacing the tank with a larger new tank including the replacement cost of the cylinder and the cost of labour and disruption replacing an existing tank with one in which PCM material is integrated built into the cylinder.

The system is modular in nature with a plurality of modules being used together to cover an area of the hot water tank. Although a variety of different shapes may be employed, the exemplary system described herein is triangular in shape and offers certain advantages. Thus, as shown in Fig. 3, 5 triangular shaped modules 20a-e are linked together to cover the curved surface at the top of the cylinder. The modules are suitably equilateral triangles to facilitate interaction with adjoining modules. The modules may be joined together for example along the edges, so as for example to provide a blanket like feature which may be wrapped around the top or sides of a hot water cylinder. In such a configuration, the blanket may be made up of a plurality of modules each with phase change material reservoirs\segments (as previously described). Alternatively, there may be a single module as such with a plurality of reservoirs and segments. Although this is less desirable as the resulting blanket may not conform readily to the underlying curved surface of the hot water cylinder. The blanket suitably has an opening (slit) from its centre to its perimeter to allow the blanket to be slid into place around the water outlet on the dome of a hot water cylinder. The slit may be closeable by a suitable fastener, e.g. a zip, laced, snap fit, hook and loop (e.g. VELCRO™) type closure. The blanket is shaped such that when placed on cylinder it conforms to and substantially covers the curved top surface

(dome) of the cylinder. The blanket may be formed using a plurality of the previously described triangular modules. In this case, each module may be joined to an adjacent module at their common interface (i.e. adjoining sides of the respective triangles). This blanket like structure may be combined with other phase change material modules to extend the coverage down the sides of the cylinder using for example suitable fasteners.

Although, in view of the weight of the PCM material and its rigidity when solid, it is preferable not to provide a one piece structure but to use a plurality of separate modules which are assembled together when retrofitting about a hot water cylinder. This also allows for improved manufacturing and shipping as the system may be manufactured in smaller pieces thus allowing for efficient packing and ease of production. Each of the modules provides a heat transfer surface which is in contact with the outer surface of the cylinder tank underneath. In the exemplary arrangement shown, the area surrounding the element fitting 10 is left uncovered by a module. Equally, a specific module may be provided to accommodate the element. For example, a set of smaller triangular modules (for example a quarter of the size of the modules 20a-e) may be provided to cover the space around the element fitting 10 and leaving the element fitting itself exposed.

Each of the triangular modules is provided with a fixing means, explained in greater detail below, with which it can be fixed to adjoining modules. This allows for the individual placement of modules onto the cylinder which assists retro fitting as space may be tight about the hot water cylinder. For convenience, a bridle (not shown) may be provided about the water fitting 8 at the top of the cylinder. This bridle may be provided in an open form to allow placement around the hot water pipe 6 and fitting with a closure mechanism to close the bridle about the fitting 8. Once in place, modules 20 may be fixed to the bridle and thus allowed hang down from it. In one exemplary form, the bridle provides a plurality of clips on a loop with a closure. Each of the clips may be used to clip to a corresponding loop on a module. A similar arrangement may be employed to link modules together. The two modules 20a, 20e adjacent to the element fitting 10 may be linked together at their respective bottom corners adjacent to the element by a strap or similar connection means extending between their respective fixing means. Modules 24a-f may also, as shown in Fig. 4, be deployed about the upper side wall of the cylinder. These modules may be connected to and hung from corresponding modules located about the curved top surface of the cylinder. These Modules 24a-f are suitably the same as the previously described modules placed about the top curved surface of the tank.

As the surface of the hot water cylinder is curved, it is desirable that the heat transfer surface 44 of the modules is flexible to accommodate the curved surface to maximise the efficiency of the heat transfer between the modules and the cylinder.

The present application provides this flexibility by forming each module 40 as a plurality of individual segments/reservoirs 42a-h. Each segment is articulably connected to an adjacent segment so that the bottom surface 52 of each segment each segment can flex relative to the edge of the bottom surface of each adjacent segment. In the exemplary arrangement of Fig. 5 and Fig. 6 and in the individual segment shown in Fig. 7 and Fig. 7A in which a triangular module is employed, the base 52 and top 54 of each of the segments are also triangular in shape. In the arrangement shown, the individual segments are articulably connected at their bases. Whilst the use of triangles for the individual reservoirs\segments is advantageous, the application is not so limited. Thus the segments\reservoirs may be cylindrical in shape so that a plurality of circles are combined to make up the overall shape of the triangular modules. Similarly, a combination of different shapes may be employed for the segments and reservoirs to make up the overall module surfaces. The structure of each segment may be formed, for example, from a polymeric material or laminated packaging film material. These materials may be provided in a laminate form and formed around the PCM material using a suitable heat sealing or other process.

Thus, for example, a first (bottom) layer of the material may be provided onto which the solid PCM materials which have been pre-formed to a desired shape are place. A second (top) layer of material is applied on top and a suitable heating process, e.g. a heated jig is used to force the top layer to accommodate around the pre-formed PCM shapes thus forming the walls of the segments. A combination of heat and pressure ensure that the top and bottom layers join and form a seal at base of each wall. It will be appreciated that other processes may also be used to manufacture the segments. It will be appreciated that different materials may be employed for the top and bottom layers. As the bases of the segments are formed from a common sheet of flexible material, the space between the walls may provide an inherent articuable connection. If this is not sufficient, fold lines may be defined in the material at along the edges of the triangular base of each segment. In this way, the module provides an overall heat transfer surface 44 comprising the individual heat transfer surfaces comprising the base of each triangular segment. As the overall heat transfer surface is flexible, it may accommodate to the underlying surface of a cylinder when placed. So as to allow each segment 42a-h to move relative to each other, each cylinder tapers slightly as it goes from the base triangular surface to the top triangular surface. Other less desirable arrangements are possible, for example the segments may be joined at the top surface in which case the tapering will be in the opposite direction. Equally, the segments may be joined at any height between the top and bottom surface with appropriate tapering provided so as to allow the bottom surface accommodate to the curved surface of the cylinder.

An exemplary segment 42, as illustrated in Fig's 7 and 7a, has an equilateral triangular base 52. Where the length of the side of a module is 250mm, the length of sides of individual segments (I) is suitably about 31 mm. The top surface is also generally that of an equilateral triangle. The top surface segment may be curved in shape or flat (as shown). The height of each segment is about 60-90mm and suitably 75mm.

Each segment stores an amount of PCM material 50.

To facilitate installation and fixing, each module 40 may be provided with a support frame 61 around its edges, as illustrated in Fig. 8. The support frame which may be integrally formed with the base (heat transfer surface) 44 of the module provides some support and form to the individual segments. A wire 64, as shown in Fig. 9, may pass through a resilient edge strip 62. The edge strip in turn provides additional strength when handling, secondary sealing protection and rigidity when the PCM material melts. Each wire 64 extends between two corners of the triangle where it is suitable connected to a fixing means. In the exemplary arrangement, the fixing means is a ring or loop which may be clipped or otherwise connected to corresponding rings on adjacent modules or as described above onto a bridle.

The process for retrofitting the above described system to a hot water cylinder is relatively straightforward as will now be understood from the exemplary steps explained below.

Initially, any lagging jacket or other insulation present is removed or loosened to provide access to the upper part of the cylinder. The previously described bridle may then be clipped around the water outlet fitting 6 at the top of the cylinder, when installing only the top set of modules 20 the process continues as follows: A first module is then clipped at its top corner to the bridle. The first module is then slid around the cylinder to provide space for the second module, which in turn is clipped to the bridle and to the bottom corner of the first module. The first and second modules are then rotated further around the cylinder to make space for the third module and thus the process is repeated until all of the modules are in place. The fixing means at the opposing corners of the first and fifth modules may then be joined by a strap or similar fastening means. The insulation may then be replaced and re- fixed about the cylinder.

When the second set of modules 24 are also being installed, the process is largely the same with the additional step that after a module is fitted to the top, two modules are connected to the bottom, the first facing upwards and the second facing downwards. When the final top two modules 20a and 20e have been joined together with the strap or similar fastening means, further modules may be hung from the strap or fastening means to complete the encirclement of the modules 24 about the upper side wall of the cylinder.

It will be appreciated that the use of certain phase change materials may be advantageous with respect to others for example when considerations such as by way of example heat transfer efficiency, heat capacity, cost, manufacturability are taken into consideration. Where a plurality of such criteria are applied, it may well be that a plurality of PCM materials may be suitable with each offering advantages over the other. In a further aspect of this application, a hybrid PCM arrangement is provided. In this hybrid arrangement, a reservoir of PCM material may be provided with more than one type of phase change material. Thus, for example a reservoir may be employed to store two separate phase change materials. In such an arrangement, an improved PCM reservoir might be provided which combines the advantages of the individual PCM materials. In one exemplary construction, an individual reservoir might contain an inner reservoir and an outer reservoir. The outer reservoir suitably surrounds and contains the inner reservoir. The inner reservoir may be used to store a first type of PCM material. The inner reservoir suitably has an outer surface, e.g. of plastics material, to retain the first type of PCM material. A second type of PCM material may be stored in the outer reservoir.

In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. For example, whilst the application has been described with reference to situations in which the tank/ fluid reservoir is a cylindrical hot water tank, this is because it is the conventional shape for same. However, it will be appreciated that the tank need not be cylindrical and that the system may be used with a wide variety of different tanks. It will be appreciated that application is not limited to domestic applications and equally may have application in industrial settings. It will be appreciated that the size of the modules and the choice of PCM materials may be selected based on the industrial application. Equally, while the present system has been described with respect to placement of the modules on the outside, this is because most tanks are sealed. It will be appreciated that where the tank is not so sealed and access is available to the interior of the tank that the modules may be employed within the tank. Similarly, the present application is not limited to situations where the fluid being heated is water and may equally be employed with other fluids, in which case the PCM materials may be selected based on the required operating temperatures.

Equally, whilst the application has been described with respect to providing a heating effect from the PCM, it will be understood that in certain situations it may also be employed to provide a cooling effect (by appropriate selection of the phase change material) and thus may have application in refrigeration of air conditioning systems. It will be appreciated that in all of these situations the flexible nature of the modules is advantageous as it provides a flexible substrate for retrofitting to an existing apparatus. However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other elements or steps than those listed in a claim. Furthermore, the terms "a" or "an," as used herein, are defined as one or more than one. Also, the use of introductory phrases such as "at least one" and "one or more" in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an." The same holds true for the use of definite articles.

Unless stated otherwise, terms such as "first" and "second" are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. It will be appreciated that the claims have which follow have been written to be relatively concise. Thus claims which are dependent on one independent claim may not have a corresponding claim dependent on another independent claim. Nonetheless, it should be taken unless otherwise specified that when a feature is provided or further defined in dependent form for one independent claim it should be taken as being provided for with respect to all other independent claims unless the context otherwise dictates.

Claims

A module for use in a modular phase change material system for retrofitting to a hot water cylinder comprising:

a plurality of reservoirs, each reservoir storing an amount of phase change material and having a heat transfer surface for transferring heat between the reservoir and the tank, wherein each reservoir is articulably connected to adjacent reservoirs so that in use the module can accommodate its shape to the underlying cylinder so that each heat transfer surface is in contact with the underlying cylinder, wherein the heat transfer surfaces of each of the reservoirs combine to provide an overall heat transfer surface for the module, wherein the overall heat transfer surface is triangular in shape.

A module according to claim 1 , wherein the heat transfer surface of at least one reservoir is triangular in shape.

A module according to claim 2, wherein an articulable connection is provided along the sides of the triangular shape.

A module according to any preceding claim wherein the heat transfer surface defines a base of the reservoir and the reservoir extends a height in a direction transverse to the base.

A module according to claim 4, wherein the length of an edge of the base is in the range 20mm to 45mm.

A module according to claim 5, wherein the length of an edge of the base is 31 mm.

A module according to any one of claims 4 to 6, wherein the height of at least one reservoir is between 60 and 90 mm.

A module according to claim 7, wherein the height of the at least one reservoir is approximately 75mm.

A module according to any preceding claim, further comprising a fixing means for fixing the module to an adjacent module or other feature.

A module according to any preceding claim, wherein the phase change material is an organic hydro-carbon based wax, for example paraffin, or a salt hydrate based phase change material.

A module according to any preceding claim, wherein at least one reservoir comprises an inner reservoir storing a different phase change material to the phase change material stored in the at least one reservoir.

12. A modular phase change material system comprising a plurality of modules according to any proceeding claim.

13. A modular phase change material system for retro fitting to a hot water

cylinder, the system comprising:

a plurality of modules, each module having a surface for abutting with the surface of the hot water cylinder and each module containing a phase change material, wherein each of the modules are shaped to co-operate with adjoining modules in use so as to substantially cover an upper region of the tank.

14. A modular phase change material system according to claim 12, wherein the surface for abutting the tank is substantially triangular in shape.

15. A modular phase change material system according to claim 13 or claim 14, wherein each module comprises a plurality of reservoirs with each reservoir containing a phase change material and each module having a surface for abutting with the surface of the hot water cylinder.

16. A modular phase change material system according to claim 15, wherein the surface of the module for abutting the hot water cylinder is substantially triangular in shape.

17. A modular phase change material system according to any one of claims 13 to 16, wherein a fixing means is provided at each corner of the modules to allow fixing with an adjacent module.

18. A module according to any one of claims 1 to 1 1 or a modular phase change material system according to any one of claims 12 and 15 to 17, wherein at least one reservoir comprises an inner reservoir storing a separate phase change material to the at least one reservoir.

19. A kit for retrofitting a phase change material system to a hot water cylinder, the kit comprising:

a) a plurality of phase change modules, each module storing an amount of phase change material; and

b) a bridle for placing about a water outlet of the hot water cylinder to provide a fixing means for the phase change modules.

20. A method of fitting a phase change material system to a hot water cylinder having a water outlet fitting at the top of the cylinder, the method comprising the steps of:

a) placing a bridle around the water outlet fitting and closing the bridle to form a loop about the water outlet; b) connecting a PCM module storing an amount of PCM material to the bridle; and

c) repeating step b) for one or more PCM modules.

21. A phase change material system for retrofitting to a hot water cylinder having a curved top surface with a water outlet, the system comprising a blanket made up of a plurality of phase change material reservoirs, wherein the blanket has an opening from its center to its perimeter to allow the blanket to be slid into place around the water outlet on the top surface and wherein the blanket is shaped such that when placed on cylinder it conforms to and substantially covers the curved top surface of the cylinder.