Thermal diode-phase change radiation refrigeration roof

Abstract

The invention discloses a thermal diode-phase change radiation refrigeration roof which comprises an optical projection film layer, an air thermal resistance layer, a radiation refrigeration layer, a thermal diode layer and a phase change material layer which are sequentially arranged from top to bottom. The air thermal resistance layer is a hollow layer between the optical transmission film layer and the radiation refrigeration layer, the thermal diode layer is constructed into a transverse U-shaped thermal diode, two opposite horizontal sections of the thermal diode layer are embedded into heat conduction metal plates located on the upper side and the lower side of the thermal diode layer respectively, and the thermal diode is embedded into the horizontal section of the heat conduction metal plate on the upper side to form a condensation section. The thermal diode is embedded into the horizontal section of the lower heat-conducting metal plate to form an evaporation section, a heat insulation layer is arranged on the outer side of the middle section of the thermal diode, and the sides, deviating from each other, of the upper and lower heat-conducting metal plates are bonded with the radiation refrigeration layer and the phase-change material layer respectively. According to the invention, day-cycle roof thermal disturbance self-balancing can be realized, energy consumption is reduced, and energy shortage is relieved.

Description

Technical Field

[0001] This invention relates to the field of building energy conservation, specifically to a thermal diode-phase change radiative cooling roof. Background Technology

[0003] The heating and cooling loads of a building primarily enter the interior through the building envelope. In summer, roofs receive prolonged and intense solar radiation. Statistics show that roof energy consumption accounts for approximately 20-40% of total building energy consumption across different regions and building types. Therefore, high-insulation roofs play a positive role in improving the indoor thermal environment of top-floor rooms, reducing air conditioning energy consumption, decreasing greenhouse gas emissions, and mitigating urban heat island effects. Currently available passive energy-saving roofs include vacuum-insulated roofs, ventilated roofs, water-retaining roofs, green roofs, high-reflectivity roofs, phase change material roofs, radiative cooling roofs, and evaporative cooling roofs, among others. The significant latent heat of phase change materials can improve the roof's daytime insulation performance, reduce the magnitude of peak cooling loads, and delay the occurrence of peak loads. Radiative cooling materials can reduce absorbed solar radiation heat while simultaneously radiating heat into outer space at a high emissivity within the 8-13 μm wavelength range.

[0004] During the day, the phase change material (PCM) roof absorbs solar radiation heat, changing from a solid to a liquid state and storing heat. At night, as the ambient temperature drops, the PCM releases the heat stored during the day, gradually changing back from a liquid to a solid state and restoring its heat storage capacity. However, a problem with PCM roofs is that under prolonged hot weather, the rate of heat gain during the day exceeds the rate of heat dissipation at night, causing an imbalance between heat storage and heat dissipation, leading to the eventual failure of the thermal buffer. Summary of the Invention

[0005] This invention proposes a thermal diode-phase change radiative cooling roof, which utilizes the unidirectional heat transfer characteristics of thermal diodes to improve the phase change radiative cooling roof. During the day, it constructs a high thermal resistance and high heat insulation capacity to reduce the radiative energy reaching the phase change material, while at night, it constructs a low thermal resistance and high heat dissipation capacity to promote the recovery of the phase change material's heat storage capacity, achieve self-balance of the roof's heat gain disturbance during the daily cycle, reduce energy consumption, and alleviate energy shortages.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a thermal diode-phase change radiative cooling roof, comprising, from top to bottom, an optical transmission film layer, an air thermal resistance layer, a radiative cooling layer, a thermal diode layer, and a phase change material layer; the air thermal resistance layer is a hollow layer between the optical transmission film layer and the radiative cooling layer; the thermal diode layer includes a thermal diode bent into a U-shape, with the thermal diode arranged such that its middle section is vertical to the radiative cooling layer; two opposing horizontal sections of the thermal diode are respectively embedded in thermally conductive metal plates located on the upper and lower sides of the thermal diode layer; wherein, the horizontal section of the thermal diode embedded in the upper thermally conductive metal plate forms a condensation section, and the horizontal section of the thermal diode embedded in the lower thermally conductive metal plate forms an evaporation section; a heat insulation layer is formed on the outer side of the middle section of the thermal diode; and the two opposing sides of the upper and lower thermally conductive metal plates are respectively bonded to the radiative cooling layer and the phase change material layer.

[0007] When the thermal diode layer operates in the anti-gravity direction, the evaporation section (hot end) is located at a lower position. After being heated, the working fluid inside the evaporation section absorbs heat from the tube wall and evaporates. The vapor flows to the condensation section (cold end), where it liquefies upon cooling and transfers its latent heat to the external medium. The condensed liquid flows back to the evaporation section under gravity. The thermal diode layer utilizes the evaporation and condensation of the working fluid for efficient heat transfer in the anti-gravity direction. However, when the thermal diode layer operates in the gravity direction, without a wick structure, the working fluid cannot overcome gravity to flow back, resulting in a large vacuum thermal resistance. The working fluid is located in the lower evaporation section of the thermal diode layer, where it evaporates slowly. The upper condensation section has a higher temperature, making it difficult for the working fluid to condense. The heat transfer cycle of the thermal diode layer is interrupted. Therefore, the optical transmission film layer, air thermal resistance layer, and radiative cooling layer have difficulty transferring heat to the phase change material layer, reducing the heat absorbed by the phase change material layer.

[0008] The thermally conductive metal plates are coated with an interfacial thermally conductive material on opposite sides. The thermally conductive material is thermally conductive grease or self-adhesive thermally conductive silicone. The thermally conductive metal plates are thermally conductive aluminum plates or copper plates with a thermal conductivity of 150~350 W / (m·K). The thermal conductivity of the thermally conductive grease or self-adhesive thermally conductive silicone is 1-12 W / (m·K).

[0009] The U-shaped thermal diode is a copper tube. The copper tube is evacuated and filled with working fluid. Under sealed conditions, the non-condensable working fluid is discharged from the copper tube to form a vacuum sealed cavity. The thermal diode layer is in the high-efficiency operating range of 10~50℃, and the thermal conductivity is about 5000-40000 W / (m·K).

[0010] The working fluid is liquid acetone or R-134a (1,1,1,2-tetrafluoroethane (CH2FCF3)).

[0011] The optical transmission film is a polyethylene (PE) protective film.

[0012] The radiation cooling layer includes a coating applied to a metal plate, the coating being selected from one of polyvinyl chloride (PVC), polyvinyl fluoride (PVF), and polymethylpentene (TPX) based polymer films.

[0013] The phase change material layer is a paraffin material with a phase change temperature of 26~28 ℃ thermal comfort temperature.

[0014] Beneficial effects: This invention, a thermal diode-phase change radiative cooling roof, replaces traditional roofs. In summer, it passively and with zero energy consumption creates a roof that self-processes and dissipates heat, maintaining a stable low temperature on the inner surface of the roof. This significantly reduces or eliminates the cooling load caused by the roof, achieving energy savings. Furthermore, the materials used in this roof do not increase the load compared to traditional roofs and are cost-effective. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a thermal diode-phase change radiative cooling roof according to the present invention; Figure 2 This is a schematic diagram of the thermal diode structure of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0017] like Figure 1-2 As shown, a thermal diode-phase change radiative cooling roof includes, from top to bottom, an optical transmission film layer, an air thermal resistance layer 2, a radiative cooling layer 3, a thermal diode layer, and a phase change material layer 5. The air thermal resistance layer 2 is a hollow layer between the optical transmission film layer 1 and the radiative cooling layer 3. The thermal diode layer includes a U-shaped thermal diode, with the middle section of the U-shaped thermal diode vertically aligned with the radiative cooling layer 3. The opposite ends are embedded in thermally conductive metal plates 7 located on the upper and lower sides of the thermal diode layer, respectively. The horizontal section of the thermal diode embedded in the upper thermally conductive metal plate 7 forms a condensation section 41, and the horizontal section of the thermal diode embedded in the lower thermally conductive metal plate 7 forms an evaporation section 44. An insulation layer 42 is provided on the outer side of the middle section of the thermal diode. The opposite sides of the upper and lower thermally conductive metal plates 7 are bonded to the radiative cooling layer 3 and the phase change material layer 5, respectively.

[0018] Furthermore, the opposing sides of the thermally conductive metal plates 7 are coated with an interfacial thermally conductive material 6. The thermally conductive material 6 is thermally conductive silicone grease or self-adhesive thermally conductive silicone, and is bonded to the radiation cooling layer 3 above the thermal diode layer and the phase change material layer 5 below the thermal diode layer, respectively. The thermal conductivity of the thermally conductive silicone grease or self-adhesive thermally conductive silicone is about 1-12 W / (m·K). The thermally conductive metal plate 7 is preferably a thermally conductive aluminum plate or copper plate with a thermal conductivity of 150~350 W / (m·K).

[0019] Furthermore, the U-shaped thermal diode is made of copper tubing, which is evacuated and filled with a working fluid. The working fluid is selected from liquid acetone or R-134a (1,1,1,2-tetrafluoroethane (CH2FCF3)). The copper tubing discharges non-condensable working fluid under sealed conditions to form a vacuum-sealed cavity. The horizontal sections at both ends of the thermal diode are embedded in the heat-conducting metal plate 7 to increase the heat transfer area. The working fluid allows the thermal diode to operate in its high-efficiency range of 10~50℃, with a thermal conductivity of approximately 5000-40000 W / (m·K). Furthermore, the optical transmission film 1 is a polyethylene (PE) protective film, which allows more than 80% of the incident light to pass through in the far-infrared band of 8~13μm.

[0020] Furthermore, the radiative cooling layer 3 includes a coating applied to the metal plate. The coating is selected from one of polyvinyl chloride (PVC), polyvinyl fluoride (PVF), or polymethylpentene (TPX) based polymer films. The coating has good chemical stability and strong weather resistance (suitable for long-term outdoor use). Its emissivity can reach above 0.9 within the 8–13 µm atmospheric window, and its solar absorption rate is extremely low. It is a high-performance radiative cooling material, meaning that the coating is almost "transparent" to infrared radiation in the 8–13 µm range. The coating does not block the upward infrared thermal radiation emitted by the material below the coating.

[0021] Furthermore, the phase change material layer 5 is a paraffin material with a phase change temperature of 26~28 ℃ thermal comfort temperature.

[0022] In this embodiment, the metal plate in the radiative cooling layer 3 is a 2 mm thick aluminum plate. Aluminum has extremely high solar reflectivity, capable of reflecting over 90% of sunlight within the 0.3~2.5µm range, effectively blocking solar heat absorption. An optical transmission film 1 and a radiative cooling coating 3 are disposed on top, forming a combined plate consisting of an optical transmission film layer 1, an air thermal resistance layer 2, and a radiative cooling layer 3. The thermal diode is a 6 mm diameter copper tube, which is evacuated and injected with acetone in the middle, while ensuring the airtightness of the copper tube and removing non-condensable gases.

[0023] During the summer daytime, the optical transmission film layer 1, the air thermal resistance layer 2, and the radiative cooling layer 3 reflect most of the sunlight. The aluminum plate of the radiative cooling layer 3 is heated, and then the aluminum plate transfers heat to the phase change material layer 5 through the thermal diode layer. The paraffin in the phase change material layer 5 melts and stores heat, keeping the temperature of the space under the roof below 26~28℃. The temperature of the aluminum plate in the radiative cooling layer 3 is higher than that of the thermal diode layer and the phase change material layer 5. Since the working fluid in the thermal diode cannot flow back against gravity, the working fluid is located in the evaporation section 44 at the bottom of the thermal diode layer, and the temperature is kept below 26~28℃ for a long time, resulting in slow evaporation. The temperature in the condensation section 41 at the top of the thermal diode layer is higher, making it difficult for the working fluid to condense. The heat transfer cycle of the thermal diode layer is interrupted. Therefore, it is difficult for the optical transmission film layer 1, the air thermal resistance layer 2, and the radiative cooling layer 3 to transfer heat to the phase change material layer 5, reducing the heat absorbed by the phase change material layer 5.

[0024] During summer nights, the optical transmission film layer 1, the air thermal resistance layer 2, and the radiative cooling layer 3 cool down rapidly, reaching a temperature lower than the phase change material layer 5. During the day, the paraffin wax within the phase change material layer 5 solidifies and releases heat. The working fluid, located in the evaporation section 44 below the thermal diode layer, absorbs the heat released by the phase change material layer 5 and evaporates, rising to the condensation section 41 above the thermal diode layer. The working fluid condenses in the condensation section 41, transferring heat to the low-temperature radiative cooling layer 3, accelerating the heat dissipation of the phase change material layer 5 to the outside. This balances the heat storage and dissipation of the phase change material layer 5 during summer, ensuring that the phase change material layer 5 does not fail.

[0025] This embodiment utilizes radiative cooling materials to reduce the temperature at the outer boundary of the roof, and further slows down the daytime melting rate of the phase change material by utilizing the high thermal resistance of the cavity. Simultaneously, the unidirectional heat transfer characteristics of the thermal diodes are used to accelerate the passive heat dissipation and solidification of the phase change material at night.

[0026] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A thermal diode - phase change radiative roofing, characterized by, The application relates to a heat dissipation film, which comprises, from top to bottom, an optical transmission film layer (1), an air heat resistance layer (2), a radiation refrigeration layer (3), a heat diode layer and a phase change material layer (5); the air heat resistance layer (2) is a hollow layer between the optical transmission film layer (1) and the radiation refrigeration layer (3); the heat diode layer comprises a U-shaped heat diode, the heat diode is arranged with a middle section vertically to the radiation refrigeration layer (3), and opposite horizontal sections of the heat diode are embedded into upper and lower heat-conducting metal plates (7) on the upper and lower sides of the heat diode layer respectively, wherein the horizontal section of the heat diode embedded into the upper heat-conducting metal plate (7) forms a condensation section (41), the horizontal section of the heat diode embedded into the lower heat-conducting metal plate (7) forms an evaporation section (44), an adiabatic heat insulation layer (42) is arranged outside the middle section of the heat diode, and the opposite sides of the upper and lower heat-conducting metal plates (7) are bonded to the radiation refrigeration layer (3) and the phase change material layer (5) respectively.

2. A thermal diode - phase change radiant cooling roof according to claim 1, characterized in that, The opposite sides of the heat-conducting metal plates (7) are coated with interface heat-conducting materials (6), the heat-conducting materials (6) are heat-conducting silicon grease or self-adhesive heat-conducting silica gel, and the heat-conducting metal plates (7) are heat-conducting aluminum plates or copper plates.

3. A thermal diode - phase change radiant cooling roof according to claim 1, characterized in that, The U-shaped heat diode is a copper pipe, the copper pipe is vacuumized and filled with working fluid, the copper pipe discharges non-condensable working fluid to form a vacuum closed cavity under airtight conditions, the heat diode is in a high-efficiency working interval of 10-50 DEG C, and the heat conductivity coefficient is about 5000-40000 W / (m.K).

4. A thermal diode - phase change radiant cooling roof according to claim 3, characterized in that, The working fluid is liquid acetone or R-134a (1,1,1,2-tetrafluoroethane (CH2FCF3)).

5. A thermal diode - phase change radiant cooling roof according to claim 1, characterized in that, The optical transmission film layer (1) is a polyethylene (PE) protective film.

6. A thermal diode - phase change radiant cooling roof in accordance with claim 1, characterized by, The radiation refrigeration layer (3) comprises a coating layer coated on a metal plate, and the coating layer is selected from one of polyvinyl chloride (PVC), polyvinyl fluoride (PVF) and polymethylpentene TPX-based polymer film.

7. A thermal diode - phase change radiant cooling roof according to claim 1, characterized in that, The phase change material layer (5) is a paraffin material with a heat comfort temperature of 26-28 DEG C as a phase change temperature.

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