Pdh / t-rc radiative cooling film and greenhouse water circulation system with same

Abstract

This invention relates to the field of water-saving irrigation and environmental control technology in facility agriculture, and discloses a PDH / T-RC radiative cooling composite membrane and a greenhouse water circulation system incorporating it. The composite membrane has a five-layer gradient structure, consisting of a weather-resistant protective layer, a near-infrared high-reflectivity layer, a high-radiation emission layer, a PDH hydrogel composite adhesive layer, and a hydrophilic condensation functional layer from top to bottom. This enables passive day and night cooling, high transmittance of photosynthetically active radiation, and efficient water vapor condensation. The water circulation system uses this composite membrane as the covering material, and is equipped with a condensate drainage structure, a water storage unit, and a drip irrigation unit to form a fully closed-loop passive water circulation system. This invention can reduce the greenhouse temperature by 3-10℃, increase irrigation water recovery rate by more than 50%, reduce water consumption by 30%-60%, stabilize greenhouse humidity, reduce the incidence of pests and diseases, increase crop yield by 10%-30%, operate with zero energy consumption throughout, and is suitable for the construction and renovation of various greenhouses.

Description

Technical Field

[0001] This invention relates to the fields of water-saving irrigation, passive refrigeration and environmental control technology in facility agriculture, specifically to a PDH / T-RC radiative cooling film and a greenhouse water circulation system having the same. Background Technology

[0002] Greenhouses, as the core carrier of modern facility agriculture, effectively overcome the limitations of natural climate by constructing a relatively closed, artificially controllable environment, enabling off-season crops, high multiple cropping indices, and intensive production. They have become key facilities for ensuring a stable supply of agricultural products such as vegetables, fruits, and flowers. However, greenhouses are highly sealed and relatively independent, resulting in continuous and vigorous crop transpiration and soil evaporation, leading to a large accumulation of water vapor inside and creating operating characteristics of high temperature, high humidity, high water consumption, and high energy consumption. Currently, greenhouse cooling, dehumidification, water collection, and irrigation technologies have significant shortcomings, with prominent problems such as high energy consumption, large water consumption, unstable temperature and humidity control, low water resource recycling rates, and insufficient system integration, making it difficult to meet the needs of coordinated development of water conservation, energy saving, humidity control, and stable yield.

[0003] From the perspective of environmental regulation mechanisms, the heat inside a greenhouse mainly comes from solar radiation and crop respiration, while moisture comes from soil evaporation and plant transpiration. In a closed space, heat and moisture are difficult to dissipate naturally, leading to excessively high temperatures during the day and high humidity at night, which can cause condensation and disease growth. Traditional regulation methods primarily focus on heat and moisture removal, failing to achieve water vapor resource recovery, resulting in significant waste of water and energy. Related data shows that approximately 98% of the water absorbed by greenhouse crops is lost as water vapor, with only a small amount used for physiological metabolism. If water vapor inside the greenhouse can be efficiently condensed, recovered, and reused in a closed loop, irrigation dependence can be significantly reduced, achieving water self-sufficiency.

[0004] Existing greenhouse cooling and water collection technologies can be mainly divided into three categories, each with its own insurmountable drawbacks. The first category involves mechanical refrigeration and air conditioning dehumidification, relying on compressors, refrigerants, and other active cooling equipment for forced cooling and dehumidification. While this provides precise temperature control, it is extremely energy-intensive and expensive to operate. Furthermore, the condensate recovery process is inefficient, resulting in very low utilization rates. Additionally, drastic temperature fluctuations can disrupt crop photosynthetic rhythms and growth balance, making large-scale adoption economically unfeasible. The second category involves evaporative cooling technologies such as spray cooling. These use water as a medium to absorb heat through evaporation. While the equipment is simple and low-cost, it consumes a huge amount of water, has poor cooling uniformity, and its cooling efficiency drops sharply in high-humidity environments. Moreover, it cannot stably recover water vapor, easily leading to excessive humidity inside the greenhouse, significantly increasing the probability of mold and pest infestations, and raising risks associated with pesticide use and quality control. The third category consists of passive heat insulation methods such as ordinary sunshades and reflective films, which can only reflect part of the solar radiation and reduce daytime heat gain. They do not have the ability to cool at night, cannot provide a continuous low-temperature condensation surface, and cannot achieve continuous water collection and closed-loop water circulation day and night. The cooling and water collection functions are completely separated, and the system integration and coordination are extremely poor.

[0005] In recent years, radiative cooling technology has developed rapidly, providing a new approach for passive cooling of greenhouses. PDH / T-RC radiative cooling membranes can radiate heat into space through 8-13μm atmospheric windows around the clock, reflecting sunlight highly during the day and providing continuous cooling at night. The membrane surface temperature can be stably lower than the ambient temperature, providing an ideal low-temperature interface for the condensation of high-humidity air. However, existing technologies have significant limitations: First, the radiative cooling film is not sufficiently coupled with the greenhouse water cycle and condensation water collection, resulting in a disconnect between cooling and water collection functions and the lack of an integrated synergistic mechanism. Second, there is a lack of a continuous condensation design that alternates between day and night, leading to strong cooling during the day and weak cold preservation at night, resulting in poor water collection stability. Third, the PDH temperature-sensitive hydrogel and the radiative cooling film do not achieve functional synergy, and the advantages of cold preservation, water release, and light regulation are not fully utilized, significantly reducing condensation efficiency and cooling effect. Fourth, the lack of condensate collection, diversion, pressure stabilization, and irrigation distribution systems makes it impossible to form a fully automatic closed-loop water cycle and achieve irrigation water self-sufficiency. Fifth, the contradiction between cooling and light transmission in the covering material is prominent; strong cooling results in weak light transmission, affecting the effective radiation transmission for photosynthesis and inhibiting crop photosynthesis. Sixth, temperature and humidity control is crude, with large humidity fluctuations, leading to a high incidence of pests and diseases, and traditional methods cannot simultaneously achieve the goals of cooling, humidity control, and stable yield. From a system integration perspective, existing greenhouse water cycles are mostly open-loop models of "water supply-irrigation-discharge," failing to integrate processes such as water vapor evaporation inside the greenhouse, condensation on the membrane surface, collection and reuse, and soil recirculation. This results in low water resource reuse rates, high dependence on external water sources, and limited adoption in arid and water-scarce regions. Furthermore, passive refrigeration struggles to achieve continuous and stable operation 24 hours a day, providing insufficient cooling during extreme high temperatures and failing to effectively control high humidity at night, leading to significant fluctuations in crop yield and quality.

[0006] Therefore, there is an urgent need for a technical solution that integrates passive day and night cooling, efficient condensation water extraction, closed-loop water circulation irrigation, and precise temperature and humidity control to promote the transformation and upgrading of greenhouse agriculture towards low-carbon, water-saving, intelligent, and efficient directions. Summary of the Invention

[0007] To address a series of problems in existing greenhouses, such as the disconnect between the functions of PDH hydrogel and radiative cooling film, the lack of an integrated system for condensation, collection, diversion, pressure stabilization, and irrigation, the common contradiction between cooling and light transmission in greenhouse covering materials, and the drastic fluctuations in temperature and humidity caused by traditional control methods, leading to pests and diseases in high-humidity environments, this invention aims to provide a system for greenhouse water circulation based on a PDH / T-RC radiative cooling film to solve the following technical problems: (1) Solve the problems of high energy consumption and large water consumption in traditional greenhouse cooling, and the inability of passive refrigeration to achieve continuous and stable cooling day and night; (2) Solve the problem of low water vapor condensation efficiency and low recycling rate in the greenhouse, making it difficult to achieve self-sufficiency in irrigation water; (3) Solve the problem of functional disconnect between PDH hydrogel and radiation cooling membrane, which fails to form synergistic cooling and condensation enhancement; (4) Solve the problem of the lack of a condensate collection, diversion, pressure stabilization and distribution system, which makes it impossible to achieve a fully automatic closed-loop water circulation; (5) Solve the problem of the contradiction between cooling and light transmission of greenhouse covering materials, which affects the effective radiation transmission of crop photosynthesis; (6) Solve the problems of large humidity fluctuations, high incidence of pests and diseases in greenhouses, and the impact of traditional control methods on crop photosynthesis and yield.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a PDH / T-RC radiation cooling composite membrane, comprising: Weather-resistant protective layer; A near-infrared high reflectivity layer is attached to the lower surface of the weather-resistant protective layer to reflect near-infrared radiation in sunlight and transmit photosynthetically active radiation. A high-emissivity emitting layer is attached to the lower surface of the near-infrared high-reflectivity layer and is used to radiate heat to the outer space through an 8-13 μm atmospheric window. The PDH hydrogel composite adhesive layer is attached to the lower surface of the high-emissivity layer to achieve multiple functions such as cold preservation, water release, evaporative cooling and temperature-sensitive light modulation. A hydrophilic condensation functional layer is attached to the lower surface of the PDH hydrogel composite adhesive layer to contact with humid air and promote the condensation of water vapor on its surface.

[0009] As a preferred embodiment of the present invention, the total thickness of the composite film is 80-200 μm.

[0010] As a preferred embodiment of the present invention, the weather-resistant protective layer is selected from at least one of transparent weather-resistant PC film, transparent weather-resistant PET film, and transparent weather-resistant PMMA film, and its thickness is 25-50 μm.

[0011] As a preferred embodiment of the present invention, the near-infrared high reflectivity layer is selected from at least one of metal-based nano-reflective film, transparent conductive oxide reflective film, and polymer-based composite reflective film, and has a reflectivity of ≥85% for near-infrared radiation in sunlight, a transmittance of ≥85% for photosynthetically active radiation, and a thickness of 15-30 μm.

[0012] As a preferred embodiment of the present invention, the high-emissivity emissivity of the high-emissivity emissivity layer to the 8-13μm atmospheric window band is ≥90%, and its thickness is 20-40μm.

[0013] As a preferred embodiment of the present invention, the water retention rate of the PDH hydrogel composite adhesive layer is ≥90%, and its thickness is 15-40μm.

[0014] As a preferred embodiment of the present invention, the surface of the hydrophilic condensation functional layer has a microstructure and a thickness of 5-20 μm.

[0015] Secondly, the present invention provides a greenhouse water circulation system, comprising: PDH / T-RC radiative cooling composite film, which is used as a covering material for the top and / or side walls of a greenhouse; A condensate guiding structure is disposed below the composite membrane to collect water droplets or water films formed on the condensation interface and guide the condensate to flow in a specific direction. A water storage unit is located below the condensate guide structure and connected to its outlet, for storing the collected condensate; An irrigation unit, located below the water storage unit and connected to its outlet, is used to deliver condensate to the roots of the crop.

[0016] As a preferred embodiment of the present invention, the condensate drainage structure includes a hydrophobic drainage channel arranged circumferentially on the inner wall of the greenhouse; the installation slope of the composite membrane is not less than 3°, so that the condensate can flow by gravity along the surface of the composite membrane to the hydrophobic drainage channel below.

[0017] As a preferred embodiment of the present invention, the water storage unit includes a sealed water storage tank, and the outlet of the condensate diversion channel of the condensate diversion structure is connected to the sealed water storage tank below through a first water supply pipe.

[0018] As a preferred embodiment of the present invention, the irrigation unit includes a drip irrigation terminal, and the outlet of the sealed water storage tank of the water storage unit is connected to the drip irrigation terminal below through a second water supply pipe.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention achieves passive, continuous day and night cooling, significantly alleviating high-temperature stress. Utilizing the all-weather radiative heat dissipation capability of the PDH / T-RC radiative cooling composite film, combined with the synergistic effects of PDH hydrogel insulation, water release, and evaporative cooling, it can achieve continuous and stable passive cooling 24 hours a day without relying on electricity or compressors. During the day, it achieves dual cooling through high-reflectivity near-infrared radiation and high-radiative heat dissipation; at night, it continuously radiates cooling into space and maintains a low-temperature interface, reducing the overall temperature inside the greenhouse by 3-8°C. In extreme heat, the temperature reduction can reach 3-10°C, effectively preventing crops from suffering from daytime sun scorching and high-temperature heat stress. It also eliminates the problem of stuffy, humid conditions inside the greenhouse at night, providing crops with a suitable temperature range for growth. This overcomes the limitations of traditional passive cooling technology, which only provides daytime insulation and fails at night. This invention significantly improves water resource utilization and achieves high-efficiency water conservation. The system continuously collects water vapor inside the greenhouse through low-temperature membrane condensation, increasing the condensate recovery rate by more than 50%. Relying on a fully closed-loop water circulation system, the recovered water is directly used for irrigation, reducing greenhouse irrigation water consumption by 30%-60%. Water vapor generated by crop transpiration and soil evaporation is no longer directly discharged but is converted into usable irrigation water, realizing a cycle of "evaporation-condensation-reuse-re-evaporation." This significantly reduces dependence on external water sources and has outstanding water-saving advantages in arid, semi-arid, and water-scarce mountainous areas, fundamentally solving the industry pain points of high water consumption and serious water waste in greenhouses.

[0020] This invention possesses excellent photosynthetic friendliness, ensuring normal photosynthesis in crops. The PDH / T-RC composite film employs a precise optical structure design, highly reflecting near-infrared heat while transmitting high levels of photosynthetically effective radiation. It achieves efficient cooling without obstructing or attenuating the light required for crop growth, completely resolving the inherent contradiction of traditional cooling covering materials that "cooling necessarily involves shading, while light transmission does not cool." Combined with the temperature-sensitive light-regulating properties of the PDH hydrogel, it can moderately scatter light during periods of strong light and maintain high light transmittance during periods of weak light, optimizing the light environment inside the greenhouse, ensuring stable photosynthetic efficiency, and providing sufficient light for crop nutrient accumulation, flowering, fruit setting, and healthy growth.

[0021] This invention optimizes the microenvironment within greenhouses, significantly reducing the incidence of pests and diseases. The system achieves simultaneous dehumidification through continuous film condensation, stably controlling the relative humidity within the greenhouse, reducing condensation on leaves and film surfaces, and disrupting the conditions for the growth and reproduction of mold, bacteria, and pests. This substantially reduces the incidence of diseases, decreases pesticide use, and improves the green and safe level of agricultural products. Simultaneously, it significantly narrows the fluctuation range of temperature and humidity, avoiding drastic environmental changes caused by traditional cooling methods, creating a stable and comfortable growth microenvironment for crops, which is beneficial for improving the taste, color, and commercial quality of fruits.

[0022] This invention is low-carbon and zero-energy, with low operation and maintenance costs, and is suitable for large-scale promotion. It employs a purely physical passive cooling mode, requiring no electricity and emitting no energy from equipment, aligning with low-carbon agriculture and dual-carbon development goals. The system has a simple structure, and its installation method is consistent with traditional greenhouse films, allowing for direct application and compatibility with various newly built and renovated greenhouses. The PDH / T-RC composite film boasts strong weather resistance and a long service life, requiring no complex daily maintenance. This significantly reduces long-term greenhouse operating costs, including electricity, water, equipment repair, and consumables, demonstrating excellent economic efficiency and high value for large-scale industrialization.

[0023] This invention provides a system that is stable and reliable around the clock, with minimal impact from environmental fluctuations. Operating based on physical mechanisms such as gravity flow, radiative cooling, and interfacial condensation, the system is unaffected by weather or day / night cycles. It can continuously and stably collect water through condensation in sunny, cloudy, and nighttime conditions, exhibiting high operational reliability. With no electrical control components or pump / valve failure risks, the overall structure is highly durable, enabling long-term continuous and stable operation. This meets the year-round production needs of different climate zones and crop types, solving the problem of unstable water collection in traditional technologies.

[0024] This invention synergistically promotes increased crop yield and quality, enhancing the overall benefits of facility agriculture. Through the combined effects of multiple technologies, including passive cooling, efficient water supply, stable humidity, and optimized lighting, crop photosynthetic efficiency is significantly improved, nutrient conversion is more complete, and yields can be increased by 10%-30%. Attached Figure Description

[0025] Figure 1 This is a structural diagram of the PDH / T-RC composite membrane layer of the present invention.

[0026] Figure 2 This is a schematic diagram of the overall structure of the greenhouse water circulation system of the present invention.

[0027] Figure 3 This is a schematic diagram illustrating the working principle of the greenhouse water circulation system of the present invention, which operates through alternating day and night condensation.

[0028] Figure 4 This is a closed-loop flow chart of the greenhouse water circulation system of the present invention.

[0029] In the diagram: 1. Composite membrane; 101. Weather-resistant protective layer; 102. Near-infrared high reflectivity layer; 103. High-emissivity emission layer; 104. PDH hydrogel composite adhesive layer; 105. Hydrophilic condensation functional layer; 2. Greenhouse; 3. Hydrophobic drainage channel; 4. Sealed water storage tank; 5. First water delivery pipe; 6. Second water delivery pipe; 7. Drip irrigation terminal. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present patent. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present patent.

[0031] This invention belongs to the field of water-saving irrigation, passive refrigeration, and environmental control technology in facility agriculture. Specifically, it relates to a greenhouse system that integrates PDH temperature-sensitive hydrogel and radiative cooling functions, enabling continuous day and night condensation and water collection, closed-loop water circulation irrigation, and coordinated temperature and humidity control. To enable those skilled in the art to clearly understand and fully implement the technical solution of this invention, the following description, in conjunction with the appendix, is provided. Figure 1-4 The present invention will be described in detail, including specific embodiments, the core component structure, system assembly method and operating principle.

[0032] like Figure 1 As shown, the PDH / T-RC radiation cooling composite film of the present invention has a five-layer gradient composite structure, consisting of a weather-resistant protective layer 101, a near-infrared high reflectivity layer 102, a high radiation emission layer 103, a PDH hydrogel composite adhesive layer 104, and a hydrophilic condensation functional layer 105, from top to bottom. The total thickness of the composite film is strictly controlled within the range of 80-200μm. It has the characteristics of being rollable, easy to cover, aging resistant, and having high mechanical strength. It can directly replace traditional PO film, shade net, reflective film and other multi-layer covering materials, and is suitable for the installation requirements of the top and side walls of various greenhouses.

[0033] The weather-resistant protective layer 101 is located on the outermost side of the composite film, directly exposed to the external atmospheric environment. Its core functions are to resist ultraviolet aging, wind and rain erosion, and sand and dust abrasion, while ensuring high transmittance of visible light and photosynthetically active radiation. In this embodiment, the weather-resistant protective layer is a transparent weather-resistant PET film with a thickness of 25-50 μm. This film is modified by blending ultraviolet absorbers and antioxidants, achieving an outdoor service life of 5-8 years, a yellowing index ≤3, and a visible light transmittance ≥92%. As an alternative, a transparent weather-resistant PC film or PMMA film of the same thickness can also be used. PC film has better impact resistance and is suitable for areas with frequent hail and strong winds; PMMA film has better light transmittance and is suitable for high-latitude areas with insufficient sunlight.

[0034] The near-infrared high-reflectivity layer 102 serves as the daytime heat-insulating core layer, attached to the lower surface of the weather-resistant protective layer, with a thickness controlled at 15-30 μm. In this embodiment, a silver nanowire / polyimide (AgNWs / PI) composite reflective film is used, prepared by solution coating. The silver nanowires have a diameter of 20-30 nm, a length of 10-20 μm, and a filling amount of 15 wt%. This layer exhibits a reflectivity ≥88% for near-infrared radiation in the 780-2500 nm wavelength band of sunlight, blocking over 85% of solar heat radiation from entering the greenhouse. Simultaneously, it has a transmittance ≥88% for photosynthetically active radiation (PAR) in the 400-700 nm wavelength band, fully meeting the light requirements for crop photosynthesis and completely resolving the inherent contradiction of traditional cooling covering materials that require shading for cooling but not cooling for light transmission. As an alternative, an ITO transparent conductive oxide reflective film or a titanium dioxide / polyacrylate polymer-based composite reflective film can also be used, with optical properties essentially consistent with this embodiment.

[0035] The high-emissivity emitting layer 103 serves as the core layer for radiative cooling, affixed to the lower surface of the near-infrared high-reflectivity layer, with a thickness of 20-40 μm. In this embodiment, a silicon dioxide / silicon carbide (SiO2 / SiC) composite ceramic coating is used, prepared via plasma spraying, with a SiO2 to SiC mass ratio of 7:3 and a surface roughness Ra ≤ 0.8 μm. This layer exhibits an emissivity ≥ 92% in the 8-13 μm atmospheric window band, enabling it to radiate heat from inside the greenhouse into outer space in the form of infrared electromagnetic waves throughout the day, achieving passive cooling. During the day, it works in conjunction with the near-infrared high-reflectivity layer to form a dual cooling mechanism of external reflection and internal radiation. At night, when there is no solar radiation, it maintains high emissivity, continuously lowering the membrane surface temperature to 2-5°C below ambient temperature, providing a stable low-temperature interface for water vapor condensation.

[0036] The PDH hydrogel composite adhesive layer 104 is the key functional synergistic layer of this invention. It is attached to the lower surface of the high-emissivity layer, with a thickness of 15-40 μm, and simultaneously performs four functions: adhesion, cold insulation, water release and evaporation cooling, and temperature-sensitive light modulation. In this embodiment, the PDH hydrogel is a known hydrogel material, which can be prepared using methods known in the art or methods previously disclosed by the applicant. This layer has a water retention rate ≥92%, absorbing and storing nighttime cold energy, and slowly releasing water during the day to form a continuous evaporative cooling effect, further reducing the film surface temperature by 1-3°C. It also possesses temperature-sensitive light modulation characteristics; when the ambient temperature is above 30°C, the hydrogel undergoes a volume phase change, scattering strong light and preventing crops from being scorched by strong light; when the temperature is below 25°C, the hydrogel returns to a transparent state, ensuring sufficient light inside the greenhouse.

[0037] The hydrophilic condensation functional layer 105 is located on the innermost side of the composite film, directly contacting the high-humidity air inside the greenhouse, with a thickness of 5-20 μm. In this embodiment, a PET film with a plasma-etched surface is used, forming a uniformly distributed micron-sized columnar microstructure (5 μm high, 3 μm diameter, 2 μm spacing) on ​​the surface, coated with a layer of nano-titanium dioxide hydrophilic coating, ensuring a surface water contact angle ≤15°. This microstructure design significantly increases the water vapor condensation nucleation density, allowing water vapor to quickly form a continuous water film on the film surface instead of discrete large water droplets, preventing water droplets from causing waterlogging on crop leaves and the growth of diseases; simultaneously, its low adhesion properties ensure that the water film can quickly flow along the slope of the film surface without water accumulation.

[0038] like Figure 2 As shown, the greenhouse water circulation system of the present invention uses PDH / T-RC radiation cooling composite membrane 1 as the core covering material, and is equipped with a condensate diversion structure, a water storage unit and an irrigation unit to form a fully closed-loop passive water circulation system of evaporation-condensation-collection-storage-irrigation-recirculation-recondensation. The entire process relies on gravity flow and physical effects to operate, without the need for electric drive and human intervention.

[0039] The composite film, used as the top and side wall covering material for greenhouse 2, is installed using the same strip fixing method as traditional greenhouse films. The greenhouse top is installed with a 3°-5° double-slope structure to ensure that condensate can flow down the film surface by gravity. In this embodiment, the joints of the composite film are heat-sealed with a weld width ≥5cm to ensure sealing performance and prevent rainwater infiltration and moisture leakage from inside the greenhouse.

[0040] The condensate drainage structure includes a circumferentially arranged hydrophobic drainage channel 3 on the inner wall of the greenhouse. In this embodiment, the hydrophobic drainage channel is made of U-shaped PVC material, with a cross-sectional width of 50mm and a depth of 30mm. The inner wall is coated with a hydrophobic polytetrafluoroethylene (PTFE) coating, with a water contact angle ≥110°, which can effectively reduce the flow resistance of condensate. The hydrophobic drainage channel is arranged along the length of the greenhouse at the lower edge of the top composite film and the lower edge of the side wall composite film. The channel is inclined towards the end of the greenhouse with a slope of 1° to ensure that the condensate can flow by gravity to the outlet of the drainage channel. The outlet of the drainage channel is connected to the water storage unit through a first water supply pipe 5. The first water supply pipe is a 50mm diameter PE pipe with a smooth inner wall and low flow resistance.

[0041] The water storage unit includes a sealed water storage tank 4, which in this embodiment is made of food-grade PE material. A vent valve is installed at the top of the tank to prevent negative pressure from forming inside and affecting the inflow of condensate; a float valve is installed inside to automatically replenish the external water source when condensate is insufficient, ensuring continuous irrigation; a drain outlet is installed at the bottom to periodically discharge sediment from the tank. The inlet of the sealed water storage tank is connected to the outlet of the drainage channel 3 via a first water supply pipe 5, and the outlet is connected to the irrigation unit via a second water supply pipe 6.

[0042] The irrigation unit includes a drip irrigation terminal 7. In this embodiment, a pressure-compensated dripper is used, with a single dripper flow rate of 3L / h and a dripper spacing of 30cm, matching the planting row spacing of the crops. This drip irrigation system relies on the water pressure formed by the liquid level in the storage tank to achieve stable water supply, eliminating the need for an electric pump and pressure valve. The irrigation uniformity is ≥90%, and it can accurately deliver condensate to the crop roots, avoiding water accumulation on leaves and water waste.

[0043] like Figure 3 and Figure 4 As shown, this system relies on the all-weather cooling capability of the PDH / T-RC composite membrane to achieve continuous condensation and water collection in both day and night modes, as well as closed-loop water circulation. The specific working process is as follows: Daytime Operation Mode: When solar radiation hits the surface of the composite film, the weather-resistant protective layer transmits visible light and photosynthetically active radiation, while the near-infrared high-reflectivity layer reflects over 88% of near-infrared thermal radiation, reducing heat gain inside the greenhouse. The high-radiation emission layer continuously radiates heat into space through an 8-13μm atmospheric window. The PDH hydrogel composite adhesive layer releases stored nighttime cooling energy and slowly releases moisture to form evaporative cooling, further reducing the film surface temperature. At this time, the temperature of the hydrophilic condensation functional layer is lower than the dew point temperature of the air inside the greenhouse (usually 2-4℃ lower). A large amount of water vapor generated by crop transpiration and soil evaporation inside the greenhouse quickly condenses into a continuous water film on the surface of the hydrophilic condensation functional layer. The water film flows by gravity along the installation slope of the composite film to the drainage channel, and then flows into the sealed water storage tank through the first water supply pipe.

[0044] Nighttime Operation Mode: During nighttime operations without solar radiation, the high-emissivity emissive layer maintains an emissivity of over 92%, continuously radiating cooling energy into space. The PDH hydrogel composite adhesive layer provides insulation, slowing the temperature rise of the membrane surface and keeping it 1-3°C lower than the ambient temperature. At night, the relative humidity inside the greenhouse rises to over 85%. This high humidity air condenses upon contact with the low-temperature membrane surface, ensuring continuous water collection throughout the night. The condensate flows along the membrane surface and the drainage channels into the water storage tank, solving the problem of nighttime water collection failure in traditional technologies.

[0045] Closed-loop irrigation and recirculation process: Condensate in the sealed water storage tank flows by gravity and is transported to the drip irrigation terminal via the second water delivery pipeline for precise irrigation of crop roots. After the irrigation water is absorbed by the crops, 98% is released into the greenhouse air through transpiration, with the remaining small amount seeping into the soil and evaporating into the greenhouse air afterward. The water vapor inside the greenhouse condenses again on the surface of the PDH / T-RC composite membrane, entering the next cycle, forming a complete evaporation-condensation-collection-irrigation-recirculation closed-loop system.

[0046] Application Examples This example was conducted in a solar greenhouse in a certain location. The greenhouse was 80m long, 10m wide, and 3.5m high. The crop planted was cucumber, with a planting density of 3 plants / m². 2 The PDH / T-RC radiation-cooling composite film described in this invention is used as the top cover material. The total thickness of the composite film is 120 μm, and the parameters of each layer are as follows: 30 μm weather-resistant protective layer PET film, 20 μm near-infrared high-reflectivity layer AgNWs / PI composite film, 30 μm high-emissivity emission layer SiO2 / SiC composite coating, 30 μm PDH hydrogel composite adhesive layer, and 10 μm hydrophilic condensation functional layer microstructured PET film. The system is equipped with a 6m... 3 Sealed water storage tank, circumferential U-shaped drainage channel and drip irrigation system.

[0047] Three consecutive months of operational data show that, compared to the control greenhouse using traditional PO film, this system reduces the average daytime temperature inside the greenhouse by 5-7℃, and by 8-10℃ under extreme high temperatures; the average nighttime temperature decreases by 2-4℃; the relative humidity inside the greenhouse remains stable at 60%-75%, with humidity fluctuations of less than 10%; and the average daily condensate collection is approximately 0.8m³. 3 Irrigation water consumption is reduced by 45%, achieving self-sufficiency in irrigation water under normal climatic conditions; the incidence of cucumber diseases such as downy mildew and gray mold is reduced by 62%, and pesticide use is reduced by 58%; cucumber yield per unit area increases by 22%, soluble sugar content in fruits increases by 15%, and the marketable fruit rate rises to over 95%. Simultaneously, the system operates with zero energy consumption throughout, saving approximately 12,000 yuan annually in electricity, water, and pesticide costs, demonstrating significant economic and ecological benefits.

[0048] The above are merely specific embodiments of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features of the invention herein.

Claims

1. A PDH / T-RC radiation-cooled composite membrane, characterized in that, include: Weather-resistant protective layer; A near-infrared high reflectivity layer is attached to the lower surface of the weather-resistant protective layer to reflect near-infrared radiation in sunlight and transmit photosynthetically active radiation. A high-emissivity emitting layer is attached to the lower surface of the near-infrared high-reflectivity layer and is used to radiate heat to the outer space through an 8-13 μm atmospheric window. The PDH hydrogel composite adhesive layer is attached to the lower surface of the high-emissivity layer to achieve multiple functions such as cold preservation, water release, evaporative cooling and temperature-sensitive light modulation. A hydrophilic condensation functional layer is attached to the lower surface of the PDH hydrogel composite adhesive layer to contact with humid air and promote the condensation of water vapor on its surface.

2. The PDH / T-RC radiation cooling composite membrane according to claim 1, characterized in that, The total thickness of the composite membrane is 80-200 μm.

3. The PDH / T-RC radiation cooling composite membrane according to claim 1 or 2, characterized in that, The weather-resistant protective layer is selected from at least one of transparent weather-resistant PC film, transparent weather-resistant PET film, and transparent weather-resistant PMMA film, and its thickness is 25-50μm.

4. The PDH / T-RC radiation cooling composite membrane according to claim 1 or 2, characterized in that, The near-infrared high reflectivity layer is selected from at least one of metal-based nano-reflective film, transparent conductive oxide reflective film, and polymer-based composite reflective film. It has a near-infrared radiation reflectivity of ≥85% in sunlight and a transmittance of ≥85% in photosynthetically active radiation, with a thickness of 15-30 μm.

5. The PDH / T-RC radiation cooling composite membrane according to claim 1 or 2, characterized in that, The high-emissivity emitting layer has an emissivity of ≥90% in the 8-13μm atmospheric window band and a thickness of 20-40μm; the PDH hydrogel composite adhesive layer has a water retention rate of ≥90% and a thickness of 15-40μm.

6. The PDH / T-RC radiation-cooling composite membrane according to claim 1 or 2, characterized in that, The surface of the hydrophilic condensation functional layer has a microstructure and a thickness of 5-20 μm.

7. A greenhouse water circulation system, characterized in that, include: The PDH / T-RC radiative cooling composite film as described in any one of claims 1 to 6 is used as a covering material for the top and / or side walls of a greenhouse. A condensate guiding structure is disposed below the composite membrane to collect water droplets or water films formed on the condensation interface and guide the condensate to flow in a specific direction. A water storage unit is located below the condensate guide structure and connected to its outlet, for storing the collected condensate; An irrigation unit, located below the water storage unit and connected to its outlet, is used to deliver condensate to the roots of the crop.

8. The greenhouse water circulation system according to claim 7, characterized in that, The condensate drainage structure includes a circumferentially arranged drainage channel on the inner wall of the greenhouse; the installation slope of the composite membrane is not less than 3°, so that the condensate can flow by gravity along the surface of the composite membrane to the drainage channel below.

9. The greenhouse water circulation system according to claim 7, characterized in that, The water storage unit includes a sealed water storage tank, and the outlet of the condensate diversion channel of the condensate diversion structure is connected to the sealed water storage tank below through a first water supply pipe.

10. The greenhouse water circulation system according to claim 7, characterized in that, The irrigation unit includes a drip irrigation terminal, and the outlet of the sealed water storage tank of the water storage unit is connected to the drip irrigation terminal below through a second water delivery pipe.

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