Radiation cooling device

Abstract

To provide a radiation cooling device that performs cooling by radiating heat from a heat source and suppressing heat transfer from outside of a building.SOLUTION: A radiation cooling device for a building includes: a heat conduction layer 13 coming into contact with a heat source layer 12 to which a heat exchange medium heated by heat within the building flows in; a radiation layer 14 that has a first surface coming into contact with the heat conduction layer and a second surface opposing to the first surface and radiates heat transferred from the heat conduction layer as infrared radiation; a heat insulation layer 15 that is disposed on the second surface side and which the infrared radiation radiated from the radiation layer can permeate; and a permeation layer 16 that opposes to the radiation layer via the heat insulation layer and which the infrared radiation radiated from the radiation layer can permeate. The heat conduction layer is constituted by a material quality that reflects the incident infrared radiation via the permeation layer and the infrared radiation from the radiation layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a radiative cooling device having a radiative cooling effect. [Background technology]

[0002] Radiative cooling devices that use radiative cooling are known, and are particularly advantageous in terms of energy conservation. Patent Document 1 discloses a radiative cooling membrane material used on roofs of tent warehouses, truck canopies, and the like. This membrane material can cool itself through radiative cooling in daytime solar radiation environments. A radiative cooling layer is attached to the outer surface of this membrane material. The radiative cooling layer includes an infrared radiation layer that emits infrared light from its radiation surface and a light-reflecting layer located on the opposite side of the infrared radiation layer. The infrared radiation layer is a resin material layer adjusted to a thickness that emits thermal radiation energy greater than the absorbed solar energy, and the light-reflecting layer contains silver or a silver alloy. Using this membrane material on roofs of tent warehouses, truck canopies, and the like suppresses the temperature rise of the membrane material in daytime solar radiation environments, thereby suppressing the temperature rise of the space surrounded by the membrane material. Therefore, such a membrane material is suitable for use in a radiative cooling device.

[0003] Additionally, insulation is also important for radiative cooling devices for buildings. Cooling devices cool by transferring heat from a heat source to the outside of a building, for example, by radiation. However, if the insulation between the radiative cooling device and the building or its internal space is insufficient, the radiative cooling device will cause the temperature of the building or internal space to rise. Therefore, technology to block or suppress the transfer of heat from the radiative cooling device is also important. Heat transfer occurs through radiation, convection, and conduction, and it is necessary to suppress each of these three forms of heat transfer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-143796 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 prevents the temperature of the membrane material used in the radiative cooling device from rising due to sunlight, and prevents heat transfer from outside the building. Therefore, there is no disclosure about releasing heat from the heat source to the outside. On the other hand, when cooling a building such as a data center, it is important to cool the interior space of the building and the heat source inside the building. Therefore, simply suppressing the temperature rise due to heat transfer from outside the building is not sufficient for cooling performance.

[0006] The object of the present invention is to provide a radiative cooling device that cools a building by radiating heat from a heat source and suppressing the transfer of heat from outside the building. [Means for solving the problem]

[0007] The radiative cooling device for buildings according to the present invention comprises: a thermally conductive layer in contact with a heat source layer into which a heat exchange medium heated by heat inside a building flows; a radiative layer having a first surface in contact with the thermally conductive layer and a second surface opposite the first surface, and radiating heat transferred from the thermally conductive layer as infrared rays; a thermal insulating layer arranged on the second surface side and allowing the infrared rays radiated from the radiative layer to transmit therethrough; and a transmissive layer facing the radiative layer across the thermal insulating layer and allowing the infrared rays radiated from the radiative layer to transmit therethrough, wherein the thermally conductive layer is made of a material that reflects infrared rays incident through the transmissive layer and infrared rays from the radiative layer. [Effects of the Invention]

[0008] According to the present invention, a radiative cooling device can be provided that performs cooling by radiating heat from a heat source and suppressing the transfer of heat from outside a building. [Brief explanation of the drawings]

[0009] [Figure 1]Partial cross-sectional view of a radiative cooling device. [Figure 2] An explanatory diagram of a radiative cooling device installed in a building. [Figure 3] FIG. 1 is a schematic diagram of another embodiment of a radiative cooling device. DETAILED DESCRIPTION OF THE INVENTION

[0010] An example in which the radiative cooling device for buildings 1 according to this embodiment is used to cool the entire building such as a data center will be described below.

[0011] In this embodiment, "heat insulation" means that thermal conduction is suppressed. While there are no particular limitations on the specific thermal conductivity, it is preferably 0.1 W / (m·K) or less, and more preferably 0.08 W / (m·K) or less. In this specification, emissivity, reflectivity, and absorptivity are physical quantities that describe the behavior of a material when it receives electromagnetic waves. Electromagnetic waves received by a material are divided into radiation, reflection, and absorption. Emissivity represents the strength of thermal radiation emitted by a material, reflectivity represents the strength of light reflection by a material, and absorptivity represents the strength of light absorption by a material. According to Kirchhoff's law, emissivity ε and absorptivity α are equal. As is well known, the following relationship holds: Transmittance + reflectance + absorptance (emissivity) = 1

[0012] Fig. 1 shows a partial cross-sectional view of a radiative cooling device 1, and Fig. 2 shows an explanatory diagram of a radiative cooling device 1 installed in a building. As shown in Fig. 1, the cooling device comprises a heat blocking layer 11 with low thermal conductivity to prevent heat from transferring from the radiative cooling device 1 to the inside of the building, a heat source layer 12 through which a heat source flows, a reflective and thermally conductive layer 13 with high electromagnetic wave reflectivity, especially infrared reflectivity, and higher thermal conductivity than the heat blocking layer 11, a radiative layer 14 with high emissivity and electromagnetic wave transmittance and higher thermal conductivity than the heat blocking layer 11, a heat insulating layer 15, and a transparent layer 16 with high heat transmittance, which are arranged in this order, and are supported by a first side wall 17 and a second side wall 18.

[0013] In addition, in FIG. 1, the first side wall 17 is on the upper side of the building, the second side wall 18 is on the lower side of the building, the thermal insulation layer 11 faces the inside of the building, and the permeable layer 16 faces the outside of the building. The thermal insulation layer 11 is provided separate from the exterior wall of the building, but may also be provided in contact with the exterior wall. The heat source layer 12 is fluidly connected to the heat exchanger 23 shown in FIG. 2 through a first flow path 21 and a second flow path 22. The heat exchange medium of the heat exchanger 23 can move between the radiative cooling device 1 and the heat exchanger 23 through these first flow path 21 and second flow path 22, which are provided in the form of piping.

[0014] In the radiative cooling device 1, the heat of the heat exchange medium heated by the heat inside the building and flowing from the heat exchanger 23 into the heat source layer 12 is blocked by the thermal insulation layer 11. Therefore, heat transfer from the heat source layer 12 toward the inside of the building is suppressed. On the other hand, the reflective and thermally conductive layer 13 that is in contact with the heat source layer 12 is made of a material with a higher thermal conductivity than the thermal insulation layer 11, so most of the heat from the heat exchange medium in the heat source layer 12 transfers to the reflective and thermally conductive layer 13 and then to the radiative layer 14.

[0015] The radiative layer 14 is made of a material with high emissivity, and heat transferred from the heat exchange medium in the heat source layer 12 to the radiative layer 14 is radiated from the radiative layer 14 as electromagnetic waves (mainly infrared rays). Here, on the exterior side of the building of the radiative layer 14, a thermal insulation layer 15 and a transmission layer 16, each of which is capable of transmitting the infrared rays radiated from the radiative layer 14, are provided in this order. In this embodiment, a vacuum insulation layer is used as the thermal insulation layer 15. Therefore, heat transfer by conduction and convection between the exterior of the building and the heat source layer 12 is almost entirely suppressed by the thermal insulation layer 15. On the other hand, heat radiated as infrared rays from the heat exchange medium in the heat source layer 12 moves to the outside without transmitting through the thermal insulation layer 15 and the transmission layer 16.

[0016] Because the reflective and thermally conductive layer 13 is provided on the building side of the radiative layer 14, most of the heat radiated from the radiative layer 14 towards the building is reflected by the reflective and thermally conductive layer 13, and although some of it is absorbed by the radiative layer 14, most of it heads towards the outside of the building and moves towards the outside of the building as described above. On the other hand, 95% of the infrared rays radiated from the radiative layer 14 towards the inside of the building are reflected by the reflective layer and thermally conductive layer 13 and radiated towards the outside of the building. Therefore, most of the infrared rays radiated in all directions from the radiative layer 14 are radiated towards the outside of the building, and very little of them penetrate into the inside of the building.

[0017] As described above, the heat exchange medium is heated by the heat inside the building and its temperature rises, but the heat of the heat exchange medium that flows into the heat source layer 12 is transferred to the outside of the building by radiation, and the transfer of heat from the heat exchange medium in the heat source layer 12 to the inside of the building is suppressed by the thermal insulation layer 11.

[0018] Regarding heat transfer from outside the building, heat transfer by conduction and convection is suppressed by the insulating layer 15. On the other hand, heat due to radiation (infrared rays) is partially reflected by the transparent layer 16 and does not transfer into the radiative cooling device 1. As will be described later, the wavelength of infrared rays from outside the building is 8 to 14 μm, so it is preferable that the transparent layer 16 has a high reflectance for infrared rays in this wavelength range.

[0019] The infrared rays that have passed through the transparent layer 16 reach the reflective and thermally conductive layer 13 through the thermal insulating layer 15. The reflective and thermally conductive layer 13 reflects 95% or more of visible light and infrared rays, so the infrared rays are reflected by the reflective and thermally conductive layer 13 and radiated to the outside of the building through the thermal insulating layer 15 and the transparent layer 16, preventing heat from entering the building. Approximately 5% of the infrared rays and other rays that enter the radiative cooling device 1 are absorbed by the radiative layer 14. The electromagnetic waves absorbed by the radiative layer 14 increase the temperature of the radiative layer 14, and are radiated from the radiative layer 14 as electromagnetic waves such as infrared rays. Therefore, most of the heat from outside the building is returned to the outside of the building.

[0020] With this configuration, most of the heat transferred from the heat exchange medium in the heat source layer 12 to the radiation layer 14 through reflection and the thermal conduction layer 13 is radiated outside the building, so that the heat from the heat exchange medium can be discharged outside the building for cooling.

[0021] Furthermore, because the heat exchange medium is a liquid, the specific gravity of the cooled heat exchange medium increases, and it moves vertically downward through the second flow path 22 to the heat exchanger 23 inside the building. Accordingly, the high-temperature heat exchange medium inside the building moves into the radiative cooling device 1 through the first flow path 21. In this way, convection occurs in the heat exchange medium in the heat source layer 12, and the heat exchange medium can be continuously cooled by the radiative cooling device 1. Note that convection also occurs when the heat exchange medium is a gas, and the radiative cooling device 1 can continuously cool the heat exchange medium.

[0022] On the other hand, if the heat exchange medium is solid, convection does not occur, but cooling the heat exchange medium in the heat source layer 12 of the radiative cooling device 1 creates a temperature gradient with the heat exchange medium inside the building, cooling the heat exchange medium inside the building by conduction, and as a result, cooling the inside of the building. As such, the radiative cooling device of this embodiment is less susceptible to the influence of outside air temperature due to the provision of the insulating layer 15, and is excellent at stably cooling indoors that are constantly heated, such as data centers.

[0023] The materials constituting the thermal insulation layer 11 and the like are described below. The thermal insulation layer 11 may be made of any material that can sufficiently suppress heat transfer by conduction, convection, and radiation from the heat exchange medium in the heat source layer 12 to the interior of the building, and any material can be used, such as urethane foam, glass wool, rock wool, or cellulose fiber insulation. In this embodiment, urethane foam is used.

[0024] Any heat exchange medium can be used, preferably a fluid (gas or liquid). In this embodiment, a chlorofluorocarbon (HFC) alternative, which is a compound of hydrogen, fluorine, and carbon, is used. In the case of a solid, a material with high thermal conductivity, such as a metal, is used.

[0025] The reflective and thermally conductive layer 13 can be made of any material that reflects electromagnetic waves and has high thermal conductivity, such as a metal such as silver or aluminum. Aluminum is preferably used because it is lightweight and inexpensive. In this embodiment, an aluminum vapor deposition layer is used.

[0026] The emissive layer 14 is preferably made of a material with high thermal conductivity and emissivity. For example, a glass layer, particularly a material such as glass ceramic, artificial quartz, or sapphire glass, is preferably used. In this embodiment, a glass layer is used. The emissive layer 14 preferably emits infrared rays with a wavelength that is easily transmitted through the transmission layer 16. This is because the infrared rays from the emissive layer 14 are emitted to the outside of the building. Furthermore, the emissive layer 14 preferably has high transmittance for infrared rays in the wavelength range of 8 to 14 μm from outside the building, which reach the building through the thermal insulation layer 15 without being reflected by the transmission layer 16. This is because the infrared rays from outside the building are transmitted and reflected, and then reflected by the thermally conductive layer 13 and emitted to the outside of the building, preventing heat absorption. For example, an emissive layer 14 with the above-described properties can be manufactured by coating the surface of a glass plate to achieve these properties.

[0027] In this embodiment, the heat insulating layer 15 is a vacuum layer, and is formed by sealing the space between the emitting layer 14 and the transmitting layer 16 to create a vacuum. Vacuum insulation materials made of a multi-layered glass fiber structure that is evacuated, or vacuum insulation materials made of glass wool or polystyrene covered with a laminate film and the air inside removed can be used. It is preferable to use a material as the heat insulating layer 15 that prevents heat transfer by conduction or convection and that allows infrared rays from the emitting layer 14 to pass through.

[0028] A glass layer was used as the transmission layer 16. The transmission layer 16 is preferably made of a material that has high transmittance in the wavelength range of the infrared rays emitted from the emitting layer 14. This is because the infrared rays from the emitting layer 14 are emitted to the outside of the building. The transmission layer 16 is also preferably made of a material that has high reflectivity for infrared rays in the wavelength range of 8 to 14 μm from the outside of the building. For example, a transmission layer 16 having the above-mentioned properties can be manufactured by coating the surface of a glass plate so that such properties are obtained. For example, heat-reflecting glass in which a thin film of oxide, nitride, metal, or the like is formed on the surface of the glass plate may be used.

[0029] If the reflective and heat conductive layer 13 and the radiative layer 14 are arranged in reverse, the aluminum with low emissivity is on the outer side, which reduces the efficiency of radiation, so it is preferable to arrange them in the order shown in the figure.

[0030] Figure 2 shows an example of the radiative cooling device 1 installed in a building. As shown in the figure, the heat exchanger 23 and the radiative cooling device 1 are in fluid communication through a first flow path 21 and a second flow path 22, and the fluid heat exchange medium (liquid in this example) of the heat exchanger 23 can move between the heat exchanger 23 and the radiative cooling device 1.

[0031] As described above, the heat insulating layer 11 of the radiative cooling device 1 prevents heat transfer from the radiative cooling device 1 to the building. Heat inside the building, or heat from heat-generating devices such as computers and servers inside the building, is transferred to the heat exchange medium, which is the refrigerant of the heat exchanger 23, and in the radiative cooling device 1, it is radiated to the outside of the building through the reflective and thermally conductive layer 13, radiative layer 14, insulating layer 15, and permeable layer 16, as described above. The radiatively cooled heat exchange medium returns to the heat exchanger 23 inside the building by convection, as described above, and can continuously cool the inside of the building. The radiative cooling device 1 is preferably installed on a shaded side. The radiative cooling device 1 can be installed on a flat surface such as a rooftop, and can also be installed diagonally, standing upright like a partition.

[0032] In the example shown in FIG. 1 , both surfaces of the emissive layer 14 are flat. However, preferably, the surface of the emissive layer 14 facing the reflective and thermally conductive layer is designated the first surface, and the surface facing the thermal insulating layer 15, facing the first surface, is designated the second surface. The first surface is not flat, but has an uneven or curved shape. For example, the first surface can have a shape with multiple grooves or a curved surface. As a result, the surface area is increased compared to when the first surface is formed flat. Furthermore, since the reflective and thermally conductive layer 13 is formed on the first surface of the emissive layer 14 and has the same shape as the first surface, the contact area between the reflective and thermally conductive layer 13 and the heat source layer 12 is also increased. Therefore, heat transfer from the heat exchange medium in the heat source layer 12 to the reflective and thermally conductive layer 13 is also promoted, resulting in an advantage of increased heat exchange efficiency.

[0033] Furthermore, by depositing the reflective and thermally conductive layer 13 on the first surface of the radiative layer 14 as in this embodiment, it is possible to form a reflective and thermally conductive layer 13 having the same shape as the first surface. By forming the first surface of the radiative layer 14 into an uneven structure, it is possible to increase the surface area compared to the second surface. In particular, by depositing aluminum on the first surface in a zigzag shape with parallel grooves or groove portions (hereinafter simply referred to as grooves), it is possible to form a reflective and thermally conductive layer 13 having the same shape as the first surface. In this case, it is preferable to make the depth of the grooves shorter than the distance between the grooves, which facilitates processing such as aluminum deposition. Furthermore, in order not to impede the vertical movement of the heat exchange medium due to convection in the radiative cooling device 1, it is preferable to form each groove in a direction extending vertically when the radiative cooling device 1 is installed in a building.

[0034] With this configuration, the surface area of ​​the first surface, on which thermally conductive layer 13 is provided and which functions as a radiation surface, can be increased compared to the second surface, which is exposed to the outside air and is flat. Furthermore, since the surface area of ​​reflective and thermally conductive layer 13 is increased, the area radiating infrared rays and the like is also increased, which further improves the cooling efficiency in addition to the insulating effect of heat-insulating layer 15. For example, if the first surface has a shape with multiple grooves, radiation also occurs from the side surfaces of the grooves, so the area from which radiation occurs is larger compared to when the first surface is flat.

[0035] A portion of the infrared rays emitted from the side surfaces is radiated directly to the outside of the building through the heat insulating layer 15 and the transmission layer 16. Furthermore, the infrared rays radiated from the side surfaces toward the reflective and thermally conductive layer 13 are reflected by the reflective and thermally conductive layer 13, and as a result, most of the infrared rays are transmitted through the heat insulating layer 15 and the transmission layer 16 on the second surface side and radiated to the outside of the building. Therefore, only a small portion of the infrared rays radiated from the side surfaces is absorbed by the reflective and thermally conductive layer 13 or the radiation layer 14, resulting in high cooling efficiency.

[0036] Infrared rays are further classified into near-infrared (0.7μm-2.5μm), mid-infrared (2.5-4μm), and far-infrared (4-1000μm). Infrared rays also include wavelengths that are highly transmittable through the atmosphere and wavelengths that are less transmittable, with the wavelength range of 8-14μm, which is particularly transparent, often referred to as the "atmospheric window."

[0037] Therefore, as mentioned above, it is preferable to use a material for the transmission layer 16 that has a high reflectance for infrared rays in the 8 to 14 μm wavelength range that enter the radiative cooling device 1 from outside the building through the atmosphere. In particular, the transmission layer 16 preferably has a reflectance for infrared rays in the 8 to 14 μm wavelength range of 0.7 or higher, preferably 0.8 or higher, more preferably 0.85 or higher, more preferably 0.9 or higher, more preferably 0.95 or higher, and even more preferably 0.98 or higher. For example, Low-E glass, in which a thin film of tin oxide or silver is applied to the surface of plate glass, can be used. Known methods for forming the thin film include depositing the film during the plate glass manufacturing process and depositing the film by sputtering in a vacuum chamber. Sputtering-based glass is sometimes called high-performance heat-reflecting glass, and offers a high degree of freedom in thin film configuration and easy adjustment of the wavelength of reflectance.

[0038] On the other hand, the wavelength of the infrared rays emitted from the emitting layer 14 depends on the material of the emitting layer 14. It is preferable that the infrared rays emitted from the emitting layer 14 are directly emitted outside the building without being reflected by the transmitting layer 16. Therefore, when a material that reflects wavelengths in the 8 to 14 μm range is used for the transmitting layer 16, it is preferable that the material used for the emitting layer 14 has a low emissivity at wavelengths of 8 to 14 μm and an emissivity in the wavelength range of longer than 14 μm and equal to or less than 1000 μm that is relatively higher than the emissivity at wavelengths of 8 to 14 μm, in order to prevent reflection by the transmitting layer 16.

[0039] The emissivity of the emitting layer 14 at wavelengths of 8 to 14 μm is preferably 0.5 or less, more preferably 0.3 or less, more preferably 0.2 or less, more preferably 0.1 or less, and even more preferably 0.05 or less. The emissivity of the emitting layer 14 in the wavelength range from longer than 14 μm to 1000 μm is preferably higher than the emissivity at wavelengths of 8 to 14 μm, and is preferably 0.6 or higher, preferably 0.7 or higher, more preferably 0.8 or higher, more preferably 0.9 or higher, and even more preferably 0.95 or higher. Furthermore, since the required properties are different, it is preferable that the material used for the emitting layer 14 and the material used for the transmitting layer 16 are different.

[0040] <Modification> Figure 3 shows a modified radiative cooling device 2 with a cylindrical structure. In this radiative cooling device 2, a heat source layer 12 is arranged in the center, and a reflective and thermally conductive layer 13, a radiative layer 14, a thermal insulating layer 15, and a transmissive layer 16, each of which has a hollow cylindrical shape, are provided to surround the heat source layer 12. The reflective and thermally conductive layer 13, the radiative layer 14, the thermal insulating layer 15, and the transmissive layer 16 are arranged in this order and concentrically with respect to the central heat source layer 12.

[0041] In the radiative cooling device 1 shown in Figures 1 and 2, a thermal barrier layer 11 is provided to insulate the heat exchange medium in the heat source layer 12 from the interior of the building, but in the radiative cooling device 2 shown in Figure 3, the heat source layer 12 is located in the center and does not face the interior of the building. Therefore, the radiative cooling device 2 does not have a thermal barrier layer 11. The radiative cooling device 2 is installed outside the building, and the permeable layer 16 forms its side surface.

[0042] The radiative cooling device 2 in this modification differs from the radiative cooling device 1 in that it does not have a thermal insulation layer 11, but the rest of the configuration is similar to that of the radiative cooling device 1 shown in Figures 1 and 2. The heat exchange medium is heated by the heat inside the building and flows into and out of the heat source layer 12 in the radiative cooling device 2 through the first flow path 21 and the second flow path 22. The heat of the heat exchange medium in the heat source layer 12 is discharged to the outside of the building through the reflective and thermally conductive layer 13, the radiative layer 14, the insulating layer 15, and the transparent layer 16, as explained in the radiative cooling device 1, resulting in the cooling of the heat exchange medium.

[0043] The heat exchange medium is a liquid (or fluid), and although not shown, the first flow path 21 and the second flow path 22 are fluidly connected to the heat exchanger 23, similar to the radiative cooling device 1. Therefore, the heat exchange refrigerant can move between the heat exchanger 23 and the radiative cooling device 2. As with the above-mentioned radiative cooling device 1, convection occurs in the heat exchange medium, and it is continuously cooled by the radiative cooling device 2. The installation location of the radiative cooling device 2 is arbitrary, and it can be installed, for example, at the four corners of a building. Furthermore, it is preferable to install the radiative cooling device 1 so that the permeable layer 16 is on the shaded side, and the orientation of the permeable layer 16 needs to be adjusted during installation.

[0044] In a modified example, it is necessary to form the reflective and thermally conductive layer 13 on the inner surface of the cylindrical radiant layer 14. Any method for forming the radiant layer 14 may be used, but for example, a cylindrical glass tube may be used as the radiant layer 14, and the glass tube may be cut into half pipes, and aluminum may be vapor-deposited on the inner surface to form the reflective and thermally conductive layer 13. After the vapor deposition, the half pipes may be bonded together to produce the radiant layer 14 on which the reflective and thermally conductive layer 13 is formed.

Claims

1. A radiative cooling device for a building, comprising: a heat transfer layer in contact with a heat source layer into which a heat exchange medium heated by heat in the building flows; an emitting layer having a first surface in contact with the thermally conductive layer and a second surface opposite to the first surface, and emitting heat transferred from the thermally conductive layer as infrared rays; a heat insulating layer disposed on the second surface side and capable of transmitting infrared rays emitted from the radiation layer; a transmission layer that faces the radiation layer with the heat insulating layer interposed therebetween and that is capable of transmitting infrared rays emitted from the radiation layer, the thermal conduction layer is made of a material that reflects infrared rays incident through the transmission layer and infrared rays from the radiation layer. Radiative cooling device for buildings.

2. The first surface has irregularities and a larger surface area than the second surface.

10. The radiative cooling device of claim 1.

3. The first surface has a plurality of grooves formed in a direction extending vertically when installed in a building.

10. The radiative cooling device of claim 1.

4. the thermally conductive layer is formed of a metal; a depth of each of the plurality of grooves is shorter than a distance between the grooves; the metal is formed on the first surface by vapor deposition; 4. The radiative cooling device of claim 3.

5. the heat conduction layer, the radiation layer, the heat insulation layer, and the transmission layer have a hollow cylindrical shape; The hollow cylindrical heat conduction layer, the radiation layer, the heat insulation layer, and the transmission layer are arranged in this order so as to be concentric with the heat source layer.

10. The radiative cooling device of claim 1.

6. the emissive layer has a first emissivity that is the emissivity of infrared rays in a wavelength range of 8 to 14 μm, and a second emissivity that is the emissivity of infrared rays in a wavelength range of more than 14 μm and not more than 1000 μm, the value of the second emissivity being higher than the first emissivity; the transmission layer has a reflectance of 0.8 or more for infrared rays in the wavelength range of 8 to 14 μm; 10. The radiative cooling device of claim 1.

7. the first emissivity is 0.2 or less; the second emissivity is 0.8 or greater; 7. The radiative cooling device of claim 6.

8. the first emissivity is 0.1 or less, the second emissivity is 0.9 or greater; 7. The radiative cooling device of claim 6.

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