Radiative cooling panel and cooling system comprising the same

Abstract

To realize an overall weight reduction by efficiently cooling a refrigerant even when cooling a relatively high-temperature refrigerant, while improving economical efficiency.SOLUTION: A radiative cooling panel H cools a first refrigerant W1 flowing through a first refrigerant flow pipe L provided along a panel surface, where an upstream first refrigerant flow pipe JL, which is an upstream flow pipe including a first refrigerant inflow part EN that is an inflow part where the first refrigerant W1 flows into the first refrigerant flow pipe L, is provided with a fin for exchanging heat between the first refrigerant W1 and outside air on one side in a cross direction intersecting with the panel surface, and a downstream first refrigerant flow pipe KL, which is a downstream flow pipe including a first refrigerant outflow part ET that is an outflow part where the first refrigerant W1 flows out from the first refrigerant flow pipe L, is provided with a cooling layer on the other side in the cross direction. The cooling layer includes an infrared radiation layer that emits infrared light from a radiation surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiative cooling panel that cools a first refrigerant flowing through a first refrigerant flow pipe provided along a panel surface, and a cooling system including the same. [Background technology]

[0002] Conventionally, radiative cooling panels have been known that have a first refrigerant flow pipe that is provided along the panel surface and through which a first refrigerant flows, and an infrared emitting layer that emits infrared light from a radiation surface that is the panel surface (see Patent Documents 1 to 3). In radiative cooling panels, the infrared emitting layer radiates infrared light into space, thereby cooling the refrigerant flowing through the first refrigerant flow pipe. As an example of a cooling system using the radiative cooling panel, Patent Document 1 discloses a cooling system that includes a first refrigerant circulation path that connects the inlet and outlet of a first refrigerant flow pipe of a radiative cooling panel, and a heat pump that includes a compressor that compresses a second refrigerant, a condenser that condenses the second refrigerant compressed by the compressor, an expansion valve that expands the second refrigerant condensed by the condenser, an evaporator that evaporates the second refrigerant expanded by the expansion valve, and a second refrigerant circulation path that circulates the second refrigerant in the listed order, and that performs a cooling (freezing) function by exchanging heat between the first refrigerant circulating through the first refrigerant circulation path and the second refrigerant at the outlet of the condenser in the second refrigerant circulation path. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 140082 [Patent Document 2] International Publication No. 2020 / 214989 [Patent Document 3] International Publication No. 2021 / 142431 Summary of the Invention [Problem to be solved by the invention]

[0004] The radiative cooling panels disclosed in the above Patent Documents 1 to 3 only show a configuration in which the infrared radiation layer is provided over the entire area from the upstream side to the downstream side of the first refrigerant flow pipe provided along the panel surface. In this way, when a relatively expensive infrared radiation layer is provided over the entire area from the upstream side to the downstream side of the first refrigerant flow pipe, a relatively expensive material constituting the infrared radiation layer is used in large amounts, so there is room for improvement from the viewpoint of economy. In addition, particularly when a first refrigerant at a relatively high temperature (e.g., a temperature higher than the ambient temperature) flows through it, the first refrigerant is not necessarily cooled efficiently in the radiative cooling panel, and there is room for improvement.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a radiative cooling panel and cooling system that can efficiently cool a refrigerant even when cooling a relatively high-temperature refrigerant, while improving economic efficiency and reducing the overall weight. [Means for solving the problem]

[0006] The radiative cooling panel to achieve the above objectives is: A radiative cooling panel that cools a first refrigerant flowing through a first refrigerant flow pipe provided along a panel surface, and its characteristic configuration is as follows: an upstream first refrigerant flow pipe that is an upstream flow pipe including a first refrigerant inlet portion that is an inlet portion through which the first refrigerant flows into the first refrigerant flow pipe is provided with a fin that exchanges heat between the first refrigerant and outside air on one side in a cross direction that crosses the panel surface; a cooling layer is provided on the other side of the cross direction of a downstream first refrigerant flow pipe that is a downstream flow pipe including a first refrigerant outflow portion that is an outflow portion through which the first refrigerant flows out of the first refrigerant flow pipe, The cooling layer includes an infrared emitting layer that emits infrared light from an emitting surface.

[0007] According to the above-mentioned characteristic configuration, the upstream first refrigerant flow pipe, which is a flow pipe on the upstream side of the first refrigerant flow pipe, is provided with fins on one side in a cross direction (for example, a direction perpendicular to the panel surface) crossing the panel surface, which exchange heat between the first refrigerant and outside air, and the downstream first refrigerant flow pipe, which is a flow pipe on the downstream side of the first refrigerant flow pipe, is provided with a cooling layer including an infrared emitting layer that emits infrared light from a radiation surface on the other side of the cross direction, so that, for example, when the first refrigerant flows into the first refrigerant flow pipe at a temperature higher than the environmental temperature (for example, the outside air temperature), the first refrigerant can be efficiently cooled by exchanging heat with the outside air through the fins during the flow process of the upstream first refrigerant flow pipe. This makes it unnecessary to cool the upstream first refrigerant flow pipe with a cooling layer including a relatively expensive infrared emitting layer, which improves economy. In addition, the first refrigerant cooled while passing through the upstream refrigerant flow pipe is cooled by a cooling layer including an infrared radiation layer while passing through the downstream first refrigerant flow pipe, so the first refrigerant can be cooled to a temperature lower than the ambient temperature by the radiative cooling effect. This allows the first refrigerant to be efficiently cooled, reducing the panel area required to cool the first refrigerant to the target temperature, and reducing the weight of the entire panel. As a result, it is possible to realize a radiative cooling panel that can efficiently cool a refrigerant even when cooling a relatively high-temperature refrigerant, while improving economic efficiency and reducing the overall weight.

[0008] Further features of the radiative cooling panel include: The downstream first refrigerant flow pipe is provided, on one side in the intersecting direction, with a heat insulating layer that insulates the first refrigerant from outside air.

[0009] According to the above characteristic configuration, the first refrigerant, which has been cooled to a relatively low temperature by flowing through the upstream first refrigerant flow pipe and which may be cooled in the downstream first refrigerant flow pipe by the radiative cooling effect of the cooling layer to a temperature lower than the ambient temperature, is insulated from the outside air by the insulating layer on one side of the intersecting direction, thereby preventing the first refrigerant from being heated by the outside air, and the first refrigerant can be cooled even more efficiently.

[0010] Further features of the radiative cooling panel include: The heat insulating layer is provided such that the coefficient of thermal conductivity between the first refrigerant and the outside air decreases toward the downstream side of the downstream first refrigerant flow pipe.

[0011] According to the configuration described so far, the first refrigerant becomes colder toward the downstream side as it flows through the downstream first refrigerant flow pipe due to the radiative cooling effect of the cooling layer, and heat is more likely to be input from the environment such as the outside air, but according to the above characteristic configuration, the insulating layer is provided so that the thermal conductivity between the first refrigerant and the outside air becomes lower toward the downstream side of the downstream first refrigerant flow pipe, so that it is more difficult for heat to be input from the outside air, etc. to the first refrigerant toward the downstream side of the downstream first refrigerant flow pipe. As a result, the cooling efficiency of the first refrigerant can be further improved.

[0012] Further features of the radiative cooling panel include: The thickness of the heat insulating layer in the intersecting direction is set to be greater on the downstream side of the downstream first refrigerant flow pipe.

[0013] As in the above characteristic configuration, by making the thickness of the insulating layer in the intersecting direction thicker toward the downstream side of the downstream first refrigerant flow pipe, the cooling efficiency of the first refrigerant can be further improved.

[0014] Further features of the radiative cooling panel include: The upstream first refrigerant flow pipe is provided, on the other side of the intersecting direction, with either an infrared emitting layer that emits infrared light from a radiation surface or a light reflective layer that reflects sunlight.

[0015] According to the above characteristic configuration, the upstream first refrigerant flow pipe has either an infrared radiation layer or a light reflecting layer provided on the other side in the intersecting direction. Therefore, while the first refrigerant flowing through the upstream first refrigerant flow pipe is cooled on one side in the intersecting direction by heat exchange with the outside air via the fins, on the other side in the intersecting direction, radiative cooling by the infrared radiation layer or prevention of temperature rise due to solar reflection by the light reflecting layer can be achieved, and an even greater cooling effect can be expected.

[0016] The cooling system for achieving the above object has the following features: The radiative cooling panel according to the present invention is provided. The first refrigerant flowing out from the first refrigerant outlet port is used to cool another fluid.

[0017] According to the above characteristic configuration, a cooling system can be realized that can effectively cool other media by the first refrigerant cooled by the radiative cooling panel.

[0018] Further features of the cooling system include: a heat pump unit having a second refrigerant circulation path that circulates the second refrigerant in the order of a compressor that compresses a second refrigerant, a condenser that condenses the second refrigerant compressed by the compressor, an expansion valve that expands the second refrigerant condensed by the condenser, and an evaporator that evaporates the second refrigerant expanded by the expansion valve; A first refrigerant circulation unit including a first refrigerant circulation path that guides the first refrigerant flowing out from the first refrigerant outflow part of the radiative cooling panel to the first refrigerant inflow part of the radiative cooling panel and a pressure pump that pressure-feeds the first refrigerant through the first refrigerant circulation path; The compressor has a heat exchanger that exchanges heat between the second refrigerant guided from the compressor to the expansion valve and the first refrigerant flowing through the first refrigerant circulation path.

[0019] According to the above-described characteristic configuration, a heat exchanger is provided that exchanges heat between the second refrigerant guided from the compressor of the heat pump section to the expansion valve and the first refrigerant flowing through the first refrigerant circulation path. Therefore, compared to conventionally known cooling systems using only a heat pump, the condensation heat of the second refrigerant compressed by the compressor can be efficiently recovered by the first refrigerant, which can be sufficiently lower than the environmental temperature (e.g., the outside air temperature), thereby realizing a cooling system with high cooling capacity.

[0020] Further features of the cooling system include: The point is that a plurality of the radiative cooling panels are connected in parallel.

[0021] This makes it possible to appropriately supply the cooling capacity of the first refrigerant in accordance with the cooling capacity required by the heat pump unit, for example. [Brief description of the drawings]

[0022] [Figure 1] 1A and 1B are plan views of a radiative cooling panel according to an embodiment, and a schematic diagram illustrating an example of a cooling system including the radiative cooling panel. [Diagram 2] FIG. 1 is a cross-sectional view of a radiative cooling panel according to a first embodiment (Example 1). [Diagram 3] FIG. 13 is a cross-sectional view of a radiative cooling panel according to a second embodiment (Example 2). [Figure 4] FIG. 1 is a cross-sectional view of a radiative cooling panel according to a comparative example. [Diagram 5] FIG. 11 is a schematic configuration diagram illustrating an example of a cooling system according to another embodiment. [Figure 6] FIG. 13 is a cross-sectional view of a radiative cooling panel according to another embodiment. [Figure 7] FIG. 13 is a cross-sectional view of a radiative cooling panel according to another embodiment. [Figure 8] FIG. 13 is a plan view of a radiative cooling panel according to another embodiment. [Figure 9] FIG. 4 is a diagram showing the relationship between the light absorptance of a resin material and the wavelength. [Figure 10] FIG. 1 is a diagram showing the emissivity spectrum of polyvinyl chloride resin. [Figure 11] FIG. 2 is a diagram showing the emissivity spectrum of vinylidene chloride resin. [Figure 12] FIG. 2 shows the light reflectance spectrum of a silver-based light reflective layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The radiative cooling panel H and the cooling system 100 according to the embodiment of the present invention relate to those capable of efficiently cooling a refrigerant even when cooling a relatively high temperature refrigerant, while improving the economic efficiency, and achieving overall weight reduction. Hereinafter, the radiative cooling panel H and the cooling system 100 will be described with reference to the drawings.

[0024] The cooling system 100 exerts a cooling (cooling) capacity by a first refrigerant W1 cooled by one or more radiative cooling panels H, as shown in FIG. The radiative cooling panel H will be described in detail later. As shown in Fig. 2 or 3, a cooling layer CL including at least an infrared radiative layer RC is provided on the outer surface of a first refrigerant flow pipe L through which a first refrigerant W1 flows. The cooling layer CL includes an infrared radiative layer RC that radiates infrared light from the radiative surface and a light reflecting layer RF that reflects sunlight.

[0025] The light reflective layer RF reflects light such as sunlight, and its reflection characteristics are a reflectance of 90% or more at wavelengths of 400 nm to 500 nm, and a reflectance of 96% or more at wavelengths longer than 500 nm. The solar spectrum exists in the wavelength range from 300 nm to 4000 nm, and the intensity increases as the wavelength increases from 400 nm, and is particularly strong in the wavelength range from 500 nm to 1800 nm.

[0026] In this embodiment, light includes ultraviolet light (ultraviolet rays), visible light, and infrared light, and when these are described in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). Incidentally, in this document, the wavelength range of ultraviolet light (ultraviolet rays) is between 295 nm and 400 nm.

[0027] Since the light-reflecting layer RF exhibits a reflectance of 90% or more from wavelengths of 400 nm to 500 nm and a reflectance of 96% or more at wavelengths longer than 500 nm, the solar energy absorbed by the light-reflecting layer RF can be reduced to 5% or less; in other words, the solar energy absorbed at noon in summer can be reduced to approximately 50 W.

[0028] The light reflecting layer RF is preferably made of silver or a silver alloy, or a laminated structure of silver or a silver alloy and aluminum or an aluminum alloy, as described in detail below. Alternatively, it may be made of metal such as gold or copper. Furthermore, it may be made of a resin layer containing a pigment such as titanium oxide, silicon dioxide, aluminum oxide, or magnesium oxide.

[0029] The infrared radiation layer RC is made of polyvinyl chloride resin or vinylidene chloride resin with a thickness adjusted to emit thermal radiation energy in the wavelength range from 8 μm to 14 μm that is greater than the absorbed solar energy, and details of this will be described later.

[0030] The resin material that forms the infrared radiation layer RC has a change in light absorptivity and emissivity (light emissivity) depending on the thickness. Therefore, it is necessary to adjust the thickness so that it absorbs as little sunlight as possible and emits large thermal radiation in the so-called atmospheric window wavelength band (wavelength band from 8 μm to 14 μm).

[0031] Specifically, from the perspective of the light absorptance of sunlight, the thickness of the infrared radiation layer RC needs to be adjusted to a thickness such that the wavelength average of the light absorptance from wavelengths of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance from wavelengths of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance from wavelengths of 0.8 μm to 1.5 μm is within 1%, the wavelength average of the light absorptance from wavelengths of 1.5 μm to 2.5 μm is 40% or less, and the wavelength average of the light absorptance from wavelengths of 2.5 μm to 4 μm is 100% or less. In the case of such an absorptance distribution, the light absorptance of sunlight is 10% or less, which corresponds to 100 W or less in terms of energy.

[0032] As described later, the light absorption rate of the resin material increases as the thickness of the resin material increases. When the resin material is made thick, the emissivity of the atmospheric window becomes almost 1, and the thermal radiation emitted into space is 125 W / m 2 from 160 W / m 2 The solar light absorption in the light reflecting layer RF is 50 W / m 2The sum of the solar absorption in the infrared emitting layer RC and the light reflecting layer RF is 150 W / m 2 The temperature is below 100° C., and cooling will proceed if the atmospheric conditions are good. As described above, it is preferable to use a resin material that has a small light absorption rate near the peak value of the solar spectrum for the resin material that forms the infrared radiative layer RC.

[0033] Moreover, from the viewpoint of infrared radiation (thermal radiation), the thickness of the infrared emitting layer RC needs to be adjusted to a thickness such that the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm is 40% or more. 50W / m absorbed by the light reflecting layer RF 2 In order to emit that amount of thermal energy of sunlight from the infrared radiation layer RC into space through thermal radiation from the infrared radiation layer RC, the infrared radiation layer RC needs to emit more thermal radiation than that. For example, when the outside temperature is 30°C, the maximum thermal radiation of the 8μm to 14μm atmospheric window is 200W / m 2 (Calculated with an emissivity of 1). This value can be obtained on a clear day in a dry environment with thin air, such as a high mountain. Since the atmosphere is thicker in lowlands than in high mountains, the wavelength band of the atmospheric window is narrower and the transmittance is lower. Incidentally, this is called the "atmospheric window becoming narrower."

[0034] In addition, the environment in which the cooling layer CL (radiative cooling film) is actually used may be humid, and in that case the atmospheric window will be narrow. When used in low altitudes, the thermal radiation generated in the atmospheric window area is 160 W / m at 30°C under good conditions. 2 (calculated with emissivity of 1). When there is haze or smog in the sky, which is common in Japan, the atmospheric window becomes even narrower, and radiation into space is estimated at 125 W / m 2 It will be about that amount. In consideration of this situation, the wavelength average of the emissivity from 8 μm to 14 μm is set to 40% or more (thermal radiation intensity in the atmospheric window band is 50 W / m 2 ) it cannot be used in low altitude areas of the mid-latitudes.

[0035] Therefore, if the thickness of the infrared radiative layer RC is adjusted so that it falls within the optically specified range taking into consideration the above points, the heat output from the atmospheric window will be greater than the heat input due to the absorption of sunlight, making it possible to achieve radiative cooling outdoors even in a solar radiation environment.

[0036] [Details of resin material as infrared radiation layer] According to Kirchhoff's law, emissivity (ε) and light absorptance (A) are equal. Light absorptance can be calculated from the absorption coefficient (α) using the relation A=1-exp(-αt) (hereafter referred to as the light absorptance relation). Here, t is the film thickness. In other words, by adjusting the thickness of the infrared radiative layer RC, a large thermal radiation can be obtained in a wavelength band with a large absorption coefficient. When performing radiative cooling outdoors, it is recommended to use a material with a large absorption coefficient in the wavelength band of the atmospheric window, that is, from 8 μm to 14 μm. In addition, to suppress the absorption of sunlight, it is advisable to use a material that has no or has a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially in the range of 0.4 μm to 2.5 μm. As can be seen from the relational equation between the absorption coefficient and the absorptance, the light absorptance (emissivity) changes depending on the film thickness of the resin material.

[0037] In order to lower the temperature below the surrounding atmosphere by radiative cooling in a solar radiation environment, if a material is selected that has a large absorption coefficient in the wavelength band of the atmospheric window and almost no absorption coefficient in the wavelength band of sunlight, then by adjusting the film thickness, it will absorb almost no sunlight but emit a lot of thermal radiation from the atmospheric window, meaning it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

[0038] The solar spectrum only contains wavelengths longer than 0.295 μm. Note that ultraviolet rays are defined as the range of wavelengths shorter than 0.4 μm, visible light is defined as the range of wavelengths from 0.4 μm to 0.8 μm, near infrared rays are defined as the range of wavelengths from 0.8 μm to 3 μm, mid infrared rays are defined as the range of wavelengths from 3 μm to 8 μm, and far infrared rays are defined as the range of wavelengths longer than 8 μm.

[0039] Regarding the carbon-chlorine bond (C-Cl), the bond energy between the carbon and chlorine in an alkene is 3.28 eV, and the wavelength is 0.378 μm, so it absorbs a lot of ultraviolet light in sunlight, but has almost no absorption in the visible range. FIG. 9 shows the absorption spectrum of a 100 μm thick polyvinyl chloride resin in the ultraviolet to visible range, and light absorption increases at wavelengths shorter than 0.38 μm. FIG. 9 shows the absorptance spectrum of a 100 μm thick vinylidene chloride resin in the ultraviolet to visible range, and a slight increase in the absorptance spectrum is observed on the shorter wavelength side than 0.4 μm.

[0040] Incidentally, FIG. 9 also shows the absorptance spectrum from ultraviolet to visible range of ethylene terephthalate resin having a thickness of 40 μm, and the absorptance spectrum from ultraviolet to visible range of ethylene resin.

[0041] Figure 10 shows the emissivity of polyvinyl chloride resin (PVC) with carbon-chlorine bonds at the atmospheric window, and Figure 11 shows the emissivity of polyvinylidene chloride resin (PVDC) with carbon-chlorine bonds at the atmospheric window. For carbon-chlorine bonds, the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. In the case of polyvinyl chloride resin, the absorption coefficient due to the bending vibration of CH of the alkene contained in the main chain appears at a wavelength of around 10 μm due to the electron-withdrawing effect of chlorine. The same is true for vinylidene chloride resin. Due to these effects, the wavelength average of the emissivity of a 10 μm thick film is 43% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0042] As shown in Figure 10, in the case of polyvinyl chloride resin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of polyvinyl chloride resin, thermal radiation in the atmospheric window occurs within a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside. As shown in FIG. 11, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

[0043] As described above, thermal radiation from the atmospheric window region generated from the surface of the resin material occurs within a depth of approximately 100 μm from the surface. If the resin becomes thicker than this, the cold generated by radiative cooling is insulated by the resin material, which does not contribute to thermal radiation. The thermal conductivity of resin materials is generally about 0.2 W / m / K. When calculations are made taking this thermal conductivity into account, if the thickness of the infrared radiation layer RC exceeds 20 mm, the temperature of the cooling surface (the surface of the first refrigerant flow pipe L) will rise.

[0044] Even if an ideal resin material that does not absorb any sunlight exists, the thermal conductivity of resin materials is generally about 0.2 W / m / K, so if the thickness exceeds 20 mm, the cooling surface (the surface of the first refrigerant flow pipe L) will be exposed to solar radiation and heat up. In other words, the thickness of the resin material used as the infrared radiation layer RC must be 20 mm or less.

[0045] [Thickness of the resin material used as the infrared radiation layer] From a practical standpoint, it is better for the infrared radiation layer RC to be thin. The thermal conductivity of resin materials is generally lower than that of metals and glass. To effectively cool the cooling surface (surface of the first refrigerant flow pipe L), it is better for the thickness of the infrared radiation layer RC to be the minimum necessary. The thicker the infrared radiation layer RC is, the greater the thermal radiation of the atmospheric window becomes, and above a certain thickness the thermal radiation energy at the atmospheric window becomes saturated.

[0046] The film thickness at which saturation occurs depends on the resin material, but in the case of resins containing carbon-chlorine bonds, saturation occurs even at a thickness of 100 μm, and sufficient heat radiation can be obtained in the atmospheric window region even at a thickness of 50 μm. The thinner the resin material, the higher the thermal conductivity and the more effectively the temperature of the object to be cooled can be lowered, so in the case of resins containing carbon-chlorine bonds, a thickness of 50 μm or less reduces the insulation and allows the object to be cooled effectively. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the object to be cooled effectively.

[0047] The benefit of making the material thinner is not just that it reduces heat insulation and makes it easier to transfer heat. It also reduces the absorption of near-infrared light from CH, CH2, and CH3, which are caused by resins containing carbon-chlorine bonds. By making the material thinner, the amount of sunlight absorbed by these compounds can be reduced, which increases the cooling capacity of the infrared radiating layer RC. From the above viewpoints, in the case of polyvinyl chloride resin and vinylidene chloride resin, which are resins containing carbon-chlorine bonds, a thickness of 50 μm or less can produce a more effective radiative cooling effect under sunlight.

[0048] [Light reflective layer] In order to provide the light-reflecting layer RF with the above-mentioned reflectance characteristics, it is preferable that the reflective material is silver or a silver alloy. As shown in Fig. 12, if the light-reflecting layer RF is made of silver as a base, the reflectance required for the light-reflecting layer RF can be obtained.

[0049] When reflecting sunlight using only silver or a silver alloy while maintaining the above-mentioned reflectance characteristics, a thickness of 50 nm or more is required. Incidentally, the "silver alloy" may be an alloy in which, for example, 0.4% to 4.5% by mass of any of copper, palladium, gold, zinc, tin, magnesium, nickel, and titanium is added to silver. A specific example is "APC-TR (made by Furuya Metal)," a silver alloy made by adding copper and palladium to silver.

[0050] In order to provide the light reflecting layer RF with the above-mentioned reflectance characteristics, it may have a structure in which silver or a silver alloy and aluminum or an aluminum alloy are laminated together. Here, when the light reflecting layer RF and the infrared emitting layer RC are laminated on the cooling surface (the surface of the first refrigerant flow pipe L), the light reflecting layer RF and the infrared emitting layer RC must be laminated in the order described above from the side closer to the cooling surface. In this configuration, the reflective material on the side where the infrared emitting layer RC exists must be silver or a silver alloy. When it is composed of two layers of silver (silver alloy) and aluminum (aluminum alloy), the thickness of the silver needs to be 10 nm or more, and the thickness of the aluminum needs to be 30 nm or more.

[0051] Incidentally, examples of "aluminum alloys" that can be used include alloys in which aluminum has been doped with copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical structures, yttrium, lanthanum, gadolinium, and terbium.

[0052] Silver and silver alloys are vulnerable to rain and humidity and need to be protected from them, and also need to be prevented from tarnishing. For this reason, it is preferable to provide a protective layer for protecting the silver or silver alloy in a form that covers the outside of the silver or silver alloy.

[0053] [Structure relating to adhesion of infrared emitting layer RC and light reflecting layer RF] When the infrared emitting layer RC and the light reflecting layer RF are provided directly on the surface of the first refrigerant flow pipe L, they are provided via the following adhesive or pressure sensitive adhesive. The adhesive or pressure-sensitive adhesive includes one or more of vinyl chloride resin, vinylidene chloride resin, polyolefin resin, polyester resin, acrylic resin, urethane resin, silicone resin, and rubber resin. Preferably, the adhesive or pressure-sensitive adhesive includes one of acrylic resin, urethane resin, vinyl chloride resin, and polyolefin resin.

[0054] When the light reflecting layer RF and the infrared radiation layer RC are laminated in the order described above on the surface of the first refrigerant flow pipe L, it is possible to apply or attach the infrared radiation layer RC to the light reflecting layer RF, and then attach the side of the light reflecting layer RF opposite to the side on which the infrared radiation layer RC is provided to the first refrigerant flow pipe L with an adhesive or pressure-sensitive adhesive. Alternatively, a light-reflecting layer RF may be formed on the infrared-emitting layer RC formed in a film form by deposition, sputtering, ion plating, silver mirror reaction, or the like, and the side of the light-reflecting layer RF opposite to the side on which the infrared-emitting layer RC is formed may be attached to the first refrigerant flow pipe L with an adhesive or pressure-sensitive adhesive.

[0055] [Configuration related to radiative cooling panel] As shown in Figures 1 and 2, the radiative cooling panel H cools the first refrigerant W1 flowing through the first refrigerant flow pipe L provided along the panel surface (the plane along the arrow XY in Figures 1 and 2). The radiative cooling panel H shown in Figure 2 may be hereinafter referred to as the radiative cooling panel H according to the first embodiment (Example 1).

[0056] In the radiative cooling panel H, the upstream first refrigerant flow pipe JL, which is an upstream flow pipe including the first refrigerant inlet portion EN, which is an inlet portion where the first refrigerant W1 flows into the first refrigerant flow pipe L, is provided with a fin F (shown in FIG. 2) that exchanges heat between the first refrigerant W1 and the outside air on one side (opposite side of the arrow Z in FIG. 1 and 2) of the cross direction (in this embodiment, the perpendicular direction perpendicular to the panel surface) that crosses the panel surface, and the downstream first refrigerant flow pipe KL, which is a downstream flow pipe including the first refrigerant outlet portion ET, which is an outlet portion where the first refrigerant W1 flows out from the first refrigerant flow pipe L, is provided with a cooling layer CL on the other side of the cross direction (side of the arrow Z in FIG. 1 and 2). Incidentally, the fin F can be suitably used as a corrugated fin or a plate fin.

[0057] In this specification, the cooling layer CL is a concept including at least the infrared emitting layer RC among the infrared emitting layer RC that emits infrared light from the emitting surface (the surface on the other side in the cross direction) and the light reflecting layer RF that reflects sunlight, and in the radiative cooling panel H shown in Figures 1 and 2, the cooling layer CL is the infrared emitting layer RC and the light reflecting layer RF. The light reflecting layer RF and the infrared emitting layer RC are laminated in the described order from the downstream first refrigerant flow pipe KL side. Incidentally, the radiative cooling panel H according to this embodiment is installed such that the other side (the side indicated by the arrow Z in Figs. 1 and 2) of the intersecting direction (in this embodiment, the perpendicular direction perpendicular to the panel surface) that intersects with the panel surface faces upward in the vertical direction.

[0058] In the radiative cooling panel H according to this embodiment, a plurality of first refrigerant flow pipes L are provided along the flow direction from the first refrigerant inlet EN to the first refrigerant outlet ET, and the first refrigerant W1 flowing in from the first refrigerant inlet EN flows along the flow direction while being distributed to each of the plurality of first refrigerant flow pipes L. In this embodiment, the upstream first refrigerant flow pipe JL is a pipe arranged in an upstream region R1 including a first refrigerant inlet EN in the plan view of Fig. 1, and the downstream first refrigerant flow pipe KL is a pipe arranged in a downstream region R2 including a first refrigerant outlet ET, and the upstream region R1 and the downstream region R2 are in contact with each other. That is, the first refrigerant flow pipe L is either the upstream first refrigerant flow pipe JL or the downstream first refrigerant flow pipe KL.

[0059] With reference to Fig. 2, the radiative cooling panel H according to the first embodiment will be described. The upstream first refrigerant flow pipe JL is provided with an infrared emitting layer RC and a light reflecting layer RF on the other side of the crossing direction (the side indicated by the arrow Z in Fig. 2) that crosses the panel surface. That is, in the radiative cooling panel H according to the first embodiment, the infrared emitting layer RC and the light reflecting layer RF are provided on the other side of the crossing direction over the entire area of ​​the first refrigerant flow pipe L, in other words, over both the upstream first refrigerant flow pipe JL and the downstream first refrigerant flow pipe KL. On the other hand, the downstream first refrigerant flow pipe KL is provided with an insulating layer IS on one side in the intersecting direction that intersects with the panel surface (the opposite side indicated by the arrow Z in Figure 2) to insulate the first refrigerant W1 from the outside air. The material of the insulating layer IS can be, for example, a mineral fiber insulating material, a wood fiber insulating material, or a foamed plastic insulating material. The insulating layer IS can be provided on the first refrigerant flow pipe L by a method such as bonding a foamed plastic insulating material with a resin adhesive, and the thickness of the insulating layer IS can be, for example, 1 mm to 300 mm when the material is a foamed plastic insulating material.

[0060] As shown in Fig. 3, the radiative cooling panel H may be configured to have a light reflecting layer RF on the other side of the upstream first refrigerant flow pipe JL in the intersecting direction intersecting with the panel surface (the side indicated by the arrow Z in Fig. 3). The other configurations are the same as those of the radiative cooling panel H according to the first embodiment (Example 1). The radiative cooling panel H shown in Fig. 3 may be hereinafter referred to as the radiative cooling panel H according to the second embodiment (Example 2).

[0061] [Configuration related to cooling system] As shown in FIG. 1, the cooling system 100 is configured to include a first refrigerant circulation path C1 that circulates a first refrigerant W1 in a plurality of radiative cooling panels H (three in FIG. 1: H1, H2, and H3), a pump P that pumps the refrigerant in the first refrigerant circulation path C1, and a heat storage tank AC that stores the cold heat of the first refrigerant W1 in a form in which the first refrigerant W1 flowing through the first refrigerant circulation path C1 is stored inside. As shown in FIG. 1, the plurality of radiative cooling panels H are provided in parallel in the first refrigerant circulation path C1. The heat storage tank AC is provided with, for example, a first heat exchanger EX1 that exchanges heat between a second refrigerant W2 (an example of another fluid) and the first refrigerant W1. The cooling system 100 having the above configuration is configured to supply the second refrigerant W2, which is cooled by heat exchange with the first refrigerant W1 in the first heat exchanger EX1, to an external cold heat demand part (not shown). Note that the heat storage tank AC does not necessarily need to be provided, and a configuration can be adopted in which the first refrigerant W1 circulating through the first refrigerant circulation path C1 is directly led to the cold heat demand part.

[0062] Furthermore, the cooling system 100 according to this embodiment includes a temperature sensor (not shown) that measures the temperature of the first refrigerant W1 at the downstream end of the upstream first refrigerant flow pipe JL, and the rotation speed of the pump P can be controlled so that the temperature measured by the temperature sensor is equal to or higher than the temperature of the outside air. This makes it possible to prevent a situation in which the temperature of the first refrigerant W1 flowing through the upstream first refrigerant flow pipe JL falls below the temperature of the outside air and the cold energy of the first refrigerant W1 is transferred to the outside air, resulting in a decrease in cooling efficiency.

[0063] [Calculation results for the cooling capacity of radiative cooling panels] The results of calculations performed to show the cooling capacity of the radiative cooling panel H according to Example 1 shown in Fig. 2 and the radiative cooling panel H according to Example 2 shown in Fig. 3 are shown below. In this calculation, the radiative cooling panel H shown in Fig. 4 was assumed as a comparative example. In the radiative cooling panel H of the comparative example shown in Fig. 4, a thermal insulation layer IS is provided on one side (the side opposite to the arrow Z in Fig. 4) of the intersecting direction (in this embodiment, the perpendicular direction perpendicular to the panel surface) of the first refrigerant flow pipe L to insulate the first refrigerant W1 from the outside air, and an infrared radiative layer RC and a light reflecting layer RF are provided on the other side (the side indicated by the arrow Z in Fig. 4) of the intersecting direction of the first refrigerant flow pipe L.

[0064] Here, the heat balance of the radiative cooling panel H is calculated by the amount of radiated heat from the infrared radiation layer RC to the radiation surface (the surface indicated by the arrow Z in Figures 2, 3, and 4) as shown in [Equation 1], Q Rad (T sc ) and the heat input to the radiative cooling panel H due to sunlight is Q Sun The amount of heat exchanged between the radiative cooling panel H and the outside air is Q, as shown in [Equation 3]. Con (T sc ) and the heat exchange amount between the radiative cooling panel H and the first refrigerant W1 is Q Con (T water ) and the heat input from the outside air to the radiative cooling panel H is Q Air The amount of radiant heat expressed by [Equation 1] is the sum of the amounts of heat expressed by [Equation 2] to [Equation 5].

[0065]

number

[0066]

number

[0067]

number

[0068]

number

[0069]

number

[0070] In the formulas 1 to 5, t represents the air permeability, and E s is the solar intensity (800W / m 2 ), Aa is the heat transfer efficiency (100%) in the radiative cooling panel H, and η a is the convection heat transfer coefficient of the outside air (10W / m 2 ·K) and T air indicates the outside air temperature (35℃ or 30℃), and η c (T water ) is the convection heat transfer coefficient of the first refrigerant W1 (determined functionally by the refrigerant temperature in the first refrigerant flow pipe L, etc.), λ is the wavelength of the emitted light, and A c indicates the effective area, and T sc is the temperature of the light reflecting layer, and T w is the refrigerant temperature in the first refrigerant flow pipe L, σ is the Stefan-Boltzmann coefficient, and ε Air denotes the atmospheric emissivity, and ε sc denotes the emissivity of the radiative layer, R denotes the radiant energy, and r denotes the solar reflectance.

[0071] For each of the radiative cooling panels H of Example 1, Example 2, and Comparative Example, the total area of ​​the radiative cooling panel required to cool the first refrigerant W1 of 44°C entering the radiative cooling panel H to 33°C, which is 2°C lower than the outside air temperature (35°C), was calculated. Incidentally, the boundary between the upstream region R1 and the downstream region R2 was calculated under the condition that the temperature of the first refrigerant W1 flowing into the downstream first refrigerant flow pipe KL is equal to the temperature of the outside air. The calculation results are shown in [Table 1]. In [Table 1], the "total area of ​​the radiative cooling panel required to cool to the target temperature" in the comparative example is set as the standard (100), and the other areas are expressed as a ratio (%) to the standard. Incidentally, the conditions other than those mentioned above are the same for Example 1, Example 2, and the Comparative Example.

[0072] [Table 1]

[0073] From the results shown in Table 1, it can be said that the radiative cooling panel H of Example 1 has a smaller “total area of ​​the radiative cooling panel required to cool to the target temperature” than the radiative cooling panel H of Comparative Example, and thus has improved cooling efficiency. In addition, the radiative cooling panels H of Examples 1 and 2 have a smaller “area of ​​the radiative cooling material (material of the infrared radiative layer RC)” than the radiative cooling panel H of the comparative example, and can provide an appropriate cooling effect while reducing the amount of the relatively expensive radiative cooling material. In addition, for Examples 1 and 2 and the Comparative Example, we also calculated the “total area of ​​the radiative cooling panel required to cool the first refrigerant W1 of 40°C entering the radiative cooling panel H to 28°C, which is 2°C lower than the outside air temperature (30°C), and the results were the same as those in Table 1 above.

[0074] [Another embodiment] (1) In the cooling system 100 according to the above embodiment, a configuration example in which a plurality of radiative cooling panels H are provided has been shown, but a configuration in which a single radiative cooling panel H is provided may also be used.

[0075] (2) In the above embodiment, the cooling system 100 has a configuration in which the heat storage tank AC and the radiative cooling panel H are connected to the first refrigerant circulation path C1 so that the first refrigerant W1 circulates between the heat storage tank AC and the radiative cooling panel H, as shown in FIG. 1. Alternatively, the cooling system 100 may include a heat pump unit HP and a radiative cooling panel H. For example, as shown in FIG. 5, a heat pump device HP (an example of a heat pump unit) having a compressor CP that compresses the second refrigerant W2, a condenser CD that condenses the second refrigerant W2 compressed by the compressor CP, an expansion valve EP that expands the second refrigerant W2 condensed by the condenser CD, an evaporator EV that evaporates the second refrigerant W2 expanded by the expansion valve EP, and a second refrigerant circulation path C2 that circulates the second refrigerant W2 in the order described above, a first refrigerant circulation unit CX including a first refrigerant circulation path C1 that guides the first refrigerant W1 flowing out from the first refrigerant outlet portion ET of the radiative cooling panel H to the first refrigerant inlet portion EN of the radiative cooling panel H and a pressure-feed pump P that pressure-feeds the first refrigerant W1 through the first refrigerant circulation path C1, and a second heat exchanger EX2 (an example of a heat exchanger) that exchanges heat between the second refrigerant W2 guided from the compressor CP to the expansion valve EP and the first refrigerant W1 flowing through the first refrigerant circulation path C1 may be provided. Although not shown in Figure 5, a configuration can be preferably adopted in which a fluid (e.g., air) for outputting cold heat exchanges with a second refrigerant W2 in an evaporator EV, and the output fluid after heat exchange is supplied to a cold heat supply source. In this other embodiment, various configurations can be adopted as long as the cold energy recovered by the first refrigerant W1 in the radiative cooling panel H can be utilized in the heat pump device HP. For example, in the configuration shown in FIG. 5, the second heat exchanger EX2 may be a condenser CD, and a configuration in which heat is exchanged between the first refrigerant W1 circulating through the first refrigerant circulation path C1 and the second refrigerant W2 in the condenser CD may be adopted. The heat pump unit may be replaced with an absorption refrigerator or the like.

[0076] (3) In the radiative cooling panel H according to the first and second embodiments, the insulating layer IS may be provided so that the thermal conductivity between the first refrigerant W1 and the outside air becomes lower toward the downstream side of the downstream first refrigerant flow pipe KL. For example, as shown in FIG. 6, a configuration can be suitably adopted in which the thickness of the insulating layer IS in the intersecting direction (the direction along the arrow Z in FIG. 6) is made thicker toward the downstream side of the downstream first refrigerant flow pipe KL. As another example of the configuration, as shown in Fig. 7, the insulating layer IS may be preferably configured to have a material with higher insulating performance toward the downstream side of the downstream-side first refrigerant flow pipe KL. Incidentally, Fig. 7 shows an example of a configuration in which a plurality of types of insulating materials with different insulating performances are provided as the insulating layer IS in order from the upstream side to the downstream side, starting from the material with the lowest insulating performance. Also, as shown in FIG. 6, the upstream first refrigerant flow pipe JL and the downstream first refrigerant flow pipe KL may be configured to have only an infrared radiation layer RC on the other side in the intersecting direction intersecting with the panel surface (the side indicated by the arrow Z in FIG. 7). Furthermore, as shown in FIG. 7, the upstream region R1 and the downstream region R2 do not necessarily have to be continuous regions, and a spaced region may be provided between them.

[0077] (4) In the above embodiment, the first refrigerant flow pipe L that flows inside the radiative cooling panel H is branched inside the radiative cooling panel H as an example. However, the present invention is not limited to this configuration, and a configuration in which a first refrigerant flow pipe L having no branching is provided may also be adopted. In this case, the first refrigerant flow pipe L without any branch can be arranged in a serpentine shape along the panel surface of the radiative cooling panel H, for example, as shown in FIG.

[0078] (5) In the embodiments described above, the first refrigerant flow pipe L is configured as a pipe having a circular cross section as described above. In other configurations, the first refrigerant flow pipe L may be a flat pipe that is provided so that its plane is aligned with the panel surface of the radiative cooling panel H.

[0079] (6) In the radiative cooling panel H shown in FIG. 2 of the above embodiment, the configuration in which the infrared radiation layer RC is provided on the other side of the upstream first refrigerant flow pipe JL in the intersecting direction intersecting with the panel surface (the side indicated by the arrow Z in FIG. 2) has been exemplified. However, a configuration in which the infrared radiation layer RC is not provided may be adopted. Furthermore, the downstream first refrigerant flow pipe KL has been illustrated as having an insulating layer IS on one side of the intersecting direction intersecting with the panel surface (the side opposite to the arrow Z in Figure 2) to insulate the first refrigerant W1 from the outside air, but a configuration in which no insulating layer IS is provided may also be adopted.

[0080] (7) In the radiative cooling panel H shown in Figs. 6 and 7 of the other embodiment, a configuration in which a light reflecting layer RF is provided on the other side of the upstream first refrigerant flow pipe JL in the intersecting direction intersecting with the panel surface (the side indicated by the arrow Z in Fig. 2) has been exemplified. However, a configuration in which the light reflecting layer RF is not provided may be adopted. Furthermore, a configuration has been exemplified in which an insulating layer IS is provided on one side of the downstream first refrigerant flow pipe KL in the intersecting direction that intersects with the panel surface (the side opposite to the arrow Z in Figure 2) to insulate the first refrigerant W1 from the outside air, but a configuration in which the insulating layer IS is not provided may also be adopted.

[0081] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, provided that no contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0082] The radiative cooling panel and cooling system of the present invention can be effectively used as a radiative cooling panel and cooling system that can efficiently cool a refrigerant even when cooling a relatively high-temperature refrigerant, while improving economic efficiency and reducing the overall weight. [Explanation of symbols]

[0083] 100: Cooling system C1: 1st refrigerant circulation path C2:Second refrigerant circulation path CD: Condenser CL: Cooling layer CP: Compressor CX: 1st refrigerant circulation section E: Magnetic material layer EN: First refrigerant inlet EP: Expansion valve ET: 1st refrigerant outlet EV: Evaporator EX2: Second heat exchanger (an example of a heat exchanger) F: Fin H: Radiation cooling panel HP: Heat pump device (an example of a heat pump section) IS: Insulation layer JL: First upstream refrigerant flow pipe KL: Downstream first refrigerant flow pipe L: 1st refrigerant flow pipe P: Pressure pump RC: Infrared radiation layer RF: light reflective layer W1: First refrigerant W2: Second refrigerant

Claims

1. A radiative cooling panel that cools a first refrigerant flowing through a first refrigerant flow pipe provided along a panel surface, an upstream first refrigerant flow pipe that is an upstream flow pipe including a first refrigerant inlet portion that is an inlet portion through which the first refrigerant flows into the first refrigerant flow pipe is provided with a fin that exchanges heat between the first refrigerant and outside air on one side in a cross direction that crosses the panel surface; a cooling layer is provided on the other side of the cross direction of the downstream first refrigerant flow pipe, the downstream first refrigerant flow pipe including a first refrigerant outflow portion that is an outflow portion through which the first refrigerant flows out of the first refrigerant flow pipe; The cooling layer is a radiative cooling panel including an infrared radiative layer that radiates infrared light from a radiative surface.

2. The radiative cooling panel according to claim 1, wherein the downstream first refrigerant flow pipe is provided on one side in the crossing direction with a heat insulating layer that insulates the first refrigerant from the outside air.

3. The radiative cooling panel according to claim 2, wherein the insulating layer is provided so that the thermal conductivity between the first refrigerant and the outside air becomes lower toward the downstream side of the downstream first refrigerant flow pipe.

4. The radiative cooling panel according to claim 2, wherein the thickness of the insulating layer in the cross direction is made thicker toward the downstream side of the downstream first refrigerant flow pipe.

5. The radiative cooling panel according to any one of claims 1 to 4, wherein the upstream first refrigerant flow pipe is provided on the other side of the crossing direction with either an infrared emitting layer that emits infrared light from a emitting surface or a light reflective layer that reflects sunlight.

6. A radiative cooling panel according to any one of claims 1 to 4, A cooling system that cools another fluid using the first refrigerant flowing out from the first refrigerant outlet.

7. a heat pump unit having a second refrigerant circulation path for circulating the second refrigerant in the order of a compressor that compresses a second refrigerant, a condenser that condenses the second refrigerant compressed by the compressor, an expansion valve that expands the second refrigerant condensed by the condenser, and an evaporator that evaporates the second refrigerant expanded by the expansion valve; A first refrigerant circulation unit including a first refrigerant circulation path that guides the first refrigerant flowing out from the first refrigerant outflow part of the radiative cooling panel to the first refrigerant inflow part of the radiative cooling panel and a pressure pump that pressure-feeds the first refrigerant through the first refrigerant circulation path; The cooling system according to claim 6 , further comprising a heat exchanger configured to exchange heat between the second refrigerant guided from the compressor to the expansion valve and the first refrigerant flowing through the first refrigerant circulation path.

8. 7. The cooling system of claim 6, wherein a plurality of the radiative cooling panels are connected in parallel.

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