Radiation cooling device

Abstract

Provided is a radiation cooling device that performs cooling by radiating heat from a heat source and suppressing heat transfer from the outside of a building. 【Solution means】A radiation cooling device for a building, comprising a heat conduction layer 13 in contact with a heat source layer 12 into which a heat exchange medium heated by heat in the building flows, a first surface in contact with the heat conduction layer, and a second surface facing the first surface, and having a radiation layer 14 that radiates the heat transferred from the heat conduction layer as infrared rays, a heat insulation layer 15 disposed on the second surface side and through which the infrared rays radiated from the radiation layer can pass, and a transmission layer 16 facing the radiation layer through the heat insulation layer and through which the infrared rays radiated from the radiation layer can pass. The heat conduction layer is made of a material that reflects the infrared rays incident through the transmission layer and the infrared rays from the radiation layer.

Description

Technical Field

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

Background Art

[0002] Conventionally, radiative cooling devices using radiative cooling have been known. In particular, radiative cooling devices are advantageous in terms of energy conservation. Patent Document 1 discloses a radiative cooling film material used for roofs such as tent warehouses and truck covers. This film material can cool itself by a radiative cooling effect in a daytime solar radiation environment. A radiative cooling layer is attached to the outer surface of this film material. The radiative cooling layer includes an infrared radiation layer that radiates infrared light from a radiation surface, and a light reflection layer located on the side opposite to the radiation surface of the infrared radiation layer. The infrared radiation layer is a resin material layer adjusted to a thickness that emits heat radiation energy greater than the absorbed solar energy, and the light reflection layer has silver or a silver alloy. By using this film material for roofs such as tent warehouses and truck covers, it is possible to suppress the temperature rise of the film material in a daytime solar radiation environment, and as a result, suppress the temperature rise of the space surrounded by the film material. Therefore, such a film material can be suitably used for a radiative cooling device.

[0003] Also, in a radiative cooling device for a building, heat insulation is also important. The cooling device cools by moving heat from a heat source, for example, to the outside of the building by radiation or the like. However, if the heat insulation between the radiative cooling device and the inside of the building or its internal space is insufficient, the temperature of the building or the internal space will rise due to the radiative cooling device. Therefore, a technique for blocking or suppressing the heat transfer from the radiative cooling device is also important. The forms of heat transfer are radiation, convection, and conduction, and it is necessary to suppress the heat transfer by these three forms respectively.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, Patent Document 1 is for preventing the temperature of the film material used in the radiative cooling device from rising due to sunlight and for preventing the transfer of heat from the outside of the building. Therefore, there is no disclosure regarding releasing the heat of the heat source to the outside. On the other hand, when cooling a building such as a data center, cooling the internal space of the building and cooling the heat sources within the building are important. Therefore, simply suppressing the temperature rise due to heat transfer from the outside of the building is not sufficient for the cooling performance.

[0006] An object of the present invention is to provide a radiative cooling device that performs cooling by radiating heat from a heat source and suppressing the transfer of heat from the outside of the building.

Means for Solving the Problems

[0007] The radiative cooling device for a building according to the present invention includes a heat conduction layer that contacts a heat source layer into which a heat exchange medium heated by the heat inside the building flows, a first surface that contacts the heat conduction layer, and a second surface that faces the first surface. The radiative cooling device also has a radiation layer that radiates the heat transferred from the heat conduction layer as infrared rays, a heat insulation layer that is disposed on the second surface side and through which the infrared rays radiated from the radiation layer can pass, and a transmission layer that faces the radiation layer through the heat insulation layer and through which the infrared rays radiated from the radiation layer can pass. The heat conduction layer is made of a material that reflects the infrared rays incident through the transmission layer and the infrared rays from the radiation layer.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a radiative cooling device that performs cooling by radiating heat from a heat source and suppressing the transfer of heat from the outside of the building.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0010] Hereinafter, an example in which the radiative cooling device 1 for a building according to the present embodiment is used for cooling the entire building such as a data center will be described.

[0011] In the present embodiment, "heat insulation" means that heat conduction is suppressed. There is no particular limitation on the specific thermal conductivity, but it is preferably 0.1 W / (m·K) or less, more preferably 0.08 W / (m·K) or less. In this specification, emissivity, reflectivity, and absorptivity are physical quantities representing the behavior of a substance when it receives electromagnetic waves. The electromagnetic waves received by the substance are distributed among radiation, reflection, and absorption. Emissivity represents the intensity of thermal radiation emitted by the substance, reflectivity represents the intensity of light reflected by the substance, and absorptivity represents the intensity of light absorbed by the substance. According to Kirchhoff's law, the emissivity ε and the absorptivity α are equal. Also, as is well known, the following relational expression holds. Transmittance + Reflectivity + Absorption (Radiation) Rate = 1

[0012] FIG. 1 shows a partial cross-sectional view of the radiative cooling device 1, and FIG. 2 shows an explanatory drawing of the case where the radiative cooling device 1 is installed in a building. As shown in FIG. 1, the cooling device includes a heat insulation layer 11 with a low thermal conductivity for preventing heat from moving from the radiative cooling device 1 to the inside of the building, a heat source layer 12 through which the heat source flows, a reflection and heat conduction layer 13 with a high reflectivity of electromagnetic waves, particularly infrared rays, and a higher thermal conductivity than the heat insulation layer 11, a radiation layer 14 with a high emissivity and transmittance of electromagnetic waves and a higher thermal conductivity than the heat insulation layer 11, a heat insulation layer 15, and a transmission layer 16 with a high heat permeability, which are provided in this order and 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, and the heat insulation layer 11 faces the inside of the building, and the transmission layer 16 faces the outside of the building. Note that the heat insulation layer 11 is provided at a distance from the outer wall of the building, but it may be provided in contact with the outer wall. The heat source layer 12 is fluidly connected to the heat exchanger 23 shown in FIG. 2 through the first flow path 21 and the second flow path 22. The heat exchange medium of the heat exchanger 23 can move between the radiation cooling device 1 and the heat exchanger 23 through these first flow path 21 and second flow path 22 provided in the form of pipes.

[0014] In the radiation cooling device 1, the heat of the heat exchange medium heated by the heat inside the building, which flows into the heat source layer 12 from the heat exchanger 23, is blocked by the heat insulation layer 11. Therefore, the transfer of heat from the heat source layer 12 in the direction facing the inside of the building is suppressed. On the other hand, since the reflection and heat conduction layer 13 in contact with the heat source layer 12 is made of a material having a higher thermal conductivity than the heat insulation layer 11, most of the heat from the heat exchange medium in the heat source layer 12 moves to the reflection and heat conduction layer 13 and further to the radiation layer 14.

[0015] The radiation layer 14 is composed of a substance having a high emissivity, and the heat transferred from the heat exchange medium in the heat source layer 12 to the radiation layer 14 is radiated from the radiation layer 14 as electromagnetic waves (mainly infrared rays). Here, on the outside of the building side of the radiation layer 14, a heat insulation layer 15 and a transmission layer 16 through which the infrared rays radiated from the radiation layer 14 can pass are provided in this order. In this embodiment, a vacuum heat insulation layer is used as the heat insulation layer 15. Therefore, most of the heat transfer by conduction and convection between the outside of the building and the heat source layer 12 is suppressed by the heat insulation layer 15. On the other hand, the heat radiated as infrared rays from the heat exchange medium in the heat source layer 12 moves to the outside without passing through the heat insulation layer 15 and the transmission layer 16.

[0016] Since the reflection and heat conduction layer 13 is provided on the building side of the radiation layer 14, most of the heat radiated from the radiation layer 14 to the building side is reflected by the reflection and heat conduction layer 13. Although a part of it is absorbed by the radiation layer 14, most of it goes toward the outside of the building and moves to the outside of the building as described above. On the other hand, 95% of the infrared rays radiated from the radiation layer 14 in the direction toward the inside of the building are reflected by the reflection layer and the heat conduction layer 13 and radiated to the outside of the building. Therefore, most of the infrared rays radiated from the radiation layer 14 in all directions are radiated to the outside of the building and hardly penetrate into the inside of the building.

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

[0018] Regarding the heat transfer from the outside of the building, the heat transfer by conduction and convection is suppressed by the heat insulation layer 15. On the other hand, regarding the heat by radiation (infrared rays), a part of it is reflected by the transmission layer 16, so it does not move into the radiation cooling device 1. Since the wavelength of the infrared rays from the outside of the building is 8 to 14 μm as described later, it is preferable that the transmission layer 16 has a high reflectance for infrared rays in this wavelength range.

[0019] The infrared rays that have passed through the transmission layer 16 reach the reflection and heat conduction layer 13 through the heat insulation layer 15. Since the reflection and heat conduction layer 13 reflects 95% or more of visible light and infrared rays, it is reflected by the reflection and heat conduction layer 13, which is a layer, and radiated to the outside of the building through the heat insulation layer 15 and the transmission layer 16, preventing the intrusion of heat into the building. About 5% of the infrared rays and the like incident on the radiation cooling device 1 are absorbed by the radiation layer 14. The electromagnetic waves absorbed by the radiation layer 14 raise the temperature of the radiation layer 14 and are radiated as electromagnetic waves such as infrared rays from the radiation layer 14. Therefore, most of the heat from the outside of the building is returned to the outside of the building.

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

[0021] In addition, since the heat exchange medium is a liquid, the cooled heat exchange medium has a higher specific gravity and moves vertically downward to move to the heat exchanger 23 inside the building through the second flow path 22. Along with this, the high-temperature heat exchange medium inside the building moves into the radiation 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 radiation cooling device 1. Note that when the heat exchange medium is a gas, convection also occurs in the same manner, and continuous cooling can be performed by the radiation cooling device 1.

[0022] On the other hand, when the heat exchange medium is a solid, convection does not occur, but when the heat exchange medium in the heat source layer 12 of the radiation cooling device 1 is cooled, a temperature gradient with the heat exchange medium on the inside of the building is generated, and the heat exchange medium in the building is cooled by conduction, and as a result, it is possible to cool the inside of the building. Thus, the radiation cooling device according to the present embodiment is less affected by the outside air temperature due to the provision of the heat insulation layer 15, and is excellent in stably cooling a room that constantly generates heat, such as a data center.

[0023] Hereinafter, the materials constituting the heat insulation layer 11 and the like will be described. The heat insulation layer 11 only needs to be able to sufficiently suppress heat transfer by conduction, convection, and radiation from the heat exchange medium in the heat source layer 12 to the inside of the building, and any material such as urethane foam, glass wool, rock wool, or cellulose fiber heat insulating material can be used. In this embodiment, urethane foam is used.

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

[0025] As the reflection and heat conduction layer 13, any material that reflects electromagnetic waves and has high thermal conductivity can be used. For example, metals such as silver or aluminum are used. Preferably, aluminum is used because it is lightweight and inexpensive. In this embodiment, an aluminum vapor deposition layer is used.

[0026] As the radiation layer 14, a material with high thermal conductivity and high emissivity is used. For example, it is preferable to use a glass layer, particularly materials such as glass ceramics, synthetic quartz, and sapphire glass. In this embodiment, a glass layer is used. Also, it is preferable that the wavelength of the infrared rays radiated by the radiation layer 14 is a wavelength that easily passes through the transmission layer 16. This is to emit the infrared rays from the radiation layer 14 to the outside of the building. Furthermore, it is preferable that the radiation layer 14 has a high transmittance for infrared rays in the wavelength range of 8 to 14 μm from the outside of the building that reaches through the heat insulation layer 15 without being reflected by the transmission layer 16. This is to prevent heat absorption by transmitting the infrared rays from the outside of the building, reflecting them with the reflection and heat conduction layer 13, and emitting them to the outside of the building. For example, by coating the surface of plate glass so as to obtain such characteristics, a radiation layer 14 having the above-described characteristics can be manufactured.

[0027] In this embodiment, the heat insulation layer 15 is a vacuum layer, which is formed by sealing the space between the radiation layer 14 and the transmission layer 16 to create a vacuum. A vacuum heat insulation material with a multi-layer structure of glass fibers in a vacuum state, or a vacuum heat insulation material obtained by coating glass wool or polystyrene with a laminate film and evacuating the internal air can be used. As the heat insulation layer 15, it is preferable to use a material that prevents heat transfer by conduction or convection and allows infrared rays from the radiation layer 14 to pass through.

[0028] As the transmission layer 16, a glass layer was used. Note that the transmission layer 16 preferably has a material with a high transmittance in the wavelength range of infrared rays radiated from the radiation layer 14. This is to release the infrared rays from the radiation layer 14 to the outside of the building. Also, for infrared rays in the wavelength range of 8 to 14 μm from the outside of the building, it is preferable to use a material with a high reflectance. For example, by coating the surface of a plate glass so as to obtain such characteristics, the transmission layer 16 having the above-described characteristics can be manufactured. For example, a heat ray reflecting glass in which a thin film of an oxide, a nitride, a metal, etc. is formed on the surface of a plate glass may be used.

[0029] Note that in the case of an arrangement in which the reflection and heat conduction layer 13 and the radiation layer 14 are reversed, aluminum with a low emissivity is on the outside, and the radiation efficiency decreases. Therefore, preferably, the arrangement is in the order shown in the figure.

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

[0031] As described above, the heat blocking layer 11 of the radiation cooling device 1 prevents the transfer of heat from the radiation cooling device 1 to the building. The heat inside the building or the heat from heat sources such as computers and servers inside the building moves to the heat exchange medium, which is the refrigerant of the heat exchanger 23, and in the radiation cooling device 1, it is radiated to the outside of the building through the reflection and heat conduction layer 13, the radiation layer 14, the heat insulation layer 15, and the transmission layer 16 as described above. The heat exchange medium cooled by radiation returns to the heat exchanger 23 inside the building by convection as described above, and it is possible to continuously cool the inside of the building. The radiation cooling device 1 is preferably installed on the shaded side. Also, the radiation cooling device 1 can be installed, for example, on a flat surface such as a rooftop, and regarding the installation position, it is also possible to install it diagonally and in a standing state like a gable.

[0032] In the example of FIG. 1, although both surfaces of the radiation layer 14 are flat, preferably, with the surface on the reflection and heat conduction layer side of the radiation layer 14 being the first surface and the surface on the heat insulation layer 15 side and opposite to the first surface being the second surface, the first surface is not flat but has an uneven shape or a curved surface. For example, the first surface can be shaped with a plurality of grooves or be a curved surface. As a result, the surface area increases compared to the case where the first surface is formed by a flat surface. Also, since the reflection and heat conduction layer 13 is formed on the first surface of the radiation layer 14 and has the same shape as the first surface, the contact area between the reflection and heat conduction layer 13 and the heat source layer 12 also increases. Therefore, the heat transfer from the heat exchange medium in the heat source layer 12 to the reflection and heat conduction layer 13 is promoted, and the advantage of increased heat exchange efficiency is obtained.

[0033] Also, by vapor-depositing the reflection and heat conduction layer 13 on the first surface of the radiation layer 14 as in this embodiment, a reflection and heat conduction layer 13 having the same shape as the first surface can be formed. By making the first surface of the radiation layer 14 have a structure with unevenness, the surface area can be made larger than the second surface. In particular, by performing aluminum vapor deposition with the first surface having a zigzag shape formed with grooves or groove portions (hereinafter simply referred to as grooves) parallel to each other, a reflection and heat conduction layer 13 having the same shape as the first surface can be formed. In this case, it is preferable that the depth of the groove is shorter than the distance between the grooves, which facilitates processing such as aluminum vapor deposition. Also, it is preferable to form each groove in a direction extending vertically when the radiation cooling device 1 is installed in a building so as not to prevent the vertical movement of the heat exchange medium in the radiation cooling device 1 due to convection.

[0034] With this configuration, while being exposed to the outside air and compared to the second surface which is flat, the heat conduction layer 13 can be provided and the surface area of the first surface which functions as a radiation surface can be increased. Also, since the surface area of the reflection and heat conduction layer 13 becomes larger, the area for radiating infrared rays and the like becomes larger, so that in addition to the heat insulation effect of the heat insulation layer 15, the cooling efficiency further increases. For example, when the first surface has a shape with a plurality of grooves, radiation is also performed from the side surfaces of the grooves, so that the area where radiation is performed becomes larger compared to the case where the first surface is flat.

[0035] A part of the infrared rays radiated from the side surfaces is directly radiated to the outside of the building through the heat insulation layer 15 and the transmission layer 16. Also, the infrared rays radiated from the side surfaces to the reflection and heat conduction layer 13 side are reflected by the reflection and heat conduction layer 13, and as a result, most of them are transmitted through the heat insulation layer 15 and the transmission layer 16 on the second surface side and radiated to the outside of the building. Therefore, among the infrared rays radiated from the side surfaces, the infrared rays absorbed by the reflection and heat conduction layer 13 or the radiation layer 14 are only a very small part, and the cooling efficiency is high.

[0036] Also, infrared rays are classified into near-infrared rays (0.7 μm to 2.5 μm), mid-infrared rays (2.5 to 4 μm), and far-infrared rays (4 to 1000 μm). Also, there are wavelengths with high atmospheric transmittance and wavelengths with low transmittance in infrared rays, and in particular, the wavelength range of 8 to 14 μm with high transparency is often called the "atmospheric window".

[0037] Therefore, as described above, for the transmissive layer 16, it is preferable to use a material with a high reflectivity for infrared rays in the wavelength range of 8 to 14 μm incident from the outside of the building to the radiative cooling device 1 through the atmosphere. In particular, the transmissive layer 16 preferably has a reflectivity for infrared rays in the wavelength range of 8 to 14 μm of 0.7 or more, preferably 0.8 or more, more preferably 0.85 or more, more preferably 0.9 or more, more preferably 0.95 or more, and even more preferably 0.98 or more. For example, Low-E glass with a thin film of tin oxide, silver, etc. applied to the surface of plate glass can be used. As methods for forming the thin film, a method of forming the film during the manufacturing process of plate glass and a method of forming the film by sputtering in a vacuum chamber are known. Those by the sputtering method are sometimes called high-performance heat ray reflective glass, have a high degree of freedom in the thin film configuration, and it is also easy to adjust the wavelength of the reflectivity.

[0038] On the other hand, the wavelength of the infrared rays radiated from the radiative layer 14 depends on the material of the radiative layer 14. It is preferable that the infrared rays radiated from the radiative layer 14 are directly radiated outside the building without being reflected by the transmissive layer 16. Therefore, when a material that reflects the wavelength range of 8 to 14 μm is used for the transmissive layer 16, as the material used for the radiative layer 14, in order to prevent reflection by the transmissive layer 16, it is preferable to use a material with a low emissivity at a wavelength of 8 to 14 μm and a relatively higher emissivity in the wavelength range longer than 14 μm and not exceeding 1000 μm than the emissivity at a wavelength of 8 to 14 μm.

[0039] The emissivity of the radiative layer 14 at a wavelength 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 radiative layer 14 in the wavelength range longer than 14 μm and not exceeding 1000 μm is preferably higher than the emissivity at a wavelength of 8 to 14 μm, preferably 0.6 or more, preferably 0.7 or more, more preferably 0.8 or more, more preferably 0.9 or more, and even more preferably 0.95 or more. Also, since the required characteristics are different in this way, it is preferable that the material used for the radiative layer 14 and the material used for the transmissive layer 16 are different.

[0040] <Modified Example> Fig. 3 shows a radiative cooling device 2 having a cylindrical structure as a modified example. In this radiative cooling device 2, a heat source layer 12 is disposed at the center, and a reflective and heat conductive layer 13, a radiative layer 14, a heat insulating layer 15, and a transmissive layer 16, each having a hollow cylindrical shape, are provided so as to surround the heat source layer 12. Further, these reflective and heat conductive layer 13, radiative layer 14, heat insulating layer 15, and transmissive layer 16 are arranged in this order and concentrically when viewed from the central heat source layer 12.

[0041] In the radiative cooling device 1 shown in Figs. 1 and 2, a heat insulation layer 11 is provided to insulate the heat exchange medium in the heat source layer 12 from the inside of the building. However, in the radiative cooling device 2 shown in Fig. 3, the heat source layer 12 is at the center and there is no portion facing the inside of the building. Therefore, in the radiative cooling device 2, the heat insulation layer 11 is not provided. The radiative cooling device 2 is provided outside the building, and the transmissive layer 16 constitutes its side surface.

[0042] Although the radiative cooling device 2 in the modified example is different from the radiative cooling device 1 in that the heat insulation layer 11 is not provided, other configurations are the same as those of the radiative cooling device 1 shown in Figs. 1 and 2. The heat exchange medium is heated by the heat in 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 heat conductive layer 13, the radiative layer 14, the heat insulating layer 15, and the transmissive layer 16 in the same manner as described for the radiative cooling device 1, and as a result, the heat exchange medium is cooled.

[0043] Also, the heat exchange medium is a liquid (or fluid). Although not shown in the figure, the first flow path 21 and the second flow path 22 are in fluid communication with the heat exchanger 23 in the same manner as the radiation cooling device 1. Therefore, the heat exchange refrigerant can move between the heat exchanger 23 and the radiation cooling device 2. Similar to the above-described radiation cooling device 1, convection occurs in the heat exchange medium, and it is continuously cooled by the radiation cooling device 2. Also, the installation location of the radiation cooling device 2 is arbitrary, but for example, it can be arranged at the four corners of a building. Further, it is preferable to arrange the radiation cooling device 1 such that the permeation layer 16 faces the shaded side, and it is necessary to adjust the orientation of the permeation layer 16 during its installation.

[0044] Also, in a modified example, it is necessary to form the reflection and heat conduction layer 13 on the inner surface of the cylindrical radiation layer 14. The forming method is arbitrary. For example, a cylindrical glass tube is used as the radiation layer 14, the glass tube is cut into a half pipe, and aluminum vapor deposition is performed on the inner surface side to form the reflection and heat conduction layer 13. After the vapor deposition, by adhering the half pipes to each other, the radiation layer 14 with the reflection and heat conduction layer 13 formed thereon can be manufactured.

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; a radiation layer having a first surface in contact with the thermally conductive layer and a second surface opposite to the first surface, and radiating 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 emitting 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 emission layer, the emissive layer has a first emissivity which is an emissivity of infrared light in a wavelength range of 8 to 14 μm, and a second emissivity which is an emissivity of infrared light 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. Radiative cooling devices for buildings.

2. The first surface has projections and recesses and has 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 on 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. A radiative cooling device according to claim 3.

5. the thermal 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 first emissivity is less than or equal to 0.2; The second emissivity is 0.8 or more.

10. The radiative cooling device of claim 1.

7. the first emissivity is less than or equal to 0.1; The second emissivity is 0.9 or more.

10. The radiative cooling device of claim 1.

8. A radiative cooling device as described in claim 1, wherein the heat exchange medium is a liquid.

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