2. Background of Invention Buildings preferably are designed and constructed so as to be energy-efficient, which reduces the costs of heating and cooling. In the case of walls and ceilings of rooms within buildings, this commonly is addressed by incorporating insulating materials such as rigid foam or heat-reflective metallic sheets into a rigid element of the walls or ceilings. Improving the thermal comfort of a room by reducing the maximum temperature it reaches in warm weather and increasing the minimum temperature in cold weather also is desirable. PCMs have been used for this purpose, as well as for reducing heating and cooling costs as discussed above. Such materials exhibit a phase change at an operational temperature, in the course of which they absorb or emit heat. This gives them thermal regulating properties. PCMs have been incorporated into plasterboard which can be used as the rigid elements of walls. Preferred forms of PCMs in such wall boards have been paraffins, waxes and fatty acids. However, paraffins and waxes can present flammability problems and fatty acids, which are generally derived from meat by-products and vegetables, can give off unacceptable levels of odors. Although use of such wall boards might be convenient when constructing a new building, incorporating such wall boards into an existing room would mean replacing the existing walling of the room, which would be inconvenient and potentially so costly as to outweigh any energy savings that could be expected. PCMs used to improve thermal efficiency preferably are contained in a suitable manner to prevent them from interacting with the environment because this type of interaction can alter their physical properties. Containment is also necessary for providing structural integrity of a product to be applied to a building. Suitable containment of PCMs can improve heat transfer between the PCM and the local environment. In addition to being incorporated directly into building products such as plaster, PCMs also can be contained via macro-encapsulation. This involves placing relatively large quantities of phase change material in discrete units such as tanks, tubes, trays, panels or spheres. Alternatively, PCMs can be contained in pellets or adsorbed into media such as porous carbon, porous silica or micro-porous polypropylene, after which the pellets or porous media are further encapsulated by an organic film. Macro- encapsulation has been used for tank heat-exchangers, for packaging applications, and within sub-floor heating systems in buildings; porous media also have been used within sub-floor heating systems, in food transportation, and in comfort and medical products. Micro-encapsulation is another incorporation or containment technique. It involves coating droplets of PCMs with a continuous film of polymer to give discrete, typically micron-sized particles or micro-capsules comprising a core of PCM and a shell of a polymer that acts as a barrier between the PCM and the external environ¬ ment. Micro-encapsulated waxes are available from several companies such as Frisby Technologies Inc., Outlast Technologies Inc., and BASF GmbH. These PCMs have found many uses in textiles, fabrics and clothing. However, no inorganic salt hydrates or similar PCMs are available commercially in a micro-encapsulated form that can be exploited for use on walls and/or ceilings of buildings as a lining product. Also, neither the commercially macro- encapsulated PCMs nor the commercially available porous media are sufficiently small to be readily incorporated within linings for walls and ceilings. A means of containing PCMs such as inorganic salt hydrates has been proposed in US Patent No. 5,532,039, which describes thermal barriers in which heat storage materials are incorporated within laminate, honeycomb, corrugated and cellular packaging configurations. However, these thermal barriers require specific, non-standard manufacturing techniques. Provision of a product for application on walls and/or ceilings of rooms in buildings as a lining material that can be manufactured more easily than known products and that can be stored, transported and applied easily remains desirable.

SUMMARY OF INVENTION In a first aspect, the present invention provides a method of forming a stiff room lining from a pair of flexible sheets. Each sheet includes a base layer, a plurality of sealed chambers extending from a first surface of the base layer, and a plurality of spaces between the chambers; the chambers are arranged in a repeating pattern and are at least partially filled with one or more PCMs. The method includes connecting the sheets such that the chambers of one of the sheets are mated with the spaces between the chambers of the other sheet, thereby conferring stiffness to the room lining. A room lining with this type of interconnected arrangement of sheets constitutes another aspect of the invention. In another aspect is provided a sheet that includes a base layer and a plurality of sealed chambers extending from a first surface thereof; the chambers are arranged in a repeating pattern and at least partially filled with one or more PCMs. At least some of the chambers include a formation mounted on an exterior surface thereof for inter¬ connecting with a formation mounted on a chamber of a further sheet, similar to the first sheet, to connect the second and first sheets. In a further aspect is provided a structure for attaching to a wall, floor, or ceiling of a room. The structure includes a pair of sheets, each of which includes a base layer, a plurality of sealed chambers extending from a first surface of the base layer, and a plurality of spaces between the chambers. The chambers are arranged in a repeating pattern and at least partially filled with one or more PCMs. The sheets are connected together such that the chambers of one of the sheets are mated with spaces between the chambers of the other sheet and such that at least a portion of the base layers of each of the sheets is not in contact with (i.e., disposed apart from) at least a portion of the chambers of the opposing or other sheet so that gaps or voids thereby are formed between the sheets. The chambers of each sheet can be elongate and extend along a dimension of the base layer of the respective sheet, and the gaps formed between the sheets can be open to the environment such that air can pass therethrough. In this type of structure, an air flow production unit can be provided and disposed so as to provide air flowing through the gaps. Preferred features of the invention are set forth below, including in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: FIG. 1 is a cross section side view of embodiments of sealed chamber configurations (not to scale); FIG. 2 is a cross section side view of a configuration of sealed chambers in which the chambers are partially filled with a PCM; FIG. 3 is a plan view of arrangements of sealed chambers in accordance with embodiments of the invention; FIG. 4 is a cross section side view of a wall and/or ceiling lining including PCM; FIG. 5 is a cross section side view of sealed chamber configurations with various additional layers; FIG. 6 is a side view of exemplary clips in accordance with embodiments of the invention; FIG. 7 includes side, plan, and perspective views of embodiments of a wall and/or ceiling lining having air channels.

DETAILED DESCRIPTION FIGs. IA through 1C show a base layer 1 comprising a plastic film such as a polyester, polyethylene, or polyproplyene film. A heat sealable layer optionally can be provided on the film. The film can suitably be metallized to improve its resistance to penetration by water vapor, or alternatively an aluminium sheet can be used. Layer 2A (or layer 2B in FIG. IB) may be made of a thermoplastic material, such as low density polyethylene, acrylics, crystalline polyester, high impact polystyrene, poly( vinyl chloride), or polycarbonate. This layer has a series of depressions that can suitably be formed by thermally treating and depressing a layer of plastic film at regular spacings with a suitably shaped machine tool. Suitable techniques include thermoforming and cold forming. FIG. 1C shows a sealed chamber configuration commonly used for encasing pharmaceutical products such as tablets and capsules; the technology currently used for producing pharmaceutical blister packs is at an advanced stage, and the ordinarily skilled artisan can envisage that the materials, apparatus and techniques used there can be adapted easily to make them suitable for use herein. Referring again to FIG. 1, the configurations shown in FIGs. IA and IB would be appropriate for use in walls or ceilings of buildings, because these configurations allow for two identical sheets of sealed chambers to be fitted together, as shown in FIG. 4, to provide a structure 13 having two flat faces comprising base layers 1. In other words, shapes such as those shown in FIGs. IA and IB tessellate so as to leave minimal air gaps between the two sheets. Adaptation of current machinery used to produce sealed chambers can allow for one or more PCMs to be inserted into the depressions in layers 2A or 2B. Preferably, the depressions are not completely filled with PCM to allow for expansion of the PCM during changes of temperature. Base layer 1 shown in FIG. 1 subse¬ quently can be sealed to depressed layer 2, as is known from current sealed chamber technology, to form sealed chambers 12 as shown in FIG. 2. The PCMs preferably are inorganic salt hydrates, which can avoid the problems associated with paraffins, waxes and fatty acids, mentioned above. Chambers 12 can be formed in repeating patterns such that two similar sheets can be fitted together easily, with the extending chambers of a first sheet fitting into the gaps between chambers of a second sheet. Some suitable arrangements are shown in FIG. 3. It can desirable to connect two sheets 11 in such a way that it is difficult or impossible to separate them once they have been fitted together. One suitable means for achieving a non-releasable connection is to use an adhesive between two sheets 11. A preferred way is to use small protrusions, or clips, which may be made of a hard plastic material, that extend from the side walls of the chambers. An example of a suitable type of clip is shown in FIG. 6. The protrusions 9 are shaped (i.e., angled or bevelled) such that when the two chambers 12 are pressed together, the chambers may compress slightly to allow the two clips 9 to pass over one another. Once the sheets have been fully pressed together such that the chamber 12 of a first sheet is in contact with the base layer 1 of a second sheet and vice versa, clips 9 prevent the sheets from separating. Alternatively, a combination of clips and adhesive may be used. The resulting wall or ceiling lining 13 has two flat surfaces 1 between which is a high density of PCMs 3. The close tessellation of the chambers of the two sheets allows for a high density of PCM within the lining 13. The thickness of the lining may suitably be between 1 and 100 mm, and is preferably under 5 mm. In one embodiment, sheets 11 are flexible such that they may conveniently be rolled for storage and transportation; nevertheless, the sheets may be rigid. Preferably, lining 13 is rigid. Most preferably, sheets 11 are flexible but when a single sheet is connected, for example by means of clips 9, to a second sheet 11, the resulting lining 13 is rigid. Lining 13 is preferably sufficiently rigid and durable that it may be painted for decoration purposes, or wallpapers or other wallcoverings may be applied to it and subsequently removed without any damage being done to lining 13. FIG. 5 shows embodiments in which additional layers have been applied to base layer 1 of sheet 11. In FIG. 5 A, a decorated sheet 6 is attached by means of an adhesive to base layer 1. Sheet 6 may be traditional wallpaper or, alternatively, a plain sheet which may be painted or otherwise decorated once the lining has been applied to a wall or a ceiling of a room. In FIG. 5B, a self-adhesive layer 7 is shown above base layer 1, and a removable backing sheet 8 is positioned above self-adhesive layer 7. In this way, once the sheet shown in FIG. 5B is connected to a further sheet 11 to form a rigid lining 13, backing sheet 8 can be removed to expose self-adhesive layer 7, and lining 13 can be applied to the wall or ceiling for which it is intended. This allows for easy application of the insulating lining 13. In a further embodiment, two sheets 11 are connected in such a way that chambers 12 of the first sheet do not contact the base layer 1 of the second sheet and vice versa. In this way, gaps 10, shown in FIG. 7 A, are created between same surfaces of the sheets. Such a configuration can be used with sheets of the arrangement shown in FIG. 3 A. The air in gaps 10 provides insulation to further improve the thermal efficiency of the room in which the lining 13 is applied. Alternatively, the arrange¬ ment of FIG. 3B can be used in conjunction with the configuration of FIG. 7A such that the gaps 10 correspond to channels. The movement of air along the channels can assist by means of convection cooling or heating a room in which lining 13 is applied. Gaps or channels 10 can be open to the environment so that air can flow along the channels, and a fan can be positioned near an edge of the lining 13 in such a way as to create a flow of air through the channels. Such an arrangement is particularly suitable for rooms or buildings having suspended ceilings. Lining 13 can be mounted between the ceiling and, for example, a soffit. A lining in accordance with the embodiments shown in FIG. 7 may suitably be between 1 and 200 mm thick, and are preferably between 5 and 100 mm thick. FIG. 7B shows one way in which two sheets 11 may be connected such that gaps 10 remain between the sheets. When the sheets are pushed together, clips 9 interlock so that further pressure on the sheets will not cause the gaps to close and so that the sheets cannot be pulled apart easily. FIG. 7C shows a further example of how sheets 11 may be connected to form the configuration shown in FIG. 7A. In FIG. 7C, protrusions are illustrated which prevent the sheets from interlocking further. An adhesive may be used in conjunction with these protrusions to prevent the sheets from being pulled apart. FIGs. 7D to 7G show further embodiments in which two sheets may be connected together in such a way that air gaps exist between the sheets. FIGs. 7D to 7F show a configuration in which the chambers 12 are of a cylindrical shape and have tapered ends. FIG. 7E is a top view of one of the chambers 12, and FIG. 7F shows the tapered end of a chamber. FIG. 7G shows a further suitable shape for the chambers, which may have circular, rectangular, or square cross section. In any of the embodiments described above, Peltier, or thermoelectric, devices can be applied to base layer 1 to transfer heat away from the PCMs. Due to their small size, such devices conveniently can be concealed behind sheets such as that shown in FIG. 1, and connected to heat sinks for dispersing the heat extracted from the PCMs. This arrangement can improve the efficiency of embodiments of the invention. Each individual feature described and shown above, and any combination of two or more such features, hereby are disclosed to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. Aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description, various modifications may be made within the scope of the invention by the ordinarily skilled artisan.