Underfloor heating

Abstract

A heating panel, comprising a layer of cementitious substrate, a carbon nanotube (CNT) and graphene layer 2 applied to the cementitious substrate 3 and at least two electrodes applied to the CNT / 5 gra

Description

15 1221 5 The present specification relates to underfloor heating, particularly underfloor heating using electric elements secured to flooring panels or tiles. Underfloor heating is a highly effective method of heating due to delivering targeted heat to the occupants which creates a warmer feeling for a given io unit of energy input than most other types of heating (such as wall mounted radiators etc). However, underfloor heating presents a number of challenges. Tall buildings are constrained in height by structural and local policy restrictions, meaning 15 that the number of habitable levels is limited by these constraints. The flooring build-up, that is the thickness or depth of the flooring structure which often comprises several layers, diminishes the habitable space within these constraints. If the flooring build-up can be reduced, then more habitable levels (or habitable space with more generous ceiling height) can be 20 accommodated in a given building than those with conventional flooring build-ups. This drive to reduce floor build-up dimensions is opposed by the inclusion of underfloor heating, because underfloor heating will generally increase the floor build-up dimensions. The systems currently available can be described in two ways:- 15 1221 "Wet" systems: pipes which carry hot water which is distributed via a manifold to various zones in the dwelling. The pipes are generally either set into a cementitious screed, or laid into a "cradle and joist" system. Electric systems: a mat containing resistive electric wires is laid under 5 the floor. However, the uptake of such designs has been limited because of disadvantages, which can include: Cost and complexity of the systems. io - Cost and complexity of the installation processes. The underfloor components are easily damaged either during installation, or via fixings from subsequent works puncturing the pipes or wires. Wet systems can leak and cause significant consequential damage to 15 property by water damage. Wear and damage resulting from installation defects can cause electric systems to short-circuit and fail or catch fire. Slow response to inputs (hysteresis) means that most occupants set their heating on to come on earlier than they require, in order to give the 20 space time to heat-up. This wastes energy. Also the cool-down time means that further unwanted energy is emitted Hysteresis can make it difficult to control temperature of the space to achieve a desired set temperature point, resulting in compromised occupant comfort. 15 1221 Electric systems use comparatively high amounts of electrical energy to heat the dwelling to the desired temperature. In addition to these disadvantages, wet underfloor heating systems add 5 additional thickness in the floor build-up dimensions. Typically a minimum of 75mm floor build-up dimension would be required to accommodate a wet underfloor heating system. The object of the present invention is to provide an underfloor heating system io which addresses these and other problems which will become apparent in the description below. According to the present invention, there is provided a heating panel according to claim 1. According to another aspect of the present invention, 15 there is provided a heating panel system according to the independent claims. The invention will now be described, by way of example, with reference to the drawings, of which 20 Figure 1 is a sectional view of an embodiment of the heating panel and flooring; Figure 2 is a sectional view of another embodiment of the heating panel and flooring; and Figure 3 is a perspective view of the edges of two heating panels being 25 joined together. 15 1221 Referring to figure 1, shows an underfloor heating product according to a first embodiment of the invention. A resilient layer 1, forms a lower layer of the product, with a CNT / graphene layer 2 above the resilient layer 1, a 5 cementitious substrate 3 located above the CNT / graphene layer 2, an underlay layer 4 located above the CNT / graphene layer 2, and a floor finish 5 forming the uppermost layer of the product. The resilient layer 1 is an optional component of the product. Its thickness io will be in the region of 5 to 15mm and may be formed of for example EPDM (ethylene propylene diene monomer) rubber. Its function is to deform to address irregularities or undulations in the substrate concrete structure that the product is to be placed on, as is a common occurrence in such concrete structures. The resilient layer 1 also provides a sound insulation function, 15 which will impede the noise of footsteps from the dwelling above transmitting to the dwelling below. The CNT / graphene layer 2 is applied to the cementitious substrate 3 as will be described below. The cementitious substrate 3 is composed of cementitious 20 board formed at thickness of around 4mm to 15mm, and comprises primarily of calcium silicate, which has been chosen because of its superior fire resisting properties, mechanical properties and it allows the IR radiation to pass through cleanly without dispersing the radiation. 15 1221 Advantageously, the cementitious substrate 3 can be manufactured by making of slurry comprising 50-70 wt% calcareous material, 15-25 wt% silica, 10-20 wt% of inorganic fillers, and 6-10 wt% cellulose or glass fibres, forming the slurry into a board in a mould, allow a hydrothermal reaction at a 5 pressure of at least lMPa. The resulting cured material has a density of 1.400kg / m3 to 1.600kg / m3 and a flexural strength of 18 - 30MPa. Carbon nanotubes may be produced by known methods, for example as described in US2018362347A1 (FGV Cambridge Nanosystems). io To apply the CNT / graphene layer 2 to the cementitious substrate 3, a formulation of CNT and graphene is first dispersed in an ink carrier. The resulting suspension provides a highly conductive printable film which is deposited by an appropriate printing method (e.g. spraypainting, inkjet, 15 screen, gravure or flexo) as a film onto the cementitious substrate 3. Once dried, the dried printed film can then act as a heater due to the fact that upon application of a voltage of 5 to 12 Volts across the CNT / graphene layer 2, the collisions of electrons and photons produce instant heat, a phenomenon called Joule heating. The efficient heat release due to high radiation along 20 with low resistance, with an average IR emissivity >0.5 in a wide wavelength range (4-14pm) rendering them very effective radiant heaters. Thin-film copper electrodes are located either side of the applied CNT / graphene layer 2, and a DC current is applied in the region of 5 to 12 25 Volts, which is sufficient to create a temperature of 35°C to 70 °C (though 15 1221 greater or lesser temperatures are also easily achievable). The carbon nanotube and graphene nanocomposite film creates infra-red heat which, once diffused through the cementitious substrate 3, is very effective at heating the human body and thus creating the feeling of warmth. For a given 5 energy input, this is much more efficient than conventional radiant heating methods. The application of the CNT / graphene layer 2 on the cementitious substrate 3 provides a number of important advantages: io - Thermal runaway occurs when a portion of a heating element becomes excessively hot, which increases the resistance of the heater, which will in turn cause the electrical power to heat it up further and so on, until the materials eventually fail. In the event of thermal runaway, the board as described herein will contain the heat build-up and will limit conductive 15 heating of adjacent materials in order to successfully contain any risk of fire. Heat generated by the CNT / graphene layer permeates the cementitious substrate in a linear fashion without being diffused, unlike other rigid layers commonly used for floor covering such as ceramic. It also obviates a requirement for materials such as polyurethane to add rigidity, but which 20 would increase the risk of thermal runaway and fire. There is no requirement for thermally reflective layer beneath CNT / graphene layer, which would increase the risk of thermal runaway and fire. The board can be as thin a 4mm whilst still being rigid and workable 25 during the rigours of a construction site. This means that a very thin build-up 15 1221 can be achieved, whilst maintaining the ease of installation and rigidity. Furthermore, the board can be machined such as to achieve a rebate lap joint as described in figure 3 so as to further enable efficient installation. The board provides mechanical protection to the CNT / graphene layer 5 from abrasion or fractures. The board is sufficiently flat in order to enable an even coating of the CNT and graphene. The formulation of the board permits linear transmission of the IR radiation, without excessively conducting heat away from the intended io target. This is key to the efficiency of the heating element, as the heat can be directed to the target (usually the occupant and the surrounding air), without wasting energy by heating unnecessary items, such as the building structure and building fixtures. The board is unaffected by the accidental application of water, this is 15 useful during installation where the building site may not be watertight, and the concrete may still be drying out; but also it is common for leaks to occur towards the end of the construction process. Leaks into the floor can be severely detrimental to electric underfloor heating systems, whereas this system will be unaffected. 20 - Applying the CNT / graphene layer directly to the cementitious substrate avoids the need for securement methods such as the use of mesh and / or adhesive or silicone glue, which are inconvenient, and can adversely affect the heating characteristics of the heating panel. 15 1221 The inclusion of a resilient layer addresses acoustic requirements of the flooring build-up and irregularities and undulations in the concrete substrate of the building structure. 5 By virtue of its formulation of calcium silicate and lightweight fibre construction, the cementitious board permits the infra-red heat through it very effectively whilst not dispersing the heat (reflective components would diffuse the heat transfer). This allows efficient heat transfer to the occupants, without wasting heat on unnecessarily heating the fabric of the building. This io particular phenomenon has two distinct benefits: More of the energy used goes directly to the occupant and thus less energy is required to create the desired comfort level. Hysteresis of the system is significantly reduced, i.e. the heat-up time is significantly reduced, and cool-down time is also significantly reduced. This 15 improvement in response-time improves the effectiveness of control systems which in-turn reduces energy use. Once the installation of the underfloor product is completed, the builder or occupant can fit their own choice of floor finishes 5 such as timber or carpet, 20 under which it is usual to fit an underlay 4. This is an important advantage of the system, as the floor finish is independent of the heating system, and therefore the floor finish can be chosen and eventually replaced without affecting the underfloor heating system. 15 1221 Referring to figure 2, the builder or occupant may choose to install a tile or stone finish 7, under which it is usual to use a tile adhesive 6 which can be applied directly to the cementitious substrate 3, or a decoupling layer may be incorporated between the cementitious substrate 3 and tile or stone 7. 5 Referring to figure 3, the board assembly will be installed in modules. Shown here are two boards 10, 10', each comprising a layer of cementitious substrate 3 onto which a CNT / graphene layer 2 has been applied on the underside. Each board 10, 10' has corresponding rebated joints fit together. io The CNT / graphene layer 2 may be made electrically continuous via the application of a polyamide tape 8 which has been printed with a layer of CNT and graphene in a similar manner to the printing process of the CNT / graphene layer 2 described above. 15 Optionally, an alternative embodiment of the system may also comprise a polyamide layer in the build-up between layers 1 and 2, which will afford extra protection to the CNT and Graphene layer, but also provide the option that layer 1 can be installed separately in an alternative embodiment. 20 The system as a whole has significant benefits over equivalent underfloor heating systems: The floor build-up dimension can be reduced by up to 50% No manifold required Low complexity 25 - Easy to install 15 1221 Damage by fixings penetrating the product has no impact on the performance of the system and risk of injury by electric shock is significantly reduced No water in the system, eliminating risk of water damage 5 - Fast response to control inputs, resulting in reduced energy use, and improved occupant comfort Direct experience of the infra-red heat by the occupant, resulting in further reduced energy use. The boards are lightweight and can be installed in a large format which io would be typically 1200mmx600mm, thus improving speed and safety of installation. The panels can be cut using a hand saw, with no special skill sets required, and no electrical wires. Electrical connections are made using simple self adhesive strips of 15 polyamide with printed carbon nanotube and graphene nanocomposite films which make the electrical connections between the panels. The optional rebated jointing methodology between the boards which incorporates the self adhesive strips of polyamide with the CNT and Graphene 20 layers printed on them in order to maintain electrical continuity. The optional resilient layer 1 performs an acoustic function (reduces the transmission of footstep noise on the floor to the dwelling below), and additionally performs a levelling function to alleviate undulations in the 25 underlying concrete structure of the building. 15 1221 This system allows separate control zones with individual temperature controls. Typically, each zone will comprise an area of CNT / graphene layer 2 between electrodes, the voltage supplied to the electrodes of each area being 5 individually controllable. The application of the CNT / graphene heating layer via printing, enables bespoke printed patterns which are easily tailored to the heat needs of a particular dwelling design, such as accommodating the furniture and fabric io layout such as to avoid heating underneath sofas etc whilst applying a greater heat density to the areas close to the windows. In particular, the different individually controllable areas of CNT / graphene layers 2 may be formed in different shapes and sizes as required. Most conveniently, the areas of individually controllable CNT / graphene layers may be shaped thereby 15 controlling the pattern of the CNT / graphene layer which is printed onto the cementitious substrate 3.

Claims

14 05 251. A heating panel, comprising;a layer of cementitious substrate,5 a first CNT and graphene layer dispersed in an ink carrier to form aconductive printable film that is applied to the cementitious substrate; andat least two electrodes applied to the first CNT and graphene layer so as to allow a voltage to be applied to the first CNT and graphene layer, wherein the panel further comprises:10 at least one rebated edge; andan electrical connection comprising a polyamide tape printed with a second CNT and graphene layer, and wherein:the tape is configured to maintain electrical continuity between the 15 first CNT and graphene layer of the heating panel and a corresponding first CNT and graphene layer of a second heating panel when the at least one rebated edge of the heating panel is aligned with a corresponding rebated edge of the second heating panel.20 2. A heating panel according to claim 1 wherein the dispersal of the first orsecond CNT and graphene layers in an ink carrier selected from the group consisting of spray painting, inkjet printing, screen printing, gravure printing, and flexographic printing.14 05 253. A heating panel according to either previous claim wherein the cementitious substrate comprises 50-70 wt% calcareous material 15-25 wt% silica5 10-20 wt% of inorganic fillers, and6-10 wt% cellulose or glass fibres.

4. A heating panel according to any previous claim wherein a resilient layer is included beneath the first CNT and graphene layer.io5. A heating panel according to any previous claim wherein a floor finish is included above the cementitious substrate.

6. A heating panel according to claim 5 wherein an underlay is included 15 between the floor finish and the cementitious substrate.

7. A heating panel system, wherein at least two heating panels according to any previous claim are joined at their edges by corresponding rebated joints.20 8. A heating panel system, according to any of claims 7 to 9 wherein twoseparate areas of the first CNT and graphene layer are electrically connected by polyamide tape having a second CNT and graphene layer.

9. A heating panel system, according to any of claims 7 or 8 wherein two separate areas of the first CNT and graphene layer are electrically isolated from each other and are independently controllable.5 10. A heating panel system, according to any of claims 7 to 9 whereinspecifically shaped heated first CNT and graphene layer areas are provided by printing a pattern of the first CNT and graphene layer according to the room layout.14 05 25

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