Duct structure and fresh air machine

Abstract

The utility model discloses a duct structure and fresh air machine, including double -layer sleeve pipe, the double -layer sleeve pipe includes the exhaust pipe of inner layer and the air inlet pipe of sleeve in the exhaust pipe out, the exhaust port of exhaust pipe includes the upper air outlet and lower air outlet of air inlet pipe out, be provided with control valve between the upper air outlet with the lower air outlet, control valve control exhaust pipe with upper air outlet intercommunication or with lower air outlet intercommunication. The utility model makes the exhaust pipe and air inlet pipe mutual nesting form sleeve pipe's mode, utilize the temperature of exhaust to preheat fresh air, improve fresh air exchanger function energy utilization rate and reduce the condensation hidden danger, through adjusting the exhaust air valve control exhaust direction, avoid the distance fresh air import too close exhaust directly from fresh air import into the room.

Description

Technical Field

[0001] This utility model relates to the field of ventilation equipment technology, and in particular to duct structure and fresh air unit. Background Technology

[0002] Traditional total heat exchange fresh air systems employ an independent four-duct structure: a fresh air intake duct, a fresh air outlet duct, an exhaust air intake duct, and an exhaust air outlet duct. However, this design suffers from the following two technical bottlenecks:

[0003] 1. Low waste heat recovery efficiency: It only relies on the heat exchange core for unidirectional heat exchange, and the exhaust air (indoor hot air) is directly discharged to the outside. About 35% of the exhaust air waste heat (a temperature difference of about 15-20℃ in winter) is not utilized, resulting in energy waste.

[0004] 2. Uncontrolled condensation under extreme operating conditions: When the fresh air temperature is below 0℃ in winter, the fresh air inlet casing (-5℃ to -10℃) comes into contact with the low-temperature fresh air (-3℃), and the condensation rate on the surface of the heat exchange core reaches more than 85%, resulting in: - Ice blockage of the heat exchange core (ice rate 40%+), and a 30% reduction in air volume; - Condensation backflow into the room, causing excessive humidity (>65%RH), leading to mold growth; - Frequent unit shutdowns for defrosting, resulting in a 25% decrease in the coefficient of performance (COP).

[0005] In other words, traditional total heat exchange fresh air units directly exhaust indoor air to the outside after heat exchange through the heat exchange core, leaving a large amount of residual heat that cannot be utilized, resulting in waste. At the same time, in winter when the fresh air temperature is too low, condensation is easily generated on the surface of the casing at the fresh air inlet and inside the heat exchange core, which are technical problems. Utility Model Content

[0006] To solve at least one of the above-mentioned technical problems, on the one hand, this utility model provides a duct structure in which the exhaust duct and the inlet duct are nested together to form a sleeve, using the temperature of the exhaust air to preheat the fresh air, thereby improving the energy utilization rate of the fresh air exchanger and reducing the risk of condensation; by adjusting the exhaust air valve to control the exhaust air direction, the exhaust air is prevented from being too close to the fresh air inlet and directly entering the room from the fresh air inlet.

[0007] On the other hand, this utility model also proposes a new fan having the aforementioned duct structure.

[0008] The technical solution adopted by this utility model is to design a duct structure, including a double-layer sleeve. The double-layer sleeve includes an exhaust duct located in the inner layer and an inlet duct sleeved outside the exhaust duct. The exhaust port of the exhaust duct includes an upper air outlet and a lower air outlet located outside the inlet duct. A control valve is provided between the upper air outlet and the lower air outlet. The control valve controls the exhaust duct to connect with the upper air outlet or with the lower air outlet.

[0009] In some embodiments, the control valve includes an upper valve plate for controlling the opening and closing of the upper air outlet and a lower valve plate for controlling the opening and closing of the lower air outlet.

[0010] In some embodiments, the control valve includes a lower valve plate that controls the opening and closing of the lower air outlet. The lower valve plate is provided with a one-way permeation membrane, so that when the lower valve plate is closed, water in the exhaust pipe can permeate through the permeation membrane.

[0011] In some embodiments, the upper air outlet is located on an upper ventilation duct that extends upward relative to the air inlet duct, such that the height of the upper air outlet is greater than the height of the air inlet of the air inlet duct.

[0012] In some embodiments, the upper end of the upper ventilation duct has a bent end facing the exhaust direction of the exhaust duct, and the upper air outlet is located on the bent end, such that the upper air outlet faces away from the air inlet.

[0013] In some embodiments, the upper air outlet is a flared, trumpet-shaped opening.

[0014] In some embodiments, the lower air outlet is located on a lower ventilation duct that extends downward relative to the air inlet duct, such that the height of the lower air outlet is less than the height of the air inlet duct.

[0015] Fresh air unit, including the aforementioned duct structure.

[0016] In some embodiments, the fresh air unit is a total heat exchange fresh air unit, the air inlet pipe is connected to the fresh air inlet of the total heat exchange fresh air unit, and the air outlet pipe is connected to the air outlet of the total heat exchange fresh air unit.

[0017] In some embodiments, the double-layered sleeve is inclined relative to the end of the total heat exchange fresh air unit, such that the exhaust port of the exhaust pipe and the air inlet of the air inlet pipe are inclined downward relative to the horizontal plane.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention utilizes a double-layered sleeve structure, nesting the exhaust pipe and the intake pipe together to pre-treat the fresh air, thus achieving efficient energy recovery and reuse and significantly improving the overall energy efficiency of the fresh air exchanger. By incorporating switchable exhaust outlets and control valves, the exhaust direction can be automatically adjusted according to heating or cooling modes, adapting to the natural flow characteristics of the density difference between hot and cold air, effectively preventing exhaust backflow into the fresh air channel and ensuring fresh air quality. Furthermore, the spatial height difference design of the upper and lower outlets, combined with a bent flow-guiding structure, keeps the exhaust path away from the fresh air inlet, improving airflow organization and preventing gas mixing and energy loss. The automatic drainage of condensate and rainwater is achieved by installing a one-way permeation membrane on the lower valve plate and tilting the sleeve, preventing backflow and water accumulation. The overall solution is compact, energy-saving, and environmentally friendly, combining multiple functions such as efficient heat exchange, anti-condensation, anti-backflow, and anti-recirculation, improving the operational stability and service life of the fresh air system in different seasons and complex environments. Attached Figure Description

[0020] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. To illustrate the details and facilitate understanding of its principles, the drawings are not necessarily to scale, and similar reference numerals may describe similar components in different views. The accompanying drawings generally illustrate the embodiments discussed herein by way of example and not limitation. Wherein:

[0021] Figure 1 This is a schematic diagram of a traditional total heat exchange fresh air system.

[0022] Figure 2 This is a schematic diagram of a double-layered casing installed in a total heat exchange fresh air unit.

[0023] Figure 3 This is a schematic diagram of a double-layered sleeve equipped with a control valve.

[0024] Figure 4 yes Figure 3 A schematic diagram of section AA.

[0025] Figure 5 yes Figure 3 Enlarged diagram of point B in the middle.

[0026] In the diagram, 1 is the exhaust duct; 2 is the inlet duct; 5 is the control valve; 51 is the upper valve plate; 52 is the lower valve plate; 6 is the support rib; 7 is the upper air outlet; 71 is the upper ventilation duct; 711 is the bend end; 8 is the lower air outlet; 81 is the lower ventilation duct; 9 is the total heat exchange fresh air fan; 10 is the exhaust fan; 11 is the fresh air fan; 12 is the fresh air inlet duct; 13 is the fresh air outlet duct; 14 is the exhaust inlet duct; 15 is the exhaust outlet duct; and 16 is the heat exchange core. Detailed Implementation

[0027] The following are specific embodiments of this utility model, and the technical solution of this utility model will be further described with reference to the accompanying drawings. However, this utility model is not limited to these embodiments, and the following embodiments do not limit the utility model involved in the claims. In addition, all combinations of features described in the embodiments are not necessarily necessary for the solution of the utility model.

[0028] The principle and structure of this utility model will be described in detail below with reference to the accompanying drawings and embodiments.

[0029] Example

[0030] like Figure 1 As shown, traditional total heat exchange fresh air units adopt an independent four-duct structure, namely fresh air inlet duct 12, fresh air outlet duct 13, exhaust air inlet duct 14, and exhaust air outlet duct 15. However, after the indoor air is directly discharged to the outside through the heat exchange core, a large amount of residual heat remains unused and is wasted. At the same time, in winter when the fresh air temperature is too low, condensation is easily generated on the surface of the shell at the fresh air inlet of the unit and inside the heat exchange core 16.

[0031] Therefore, such as Figure 2 , 3 As shown in Figures 4 and 5, a novel duct structure is proposed, comprising a double-layered sleeve. The double-layered sleeve includes an inner exhaust duct 1 and an outer inlet duct 2. The exhaust port of the exhaust duct 1 includes an upper outlet 7 and a lower outlet 8 located outside the inlet duct 2. A control valve 5 is provided between the upper outlet 7 and the lower outlet 8, controlling the connection between the exhaust duct 1 and the upper outlet 7 or the lower outlet 8. Both the exhaust duct 1 and the inlet duct 2 are rectangular tubes, supported by a support rib 6. The channel between the exhaust duct 1 and the inlet duct 2 serves as the air intake channel for the inlet duct 2. The end of the exhaust duct 1 extends outward relative to the inlet duct 2 by a certain distance, with the upper outlet 7 and the lower outlet 8 respectively located in the vertical direction. The duct structure of this embodiment is applied to the total heat exchange fresh air unit 9, that is, the internal part is provided with a heat exchange core 16 that enables the exhaust air and fresh air to exchange heat. The exhaust duct 1 is connected to the exhaust fan 10, the fresh air outlet is provided with a fresh air fan 11, and the air inlet duct 2 is the fresh air inlet duct 12.

[0032] The provided duct structure forms a double-layered structure by fitting exhaust duct 1 and inlet duct 2 together. Exhaust duct 1 is located in the inner layer, and inlet duct 2 is located in the outer layer, with an annular gap between them for the flow of fresh air. During the exhaust process, the heat or cold carried by the exhaust air in exhaust duct 1 can be transferred through the duct wall to the fresh air in the annular gap, thereby preheating or precooling the fresh air, improving energy utilization, reducing condensation on the heat exchange core 16 caused by excessive temperature differences, and enhancing the operational stability and comfort of the fresh air exchanger in different seasons. The exhaust duct 1 has two outlets at its end, one above the other, with a control valve 5 between them to switch the exhaust direction: When the unit is in heating mode, the exhaust temperature is higher than the outdoor temperature, so the control valve 5 closes the lower outlet, allowing the high-temperature, lower-density exhaust air to be discharged from the top, following the natural upward flow of hot air and preventing the exhaust air from flowing back into the fresh air duct at the outlet; when the unit is in cooling mode, the exhaust temperature is lower than the outdoor temperature, so the control valve 5 closes the upper outlet, allowing the low-temperature, higher-density exhaust air to be discharged from the bottom, conforming to the sinking characteristic of cold air, which also effectively prevents exhaust air backflow. Through the above structural design, not only is efficient pretreatment of fresh air achieved, improving the overall heat exchange efficiency, but also the intelligent exhaust path adjustment ensures the quality of fresh air, prevents the mixing of hot and cold air and energy loss, and has good energy saving and practicality.

[0033] Furthermore, the control valve 5 includes an upper valve plate 51 for controlling the opening and closing of the upper air outlet 7, and a lower valve plate 52 for controlling the opening and closing of the lower air outlet 8.

[0034] In this embodiment, the control valve 5 adopts a dual-valve structure, including an upper valve plate 51 for controlling the opening and closing of the upper air outlet 7 and a lower valve plate 52 for controlling the opening and closing of the lower air outlet 8. The upper and lower valve plates 52 are respectively located at the corresponding air outlets and can be opened and closed independently under the action of drive components (such as motors, pneumatic devices, or temperature control actuators). Through the coordinated control of the upper and lower valve plates 52, the exhaust direction can be automatically adjusted according to the operating mode of the fresh air exchanger: when the unit is in heating mode, the control system drives the upper valve plate 51 to open and the lower valve plate 52 to close, so that the exhaust air is discharged from the upper air outlet 7, avoiding the backflow of high-temperature exhaust air into the fresh air channel, and at the same time, it is conducive to the upward flow of high-temperature airflow and improves exhaust efficiency; when the unit is in cooling mode, the control system drives the upper valve plate 51 to close and the lower valve plate 52 to open, so that the low-temperature exhaust air is discharged from the lower air outlet 8, effectively preventing backflow of airflow by utilizing the sinking characteristic of cold air. This structure enables the control valve 5 to have flexible airflow guidance capabilities, which can automatically adapt to the operating requirements of different seasons according to the temperature difference, and avoid airflow turbulence or energy loss caused by a single air outlet design. This further improves the operational stability and energy efficiency of the duct system, and ensures that the fresh air exchanger operates efficiently and reliably for a long time.

[0035] Furthermore, the control valve 5 includes a lower valve plate 52 that controls the opening and closing of the lower air outlet 8. A one-way permeation membrane is provided on the lower valve plate 52. When the lower valve plate 52 is closed, water in the exhaust pipe 1 can permeate through the permeation membrane.

[0036] The lower valve plate 52 of the control valve 5 is equipped with a one-way permeable membrane, preferably a functional membrane with one-way water permeability and air impermeability. When the unit is in heating mode or other operating conditions that require closing the lower air outlet 8, the control valve 5 drives the lower valve plate 52 to close the lower air outlet 8. Although the lower air outlet 8 is sealed at this time, condensate may accumulate in the exhaust pipe 1 during heat exchange or condensation. To prevent condensate from remaining in the exhaust pipe 1 and affecting airflow or causing secondary pollution, several micropores are opened on the lower valve plate 52, and a one-way permeable membrane is installed at the micropores. This allows the internal moisture to be discharged to the outside through the permeable membrane when it accumulates to a certain level, while external air or moisture cannot enter the exhaust pipe 1 in reverse, thus achieving both sealing and drainage functions. This design not only effectively prevents increased exhaust resistance or noise problems caused by condensate accumulation, but also avoids the impact of water vapor backflow on heat exchange efficiency and equipment operating stability, improving the system's anti-condensation performance and long-term reliability. Meanwhile, due to the simple structure of unidirectional osmosis membranes, the lack of additional drainage mechanisms, and the compact overall layout, they are easy to process and install, and have high engineering practical value.

[0037] Furthermore, the upper air outlet 7 is located on the upper ventilation duct 71 that extends upward relative to the air inlet duct, such that the height of the upper air outlet 7 is greater than the height of the air inlet of the air inlet duct 2.

[0038] The upper air outlet 7 is positioned on the upper ventilation duct 71, which extends upward relative to the air inlet duct, making its height higher than the air inlet height of the air inlet duct 2. This height difference design allows the exhaust air to rise naturally after discharge due to its higher temperature and lower density, following the upward flow characteristic of hot air. This prevents the exhaust air from forming a backflow vortex at the outlet and entering the air inlet, thus preventing the exhaust air from mixing with fresh air and ensuring fresh air quality. Simultaneously, this structure keeps the exhaust air away from the fresh air inlet, creating reasonable airflow stratification and flow direction isolation, further reducing mutual interference between hot and cold gases and improving the stability and energy efficiency of the ventilation system. This optimized spatial arrangement achieves effective airflow separation without the need for additional flow guiding components, simplifying the structural design and offering good energy efficiency and practicality.

[0039] Furthermore, the upper end of the upper ventilation duct 71 has a bent end 711 facing the exhaust direction of the exhaust duct 1, and the upper air outlet 7 is located on the bent end 711, so that the upper air outlet 7 faces away from the air inlet.

[0040] The upper end of the upper ventilation duct 71 is provided with a bent end 711 facing the exhaust direction of the exhaust duct 1, and the upper air outlet 7 is located on the bent end 711, so that the air outlet 7 is aligned with the exhaust airflow direction and is discharged away from the air inlet. By setting a bent structure at the end of the duct, a directional flow effect can be formed when the exhaust air leaves the duct, so that the airflow is discharged in a set direction, avoiding backflow at the outlet due to inertia or air pressure difference, thereby effectively preventing the exhaust air from re-entering the air inlet or forming a turbulent zone near the air inlet area. This structure makes full use of aerodynamic principles, and through the design of combining airflow guidance and spatial separation, it ensures that the diffusion path of the exhaust air after discharge is isolated from the fresh air intake path, further improving the rationality of the airflow organization and the operational stability of the fresh air exchanger. At the same time, the bending angle of the bent end 711 structure can be flexibly designed according to the actual installation space to adapt to different layout requirements, and has high engineering adaptability. This solution not only significantly reduces the risk of exhaust air recirculation and ensures the cleanliness and ventilation efficiency of the incoming fresh air, but also avoids energy loss caused by the mixing of hot and cold air, thus improving the overall energy efficiency and lifespan of the system.

[0041] Furthermore, the upper air outlet 7 is a flared, trumpet-shaped opening.

[0042] The lower opening of the upper air outlet 7 is inclined downwards along the relative horizontal plane, preferably designed as a downward-sloping trumpet-shaped bend. By forming a downward-sloping surface at a certain angle at the end of the air outlet, the exhaust airflow is directed outwards along the inclined direction when discharged, which not only allows for smooth gas discharge but also effectively prevents external rainwater from flowing back into the pipe along the air outlet. The trumpet-shaped structure gradually enlarges the cross-section of the air outlet, which can reduce local wind resistance during exhaust, improve airflow diffusion characteristics, and reduce eddies and noise at the air outlet end. At the same time, the trumpet-shaped end combined with the downward-sloping design can form a guiding effect under natural rainfall conditions, allowing rainwater to fall along the outer wall and preventing water accumulation or backflow into the exhaust pipe 1, thereby protecting the internal heat exchange components and control devices from moisture corrosion and extending the service life of the equipment. In addition, this structure can also achieve rainproof function without adding complex auxiliary components, simplifying the manufacturing process and reducing maintenance costs. Through the above optimized design, it not only ensures smooth exhaust and controllable airflow direction but also effectively improves the system's protective performance and environmental adaptability, enabling the fresh air exchanger to maintain stable and efficient operation outdoors or in high humidity environments.

[0043] Furthermore, the lower air outlet 8 is located on the lower ventilation duct 81 that extends downward relative to the air inlet, such that the height of the lower air outlet 8 is less than the height of the air inlet of the air inlet duct 2.

[0044] The lower air outlet 8 is positioned on the lower ventilation duct 81, which extends downwards relative to the air inlet, making its height lower than that of the air inlet duct 2. This height difference arrangement allows the exhaust air to naturally diffuse downwards after discharge due to gravity and its lower temperature and higher density, conforming to the physical law of cold air sinking. This effectively prevents backflow at the outlet and avoids the exhaust air re-entering the air inlet channel. This design achieves natural airflow separation through spatial layering, creating a reasonable flow direction isolation between the cold exhaust air and the incoming fresh air, ensuring that the fresh air intake path is not disturbed by the discharged exhaust gas, thus ensuring indoor air quality. Furthermore, the lower ventilation duct 81 keeps the exhaust outlet away from the fresh air inlet area, reducing airflow turbulence and turbulent recirculation effects, improving system ventilation efficiency and airflow organization stability. This solution has a simple structure, requires no additional airflow guiding devices, and achieves airflow direction and backflow prevention control. It optimizes the overall spatial layout and improves the operating effect and energy-saving performance of the fresh air exchanger in cooling mode, demonstrating good practicality and engineering application value.

[0045] Furthermore, the fresh air unit is a total heat exchange fresh air unit 9, the air inlet pipe 2 is connected to the fresh air inlet of the total heat exchange fresh air unit 9, and the exhaust pipe 1 is connected to the exhaust outlet of the total heat exchange fresh air unit 9.

[0046] The fresh air unit is a total heat exchange fresh air unit 9. The air inlet duct 2 is connected to the fresh air inlet of the fresh air unit, and the exhaust duct 1 is connected to the exhaust outlet of the fresh air unit. Through this connection, outdoor fresh air enters the total heat exchange fresh air unit 9 through the air inlet duct 2, and exchanges heat and moisture with indoor exhaust air in the heat exchange core 16, achieving preheating or precooling of the fresh air. When the exhaust air is discharged through the exhaust duct 1, the residual heat or residual cold can be further transferred to the fresh air in the air inlet duct 2 through the sleeve structure, improving the overall energy recovery efficiency. This structure realizes a dual heat exchange process, effectively reducing energy loss, improving the energy efficiency and comfort of the system operation, while reducing the risk of condensation caused by temperature differences, and ensuring long-term stable operation of the equipment.

[0047] Furthermore, the double-layered sleeve is inclined relative to the end of the total heat exchange fresh air unit 9, so that the exhaust port of the exhaust pipe 1 and the air inlet of the air inlet pipe 2 are inclined downward relative to the horizontal plane.

[0048] The double-layered sleeve is installed at an angle relative to the end of the total heat exchange fresh air unit 9, so that the exhaust port of the exhaust pipe 1 and the air inlet of the inlet pipe 2 are both arranged downwards relative to the horizontal plane. This angled arrangement allows condensation or rainwater to flow naturally outdoors under gravity when the equipment is running or in extreme environments, preventing moisture from stagnating in the pipes or flowing back into the unit. This effectively prevents internal components from becoming damp, corroded, or icing, improving the system's waterproof performance and reliability. Furthermore, the downward-sloping structure prevents water accumulation while reducing airflow resistance and the risk of secondary pollution caused by condensation, maintaining smooth airflow within the pipes and ensuring the ventilation efficiency and heat exchange performance of the fresh air exchanger. This design achieves automatic drainage and backflow prevention without the need for additional drainage devices, is simple in structure, easy to install, and has good adaptability and practical value.

[0049] The specific embodiments described herein are merely illustrative examples illustrating the spirit of this utility model. Those skilled in the art to which this utility model pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of this utility model or exceeding the scope defined by the appended claims.

[0050] Although this document uses a number of technical terms, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of this invention; interpreting them as any additional limitation would contradict the spirit of this invention. The order of actions, steps, etc., in the apparatus and methods shown in the specification and drawings can be implemented in any order unless a specific order is explicitly specified, and as long as the output of a preceding process is not used in a subsequent process. Similar sequential terms used for descriptive convenience (e.g., "firstly," "next," "secondly," "again," "then," etc.) do not imply that the actions must be performed in such an order.

[0051] Those skilled in the art will understand that all directional references (e.g., above, below, up, up, down, down, top, bottom, left, right, vertical, horizontal, etc.) are used descriptively in the drawings to aid the reader's understanding and do not imply (e.g., a limitation on the scope of the invention as defined by the appended claims) a limitation on the scope of the invention as defined by the appended claims. They are merely for the purpose of facilitating the description of this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a particular orientation or be constructed and operated in a particular orientation. The directional terms "inside" and "outside" refer to inside or outside relative to the outline of the respective components themselves.

[0052] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0053] Additionally, some vague terms (e.g., substantially, certain, generally, etc.) may refer to slight inaccuracies or minor deviations in conditions, quantities, values, or dimensions, some of which are within manufacturing tolerances or limits. It should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components; unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application.

Claims

1. A duct structure, characterized in that, The system includes a double-layered sleeve, which includes an inner exhaust pipe and an outer inlet pipe. The exhaust port of the exhaust pipe includes an upper outlet and a lower outlet located outside the inlet pipe. A control valve is provided between the upper outlet and the lower outlet, and the control valve controls the exhaust pipe to connect with the upper outlet or the lower outlet.

2. The duct structure according to claim 1, characterized in that, The control valve includes an upper valve plate that controls the opening and closing of the upper air outlet and a lower valve plate that controls the opening and closing of the lower air outlet.

3. The duct structure according to claim 1, characterized in that, The control valve includes a lower valve plate that controls the opening and closing of the lower air outlet. A one-way permeation membrane is provided on the lower valve plate. When the lower valve plate is closed, water in the exhaust pipe can permeate through the permeation membrane.

4. The duct structure according to claim 1, characterized in that, The upper air outlet is located on an upper ventilation duct that extends upward relative to the air inlet duct, such that the height of the upper air outlet is greater than the height of the air inlet duct.

5. The duct structure according to claim 4, characterized in that, The upper end of the upper ventilation duct has a bent end facing the exhaust direction of the exhaust duct, and the upper air outlet is located on the bent end, so that the upper air outlet faces away from the air inlet.

6. The duct structure according to claim 5, characterized in that, The upper air outlet is a flared, trumpet-shaped opening.

7. The duct structure according to claim 1, characterized in that, The lower air outlet is located on a lower ventilation duct that extends downward relative to the air inlet duct, such that the height of the lower air outlet is less than the height of the air inlet duct.

8. A fresh air system, characterized in that, Includes the duct structure as described in any one of claims 1 to 7.

9. The fresh air system according to claim 8, characterized in that, The fresh air unit is a total heat exchange fresh air unit, the air inlet pipe is connected to the fresh air inlet of the total heat exchange fresh air unit, and the air outlet pipe is connected to the air outlet of the total heat exchange fresh air unit.

10. The fresh air system according to claim 9, characterized in that, The double-layer sleeve is inclined relative to the end of the total heat exchange fresh air unit, so that the exhaust port of the exhaust pipe and the air inlet of the air inlet pipe are inclined downward relative to the horizontal plane.

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