Stoneware heater with a rough surface

Abstract

Heating plate comprising a heating element and an outwardly facing front layer, characterized in that the front layer has a surface structure which has a roughness greater than 0.1 µm specifically to increase the emissivity of the front layer and the maximum permissible temperature.

Description

[0001] The present invention relates to a heating panel for room heating, in particular a wall or ceiling heating panel, with an outwardly radiating front layer for emitting heat by thermal radiation and convection, wherein the radiation component is specifically optimized.

[0002] The invention represents a new paradigm of radiation-optimized heating systems in which the surface structure of the radiating front layer is used as a functional feature to increase emissivity.

[0003] Heating panels with front surfaces made of natural stone, glass, ceramic, or similar materials are known from the prior art. Electrically operated infrared heaters are particularly common, where natural stone or glass surfaces are often polished or ground for purely aesthetic reasons.

[0004] Even with well-known glass heaters featuring photo fronts or decorative coatings, the focus is on visual design, while efficiency aspects play a subordinate role.

[0005] The surface structure of the radiating front layer is not specifically used as a function-determining feature to influence the heat radiation emission.

[0006] Furthermore, it is known that the emissivity of surfaces in the infrared range is material- and surface-dependent. However, smooth or polished surfaces often exhibit a comparatively low emissivity, meaning that some of the supplied heat energy is not efficiently emitted as thermal radiation.

[0007] Known solutions for improving heat dissipation are mostly based on coatings or special materials, without specifically adjusting the surface roughness of the front layer in the micro range.

[0008] All known solutions have in common that the surface roughness of the radiating front layer is not used as a specifically controlled heating performance characteristic.

[0009] The object of the invention is to provide a heating plate which: • enables increased heat radiation emission at high surface temperatures, • maximizes the proportion of radiant heat compared to convective heat, • exhibits high emissivity regardless of visible color or decoration, • suitable for both natural stone and glass fronts, • High radiation intensities are permitted while simultaneously improving touch safety, • and offers design freedom with high thermal efficiency.

[0010] In particular, the surface temperature should be optimized and the emissivity of the front layer towards smooth or polished surfaces significantly increased, without relying on complex coating systems.

[0011] The invention is based on the understanding that the heat radiation output of a heating plate is not primarily determined by the visible color or the base material, but rather significantly by the absolute temperature and the microstructure of the outward-radiating front layer.

[0012] In particular, it was found that a specifically adjusted surface roughness in the micrometer range significantly increases emissivity in the thermal infrared range and minimizes the risk of burns.

[0013] The problem is solved by a heating plate according to claim 1, comprising a heating element and an outwardly directed front layer, wherein the front layer has a surface structure that is specifically set to increase the emissivity in the thermal infrared range or in a wavelength range close to it.

[0014] Surprisingly, it was discovered that by precisely adjusting the surface roughness at the micro level, a significant increase in emissivity can be achieved without the surface appearing visually rough or distracting. At the same time, the increased surface area with its textured peaks reduces the risk of skin burns, which currently limits the maximum temperatures of infrared heaters.

[0015] For thermal radiation in the relevant infrared range of about 5 µm to 20 µm, it is not the visible roughness that is decisive, but the microstructure in a similar order of magnitude to the infrared wavelengths.

[0016] Roughness structures in the range of approximately 1 µm to 20 µm have a particularly effective effect on emissivity.

[0017] This finding applies regardless of the material used, including natural stone, glass, ceramic materials and coated front layers.

[0018] It was further recognized that the surface structure according to the invention, in combination with the low thermal conductivity of the preferably used mineral and glass-like materials, makes a significant contribution to the touch safety of the heating plate.

[0019] Natural stone, glass, ceramics, and similar materials have significantly lower thermal conductivity than metallic surfaces. Combined with the microstructured surface, this considerably reduces the actual contact area between the heating surface and the skin.

[0020] Air pockets with a heat-insulating effect remain between the contact points, which greatly reduces the heat flow to the skin.

[0021] This allows the heating plate to be touched even at elevated surface temperatures without posing a comparable risk of burns as with smooth or metallic surfaces.

[0022] Practical investigations show that surface temperatures of approximately 80 °C remain uncritical for skin contact with the structured front layer according to the invention, whereas significantly lower limit temperatures are usually required for smooth surfaces.

[0023] Thanks to the improved touch safety, the heating plate can be operated at significantly higher surface temperatures than conventional heating plates with smooth front surfaces.

[0024] Since the emitted thermal radiation power increases proportionally to the fourth power of the absolute temperature, increasing the operating temperature from about 60 °C to about 80 °C leads to a significant increase in the radiation component.

[0025] In many cases, this temperature-related increase in radiation output even exceeds the pure increase in emissivity due to the surface structure.

[0026] The roughness design according to the invention thus has a doubly radiation-optimizing effect, by both increasing the emissivity and enabling higher permissible operating temperatures.

[0027] It was found that with increasing surface roughness, the actual contact area is further reduced, thereby improving touch safety. Furthermore, roughness increases the radiation angle of the heat radiation.

[0028] For this reason, depending on the material and the application, roughness ranges up to about 20 µm and possibly even up to 100 µm can be particularly advantageous in order to enable maximum radiation power while ensuring safe skin contact and a wide radiation pattern.

[0029] The selection of the roughness takes into account both the material-specific emissivity optimum and the desired minimization of contact areas.

[0030] In a particularly preferred embodiment, the front layer has a multi-scale surface structure consisting of a coarse base roughness and a finer microstructure superimposed on it.

[0031] The base roughness is preferably in the range of about 50 µm to 300 µm, particularly about 200 µm, and serves primarily to reduce the actual contact area to improve touch safety and to create local surface inclinations that increase the effective radiation angle of the thermal radiation.

[0032] On top of this base roughness, a finer surface structure with a medium roughness in the micrometer range, especially in the range of about 0.5 µm to 3 µm, is formed, which serves specifically to increase the emissivity in the thermal infrared range.

[0033] By combining both structural levels, both maximum contact area minimization and optimal emission effect are achieved.

[0034] In addition to the thermal advantages, the multi-scale surface structure according to the invention also results in a novel optical appearance of the front layer.

[0035] The coarse base roughness creates visible microfacets, which scatter the incident light at different angles and give the surface a three-dimensional depth effect.

[0036] The fine microstructure above it causes uniform diffuse light scattering and prevents disturbing reflections.

[0037] The combination creates a high-quality, matte surface with a vibrant textured effect that differs significantly from polished, smooth, or merely coarsely textured surfaces.

[0038] This visual effect is retained even with decorative or colored coatings and contributes significantly to the design appeal of the heating plate.

[0039] The front layer preferably has a medium surface roughness Ra in the range of 0.5 µm to 3 µm.

[0040] In further embodiments, the average surface roughness Ra is in the range of 0.1 µm to 10 µm, preferably up to about 20 µm.

[0041] It was found that a roughness below approximately 0.1 µm does not result in a significant increase in emissivity, while a roughness above approximately 10 µm to 20 µm does not bring any further improvement in heat radiation in the relevant infrared range and may also be optically disadvantageous.

[0042] The targeted selection of the micro-roughness range represents the inventive core of the solution.

[0043] The surface roughness is preferably produced by grinding, in particular with a grit size in the range of 180 to 400, preferably in the range of 240 to 320, whereby coarser grits up to about 40 can also be used.

[0044] Alternatively or additionally, the surface structure can be created by blasting, etching, lasers or similar structuring methods.

[0045] The roughness is always adjusted to increase emissivity in the thermal infrared range.

[0046] For the purposes of the invention, the term "front layer" refers to any layer that forms the outermost radiating surface of the heating plate, regardless of whether it is arranged directly on a heating element, on a natural stone slab or on a support structure.

[0047] In preferred embodiments, the front layer consists of natural stone, in particular limestone, gabbro, basalt or granite.

[0048] In other embodiments, the front layer consists of natural stone, artificial stone, glass, quartz or ceramic.

[0049] In another embodiment, a glass layer is arranged as a cover layer in front of a natural stone slab, the cover layer preferably having a maximum thickness of 5 mm.

[0050] In other embodiments, the front layer consists of glass, in particular float glass, ESG or VSG, with a correspondingly structured surface.

[0051] In other embodiments, the front layer has a decorative, colored or imaging coating.

[0052] In these cases, too, the surface roughness of the outer layer significantly determines the emissivity.

[0053] It was found that the optimal roughness range can vary depending on the material of the front layer as well as the structuring method.

[0054] Material hardness, mineralogical composition, porosity, color and processing methods influence the actual microstructure produced and its interaction with infrared radiation.

[0055] Thus, for softer rocks such as limestone, lower nominal roughness values ​​may be sufficient, while for harder rocks such as igneous rocks, higher roughness values ​​may be required.

[0056] Similar shifts occur with glassy and ceramic materials.

[0057] The effective roughness range can therefore, depending on the material and process, lie between approximately 0.1 µm and 10 µm, preferably up to approximately 20 µm, whereby a material-specific emissivity optimum can be set in each case.

[0058] In view of increasing demands on the energy efficiency of heating systems, the targeted adjustment of a material-specific emissivity optimum is of particular importance.

[0059] Even slight increases in emissivity lead to significant reductions in energy consumption. The adaptability of the roughness range to different materials allows for optimal utilization of the front layer's radiation properties.

[0060] One of the many possible versions shows in Fig.A heating panel consisting of a natural stone slab made of gabbro (1) with a thickness of approximately 2 mm to 5 mm, to the back of which an electric surface heating element (2) and a thermal insulation layer (3) are attached. Optionally, a glass pane (4) approximately 1-3 mm thick is positioned in front of the natural stone slab. The stone or glass surface is ground with a 180-grit finish. The average surface roughness (Ra) is approximately 8.2 µm. The heating panel is operated at a surface temperature of approximately 80 °C and is mounted on a wall or ceiling. The emissivity of a gabbro surface at this temperature and Ra of 8.2 µm is 0.95. Limestone achieves an emissivity of 0.98 at 80 °C and Ra of 8.2 µm. An ideal blackbody radiator has an emissivity of 1. The optimized stone surfaces realistically have emissivity values ​​between 0.92 and 0.98 – practically at the physical limit.Increasing the surface roughness to 200 µm for optimized contact protection does not impair emissivity. With improved contact protection through high roughness, the radiation component can be fully utilized through temperature increases without affecting emissivity. The optimization potential through increased roughness is not limited.

[0061] Furthermore, the heating plate has a thick insulating layer on the back, suitable for temperatures up to at least 90 °C, to minimize heat loss to the rear. The heating plate can be electrically operated, preferably at a low voltage of 48 volts or below. The heating plate according to the invention offers, in particular: • significantly increased emissivity in the thermal infrared range • Improved radiation output through the highest possible temperature • great creative freedom • simple manufacturing • High energy efficiency • clear distinction from known heating systems • Easy-to-install electrical operation in the low-voltage range

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