WO2011045574A1

WO2011045574A1 - Latent heat storage materials

Info

Publication number: WO2011045574A1
Application number: PCT/GB2010/001917
Authority: WO
Inventors: Michael Trevor Berry; Janet Susan Scanlon
Original assignee: Michael Trevor Berry; Janet Susan Scanlon
Priority date: 2009-10-15
Filing date: 2010-10-15
Publication date: 2011-04-21
Also published as: GB201017444D0; GB201015418D0; EP2488463A1; GB2474544A; GB2474578A

Abstract

The invention describes novel latent heat storage material formulations formed from a mixture comprising binder, a phase change material and water wherein the weight ratio of the binder to water used in the preparation of the latent heat storage material is in the range 3:1 to 1 :5, and preferably 1 :1 to 1 :5 and processes for their preparation. It also includes composite panel assemblies or encasements including those latent heat storage materials and processes for their manufacture.

Description

Latent Heat Storage Materials

Field of Invention

This invention relates to thermal energy storage compositions that incorporate phase change materials. The compositions according to the present invention, some of which have improved fire retardant properties over known compositions that incorporate organic phase change materials, can be incorporated into a variety of building products, for instance as an additive to pre-cast concrete structures, concrete blocks, bricks and concrete slabs, or into an encasement.

For internal use, they can be used to form building products including cementitious floor screeds, foamed concrete and screeds, wall and floor tiles, ceiling tiles, chilled ceiling systems and beams, heat exchange units, wall panels, computer room floor tiles, raised access floor panels, curtain walling sections, metal extrusions, suspended ceiling sections, and heating and ventilation pipe work or ducting sleeving.

Background of the Invention

Phase change materials and compositions are well known: these are materials which reversibly undergo a change of state and act as a sink for thermal energy, absorbing or releasing heat as necessary. For example, they can be used to regulate temperatures within a desired range, or provide a degree of protection against extremes of heat or cold. Thus, a Phase Change Material (PCM) is a latent heat storer, which makes it possible to combine the advantages of modern architecture and the efficiency of lightweight construction with the use and compensating effect of thermal storage capacity for a pleasant indoor climate.

Phase Change Materials present a durable and efficient possibility for isothermal storage of peak loads, which usually occur during the day, in a defined temperature range, and releasing these again with a time delay (e.g. in the evening time or at night). Integrated into various kinds of building materials and building systems, Phase Change Materials contribute to an improved indoor climate, more comfortable living conditions and better energy efficiency, using intelligent temperature management. There are three main categories of Phase Change Materials; Organic, Inorganic and Eutectics;

Organic PCMs

Latent heat accumulator materials are by definition substances which have a phase change transition in the temperature range in which heat transfer is to be carried out. The latent heat accumulator materials preferably have a solid/liquid phase transition in the temperature range from -20 to 120°C.

As a rule, the latent heat accumulator material is an organic, preferably lipophilic substance. The following may be mentioned by way of example only as suitable substances:

Aliphatic hydrocarbon compounds such as saturated or unsaturated Ο ₀-Ο₄ο- hydrocarbons, which are branched or preferably linear, for example such as n- tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n- nonadecane, n-eicosane, n-heneicosane, n-docosane, n-tricosane, n-tetracosane, n-pentacosane, n-hexacosane, n-heptacosane or n-octacosane, and cyclic hydrocarbons, e.g. cyclohexane, cyclooctane or cyclodecane, paraffin (C_nH_2n+2);

Aromatic hydrocarbon compounds, such as benzene, naphthalene, biphenyl, ortho, meta or para-terphenyls, polychlorinated terphenyls, Ci-C4o-alkyl-substituted aromatic hydrocarbon such as dodecylbenzene, tetradecylbenzene, hexadecylbenzene, hexylnaphthalene or decylnaphthalene;

Saturated or unsaturated C₆-C₃₀-fatty acids, including fatty acids having the formula (CH₃(CH₂)₂nCOOH), such as lauric, stearic, oleic or behenic acid, preferably eutectic mixtures of decanoic acid with, for example, myristic, palmitic or lauric acid;

Fatty alcohols, such as lauryl, stearyl, oleyl, myristyl or cetyl alcohol, mixtures such as coconut fatty alcohol and so-called oxo alcohols which are obtained by hydroformylation of a-olefins and further reactions;

C₆-C₃o-fatty amines, such as decylamine, dodecylamine, tetradecylamine or hexadecylamine;

Esters, such as Ci-Ci₀-alkyl esters of fatty acids, such as propyl palmitate, menthyl stearate or menthyl palmitate, and their eutectic mixtures, or methyl cinnamate; Natural and synthetic waxes, such as montanic acid waxes, montanic ester waxes, carnauba wax, polyethylene wax, oxidized waxes, polyvinyl ether wax, ethylene/vinyl acetate wax or hard waxes obtained by the Fischer-Tropsch process;

Halogenated hydrocarbons, such as chloroparaffin, bromooctadecane, bromopentadecane, bromononadecane, bromoeicosane or bromodocosane.

Inorganic PCMs

These consist mainly of chemicals such as hydroxides or oxides, which have been diluted in an acid solution and are termed as salt hydrates or molten salt. The advantages that salt hydrates offer are; low cost in comparison to organic PCMs, they have a high latent heat per unit mass and volume, they possess a high thermal conductivity compared to organic compounds and offer a wide range of melting points from 7-117°C. However, they can also suffer from loss of water when subjected to long-term thermal cycling due to vapour pressure, although the use of airtight containerisation can prevent this.

Examples of inorganic phase change materials include:

calcium chloride hexahydrate (CaCI₂.6H₂0), sodium sulfate decahydrate - Glauber's salt (Na₂S0₄ 10H₂O), sodium carbonate decahydrate (Na₂C0₃ .10H₂O), and other salt hydrates (M_nH₂0).

Eutectic PCMs

A eutectic PCM is a combination of two or more compounds of either organic, or inorganic nature or both, which combination may have a more interesting melting point compared to their individual and separate compounds. They behave themselves as salt hydrates. The main problem with these compounds is the cost, which is typically some two or three times greater than organic or inorganic PCMs.

Examples of Eutectic phase change materials include:

Palmitic acid (organic), Mistiric acid (inorganic), Stearic acid (organic); Organic- organic, organic-inorganic, inorganic-inorganic compounds. These lists are not intended to be exhaustive but simply illustrate the wide range of materials that may be used in the present invention. The choice of materials will be made by a materials specialist.

Paraffin wax and similar organic compounds have been used as phase change materials for building applications (such as in wallboards, sheetrock, drywall, plasterboard, and fibreboard for absorbing or releasing heat energy into or from a room environment). However, these materials are flammable and this is a major drawback since it increases the combustibility of the articles containing such PCMs.

PCMs can be microencapsulated and there have been a variety of attempts to make such microcapsules more flame-resistant. US Patent No. 5,435,376 describes microencapsulated latent heat storage materials which are not combustible. However, non-combustible latent heat storage materials of this type generally store an insufficient amount of heat. The specification furthermore discloses mixtures of latent heat storage materials and flame inhibitors as a capsule core for textiles, shoes, boots and building insulation. This admixture of flame retardants only results in a slight improvement in the combustion values, or none at all.

US Patent Appl. Pub. No. 2003/0211796A1 discloses an approach that involves coating articles containing microencapsulated organic latent heat storage materials with a flame-inhibiting finish comprising intumescent coating materials of the type used as flame-inhibiting finishes for steel constructions, ceilings, walls, wood and cables. Their mode of action is based on the formation of an expanded, insulating layer of low-flammability material which forms under the action of heat and which protects the substrate against ingress of oxygen and/or overheating and thus prevents or delays the burning of combustible substrates. Conventional systems consist of a film-forming binder, a char former, a blowing agent and an acid former as essential components. Char formers are compounds which decompose to form carbon (carbonization) after reaction with the acid liberated by the acid former. Such compounds are, for example, carbohydrates, such as mono-, di- and tri- pentaerythritol, polycondensates of pentaerythritol, sugars, starch and starch derivatives. Acid formers are compounds having a high phosphorus content which liberate phosphoric acid at elevated temperature. Such compounds are, for example, ammonium polyphosphates, urea phosphate and diammonium phosphate. Preference is given to polyphosphates since they have a greater content of active phosphorus. Blowing agents, the foam-forming substances, liberate non- combustible gas on decomposition. Blowing agents are, for example, chlorinated paraffins or nitrogen-containing compounds, such as urea, dicyanamide, guanidine or crystalline melamine. It is advantageous to use blowing agents having different decomposition temperatures in order to extend the duration of gas liberation and thus to increase the foam height. Also suitable are components whose mode of action is not restricted to a single function, such as melamine polyphosphate, which acts both as acid former and as blowing agent. Further examples are described in GB2007689A, EP139401A, and US Patent No 3,969,291.

Magnesia Cements

Magnesia cement-based products are known to have good fire-resistance, for example, European Patent Application Number EP2060389A1 describes a laminate panel for flooring, wall or ceiling systems having a fire-proof core layer disposed between an upper surface layer and a lower backing layer. The core layer comprises a composition derived from a colloidal mixture of magnesium oxide, magnesium chloride and water.

A publication by Dr Mark A. Shand entitled "Magnesia Cements", referred to in WO2009/059908, details the three main types of magnesia cements, one of which is the Magnesium Oxychloride cement, otherwise known a Sorel cement. Shand suggests that superior mechanical properties are obtained from the "5-form" whose formula is given as 5Mg(OH)₂.MgCI₂.8H₂0. According to Shand, this is formed using magnesium oxide, magnesium chloride and water in a molar ratio of 5:1 :13.

WO2008/063904 discloses an approach for making the five-phase magnesium oxychloride cement composition (5Mg(OH)₂.MgCI₂.8H₂0) by mixing a magnesium chloride brine solution with a magnesium oxide composition in a selected stoichiometric ratio of magnesium chloride, magnesium oxide, and water. The cement kinetics are controlled to form the five-phase magnesium oxychloride cement composition and this results in an improved and stable cement composition. The key element would appear to be the utilisation of a magnesium chloride brine solution having a specific gravity in the range from about 28° Baume to about 34° Baume, most preferably at least about 30° Baume. After 24h, at least 98% of the five-phase compound is present, which minimises the amount of poorly water- resistant three-phase compound. Various fillers can be optionally added to give fire- proofing compositions.

Use of magnesia cement and related components is disclosed in WO2009/059908, which is concerned with the fire retardation properties of compositions including those comprising phase change material and magnesia cement. A high concentration of the 5-form is said to be preferable in inventive compositions comprising Sorel cement where superior mechanical properties are needed. The process for making these materials involves adding the phase change material to the magnesium chloride brine solution before the formation of the magnesium oxychloride cement is initiated by adding the magnesium oxide powder. These magnesia cements containing the phase change material (Examples 10-13) have molar ratios of magnesium oxide:magnesium chloride:water in the range of between about 5:1 :12 to 8:1 :16.

It will be appreciated that the chemical reactions which take place during the manufacture and curing of cement are complex, and the actual chemical composition of the resulting cements are both difficult to analyse chemically, and change over time as the cement cures and dries out. For that reason, cements are generally described by way of the starting input components and their respective relative weight ratios or molar ratios, including the amount of water used in their preparation. This convention will be used in the present description where the various cements, binders and resultant latent heat storage materials will be characterised by their inputs.

Pozzolans

Pozzolans are materials containing reactive silica and/or alumina, which on their own have little or no binding properties. When mixed with calcium Oxide (CaO) or lime as it is more commonly known, and with water, they will set and harden into a cement. These cements are referred to collectively as pozzolan cements which are used, amongst other things, as a mineral admixture with Ordinary Portland Cement (OPC) to significantly enhance the performance characteristics of cement based concretes, mortars, screeds and related products.

A wide variety of siliceous or aluminous materials may be pozzolanic, including Pulverized Fuel Ash (PFA), Rice Husk Ash (RHA), Metakaolin, silica fume and pozzolana, the volcanic ash from which pozzolans derive their name. Rice Husk Ash (RHA) has been identified as having the greatest potential of the agricultural wastes as it is widely available.

Pulverized Fuel Ash (PFA)

Pulverized Fuel Ash (PFA), which is often referred to as Fly Ash, has probably the greatest potential of the industrial wastes due to its widespread availability and its high alumina content. There are two types of PFA, depending upon the type of coal used. These are high lime and low lime, with the former having a lime content above 10% and therefore possessing some cementing properties on its own. Low lime PFA has a lime content below 10%. Both types of PFA can be used as a pozzolan.

PFA is available, in large quantities, in countries or regions using coal fired electricity generating stations. These include most of Europe, North America, the Indian sub-continent, China and Southern Africa.

The chemical composition of PFA will depend upon the type of coal used and can vary considerably, as can pozzolanic reactivity. Acceptable limits of composition, derived from various national standards are:-

The percentage of the main oxides, Si0₂ + Al₂0₃ + Fe₂0₃, should not fall below 70%;

The S0₃ content should not exceed 5% (Some standards specify 2.5%);

The gO content should not exceed 5%;

The loss on ignition should not exceed 12% (Some standards give a 5% or 6% limit). In addition some standards specify that the alkali metal (Na₂0) content should not exceed 1.5%, although this is only relevant if it is used with reactive aggregate.

Physically, PFA is a fine (less than 75 micron) powder, with a rounded particle shape and a colouring ranging from cream to dark grey. Its loose bulk density is approximately 800Kg/m³, which is roughly two-thirds that of Ordinary Portland Cement (OPC). As with all pozzolans, fineness is critical to the performance of PFA, with finer pozzolans giving faster pozzolanic reactions. Electrostatically collected PFA will be finer than PFA collected mechanically and is therefore normally preferred as a pozzolan. The Blaine method of measuring fineness is felt to be unreliable for PFA and the simpler sieving technique is often better. Standards give a maximum to be retained on a 45 micron sieve of 12.5 to 50% depending upon the country of origin.

PFA is not normally ground to produce a finer material as this will break up the rounded particle shape which is important for its water reduction and increased workability properties.

Unlike most other pozzolans, PFA requires no processing before use. It is normally transported in bulk to the cement factory or construction site where it is blended with OPC and/or lime to form a pozzolan cement.

Pozzolans can be used in combination with calcium oxide (CaO) and phase change materials (PCM). They can also be blended with ordinary Portland cement and various fillers to improve the thermal properties of lime based mortar concrete and renders, for use in a wide range of building applications.

Pulverized Fuel Ash (PFA) is commercially available from the majority of coal-fired power stations around the world and in the UK, from E.ON UK and Scot Ash. calcium oxide (CaO), or lime as it is also known, is commercially available from companies such as Singleton Birch Ltd. Typical percentage compositions of PFA include:

Rice Husk Ash (RHA)

Rice Husk Ash (RHA) is a carbon neutral green product available worldwide. Traditionally, rice husk has been considered a waste material and has generally been disposed of by dumping or burning. Nevertheless, Rice Husk Ash (RHA) has been successfully used as a pozzolan in commercial production. There is a growing demand for fine amorphous silica in the production of cement and concrete mixes. This market is currently filled by silica fume or microsilica.

Other uses of Rice Husk Ash (RHA) include green concrete, high performance concrete and flame-retardants. Rice Husk Ash is commercially available from companies such as Mid-Link International Co. Ltd, Germany

Metakaolin

Metakaolin is a dehydroxylated form of the clay mineral kaolinite. Rocks that are rich in kaolinite are known as china clay or kaolin, which is traditionally used in the manufacture of porcelain. Kaolin is a white, soft plastic clay composed of well- ordered kaolinite with a low iron content

Chemical Name: Anhydrous aluminum silicate

Chemical Formula: Al₂0₃. 2Si0₂..2H₂O or H₄AI₂Si₂0₉

The meta prefix in the term is used to denote change. In the case of metakaolin, the change that is taking place is dehydroxylation, brought on by the application of heat over a defined period of time. Beyond the temperature of dehydroxylation, kaolinite retains two-dimensional order in the crystal structure and the product is termed metakaolin. The introduction of High Reactivity Metakaolin to the High Strength Concrete market has provided an alternative to the use of silica fume. Equivalence in strength development and durability properties along with several additional features of High Reactive Metakaolin including colour and workability have effectively expanded the design boundaries of High performance concrete materials.

The particle size of Metakaolin is smaller than cement particles but not as fine as silica fume. It is commonly used as a high performance, high strength, lightweight concrete that is perfect for precast and mould poured products, mortars and stuccos. Kaolin powder is commercially available worldwide and from companies such as Imerys Performance Minerals, Cornwall, UK.

GB234434 A discloses a forming mixture comprising a dry, inert powder, such as fly ash, pulverised rock or recycled building waste, phosphogypsum and an alkaline salt. Additives such as cellulose derivatives, PVA resin, microfibres, starch ethers, water repelling agents, colour or flame-retardants, may be included. An aerating agent e.g. a carbonate may be added to yield thermally insulating materials. The addition of a phase change material is not contemplated.

U.S. Pat. Nos. 6,099,894, 6, 171 ,647 and 6,270,836 describe a magnesium oxide gel and other metal oxide gels as a coating for microencapsulated phase change, which result in improved flame protection of the capsules.

Micronal® - Phase Change Material

Micronal® is a microencapsulated phase change material from chemical company BASF. Encapsulated within a polymer shell is a wax that is specifically formulated to work at set temperatures of 21 °C, 23°C and 26°C. Micronal® is designed as a thermal energy storage material, whereby latent heat is absorbed and stored within the polymer shell of the microencapsulated PCM at levels above the set working temperature and emitted as temperatures fall.

Summary of the Invention

According to a first aspect of the present invention there is provided a latent heat storage material formed from a mixture comprising binder, a phase change material and water wherein the weight ratio of the binder to water used in the preparation of the latent heat storage material is in the range 3:1 to 1 :20, preferably 1 :1 to 1 :20, more preferably 1 :1 to 1 :5. Further preferred weight ratios include 1 :1 to 1 :3 and 1 : 1 to 1 :2.85. By using a higher weight ratio of water to binder than in prior art formulations, it has been found that significantly more PCM material by weight can be incorporated into the latent heat storage material than in previous formulations. This gives rise to latent heat storage materials with significantly higher enthalpy values than has been possible using prior art formulations. Preferably the binder is selected from the group comprising: - a cement; an Ordinary Portland Cement (OPC); a magnesia cement; a pozzolan cement; a magnesium chloride solution; and mixtures thereof. These binders have been found to be particularly effective in the formation of latent heat storage materials. In a preferred embodiment of the present invention the binder comprises a magnesia cement formed from magnesium chloride, magnesium oxide and water, and where preferably the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :15 to 1 :36 and more preferably in the range 1 :17 to 1 :32.

Preferably, during the preparation of the magnesia cement, the said magnesium chloride is dissolved in said water to give a solution having a Baume value in the range 12° to 27.5°. This range is important and is lower than ranges reported in the prior art for magnesia cements, and results in the ability to incorporate more PCM by weight into the material. It will be appreciated from the following description that secondary binder(s) and fillers can be added to this formulation as required.

Preferably the Baume value of the magnesium chloride solution used in the preparation of the magnesia cement is in the range 15° to 26°.

Preferably the molar ratio of said magnesium chloride to said magnesium oxide used in the preparation of the magnesia cement is in the range 1 :1 to 1 :5.5.

Preferably the weight ratio of magnesium chloride : magnesium oxide : water : organic phase change material is about 1 :1 :2.3:1 ± 20%. In an alternative preferred embodiment the binder comprises a pozzolan cement and preferably the pozzolan cement comprises calcium oxide and a pozzolan, and wherein said calcium oxide and said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :10 (CaO: pozzolan) by weight. It will be understood that where the storage material does not require structural strength, such as when it is enclosed in an encasement (see below), then other ratios of binder to water, outside of the range 3:1 to 1:20 can be used. That applies to all of the various binder preparations described herein, which need not necessarily be limited to any particular ratio of binder to water.

Preferably the said calcium oxide and the said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1:1 to 1 :4 (CaO:pozzolan) by weight.

In an alternative preferred range, the ratio of binder (i.e. CaO + Pozzolan) to water is in the range 1 :1 to 1 :5 binder to water by weight.

Preferably the pozzolan is selected from the group comprising:- pulverised flue ash (PFA) kaolin, including metakaolin; rice husk ask (RHA); pozzolana; silica fume; ground granulated blast furnace slag; and mixtures thereof.

Preferably the pozzolan cement additionally comprising glass fibre, which adds strength to the storage material and prevents cracking over time as the cement dries out. In an alternative and particularly preferred embodiment the binder comprises a magnesium chloride solution formed from magnesium chloride and water. This binder solution is substantially free of magnesium oxide or other metal oxides. Magnesium oxide or other metal oxides are not added to this binder is subsequent steps. Substantially free in this context means that it contains less than 10% and preferably less than 5% of magnesium or other metal oxide. This magnesium chloride solution therefore comprises both the binder and the water as required in the latent heat storage material formulation as set out above.

Preferably the molar ratio of magnesium chloride to water used in preparation of the magnesium chloride solution binder is in the range 1 :15 to 1 :36 and more preferably is in the range 1 : 17 to 1 :32. Preferably during preparation of the magnesium chloride solution binder, the said magnesium chloride is dissolved in water to give a solution having a Baume value in the range 12° to 27.5° and preferably 15° to 26°

Preferably the latent heat storage material further comprises one or more fillers and preferably the filler is selected from the group comprising:- quartz; stone and stone dust including limestone; silica sand; perlite; marble; graphite; ceramic powders; wood dust flax sheaves; hemp; straw; glass fibre strands; and mixtures thereof. Preferably the phase change material comprises up to 99% by weight of the latent heat storage material, and preferably 30% - 95% by weight of the latent heat storage material.

By way of enthalpy values, in the case of a panel 20 mm thick, the heat storage capacity of the material is in the range 300 - 3500 kJ/m². It will be understood that where enthalpy is measured in kJ/m^2, it is necessary to specify the thickness of the material, in order to be able to make a meaningful measurement or comparison between different formulations. It is not intended that there should be any limitation to a panel 20 mm thick, nor to any particular thickness of panel.

According to a further aspect of the present invention there is provided a latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a magnesia cement formed from magnesium chloride, magnesium oxide and water, characterised in that the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :15 to 1 :36. Magnesia cement formulations impart improved strength and fire retarding properties to the storage material, particularly when organic phase change materials are used. Preferably the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :17 to 1 :32

In a particularly preferred embodiment, during the preparation of the magnesia cement, the said magnesium chloride is dissolved in said water to give a solution having a Baume value in the range 12° to 27.5°, and more preferably in the range 15° to 26°. Preferably the molar ratio of said magnesium chloride to said magnesium oxide used in the preparation of the magnesia cement is in the range 1 :1 to 1 :5.5.

According to a further aspect of the present invention there is provided a latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a pozzolan cement. Pozzolan cements are particularly useful for being able to incorporate large amounts of PCM, relative to the weight of cement. Preferably the pozzolan cement comprises calcium oxide and a pozzolan and water, and wherein said calcium oxide and said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :10 (CaO:pozzolan) by weight.

In a preferred embodiment the said calcium oxide and the said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :4 (CaO:pozzolan) by weight.

In an alternative preferred embodiment the ratio of CaO + pozzolan to water is in the range 1 :1 to 1 :5 (CaO + pozzolan) to water by weight.

Preferably the pozzolan is selected from the group comprising:- pulverised flue ash (PFA)

kaolin, including metakaolin;

rice husk ask (RHA);

pozzolana;

silica fume;

ground granulated blast furnace slag; and mixtures thereof. Preferably the storage material additionally comprises glass fibre.

According to a further aspect of the present invention there is provided a latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a magnesium chloride solution formed from magnesium chloride and water, the magnesium chloride solution being substantially free from magnesium oxide or other metal oxides. Preferably the molar ratio of magnesium chloride to water used in preparation of the binder is in the range 1 : 15 to 1 :36. and more preferably the molar ratio of magnesium chloride to water used in the preparation of the binder is in the range 1 : 17 to 1 :32

Preferably, during preparation of the magnesium chloride solution, the said magnesium chloride is dissolved in water to give a solution having a Baume value in the range 12° to 27.5° and more preferably in the range 15° to 26°. According to a further embodiment of the present invention there is provided a process for making a latent heat storage material comprising a binder a phase change material and water wherein said binder is a magnesia cement comprising the steps of:

(a) dissolving magnesium chloride in water to form a solution having a Baume value in the range between 12° and 27.5°;

(b) adding magnesium oxide to said magnesium chloride solution;

(c) adding a phase change material to the mixture of magnesium chloride and magnesium oxide; and

(d) baking the mixture of magnesium chloride, magnesium oxide and phase change material.

In this process the Baume value is preferably in the range between 15° to 26°, and preferably 15° to 22°. The process may additionally comprise the step of adding a secondary binder, and preferably the secondary binder comprises a pozzolan, preferably selected from the group comprising:- pulverised flue ash (PFA) kaolin, including metakaolin; rice husk ask (RHA); pozzolana; silica fume; ground granulated blast furnace slag; and mixtures thereof.

Preferably the process comprises the additional step of adding one or more fillers, wherein the filler may be selected from the group comprising:- quartz; stone and stone dust including limestone; silica sand; perlite; marble; graphite; ceramic powders; wood dust flax sheaves; hemp; straw; glass fibre strands; and mixtures thereof. According to a further aspect of the present invention there is provided a process for making a latent heat storage material comprising a binder and a phase change material wherein said binder is a magnesium chloride solution comprising the steps of:- (a) dissolving magnesium chloride in water to form a solution having a Baume value in the range of 12° to 27.5°;

(b) adding a phase change material to said magnesium chloride solution;

(c) baking the mixture.

In this particular process, no conventional cement is used and the magnesium chloride solution, substantially free from magnesium oxide or other metal oxide(s), or other potential reactive substances which might react with magnesium chloride to form a cement, constitutes the binder. This solution therefore comprises both the binder and the water as required in the latent heat storage material as set out above. This is the first time, to the applicant's knowledge, that magnesium chloride has been used in this way. The magnesium chloride gives significant fire retarding properties to the latent heat storage material.

Preferably the Baume value of the magnesium chloride solution is in the range of 15° to 26°, and more preferably 15° to 22°. These ratios are preferred but other ratios containing more water can be used, where structural strength in the storage material itself is not a requirement, for example where the storage material is encased, or incorporated into a composite panel assembly.

Preferably the process involves the additional step of adding a secondary binder and/or a filler as set out above and later in the description.

According to a further aspect of the present invention there is provided a composite panel assembly containing a latent heat storage material according to the present invention, said composite panel assembly comprising:-

(i) a panel front having a first face and an opposing second face, said panel front comprising a thermally conductive material; (ii) a latent heat storage material layer comprising a phase change material;

(iii) a plurality of support elements; wherein the support elements are embedded in the latent heat storage material layer to provide structural support to that layer. These support elements provide strength and rigidity to the latent heat storage material layer, formed from latent heat storage material according to the present invention, which otherwise may not have the necessary strength during transportation, installation and other handling procedures.

Preferably the plurality of support elements segregate part or all of the latent heat storage material layer into discrete sections. This reduces the tendency of the latent heat storage material layer to distort over time. Such distortion would result in a panel changing shape. Such shape changes are particularly noticeable in the case of ceiling tiles, which are highly visible.

Preferably the plurality of support elements extend from the opposing second face of the front panel into and substantially through the latent heat storage material layer. In a particularly preferred embodiment some or all of the support elements are formed from a thermally conductive material and are thus adapted to convey heat between the panel front and the latent heat storage material layer. By incorporating support elements which are also thermally conductive and that extend substantially through the latent heat storage material layer means that heat may be transported more rapidly into and out of the body of the latent heat storage material, making more effective use of the phase change material, in which case these features result in rapid heat exchange between the latent heat storage material layer, the front/outside of the composite panel assembly and the environment. Preferably the plurality of support elements comprise structures selected from the group comprising:- honeycomb structures; polygonal structures formed from regular or irregular polygons; fins; ribs; ribbons; crenuiations; mesh; protrusions; and combinations thereof. In an alternative preferred embodiment the latent heat storage material layer further comprises a heat conducting matrix material. By introducing heat conducting material into the latent heat storage material layer this increases the heat transfer to and from the phase change material. This can be used in conjunction with or instead of heat conduction elements.

Preferably the heat conducting matrix material comprise a matrix selected from the group comprising:- graphite;

a metal including a powdered metal or metal fragments or strips;

expanded metal foam;

heat conducting plastics;

carbon fibre; and combinations thereof. In a particularly preferred embodiment the heat storage capacity of the panel is in the range 300 - 3500 kJ/m², based on a 20 mm thick panel. The comments above in relation to the units kJ/m² apply here also.

Preferably the panel front further comprises one or more panel edges, said panel edges depending from the first face of the panel front or from the opposing second face of the panel front, and preferably the panel assembly further comprises a second panel element or a lid, the panel front, panel edges and lid, forming an encasement. By creating an encasement of this type, the latent heat storage material is substantially contained within a structure, and the structure is preferably fire resistant or fire retardant. Alternatively, the edges may be attached to the lid.

Preferably the lid is bonded to or otherwise attached to the panel front and/or panel edges, and /or the lid is bonded to the latent heat storage material layer. Preferably the panel assembly further comprises a square or tegular edge, enabling the panel to sit on or below a ceiling grid.

Preferably the composite panel assembly comprises a structure selected from the group comprising:- a ceiling tile, including an acoustic ceiling tile; a floor tile; a raised access/computer floor tile; a chilled ceiling panel; a wall panel; a panel e.g. for use in heat exchange systems; a desk surface; a work surface; a sleeve e.g. for heating and ventilation pipes; an encasement.

Preferably the panel assembly further comprises one or more tubes adapted to carry a cooling or heating fluid, wherein the tube(s) pass through the latent heat storage material layer. Preferably the panel assembly further comprises an insulating layer and preferably the insulating layer is located on the side of the latent heat material layer furthest from the panel front.

Importantly, panel assemblies according to the present invention can be formed from existing tiles or encasements by incorporating a latent heat storage material together with a plurality of heat conduction elements. Thus, an existing ceiling or floor tile, or other suitable encasement, can be converted into, or refurbished to form, a composite panel assembly according to the present invention by way of a retro-fit operation. If desired an insert of the correct size, shape and thickness, consisting of latent heat storage material cast around a plurality of heat conduction elements, may be pre-formed and inserted into an existing tile or encasement. Such inserts can be cemented into the tile for added security and improved heat transfer.

This refurbishment possibility is most important commercially as it leads to significant cost savings and has the added environmental advantage that waste is reduced or eliminated because the existing ceiling tiles are reused. It can be applied to any of the processes listed below and described herein. So, in the context of this invention, the term 'manufacture' includes refurbishment using existing panel elements.

According to a still further aspect of the present invention there is provided a process for the manufacture of a composite panel assembly comprising the steps of

(a) providing a first panel element and a plurality of support elements;

(b) providing a phase change material in a binder in an unset form;

(c) locating the plurality of support elements adjacent to the first panel element; (d) substantially surrounding the support elements with the phase change material and allowing it to set;

(e) optionally providing and fitting a second panel element over the phase change material/support elements combination and optionally securing the second panel element to the first panel element.

According to a still further aspect of the present invention there is provided a process for the manufacture of a composite panel assembly comprising of the steps of:- (a) providing a first panel element and a plurality of support elements;

(b) securing the support elements to one face of the first panel element;

(c) providing a second panel element with upstanding edges which, in combination, form a shallow tray;

(d) substantially filling the tray with a phase change material in a binder in unset form;

(e) placing the first panel element over the second panel element such that the support elements become embedded in the phase change material.

According to a still further aspect of the present invention there is provided a process for manufacturing a composite panel assembly comprising the steps of:-

(a) providing a tile comprising a tray element and, optionally, a back or lid element;

(b) providing a plurality of support elements with a latent heat storage material precast around the support elements in a size and shape that will fit into said tray element;

(c) placing a binder cement layer into the bottom of said tray element;

(d) placing the precast element from step (b) into the tray element and optionally fitting the back or lid element.

In the processes of the invention set out above, the phase change material in a binder or the latent heart storage material may be a latent heat storage material according to the present invention.

The present invention also extends to cover the latent heat storage materials described herein, their methods of manufacture, and to the methods of manufacture of composite panel assemblies containing those latent heat storage materials. Also encompassed within the present invention are methods of improving the environmental performance of a space using composite panel assemblies.

Brief Description of Drawings

The present invention will now be described, by way of example only, with reference to the accompanying drawing in which:

Figure 1 shows a composite panel assembly in the form of an encasement for a ceiling tile, with the lid removed and part of the edge of the encasement not shown for clarity purposes;

Figure 2 shows details of the honeycomb structure of the encasement shown in Figure 1 ; of the present invention;

Figure 2a shows details of ribbed, ribboned and finned wall sections of the heat conducting elements used in encasements of the present invention;

Figure 3 shows an encasement of the present invention for a ceiling tile encasement having a square mesh honeycomb;

Figure 4 shows an encasement of the present invention for a ceiling tile encasement having a tegular edge.

Figure 5 shows a further encasement of the present invention for an infill for ceiling tile encasement having a tegular edge;

Figures 6 and 6A show front and rear views of an encasement according to the present invention for a wall or a ceiling panel;

Figure 7 shows perspective and side views of an encasement of the present invention for a raised access floor tile;

Figure 8 shows close up and perspective views of an encasement of the present invention for a worktop or desk;

Figures 9a-c show an encasement of the present invention for a cooling tile; and

Figure 9d shows a cooling circuit for use with the encasement of Figures 9a-c;

Figure 10 illustrates graphically the change in surface temperature over time of a conventional metal ceiling tile and a tile according to the present invention in a thermal test chamber experiment, together with a graph showing the power usage over time of the air conditioning unit under those test conditions; Figures 11 to 15 inclusive illustrate perspective and outside elevations respectively of a test cell;

Figure 16 illustrates a cross-section of the ceiling of the test cell illustrated in Figures 11 to 15

Description of the preferred embodiments

Preferred embodiments will now be described, by way of example only. These embodiments represent the best ways known to be applicant of putting the invention into practice, but they are not the only ways in which this can be done. Embodiments of the present invention and their technical advantages may be better understood by referring to the following disclosure. A wide variety of binders can be used in the latent heat storage materials of the present invention. Examples of the preparation of various binders will be described, again by way of example only.

Magnesia cements

A preferred process for the preparation of Magnesia cement containing latent heat storage materials is as follows. In a first step, magnesium chloride is dissolved in water of reasonable purity (such as tap water) by mixing for a minimum of 15 minutes at high speed and then left for a minimum of 24 hours to ensure that the magnesium chloride is completely dissolved. The dissolution step is performed under ambient conditions, typically 10 - 13°C for the tap water and 15 - 18°C for the resulting solution. Magnesium chloride hexahydrate preparations are commercially available and suitable for use in the present invention. For example nedMag C flakes, which are small white flakes of magnesium chloride hexahydrate (MgCI₂.6H₂0) with a MgCI₂ content of 47%, are available from Nedmag Industries Mining & Manufacturing B.V. The Baume is measured in order to be able to determine the quantity of magnesium oxide to be added in the next step (see below). The proportion of magnesium oxide in the binder affects its density and to some extent determines the quantity of the phase change material and thus the enthalpy measure of the finished binder. The Baume measures the density of a liquid, which can be either heavier or lighter than water. In the case of the present invention, the liquid density is heavier than water. Typically the weight ratio of magnesium chloride : water is chosen to give a Baume value in the range between 12° and 27.5°. This is lower than the Baume value of 28° to 34° taught in WO2008/063904 which also teaches a molar ratio of magnesium chloride : magnesium oxide of between about 1 :4 and 1 :5.

In a second step magnesium oxide is added to the magnesium chloride solution prepared in the first step and stirred for a minimum of 10 minutes with a high speed paddle drill. Magnesium oxide preparations are commercially available and suitable for use in the present invention. For example, Baymag magnesium oxide is available from Baymag Inc. and comprises 94-98% (wt/wt) of magnesium oxide and 1.5 - 4% (wt/wt) of calcium oxide.

In a third step the phase change material (PCM) is added directly after the MgO: MgCI₂ solution has been stirred for at least 15 minutes, and is mixed vigorously. This differs from the process disclosed in WO2009/059908 in which the PCM is added to the magnesium chloride solution. Preferred PCMs are microencapsulated organic, water insoluble materials that undergo solid-liquid/liquid-solid phase changes at temperatures in the range of 0° to 80°C. Candidate materials include those listed above. These materials are generally substantially water insoluble, which means they may be formulated in an emulsion form or encapsulated form.

Including a phase change material in the binder mix decreases its fire resistant properties and also alters the physical characteristics of the binder when cured. It is therefore desirable that the enthalpy of phase change is high (typically >50 kJ/kg, preferably >100 kJ/kg and most preferably >150 kJ/kg) so that smaller quantities of PCM can be used in the binder. Preferably, the phase change material is a commercially available encapsulated formulation, such as Micronal®, which has an enthalpy of 110kJ/kg or Encapsulance, which has a higher enthalpy, in the range of 150 - 160kJ/kg. These materials are provided in granular form and may be added to the magnesia cement binder straight out of the container. Using a weight ratio of magnesia cement materials : PCM in the range of 1 :2 to 1 :3, where the weight of the magnesia cement materials includes the water used in the preparation of the cement binder, gives a binder product having an enthalpy measure of about 50 kJ/kg. The quantity of PCM used is chosen so that the enthalpy measure of the binder is at or below 50kJ/kg. This typically corresponds to a minimum European fire rating of Euroclass D, which is described as having an "Acceptable contribution to fire" (the class system is rated on a scale of A1 , A2, B, C, D, E and F, where A1 has no contribution to fire and where F has no performance requirements).

In an optional fourth step glass fibre strands can be added to the phase change material and MgCI₂(H₂0)_x suspension to prevent cracking during curing and also shrinkage that can occur through the evaporation of the water content.

In an optional fifth step a secondary binder as defined above, such as a pozzolan, can be added to the mixture with stirring.

In an optional sixth step, filler materials can be added whereby the filler materials can include silica sand, magnesium oxide, stone dust, quartz, perlite, marble, ceramic powders, wood dust, flax sheaves, hemp, straw and graphite.

In a final step the mixture, which is a latent heat storage material that in its liquid state, is typically moulded or cast to suit any shape or form for use and baked for no more than 24h at about 40°C so that the binder composition cures and dries slowly.

Some Examples of PCM/magnesia cement binder compositions, and the corresponding molar ratios for the magnesia cement components, are given in Tables 1 to 8.

Table 1. Where the Baume of the Solution is 26°:

Example 1 Example 2

NEDMAG(RTM) MgCI₂ (g) 500 500

Water (g) 500 500

Baymag MgO - comprising of:

Magnesium Oxide: 94 - 98% (wt.wt) 400 250 Calcium Oxide: 1.5 - 4%

BASF Micronal mPCM 600 600

Enthalpy Measure (kj/kg) 29.5 48.9

Euroclass Fire Rating C D

Table 2. Where the Baume of the Solution is 23°:

Example 3 Example 4

NEDMAG(RTM) MgCI₂ (g) 262 262

Water (g) 338 338

Baymag MgO - comprising of:

Magnesium Oxide: 94 - 98% (wt.wt) 250 50 Calcium Oxide: 1.5 - 4%

CIBA Encapsulance mPCM 1000 1000

Enthalpy Measure (kj/kg) 68.1 102.6

Euroclass Fire Rating E E/F

Table 2a. Where the Baume of the Solution is 19°:

Table 2b Where the ratio of MgCI₂ : MgO is 1 :1 and 0.5:1

1 : 1 (MgCI₂ : MgO) 0.5 : 1 (MgCI₂ : MgO)

MgCI₂ (grams) 1000 500

Water (grams) 1000 1000

Baume of MgCI₂ : water

26° 18° solution

Magnesium Oxide (MgO)

1000 1000 (grams)

BASF Micronal mPCM

500 700

(grams)

Table 2c Where the Baume value is 15° and 26°

Table 2d Examples of preferred Baume values of MgCI₂ solutions

In another illustration (Example 4b) shown in Table 3 below, the magnesium chloride solution is prepared from 1000g Nedmag and 2300g water, giving a Baume value of 15° and corresponding to a molar ratio of magnesium chloride : water of 1 :32.0. In a further illustration (Example 4c), the magnesium chloride solution is prepared from 1000g Nedmag and 1400g water giving a Baume value of 22° and corresponding to a molar ratio of magnesium chloride : water of 1:21.8. Example 4b, 4c and 4d serve to illustrate the relative amounts of magnesium chloride and water used to form magnesium chloride solutions of various Baume values. These solutions can be used in various formulations as required or, as will be seen below, can be used as a binder in their own right, without the addition of any magnesium oxide or other metal oxide or hydroxide. Table 3. Molar ratios for MgO:MgCI₂:H₂0 and weight ratios for cement:PCM in Examples 1 -4d, based on magnesium chloride hexahydrate.

In Examples 1 and 2, the molar ratio of magnesium chloride : water is 1 :17.3, corresponding to a Baume value of 26°, and in Examples 3 and 4, the molar ratio of magnesium chloride : water is 1 :20.6, corresponding to a Baume value of 23°. This is lower than the Baume value of 28° to 34° taught in WO2008/063904. In Example 4c, the molar ratio of magnesium chloride : water is 1 :21.8, corresponding to a Baume value of 22°. In Example 4a, the molar ratio of magnesium chloride : water is 1 :26.3, corresponding to a Baume value of 19°. In Example 4b, the molar ratio of magnesium chloride: water is 1 :32.0, corresponding to a Baume value of 15°. In Example 4d, the molar ratio of magnesium chloride: water is 1 :36.0, corresponding to a Baume value of 12°. Examples 4b to 4d are given by way of example only and are intended to demonstrate the molar ratios of magnesium chloride and water necessary to form magnesium chloride solutions of various Baume values. These solutions may then be used in various formulations where magnesium chloride is required, or as a binder solution in their own right. Examples 4b to 4d are not intended to be fully documented Examples and some PCM will be required in addition at least to make a latent heat storage material according to the present invention.

In Examples 1 , 3 and 4a the molar ratio of magnesium chloride : magnesium oxide is between about 1 :4 and 1 :5. The molar ratio of MgO:MgCI₂:H₂0 in the magnesia cement of the present invention thus varies in the ranges 4-5:1 : 17.3-26.3. This is considerably different from the magnesia cements utilised in Examples 10 and 1 1 of WO2009/059908 (a ratio of 5.3:1 : 12) and Examples 12 and 13 of WO2009/059908 (a ratio of 8:1 : 16).

The molar ratio of the added magnesium oxide : magnesium chloride is generally in the range of about 4: 1 to about 5:1 , but much lower molar ratios (as low as about 1 :1) are utilised when a larger quantity of phase change material is to be incorporated into the binder. The greater the volume of phase change material that can be incorporated into the present invention, the higher the enthalpy measure and subsequently the greater the heat storage capacity of the material. In addition, where the Baume of the solution is reduced to 12° or 15°, the volume of magnesium oxide in the binder is also reduced as a result (to keep the molar ratio of magnesium chloride : magnesium oxide in the same range). Therefore a higher volume of phase change material can be incorporated into the mixture. Some of the increase in water content of the solution will evaporate during the curing stages of the binder/mixture.

For the higher Baume formulations of Examples 1 and 2, a weight ratio of magnesia cement materials : PCM in the range of 1 :2 to 1 :3 gives a binder product having an enthalpy measure of about 50 kJ/kg. For the lower Baume formulation of Example 4a, a weight ratio of magnesia cement materials : PCM in the same range gives a binder product having an enthalpy measure of about 70 kJ/kg. The binder product of the present invention is thus superior to that disclosed in WO2009/059908 in which the weight ratio of magnesia cement materials : PCM is in the range of 1 :0 to 1 :2 and the enthalpy measures are in the range of 13 to 33 kJ/kg.

The microencapsulated phase change material alone is highly flammable, and the Euroclass fire rating is low: casting the mixture into aluminium, copper or graphite encasements prior to baking protects the binder from fire and give the binder a practical format with high thermal conductivity benefits for a number of applications (see below).

In a second embodiment of the present invention in which a high enthalpy is secondary to the density and strength requirements of the latent heat storage material, aggregate fillers such as, but not limited to, silica sand, stone dust including limestone, quartz, perlite, marble, ceramic powders, glass fibre strands, wood strands or graphite can be added to the binder with phase change material mixture. This gives the material additional strength and durability characteristics for other applications where aluminium, copper or graphite casing are not necessary or practical.

Table 4. Where the Baume of the Solution is 26° and incorporating Quartz into the Binder mixture

Table 5. Molar ratios for MgO:MgCI₂:H₂0 and weight ratios for cement:PCM in Examples 5 and 6

The molar ratio of Mg0:MgCI₂:H₂0 in the magnesia cement of this second embodiment thus varies in the ranges 4-5:1 :17.3, considerably different from the magnesia cements utilised in Examples 10 and 11 of WO2009/059908 (a ratio of 5.3:1 :12) and Examples 12 and 13 of WO2009/059908 (a ratio of 8:1 :16). Prior to the baking step, these formulations can be cast to form wall and floor tiles, floor coatings and screeds, worktops, furniture, exterior cladding and siding panels, construction boards and building blocks and internal and external architectural mouldings. Also organic fillers including, but again not limited to, wood dust, flax sheaves, hemp and straw can be added as fillers in the manufacture of a construction board for interior/exterior walls and also ceilings.

In a further embodiment in which the enthalpy of the binder exceeds 50kJ/kg, the fire rating reduces to Euroclasses E and F and is therefore limited in its use as a building material. In order to overcome this, an intumescent agent of the type disclosed in U.S. Patent Appl. Pub. No. 2003/0211796A1 may be added, again with mixing, to the binder and phase change material mixture. Typical intumescents are latex aqueous dispersions. Preferred intumescents include Thermasorb and A/D Firefilm III from Carboline, which are water-based intumescents. Example 8 in Table 6 shows how the addition of Thermasorb alters the Euroclass Fire Rating for a magnesia cement containing Encapsulance from E (Example 7 in the absence of Thermasorb).

Table 6. Baume 26° and intumescent material incorporated into the Binder mixture of Example 8, Example 7 having no intumescent.

Example 7 Example 8

NEDMAG(RTM) gCI₂ (g) 300 300

Water (grams) 300 300

Baymag MgO - comprising of:

Magnesium Oxide: 94 - 98% (wt/wt) 250 250

Calcium Oxide: 1.5 - 4%

CIBA Encapsulance mPCM 1000 1000

Intumescent - Carboline Thermasorb 0 200

(grams)

Enthalpy Measure (kJ/kg) 66.3 48.9

Euroclass Fire Rating E C Table 7. Molar ratios for MgO:MgCI₂:H₂0 and weight ratios for cement:PCM in Examples 7 and 8

For high enthalpy binders with poor Euroclass Fire Ratings, the mixtures are cast into an encasement or composite panel assembly such as a ceiling tile, with or without support elements or heat conduction elements within the encasement, which preferably comprises aluminium or copper or a combination thereof, prior to the baking step. These materials have good thermal conductivity (aluminium - 237 W/(m K); copper - 401 W/(m K) as opposed to other encasements made with plain steel, for an example, which has a thermal conductivity value of 45-65 W/(m K). They therefore maximise the efficiency of the phase change material and are described in more detail below.

The encasements can be formed into various embodiments including, but not limited to, ceiling tiles, chilled ceiling systems, heating and cooling exchange units, wall panels, computer room floor tiles, raised access floor panels, curtain walling sections, suspended ceiling sections, extrusions for lightweight concrete floors, window and door frames, sleeving for heating and ventilation pipe work or ducting, and telecommunication and data rooms.

In a further embodiment, a binder formulation having very high enthalpy, for example over 100kJ/kg, or over 150kJ/kg, utilising a secondary binder of the type disclosed in GB2344341 (so-called PFA binder) is detailed in Examples 9 and 10. Table 8. Where a secondary binder is utilised.

Table 9. Molar ratios for MgO:MgCI₂:H₂0 and weight ratios for cement:PCM in Examples 9 and 10

This gives a binder having a Euroclass fire rating of E/F. This secondary binder comprises a dry, inert powder such as fly ash, pulverised rock or recycled building waste, phosphogypsum which is a by product of phosphoric acid production for phosphate fertiliser, and an alkaline salt of any metal and so may also be an industrial waste or by-product, for example, from cellulose production. The dry, inert powder may be a major proportion by weight and may comprise 65-85%, preferably 74-76% by weight of the secondary binder. The alkaline salt may comprise 0.2- 1.0%, preferably 0.4-0.6% by weight of the secondary binder. By way of example only, a secondary binder comprising fly-ash (75%), phosphogypsum (24.5%) and an alkaline salt (0.5%) would be preferred for a variety of constructional materials. A suitable secondary binder is available from AMPC International Technologies (Cyprus) Ltd and has the product code 1ST. It is a quick setting, fireproof, lightweight, high thermal resistance compound. A wide variety of secondary binders may be used as described below.

In the formulation process where a magnesium cement binder and phase change material is used, preferably the secondary binder is added when both of the aforementioned components have been mixed. It is recommended that the mixture of magnesium cement binder, phase change material and secondary binder is stirred vigorously for a further 10-15 minutes at high speed after the secondary binder has been added. This is to ensure that there is even dispersion of the secondary binder within the mixture. In this formulation, the weight : weight ratio of secondary binder to phase change material is 1 :3.

The use of a secondary binder provides components that can be used in cooling systems, both passive and mechanical. These include chilled beam systems, ceiling tiles and computer/raised access floor panels, wall panels for computer data and server rooms, isolated telecommunication rooms. The important aspect of using the secondary binder with the phase change material is that it is preferably used in an encasement which is made from either aluminium, copper, steel, rigid PVC, timber, plastics, glass, graphite, concrete, and cementitious or gypsum floor screeds.

In a further embodiment, a secondary binder, including a secondary binder of the type described above, may be used alone. In this context the secondary binder therefore takes on the role of a primary binder. A mixture of a secondary binder along with the phase change material, and excluding a magnesium cement binder, yields higher enthalpy values of 150kJ/kg and above. This is because the nature of the secondary binder allows for a higher volume of phase change material by weight to be added to a small volume by weight of the secondary binder. However the drawback of the secondary binder, when used in this way, is that it has limited or non-existent fire resistant properties and therefore will only achieve Euroclass classification F. As such the formulation can only be used in embodiments that consist of an encasement of some description that meets the local or national minimum building regulation standard. Examples of suitable encasement materials include but not limited to aluminium, copper, steel, graphite, timber, rigid P.V.C. and these encasements are described in more detail below.

Where the formulation does not include a magnesium cement binder, the secondary binder, or in that case the binder, and water are mixed for 5-10 minutes at high speed prior to the phase change material being added. After adding the phase change material the mixture is mixed for a further 10 - 15 minutes.

In this formulation, the weight ratio of secondary binder to phase change material is 1 :5. The average mean enthalpy of preparations of this type is far superior than any achieved using a Sorel cement formulation. However they generally need to be encased in aluminium or copper to give fire resistance.

In these high enthalpy embodiments, an intumescent agent of the type described above may also be added.

Pozzolan Cements

In a first step, a pozzolan i.e. Pulverised Fuel Ash (PFA), Rice Husk Ash (RHA) or Metakaolin, is blended with Calcium Oxide (CaO)/lime in a ratio range of 1 : 1 to 1 :4 (CaO: pozzolan) by weight to form the basis for a high strength pozzolan cement or alternatively a ratio of 1 :5 to 1 :10 by weight for a weaker formulation where strength is not a requirement, such as when the latent heat storage material is used in an encasement or composite panel assembly as described below.

The blend of pozzolan and CaO is suspended in water of a reasonable purity such as tap water, in which Calcium Hydroxide (Ca(OH)₂) is formed, by mixing for a minimum of 15 minutes to form the pozzolan cement.

Microencapsulate phase change material such as Micronal® from chemical company BASF, is slowly mixed to the pozzolan cement. The addition of glass fibres can be added to the pozzolan with PCM to prevent cracking during the curing stages.

Fillers can be added to the pozzolan cement/PCM composition where a higher density and strength characteristics are required. The said fillers can include but are not limited to, quartz, stone, limestone, silica sand, stone dust, perlite, marble or graphite.

Some examples of pozzolan cement/PCM compositions as well as magnesia cements and magnesium chloride binder compositions are given in Tables 10, 11 and 12 and Tables A - F.

Table 10: Where Pozzolan used is Pulverised Fuel Ash (PFA)

Table 1 : Where Pozzolan used is Rice Husk Ash (RHA)

Example 14 Example 15 Example 16

Rice Husk Ash (RHA)

100 100 400 (grams)

Calcium Oxide (CaO)

100 100 100 (grams)

Water (grams) 600 400 1000

Silica Sand (grams) 100 - -

BASF Micronal® PCM 700 400 1000 (grams) Table 12: Where Pozzolan used is Kaolin

Table A

Table A1

Table A2

Table A3

Table B

Table C

Table D

Table E provides an example of a latent heat storage material using magnesium chloride as a binder.

Table E

Table F

Sample using Organic Microencapsulated Phase

Sample 6

Change Material and Baume of 12°

BASF Micronal® DS 5000X (grams) 2500

NEDMAG(RTM) MgCI₂ (grams) 1000

10

Glass Fibre Strands (grams)

Baymag MgO - comprising of:

Magnesium Oxide: 94 - 98% (wt wt) 1000

Calcium Oxide: 1.5 - 4%

Water 2750 Table G 1 :10 CaO:pozzolan example

Table H Various ratios of CaO to Pozzolan

According to a further aspect of the present invention there is provided a composite panel assembly in the form of an encasement having an interior region, in which the interior region includes a latent heat storage material as defined herein and where the interior region further includes a honeycomb structure including a number of cells partitioned by partition walls and extending substantially across the interior region, and wherein the latent heat storage material is disposed within the cells. The shape of a section of the cell can be a polygonal shape. The polygonal shape can be a square shape, a rectangular shape, a triangular shape, or a hexagonal shape.

The honeycomb structure serves a number of functions. Firstly, because it is formed from a heat conductive material, it acts as a plurality of heat conductive elements to conduct heat from the front of the panel assembly into the body of the latent heat storage material layer. This results in a significant improvement in performance since the binders used to bind the phase change material generally have insulating properties. The binders can therefore have the effect of delaying somewhat heat transfer into the bulk of the latent heat storage material.

The honeycomb structure also acts as a support element and adds strength and rigidity to the composite panel assembly encasement without adding significantly to the weight. In this disclosure the terms "composite panel assembly" and "encasement" are used interchangeably. This additional strength and rigidity is particularly important in certain applications such as ceiling tiles and floor tiles. A further advantage of a honeycomb structure is that it segregates the latent heat storage material into small, discrete pockets or cells. Certain cement binders used to bind the PCM have a tendency to distort over time. By dividing the bulk of the latent heat storage material into discrete cells or aliquots, this tendency is very much reduced and often substantially eliminated. This means that a very much wider range of cements can be used than would otherwise be the case.

Furthermore, it is not necessary that the support elements or the heat conducting elements take the form of a honeycomb or other polygonal structure. They can also be fins or ribs, optionally the length and width of the panel as shown in diagram 2a. In fact, these elements can take a wide variety of structural form, including ribbons, crenulated divisions, mesh and a plurality of protrusions. This list is not intended to be exhaustive but simply illustrates the wide range of structures that can be used to create the desired effect(s).

It will be appreciated that it is advantageous that the support elements/heat conducting elements extend substantially throughout the latent heat storage material layer. However this is not essential and the elements may extend only partially through the latent heat storage material layer. Thus, in this context, the term substantially means more than at least about 30% through the latent heat storage material layer, and preferably more than at least about 50% through that layer.

The partition walls of the honeycomb, or other support elements/heat conducting elements, can comprise a metal, and the metal can be aluminium, copper, stainless steel, mild steel or a plastic such as glass-reinforced plastic (also known as fibreglass), carbon fibre reinforced plastic, Nomex (RTM) reinforced plastic, Kevlar (RTM) reinforced plastic. The latent heat storage material can include a binder and a phase change material. The binder can include calcium oxide and a pozzolana material in a ratio range of 1 :1 to 1 :50 (CaO: pozzolana) by (wt/wt), preferably 1 :1 to 1 :30 and more preferably 1 : 1 to 1 :20 by (wt/wt).

Referring now to Figure 1 , which shows an encasement having a tray part 102 and a lid part 104 forming in combination an interior region, where the interior region includes a honeycomb structure 108.

Referring now to Figure 2, which shows a plan view of the honeycomb structure 108, the structure of which includes a number of cells 1 10 partitioned by partition walls 1 12 and extending across the interior region. Individual cells tessellate or interlock with their neighbours. The shape of a section of the cell can be a polygonal shape. The shape can be, for example, a square shape, a rectangular shape, a triangular shape, or a hexagonal shape.

Referring to Figure 2a this shows a plan view of alternative heat conducting elements, being ribbed, ribboned or finned wall structures extending substantially across the interior region.

In both Figures 2 and 2a, the partition walls can comprise a metal, for example aluminium, copper, mild steel or stainless steel or a plastic such as glass-reinforced plastic (known as fibreglass), carbon fibre reinforced plastic, Nomex (RTM) reinforced plastic, and Kevlar reinforced plastic. Thermally conductive plastics are also known, and can be used in the present invention. The walls extend substantially through the layer of latent heat storage material.

Referring now to Figure 3, which shows an encasement having a tray part 102 and a lid part 104 forming an interior region, the interior region includes a polygonal structure 108 having cells of a square shape. Referring again to Figures 1 and 3, the latent heat storage material 106 is disposed in the cells, ribbed, ribboned or finned interior region. The interior region of the tray is enclosed at its side by edges. Although only part of the edges 102A are shown in Figures 1 and 3, it will be appreciated that these edges surround substantially all sides of the encasement, to form what is, in effect, a tray. The tray has a front panel which has a first, front face, which is usually the side of the assembly which is on view when the panel assembly is in its "in use" position. The front panel also has an opposing, second face which faces inside the tray. The terms "panel front" and "front panel" are used interchangeably in this context.

Example ceiling tile sizes can be 300mm x 300mm 595mm x 595mm, 600mm x 600mm or 600mm x 1200mm to suit standard manufactured sizes, but can also be of any size. The tiles can be used in either a new build or retrofit project without the need to replace the suspended ceiling grid. The number of ceiling tiles required in a project is determined by the cooling capacity requirements of the building.

The encasement is formed from a material providing strength, heat conductance and fire-resistance. A number of such materials will suggest themselves to the person of ordinary skill in the art; particularly suitable materials include aluminium, copper, graphite, mild steel or stainless steel. Such an encasement can be used as a ceiling tile, particularly a ceiling tile which forms part of a suspended ceiling. It is also equally applicable to floor tiles or to the group of structures set out above.

The tile can, for example, incorporate an aluminium honeycomb (hexagonal cells) or mesh core (square cells) or incorporate ribbed, ribboned or finned wall sections. These can be bonded with a two part solvent free polyurethane or acrylic adhesive to what will be the underside of the surface finish of the tile and that should preferably be made of aluminium, copper, graphite, mild steel, magnesium oxide board or calcium silicate board, or gypsum plasterboard. Around the perimeter of the tile, an edge strip 102A can be incorporated which is applied to the same height as the honeycomb core. The cells within the honeycomb or mesh core, or the ribbed, ribboned or finned sections are filled with the latent heat storage material. Dependent on the latent heat storage material, which will have different fire retardant properties, a lid component can be bonded with, for example, a two part solvent free polyurethane or acrylic adhesive, to the adjacent side of the honeycomb or mesh core, and/or the edges of the front panel, thus encasing the latent heat storage material. The lid can be made of different materials but preferably aluminium, copper, graphite, mild steel, stainless steel, magnesium oxide board, calcium silicate board, gypsum plasterboard or woven glass fibre mesh. Alternatively, the lid can be formed from or incorporate an insulating material such as mineral wool, Expanded Polystyrene (EPS), polyurethane (PU), polyisocyanurate (PIR) or Aerogel blanket.

Referring now to Figure 4, which shows a ceiling tile infill comprising a honeycomb or mesh core 108 bonded to a lid 104, the cells within the honeycomb or mesh core are filled with latent heat storage material 106. The honeycomb can be aluminium. The honeycomb can be bonded with a two part solvent free polyurethane or acrylic adhesive to a sheet of material 104 that is made preferably either of aluminium, copper, graphite, mild steel, stainless steel, magnesium oxide board, calcium silicate board, gypsum plasterboard or woven glass fibre mesh and which forms the lid of the tile. With the honeycomb or mesh core face down, the tile infill is inserted into any preformed metal ceiling tile tray 102 that may form part of an existing metal ceiling system

In this case of a retro-fit operation, one would take the empty metal ceiling tile, spread a thin layer of aqueous compound or cement onto the inner surface of the empty tile and embed the honeycomb panel that has been pre-filled with latent heat storage material into the cement. It is important to ensure that substantially 100% contact is made between the ceiling tile and honeycomb core. If contact between both elements is not good then air gaps will be formed, which reduce the conductivity of heat as air is an insulating element.

Referring now to Figure 5, which shows an alternative method of assembly for the ceiling tile infill, the aluminium honeycomb or mesh 108 can be bonded to a sheet of lid 104. The lid can be made preferably either of aluminium, copper, graphite, mild steel, stainless steel, magnesium oxide board, calcium silicate board, gypsum plasterboard or woven glass fibre mesh. The honeycomb can be bonded to the lid using a two part solvent free polyurethane or acrylic adhesive. The latent heat storage material 106 can then be cast into the preformed tray 102 and the 'lid' component embedded honeycomb or mesh face down into the latent heat storage material and left to cure, ensuring that the honeycomb or mesh of the lid makes contact with the inside surface of the preformed tile.

Where the depth of honeycomb or mesh is not of the same depth as the preformed tile and so contact with the internal surface of the preformed tile is not made, the preferred method of assembly is for the honeycomb or mesh to be inserted into the preformed tile prior to the casting of the latent heat storage material. A lid component that is made preferably either of aluminium, copper, graphite, mild steel, stainless steel, magnesium oxide board, calcium silicate board, gypsum plasterboard or woven glass fibre mesh can still be embedded onto the surface of the latent heat storage material.

Referring now to Figure 6 and Figure 6A, which show a wall or ceiling panel which comprises a honeycomb 108 bonded to the internal surface of tray or panel 102. The tray or panel provides the surface finish of the wall panel. The honeycomb, which can be aluminium, copper, stainless steel, mild steel or a plastic such as glass-reinforced plastic (also known as fibreglass), carbon fibre reinforced plastic, Nomex (RT ) reinforced plastic, Kevlar(RTM) reinforced plastic can be bonded to the lid using a two part solvent free polyurethane or acrylic adhesive. The surface finish can be of varying materials but preferably made either of aluminium, copper, graphite, mild steel, stainless steel, magnesium oxide board, calcium silicate board, gypsum plasterboard, ceramic or marble. The cells within the honeycomb core are filled with the latent heat storage material 106. Once cured, a lid 104 comprising insulating material is bonded to the exposed side of the honeycomb core. The insulating material can be bonded to the honeycomb with a two part solvent free polyurethane or acrylic adhesive, or other adhesive as selected by the materials expert. The insulation material can be preferably mineral wool, Expanded Polystyrene (EPS), polyisocyanurate (PIR) or an Aerogel blanket.

The thickness and composition of the material used in construction of the panel front 102 and the panel back or lid 104 may vary, depending on the application requirements, and as determined by the material specialist. A further example is illustrated in Figure 6A.

The panels can also be of varying thickness and used as part of a metal or timber stud partitioning system or fixed directly to existing substrates. Panels are fixed to the substrate using either a mechanical fixing or adhesive bonding. They can also incorporate an inter-locking mechanism such as a cam-lock device.

The design of the wall or ceiling panels can vary, examples of which can include canopy or sails. These can be architectural features that are suspended over areas where there are specific areas with high heat gains such as refrigeration units or display lighting such as in retail environments.

Referring now to Figure 7, which shows a raised access floor tile, beneath which electrical, data and communication cabling and services are hidden. These can generate a substantial amount of heat that contributes to the overall internal heat gains of the building. In listed or old buildings with limited floor to ceiling heights where it is impossible to install modern HVAC systems, the raised access floor system with phase change material can be used as an alternative.

Most modern buildings are constructed from lightweight materials with high heat gains. Installing a raised access floor system with phase change material gives the building thermal mass using a passive system.

Used with raised flooring accessories including pedestals and bearers 702 and 703 that are already commercially available, this embodiment consists of honeycomb 108 bonded to the underside of lid 104 which can be made from a number of materials, preferably aluminium, copper, graphite, mild steel, stainless steel, ceramic or marble. The honeycomb can be an aluminium foil core and typically can have a thickness/depth of between 25mm - 50mm. The honeycomb core can be bonded with a two part solvent free polyurethane or acrylic adhesive to the underside of the finished surface material. The cells within the honeycomb core are filled with the latent heat storage material 106 and left to cure / semi-cure, before edge strips and a sheet to the underside of the raised access floor tile are bonded with a two part solvent free polyurethane or acrylic adhesive, so that the latent heat storage material is fully encased in a tray structure 102. These panels can replace existing raised access floor panels or form part of a new installation.

Referring now to Figure 8, this shows a worktop or desk 802. The principle of the invention can be used for a wide number of items of furniture or work surfaces. For example, the honeycomb core 108 of a desk can be aluminium honeycomb foil that can be of any thickness. However for the purpose of this example, an overall thickness/depth of between 15mm - 25mm for the worktop/desktop is preferred. The honeycomb is bonded to the underside of lid 104. The honeycomb can be bonded to the lid with a two part solvent free polyurethane or acrylic adhesive on one side to what will be the underside of the worktop / desktop. The cells within the honeycomb core are filled with the latent heat storage 106 material and left to cure / semi-cure, before edge strips and a sheet 102 are bonded to the underside of the worktop/desk. The edge strips and sheet can be bonded using a two part solvent free polyurethane or acrylic adhesive, so that the latent heat storage material is fully encased. The preferred material used as the surface finish, edge detail and underside of the worktop/desktop would be a good thermal conductor such as aluminium, copper, graphite, ceramic, mild steel or stainless steel that can receive various finishes including high pressure laminates (HPL), timber and plastic laminates or paint/powder coat finishes.

It will be appreciated that composite panel assemblies according to the present invention consists of a panel front, a first face of which will be visible when the panel assembly is in use, one or more support elements or heat conducting elements which transmit heat through the body of the panel, and, optionally, a panel back or lid. The interior region between the panel front and panel back is substantially filled with a latent heat storage material. The heat conducting element(s) can take a wide variety of forms but a honeycomb structure is preferred for many applications. The heat conducting elements(s) may be attached by some attachment means to the internal surface of the panel front or the panel back by some attachment means such as chemical bonding or welding. In this description the term "plurality" means one or more. As an alternative to heat conducting support elements, or as an adjunct to them, a thermally conductive matrix can be added to the body of the latent heat storage material. This matrix can take a wide variety of forms and a number of materials are known which can increase heat conduction within a composite solid, such as a cement. These materials include graphite, powdered metal or metal fragments or strips, expanded metal foam, heat conducting plastics, carbon fibre, or combinations thereof. This list is not intended to be exhaustive but simply illustrates the wide range of materials that can be used to improve heat conduction.

Referring now to Figures 9a-c, which show a cooled ceiling panel, a honeycomb core 108 is bonded to the reverse side of what will be the finished surface 102. The honeycomb, which can be aluminium, copper, mild steel, stainless steel or a plastic such as glass-reinforced plastic (also known as fibreglass), carbon fibre reinforced plastic, Nomex (RTM) reinforced plastic, Kevlar (RTM) reinforced plastic, can be bonded to surface 102 with a two part solvent free polyurethane or acrylic adhesive. The surface material should have good thermal conductivity and can be aluminium, copper, graphite, mild steel, stainless steel or ceramic. Through the cell walls of the aluminium honeycomb, along the length of the panel, pipes 902 are bored. The number of pipes through the honeycomb is determined by the width of the panel and also the speed at which the stored latent heat is to be discharged from the phase change material. The greater the number of pipes the faster the stored latent heat is discharged. The pipes are preferably copper tubes, and have connectors to allow connections to other adjoining panels or connections to the main cooling circuit to be made. In one embodiment, at either end of the panel, the ends of the tubes are bent vertically at 90° in order to protrude through the encasement lid part 104. The lid can be made of a good thermal conductive material.

Before the lid is fixed into place the cells within the honeycomb core are filled with latent heat storage material 106 and left to cure. The copper pipe returns are connected to a chilled water circuit and/or to a series of chilled ceiling panels.

Through the copper pipes a supply and return flow of water with a temperature of between 13°C and 17°C passes through a circuit. As the water passes through the panels, heat stored in the phase change material is conducted into the flow of chilled water, which returns to a chiller unit. At the chiller unit, the return flow of water, which has an increased temperature, is chilled to 13°C and 16°C before restarting the circuit.

Referring now to Figure 9d, this shows a typical circuit for cooling water. Cooled water with a temperature of between 13°C and 17°C is pumped through the copper pipe work circuit and through the ceiling tile. As the water passes through each tile, the latent heat that is stored within the high enthalpy compound is transferred through the copper tube and into the flow of cooled water. The water, which has now increased in temperature, continues through the circuit back to a heat- exchange unit such as the water coils supplied by S & P Coil Products Limited, Leicester. The heat exchange unit will contain a high heat conductive metal encasement that is also filled with a high enthalpy compound such as those described above. This is to allow the heat from the returning water supply to be transferred to the panel and thus cool the water back to between 13°C and 16°C, ready to restart the circuit.

Tempered or chilled air for night time cooling and purging daytime heat gains can also be passed through the pipes as an alternative method for discharging the stored latent heat within the building. In this instance the pipes can be connected to an external vent with a fan unit to pull the external night air through the pipe work circuit.

The diameter of the copper tube varies and can be of a diameter such as those of standard copper tubing i.e. from 15mm, 22mm, 28mm, 35mm, 42mm, 54mm, 67mm, 76mm and 108mm. The preferred diameter of copper tube is between 15mm and 28mm so as to minimise the weight and dimensions of the tile and subsequent need for structural support.

The encasement or panel assembly can be formed from a metal sheet by cutting, folding or pressing. For example, the metal sheets can be aluminium, copper, stainless steel or mild steel sheets manufactured and supplied preformed by companies such as Armstrong World Industries, Inc, USA, USG (United States Gypsum), USA, Lidner GmbH, Germany, SAS International, UK. The thickness of gauge is generally in the range 0.5 - 1.5mm.

The two parts of an encasement, a tray part 102 and a lid part 104 form an interior region which together encases an infill component 106. The encasement is a material providing strength, heat conductance and fire-resistance. Strength may be provided by incorporating honeycomb, ribbed, ribboned, or finned sections on the inside of the tray part. A number of such materials will suggest themselves to the person of ordinary skill in the art; particularly suitable materials include aluminium, copper, graphite, mild steel and stainless steel. For example, the tray part is a pressed aluminium, copper, mild steel or stainless steel base section manufactured and supplied preformed.

The latent heat storage material used as an infill component can take a wide variety of forms. It must contain a phase change material and usually contains a binder. A non-exhaustive range of suitable phase change materials are described above and it is intended that any suitable phase change material could be used, including those not yet discovered. Likewise, a wide variety of suitable binders are described above. This disclosure is intended to include all suitable binders, including those binders yet to be discovered.

One suitable range of binders is magnesia cements. Examples of latent heat storage materials including suitable magnesia cements are described in GB 2462740A (Berry and Scanlon), the entire text of which is hereby imported by reference and is intended to form an integral part of this disclosure.

The use of support elements which segregate the latent heat storage material into discrete segments is particularly beneficial when using magnesia cements. This is because magnesia cements have a tendency to deform and distort over time. Without these elements a ceiling tile would inevitably deform after a period of time. The infill component can advantageously be provided by latent heat storage formulations described above and as claimed herein. The infill component may be cast into the encasement in various ways, including the method shown in Figure 5.

The lid part is typically manufactured from aluminium, copper, graphite, mild steel or stainless steel sheet but can also be magnesium oxide board, calcium silicate board, gypsum board, woven glass fibre mesh or a plastic such as a plastic such as glass-reinforced plastic (also known as fibreglass), carbon fibre reinforced plastic, Nomex (RTM) reinforced plastic, Kevlar (RTM) reinforced plastic. The lid part is bonded to the cast aluminium base section, for example by using a polyurethane adhesive.

The performance of an encasement or panel assembly of the present invention has been investigated in a thermal test chamber. The encasements were placed in a thermal test chamber, which itself was located in a larger environmental test chamber. This allows control of conditions outside the test chamber so that temperature differentials between the interior and exterior of a building, room, or office could be simulated. Honeycomb ceiling panels were repeatedly subjected to typical summer day and night temperatures under different degrees of ventilation. The experiment examined the effect of the honeycomb ceiling panels on the temperature inside a test cell repeatedly subjected to typical summer day and night temperatures under different states of ventilation in a climate chamber. The test cell was to simulate an actual room, and contained a heater to simulate typical thermal heat loads that result from the human body, electrical and mechanical equipment, lighting, and the like. The panels contain microencapsulated PCM composite and the tests were to determine the efficiency of the tiles in maintaining lower indoor temperature compared to a situation without them. For discharging the panels, conditions of low and high ventilation rates using 17°C overnight temperature from 17hrs - 9hrs in the climate chamber was tested. In charging, 25°C was used as daytime temperature from 9hrs - 17hrs under zero, low and high ventilation rates. Results from the experiment showed that indoor temperatures were reduced by margins between 2°C and 7°C for different ventilation rates when the panels are installed. Table 13

The aim of this experiment was to test and determine the thermal performance of honeycomb ceiling tiles/panels in a semi-active cooling application. The product tested, honeycomb ceiling panels, consists of a composite impregnated with microencapsulated phase change material in a 600mm x 600mm x 5mm ceiling panel. This was experimentally investigated in an 1800mm x 1800mm x 1700mm test cell before DSC analysis was carried out. Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and a reference is measured as a function of temperature. This is used to determine enthalpy (kJ/kg). Phase change materials store energy in a latent form. They undergo an endothermic process of phase change to store heat energy when ambient temperature rises and an exothermic process to release this energy when the temperature drops. In building applications, these processes are desirable in a narrow temperature range close to the human comfort temperature with a large amount of heat being absorbed and released. Phase change materials can be incorporated into different building materials. They have been used in gypsum wallboards, plaster and concrete, and which absorb heat energy in summer to reduce peak cooling loads and this can be of serious economic benefit in reducing HVAC systems running costs.

1. Equipment and Materials

Table 14

EQUIPMENT DESCRIPTION

Climate chamber Typical summer temperatures of 25°C and 17°C at night were maintained in the climate chamber with humidity left as ambient. Humidity didn't vary much and was similar for subsequent day and night experiments

Test cell See the structure of the test cell in the

Figure 1 1 below.

Type K thermocouples These are installed in various points in and out of the test cell. The position, tag and description of each thermocouple are given in Figures 12 to 16 and Table 16.

8-port data loggers These provided logging at 1 minute

intervals

Globe thermometer This contains a type K thermocouple at the centre of a 101.6mm diameter black copper sphere to measure the mean radiant temperature as described by EN ISO 7726. This is another indicator of thermal comfort and sometimes considered better than ordinary air temperature.

Heat flux sensors These are installed on opposite surfaces of the tiles during the experiment. Data from these sensors gave the

experimental heat transfer coefficients and their variation under the different conditions simulated.

Speed Controller The fan and test cell has been calibrated to deliver a maximum ventilation flow rate of 14.91/s at normal voltage and 1 1.7l/s at 130V. This was used in changing the flow rates between these two values

Electric Heater The Heater provides 150W of cooling load

Intake & Outlet guard A zero ventilation scenario was tested using this guards to block the vents

Fan The fan was installed in the outlet vent above the ceiling grid to draw air over the tiles from the inlet. I believe this is a possible way of discharging these tiles in real building applications when the heat is not needed.

Differential Scanning Calorimeter Brand: TS instruments 2. Experimental Procedure

Climate Chamber Tests

Date & Run Start Stop Climate Ventil Heat Relative Time Time & Time & Chamber -ation -ing humidity

Date Date Set point Rate (W)

7/6/2010 16hrs 17:00hrs 9:00hrs 17°C High 0 51 17:00hrs Initial 7/6/2010 8/6/2010

Discharge

8/6/2010 8hrs 9:00hrs 17:00hrs 25°C Zero 150 69.31 9:00hrs Charge 8/6/2010 8/6/2010

8/6/2010 16hrs 17:00hrs 9:00hrs 17°C High 0 51.52 1 :00hrs Discharge 8/6/2010 9/6/2010

9/6/2010 8hrs 9:00hrs 17:00hrs 25°C Low 150 68.92 9:00hrs Charge 9/6/2010 9/6/2010

9/6/2010 16hrs 17:00hrs 9:00hrs 17°C High 0 51.39 17:00hrs Discharge 9/6/2010 10/6/2010

10/6/2010 8hrs 9:00hrs 17:00hrs 25°C Low 150 71.9 9:00hrs Charge 10/6/201 10/6/2010

0

10/6/2010 16hrs 17:00hrs 9:00hrs 17°C Low 0 54.12 17:00hrs Discharge 10/6/201 11/6/2010

0

11/6/2010 Test End 69.95 9:00hrs

Table 16: Thermocouples name meaning Inside/Outside

EW1 External wall 1 (wood) Outside

EW2 External wall 2 (wood) Outside

WB Wall Bottom (plasterboard) Inside

WM Wall Middle (plasterboard) Inside

WT Wall Top (plasterboard) Inside

CS1 Ceiling Surface 1 (plasterboard) Inside

CS2 Ceiling Surface 2 (plasterboard) Inside

CS3 Ceiling Surface 3 (plasterboard) Inside

Al Air Inlet Inside

AO Air Outlet Inside

BB Black Ball Inside

AHL Air High Level Inside

ALL Air Low Level Inside

OA1 Outside Air 1 Outside

OA2 Outside Air 2 Outside

OA3 Outside Air 3 Outside

AHL2 Air High Level 2 Inside

AHL3 Air High level 3 Inside

AHL R2 Air High Level Recessed 2 Inside

AHL R3 Air High Level Recessed 3 Inside

CEILING Heat Flux Sensor on PCM Surface Inside

WALL Heat Flux Sensor on Tile Surface Inside

Tile 1 Tile Middle Corner Inside

Tile 2 Tile Surface Centre Inside

Tile 3 Tile Middle centre Inside

Tile 4 PCM Surface Centre Inside DSC Analysis

Three samples from each of the two tiles where tested, one from the centre and two from the extreme edges of each on opposite sides to eliminate any error that could be introduced by varying concentration of the PCM within the composite. The initial test runs were done at a slow ramp rate of 2°C/min but subsequent ones were sped up to 4°C/min and isothermal times to 3min. Results from the two ramp rates exhibited similar behaviours. The test run is as follows:

Equilibrate at 20°C

Ramp at 2°C/min to 40°C

End of cycle 1

Isothermal for 5mins

Ramp at 2°C/min to -20°C

End of cycle 2

Isothermal for 5min

Ramp at 2°C/min to 40^aC

End of cycle 3

Isothermal for 5mins

Ramp at 2°C/min to -20°C

End of cycle 4

Isothermal for 5min

End of run

The two thermocouples AHL2 and AHL3 recorded similar values as they were at the same level, just spaced apart to eliminate any effect the heater might have by being directly below either thermocouple. In zero ventilation conditions the tiles containing PCM composite sample 74 maintained air temperatures which peaked at just above 26°C after an 8 hour period. Compared to the temperature profile of an ordinary test cell without the tiles, between 2°C and 7°C difference was observed.

The DSC thermal analysis is presented for the range -20°C to 40°C. The results of three DSC runs on sample 73, including average melting temperature, freezing temperature and latent heats, are given in the table 17 below. Table 17: Sample 73 Thermal Properties

Table 18: Sample 74 Thermal Properties

To determine the percentage of microencapsulated PCM in the different samples, additional DSC runs were performed on the Micro-encapsulated PCM. The results are presented in Table 19 below. Both DSC runs on the Micro-encapsulated PCM revealed the thermal property follows;

Freezing temperature of 22°C

Melting temperature of 23.24°C

Latent heat of Freezing of 122.2 J/g

Latent heat of Melting of 124 J/g

Table 19: Latent heat comparison

Further tests were carried out in the thermal chamber to compare the performance of an aluminium honeycomb tile with that of a standard metal tile, a drywall tile and a standard metal tile containing the latent heat storage material without the honeycomb structure. The results of these tests are shown in Table 20 below and Figure 10.

Table 20. Comparison of Aluminium Honeycomb Tile with latent heat storage material

Summary:

The thermal chamber was subjected to a cooling load of 300W (31 W/m²) and the AC Unit (air conditioning unit) had a set point of 26.7°C. Tests were conducted over a simulated working day period over two days. The heat gains during the day were purged through night time cooling by setting the air conditioning unit at a low operating mode of 17°C. The result of the tests shows a reduced energy requirement of 55% by utilizing the honeycomb tile with RACUS PCM compared to a standard metal tile without PCM. The heat gains that were stored in the honeycomb tile with RACUS PCM throughout the day, resulted in the air conditioning only starting running after 6 hours 47 minutes compared to a standard metal tile whereby the air conditioning started running after 3 hours 27 minutes, a difference of 3 hours 20 minutes.

Conclusion From the experimental results, the PCM composite tested has an important potential of thermal energy storage in ceiling tiles. Importantly, the possibility exists to incorporate much more PCM latent heat storage material per unit area than was present in the tiles used in these experiments.

Claims

1. A latent heat storage material formed from a mixture comprising a binder, a phase change material and water wherein the weight ratio of the binder to water used in the preparation of the latent heat storage material is in the range 3:1 to 1 :20.

2. A latent heat storage material according to Claim 1 wherein the weight ratio of the binder to water used in the preparation of the latent heat storage material is in the range 1 :1 to 1 :20 and more preferably 1 :1 to 1 :5.

3. A latent heat storage material according to Claim 1 or Claim 2 wherein the binder is selected from the group comprising:- a cement;

an Ordinary Portland Cement (OPC);

a magnesia cement;

a pozzolan cement;

a magnesium chloride solution; and mixtures thereof.

4. A latent heat storage material according to any of Claims 1 to 3 inclusive wherein the binder comprises a magnesia cement formed from magnesium chloride, magnesium oxide and water.

5. A latent heat storage material according to Claim 4 wherein the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :15 to 1 :36.

6. A latent heat storage material according to Claim 5 wherein the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :17 to 1 :32

7. A latent heat storage material according to any of Claims 4 to 6 inclusive wherein, during the preparation of the magnesia cement, the said magnesium chloride is dissolved in said water to give a solution having a Baume value in the range 12" to 27.5°.

8. A latent heat storage material according to Claim 7 wherein the Baume value of the magnesium chloride solution used in the preparation of the magnesia cement is in the range 15° to 26°.

9. A latent heat storage material according to any of Claims 4 to 8 inclusive wherein the molar ratio of said magnesium chloride to said magnesium oxide used in the preparation of the magnesia cement is in the range 1 :1 to 1:5.5.

10. A latent heat storage material according to any of Claims 7, 8, or 9 wherein the weight ratio of magnesium chloride : magnesium oxide : water : organic phase change material is about 1 :1 :2.3:1 ± 20%.

11. A latent heat storage material comprising according to any of Claims 1 , 2 or 3 wherein the binder comprises a pozzolan cement.

12. A latent heat storage material according to Claim 1 wherein the pozzolan cement comprises calcium oxide and a pozzolan and water, and wherein said calcium oxide and said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :10 (CaO: pozzolan) by weight.

13. A latent heat storage material according to Claim 12 wherein the said calcium oxide and the said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :4 (CaO: pozzolan) by weight.

14. A latent heat storage material according to any of Claims 11 to 13 inclusive wherein the ratio of binder (i.e. CaO + Pozzolan) to water is in the range 1 :1 to 1 :5 binder to water by weight.

15. A latent heat storage material according to any of Claims 11 to 14 inclusive wherein the pozzolan is selected from the group comprising:- pulverised flue ash (PFA)

kaolin, including metakaolin;

rice husk ask (RHA);

pozzolana;

silica fume;

ground granulated blast furnace slag; and mixtures thereof.

16. A latent heat storage material according to any Claims 11 to 15 inclusive additionally comprising glass fibre.

17. A latent heat storage material according to Claims 1 , 2 or 3 wherein the binder comprises a magnesium chloride solution formed from magnesium chloride and water, the magnesium chloride solution being substantially free from magnesium oxide or other metal oxides.

18. A latent heat storage material according to Claim 17 wherein the molar ratio of magnesium chloride to water used in preparation of the binder is in the range 1 :15 to 1 :36.

19. A latent heat storage material according to Claim 17or Claim 18 wherein the molar ratio of magnesium chloride to water used in the preparation of the binder is in the range 1:17 to 1 :32

20. A latent heat storage material according to Claims 17 to 19 inclusive wherein, during preparation of the magnesium chloride solution, the said magnesium chloride is dissolved in water to give a solution having a Baume value in the range 12° to 27.5° and preferably 15° to 26°.

21. A latent heat storage material according to any preceding claim wherein the material further comprises one or more fillers.

22. A latent heat storage material according to Claim 21 wherein the filler is selected from the group comprising:- quartz;

stone and stone dust including limestone;

silica sand;

perlite;

marble;

graphite;

ceramic powders;

wood dust

flax sheaves;

hemp; straw;

glass fibre strands; and mixtures thereof.

23. A latent heat storage material according to any preceding claim wherein the phase change material comprises up to 99% by weight of the latent heat storage material, and preferably 30% - 95% by weight of the latent heat storage material.

24. A latent heat storage material according to any preceding claims wherein the panel is 20 mm thick and the heat storage capacity of the material is in the range 300 - 3500 kJ/m².

25. A latent heat storage material formed from a mixture comprising binder, a phase change material and water substantially as herein described.

26. A latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a magnesia cement formed from magnesium chloride, magnesium oxide and water, characterised in that the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 :15 to 1 :36.

27. A latent heat storage material according to Claim 26 wherein the molar ratio of said magnesium chloride to said water used in the preparation of the magnesia cement is in the range 1 : 17 to 1.32

28. A latent heat storage material according to Claims 26 or 27 wherein, during the preparation of the magnesia cement, the said magnesium chloride is dissolved in said water to give a solution having a Baume value in the range 12° to 27.5°.

29. A latent heat storage material according to Claim 28 wherein the Baume value of the magnesium chloride solution used in the preparation of the magnesia cement is in the range 15° to 26°.

30. A latent heat storage material according to any of Claims 26 to 29 inclusive wherein the molar ratio of said magnesium chloride to said magnesium oxide used in the preparation of the magnesia cement is in the range 1:1 to 1 :5.5.

31. A latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a pozzolan cement.

32. A latent heat storage material according to Claim 31 wherein the pozzolan cement comprises calcium oxide and a pozzolan and water, and wherein said calcium oxide and said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1 :1 to 1 :10 (CaO:pozzolan) by weight.

33. A latent heat storage material according to Claim 32 wherein the said calcium oxide and the said pozzolan used in the preparation of the pozzolan cement are present in a ratio of 1:1 to 1:4 (CaO: pozzolan) by weight.

34. A latent heat storage material according to any of Claims 31 to 33 inclusive wherein the ratio of CaO + pozzolan to water is in the range 1 :1 to 1 :5 (CaO + pozzolan) to water by weight.

35. A latent heat storage material according to any of Claims 31 to 34 inclusive wherein the pozzolan is selected from the group comprising:- pulverised flue ash (PFA)

kaolin, including metakaolin;

rice husk ask (RHA);

pozzolana;

silica fume;

ground granulated blast furnace slag; and mixtures thereof.

36. A latent heat storage material according to any Claims 31 to 35 inclusive additionally comprising glass fibre.

37. A latent heat storage material formed from a mixture comprising a binder and a phase change material wherein the binder comprises a magnesium chloride solution formed from magnesium chloride and water, the magnesium chloride solution being substantially free from magnesium oxide or other metal oxides.

38. A latent heat storage material according to Claim 37 wherein the molar ratio of magnesium chloride to water used in preparation of the binder is in the range 1 :15 to 1 :36.

39. A latent heat storage material according to Claim 37or Claim 38 wherein the molar ratio of magnesium chloride to water used in the preparation of the binder is in the range 1 :17 to 1 :32.

40. A latent heat storage material according to Claims 37 to 39 inclusive wherein, during preparation of the magnesium chloride solution, the said magnesium chloride is dissolved in water to give a solution having a Baume value in the range 12° to 27.5°.

41. A latent heat storage material according to Claim 40 wherein, during preparation of the magnesium chloride solution, the said magnesium chloride is dissolved in water to give a solution having a Baume value in the range 15° to 26°.

42. A process for making a latent heat storage material comprising a binder a phase change material and water wherein said binder is a magnesia cement comprising the steps of:

(b) adding magnesium oxide to said magnesium chloride solution;

43. A process according to Claim 42 wherein the Baume value is in the range between 15° to 26°, and preferably 15° to 22°.

44. A process according to Claim 42 or 43 additionally comprising the step of adding a secondary binder.

45. A process according to Claim 44 wherein the secondary binder comprises a pozzolan.

46. A process according to Claim 45 wherein the pozzolan is selected from the group comprising:- pulverised flue ash (PFA)

kaolin, including metakaolin;

rice husk ask (RHA);

pozzolana;

silica fume;

ground granulated blast furnace slag; and mixtures thereof.

47. A process for making a latent heat storage material comprising a binder and a phase change material wherein said binder is a magnesium chloride solution comprising the steps of:-

(a) dissolving magnesium chloride in water to form a solution having a Baume value in the range of 12° to 27.5°;

(b) adding a phase change material to said magnesium chloride solution;

(c) baking the mixture.

48. A process according to Claim 47 wherein the Baume value is in the range of 15° to 26°, and preferably 15° to 22°.

49. A process according to Claim 47 or 48 additionally comprising the step of adding a secondary binder.

50. A process according to Claim 49 wherein the secondary binder comprises a pozzolan.

51. A process according to Claim 50 wherein the pozzolan is selected from the group comprising:- pulverised flue ash (PFA) kaolin, including metakaolin;

rice husk ask (RHA);

pozzolana;

silica fume;

ground granulated blast furnace slag; and mixtures thereof.

52. A process according to any of claims 42 to 51 inclusive wherein the process comprises the additional step of adding one or more fillers.

53. A process according to Claim 52 wherein the filler is selected from the group comprising:- quartz;

stone and stone dust including limestone;

silica sand;

perlite;

marble;

graphite;

ceramic powders;

wood dust

flax sheaves;

hemp;

straw;

glass fibre strands; and mixtures thereof.

54. A process for the preparation of a latent heat storage material substantially as wherein described.

55. A composite panel assembly containing a latent heat storage material according to any of Claims 1 to 41 inclusive, said composite panel assembly comprising:- (i) a panel front having a first face and an opposing second face, said panel front comprising a thermally conductive material;

(ii) a latent heat storage material layer comprising a phase change material;

(iii) a plurality of support elements; wherein the support elements are embedded in the latent heat storage material layer to provide support to that layer.

56. A composite panel assembly according to Claim 55 wherein the plurality of support elements segregate the latent heat storage material layer into discrete sections.

57. A composite panel assembly as claimed in Claim 55 or Claim 56 wherein the plurality of support elements extend from the opposing second face of the front panel into and substantially through the latent heat storage material layer

58. A composite panel according to any of Claims 55 to 57 inclusive wherein some or all of the plurality of support elements comprise heat conduction elements, formed from a thermally conductive material and adapted to convey heat between the panel front and the latent heat storage material layer.

59. A composite panel assembly according to any of Claims 55 to 58 inclusive wherein the plurality of support elements comprise structures selected from the group comprising:- honeycomb structures;

polygonal structures formed from regular or irregular polygons;

fins;

ribs;

ribbons;

crenulations

mesh;

protrusions; and combinations thereof.

60. A composite panel assembly according to Claim 55 to Claim 59 inclusive wherein the heat storage capacity of the panel is in the range 300 - 3000 kJ/m², based on a 20 mm thick panel.

61. A composite panel assembly according to any of Claims 55 to 60 inclusive wherein the panel front further comprises one or more panel edges, said panel edges depending from the first face of the panel front or from the opposing second face of the panel front.

62. A composite panel assembly according to Claim 61 further comprising a lid, the panel front, panel edges and lid forming an encasement.

63. A composite panel assembly according to Claim 62 wherein the lid is bonded to or otherwise attached to the panel front and/or panel edges.

64. A composite panel assembly according to any of Claims 55 to 63 inclusive further comprising a tegular edge, enabling the panel to sit in a ceiling grid.

65. A composite panel assembly according to any of Claims 55 to 64 inclusive wherein the panel assembly comprises a structure selected from the group comprising:- a ceiling tile, including an acoustic ceiling tile;

a floor tile;

a raised access/computer floor tile;

a chilled ceiling panel;

a wall panel;

a panel for use in heat exchange systems;

a desk surface;

a work surface;

a sleeve e.g. for heating and ventilation pipes;

an encasement.

66. A composite panel assembly according to any of Claims 55 to 64 inclusive further comprising one or more tubes adapted to carry a cooling or heating fluid, wherein the tube(s) pass through the latent heat storage material layer.

67. A composite panel assembly according to any of claims 55 to 66 further comprising an insulating layer.

68. A composite panel assembly according to Claim 67 wherein the insulating layer is located on the side of the latent heat material layer furthest from the panel front.

69. A composite panel assembly substantially as herein described, with reference to and as illustrated in any combination of the accompanying drawings.

70. A process for the manufacture or refurbishment of a composite panel assembly according to any of Claims 55 to 69 inclusive comprising the steps of

(a) providing a first panel element and a plurality of structural/heat conduction elements;

(b) providing a phase change material in a binder in an unset form;

(c) locating the plurality of heat conduction elements adjacent to the first panel element;

(d) substantially surrounding the heat conduction elements with the phase change material and allowing it to set; (e) optionally providing and fitting a second panel element over the phase change material/heat conduction elements combination and optionally securing the second panel element to the first panel element.

71. A process for the manufacture or refurbishment of a composite panel according to any of claims 55 to 69 inclusive comprising of the steps of

(a) providing a first panel element and a plurality of heat conducting elements;

(b) securing the heat conducting elements to one face of the first panel element; (c) providing a second panel element with upstanding edges which, in combination, form a shallow tray;

(e) placing the first panel element over the second panel element such that the heat conducting elements become embedded in the phase change material.

72. A process for manufacturing or refurbishment a composite panel assembly according to any of Claims 55 to 69 inclusive comprising the steps of:-

(a) providing a tile comprising a tray element and, optionally, a back or lid element; (b) providing a plurality of heat conduction elements with a latent heat storage material precast around the heat conduction elements in a size and shape that will fit into said tray element;

(c) placing a binder cement layer into the bottom of said tray element;

73. A process for manufacturing or refurbishing a composite panel assembly substantially as herein described, with reference to and as illustrated in any combination of the accompanying drawings.