Ventilation system and method based on reverse dual airflow of supply and return air

Abstract

A ventilation system and method based on the reverse dual airflow of supply and return air, wherein the supply air outlet is arranged in the middle of the side wall, the exhaust air outlet is arranged at the top of the room, and the return air outlet is arranged between the supply air outlet and the exhaust air outlet; the air leaving the room through the exhaust air outlet is discharged to the outside; the air leaving the room through the return air outlet is purified and heat-humidified together with the fresh air outside and then delivered to the room through the supply air outlet; the supply air flow enters the room horizontally and is delivered to the position of the human head; the return air outlet leaves the room in the reverse direction relative to the supply air flow, and the return air flow inhibits the supply air flow from sucking air from the non-working area and promotes the supply air flow from sucking air from the working area, forcing the supply air flow to enter the working area, thereby improving the air supply efficiency and creating a thermally comfortable and healthy indoor environment with high energy efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of building mechanical ventilation, and in particular relates to a ventilation system and method based on the reverse double airflow of supply and return air. Background Art

[0002] In order to create a healthy and comfortable living environment, buildings often use natural ventilation or mechanical ventilation strategies to meet indoor thermal and air quality requirements. Natural ventilation relies on the difference in indoor and outdoor air density to introduce fresh air into the room. It is an energy-saving ventilation method, but it cannot guarantee indoor health and thermal comfort in bad weather (such as high temperature and heavy outdoor air pollution). Mechanical ventilation can ensure the health and thermal comfort of the indoor environment in bad weather, but it consumes energy. Therefore, ventilation methods based on advanced airflow organization are an important means to reduce building ventilation energy consumption.

[0003] In the article "Cheng, Y., & Lin, Z. (2015). Experimental study of airflow characteristics of stratum ventilation in a multi-occupant room with comparison to mixing ventilation and displacement ventilation. Indoor air, 25 (6), 662-671.", it is pointed out that the advancement of existing airflow organization is mainly achieved through the innovation of air supply airflow, which mainly includes thermal buoyancy-driven thermal stratified ventilation method and air supply momentum-driven thermal stratified ventilation method. Displacement ventilation is a typical representative of thermal buoyancy-driven thermal stratified ventilation method. Displacement ventilation transports clean and heat-moisture-treated air to the ground, and the supply air flows upward under the action of indoor heat source, forming thermal buoyancy-driven thermal stratification. Stratum ventilation is a typical representative of air supply momentum-driven thermal stratified ventilation method. Stratum ventilation supplies air horizontally from the middle of the side wall to the room, efficiently transporting clean and heat-moisture-treated air to the area most important for air quality and thermal comfort (i.e., the human head), forming thermal stratification driven by air supply momentum. The air supply momentum driven thermal stratified ventilation method is more energy-efficient than the thermal buoyancy driven thermal stratified ventilation method. Compared with conventional ventilation methods (i.e., mixed ventilation), displacement ventilation and stratified ventilation can save 25% and 44% energy respectively.

[0004] However, the ventilation method that only innovates the supply air flow faces the bottleneck problem of ventilation energy efficiency, that is, the supply air flow sucks air from the non-working area, resulting in reduced supply air efficiency, especially the supply air momentum-driven thermal stratified ventilation method. For example, since the supply air momentum is dominant in layered ventilation, the supply air flow sucks air from the working area and the non-working area above the working area at the same time, resulting in negative pressure in the working area and the non-working area relative to the supply air flow, causing the supply air flow to enter the working area and the non-working area. Since the non-working area does not contribute to air quality and thermal comfort, the supply air flow entering the non-working area leads to a decrease in the air supply efficiency related to air quality and the air supply efficiency related to thermal comfort, thereby limiting the energy efficiency of the supply air momentum-driven thermal stratified ventilation method. Summary of the invention

[0005] In order to overcome the ventilation energy efficiency bottleneck problem faced by the prior art ventilation method that only innovates the supply air flow, that is, the supply air flow sucks the air in the non-working area, resulting in a decrease in the air supply efficiency, the purpose of the present invention is to provide a ventilation system and method based on the reverse double airflow of supply and return air. Through the reverse double airflow of supply and return air, the suction of the supply air flow from the non-working area is suppressed, and the suction of the supply air flow from the working area is promoted, thereby forcing more supply air flow to enter the working area, thereby improving the air supply efficiency and energy efficiency.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows.

[0007] A ventilation system based on the reverse double airflow of supply and return air is characterized in that the supply air outlet is arranged at the height of the working area in the middle of the side wall so that the supply airflow enters the working area; the exhaust air outlet is arranged at the top of the room, and the return air outlet is arranged between the supply air outlet and the exhaust air outlet, so that the return airflow creates a low-pressure area above the supply airflow, and the return air and supply air form a reverse double airflow effect. The return airflow leaves the room from the non-working area in the reverse direction relative to the supply airflow. The return airflow suppresses the suction of the supply airflow from the non-working area and enhances the suction of the supply airflow from the working area, forcing more supply airflow to enter the working area.

[0008] The ventilation method of the ventilation system based on the reverse dual airflow of supply and return air comprises the following steps:

[0009] Air is supplied through the air supply port, and the supply air flow enters the working area, and the return air flow leaves the room from the non-working area in the opposite direction of the supply air flow. Since the return air flow creates a low pressure area above the supply air flow, the pressure difference between the supply air flow and the space above the supply air flow, i.e., the non-working area, is reduced, thereby inhibiting the supply air flow from sucking in air from the non-working area; the reduction of the air suction from above the air flow makes the air suction from below the air flow, i.e., the working area, increase; since the amount of air sucked in by the supply air flow in the working area increases, the relative negative pressure in the working area increases, and more supply air flows into the working area, and finally leaves the indoor air through the exhaust port and is discharged to the outdoors.

[0010] The air leaving the room through the return air port is purified and heat-humidified together with the outdoor fresh air before being delivered to the room through the supply air port.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] 1. The existing layered ventilation sets the supply air outlet in the middle of the room, integrates the return air and the exhaust air (that is, the return air and the exhaust air share the air outlet) and sets them at a position far away from the supply air outlet (usually at the top of the room), so that the supply airflow and the return airflow do not interfere with each other, and the supply airflow sucks air from the working area and the non-working area at the same time. The supply airflow sucks air from the non-working area, so that the non-working area produces a negative pressure relative to the supply airflow, attracting the supply airflow into the non-working area, resulting in a decrease in the air supply efficiency of the working area. The ventilation method with reverse double airflow of supply and return air proposed in the present invention places the return air outlet between the exhaust outlet and the supply air outlet, and uses the return airflow to suppress the suction of the supply airflow from the non-working area and promote the suction of the supply airflow from the working area, forcing more supply airflow to enter the working area, thereby improving the air supply efficiency of the working area and reducing the energy consumption of creating the working area environment.

[0013] 2. The present invention places the return air outlet below the exhaust air outlet, so that there is a temperature difference between the return air temperature and the exhaust air temperature, and the return air is reused to reduce the indoor ventilation load.

[0014] In summary, the return air and supply air of the present invention form a reverse double airflow effect. The return air flow suppresses the suction of the supply air flow from the non-working area and enhances the suction of the supply air flow from the working area, which can reduce the energy consumption of creating an indoor thermal comfort environment and play a positive role in promoting the realization of the dual carbon goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of layered ventilation in the prior art.

[0016] Figure 2 A schematic diagram of a ventilation system based on the reverse dual airflow of supply and return air provided by the present invention.

[0017] Figure 3 This is a diagram showing the blowing sensation results of the layered ventilation of the present invention and the prior art under cooling conditions.

[0018] Figure 4 This is a diagram showing the head-to-foot temperature difference results of the layered ventilation of the present invention and the prior art under cooling conditions.

[0019] Figure 5 It is a result diagram of Thermal Utilization Effectiveness of the layered ventilation of the present invention and the prior art under cooling conditions.

[0020] Figure 6This is a diagram showing the energy efficiency results of the layered ventilation of the present invention and the prior art under refrigeration conditions. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0022] The embodiment of the present invention uses ANSYS Fluent to explore the effect of creating an indoor thermal comfort environment by using a ventilation method based on the reverse double airflow of supply and return air compared to a typical ventilation method (i.e., layered ventilation) for a thermal environment driven by air momentum. This embodiment is a summer cooling condition for a single-person office with a sitting posture as the main position. The office size is 3.9m×2.9m×2.6m (length×width×height). The heat dissipation of personnel is 75W, the heat generation power of the work computer used by the personnel is 180W, and there are two lamps on the ceiling for indoor lighting, and their heat generation power is 72W.

[0023] Reference Figure 1 The air supply vent of the existing layer ventilation is located in the middle of the side wall (1.3m from the floor); the exhaust and return air share the vent, and the exhaust and return air vents are located at the top of the room (2.2m from the floor).

[0024] Laminar ventilation supplies air through the air supply outlet, and the air supply volume is a typical air volume, i.e. 10ACH; the supply air is a mixture of return air and fresh air, of which 5ACH is return air and 5ACH is fresh air; the return air and fresh air are used as supply air after being treated with heat and humidity and purified; 10ACH of air volume leaves the room from the exhaust return air outlet, of which 5ACH is discharged to the outside, and the other 5ACH is used as return air. When laminar ventilation is used, the supply air flow simultaneously draws air from the working area and non-working area, resulting in a negative pressure in the working area and non-working area relative to the supply air flow, causing the supply air flow to enter the working area and non-working area at the same time, thereby reducing the air supply efficiency in the working area. Since the supply air flow only delivered to the working area improves thermal comfort and environmental quality, while the supply air flow delivered to the non-working area does not have any effect on thermal comfort and environmental quality. Therefore, the supply air flow delivered to the non-working area caused by the air drawn from the non-working area reduces the air supply efficiency.

[0025] See Figure 2 The present invention is based on a ventilation system with reverse dual airflows of supply and return air. The supply air outlet is located in the middle of the side wall (1.3m from the floor); the exhaust air outlet is located at the top of the room (2.2m from the floor); and the return air outlet is located between the supply air outlet and the exhaust air outlet (1.8m from the floor). The return airflow leaves the room from the non-working area in the reverse direction of the supply airflow, and the supply airflow enters the working area. The return airflow suppresses the entrainment of the supply airflow from the non-working area and enhances the entrainment of the supply airflow from the working area, forcing more supply airflow to enter the working area.

[0026] The ventilation method of the ventilation system based on the reverse double airflow of supply and return air, the air is supplied through the supply air outlet, and the supply air volume is 10ACH; the supply air is a mixture of return air and fresh air, of which the return air is 5ACH and the fresh air is 5ACH; the return air leaves the room through the return air outlet, and the return air and fresh air are used as supply air after being treated with heat and humidity and purified; the return air leaves the room through the exhaust air outlet with a volume of 5ACH and is discharged to the outdoors. The ventilation method based on the reverse double airflow of supply and return air proposed by the present invention forms a reverse double airflow effect with the return air and the supply air. The return airflow leaves the room from the non-working area in the reverse direction relative to the supply airflow. Since the return airflow creates a low-pressure area above the supply airflow, the pressure difference between the supply airflow and the upper space of the supply airflow, i.e., the non-working area, is reduced, thereby inhibiting the supply airflow from sucking air from the non-working area; the reduction of the air suction from the upper part of the airflow makes the air suction from the lower part of the airflow, i.e., the working area, increase; since the air sucked by the supply airflow in the working area increases, the relative negative pressure in the working area is enhanced, forcing more supply airflow to enter the working area to enhance the air supply efficiency. High air supply efficiency means that more air that has been purified and heat-humidified is sent to the working area, so that the air quality and thermal comfort of the working area are improved; finally, the air that leaves the room through the exhaust port is discharged to the outside; the air that leaves the room through the return air port is purified and heat-humidified together with the fresh air outside, and then sent to the room through the supply air port.

[0027] The supply air temperatures of the ventilation method based on the reverse double airflow of the supply and return air and the layered ventilation to achieve thermal neutral overall thermal comfort (PMV = 0) are 23.4°C and 22.0°C respectively. The calculation method of PMV refers to the thermal comfort standard ASHRAE 55. Under thermal neutral conditions, the wind sensation of the ventilation method based on the reverse double airflow of the supply and return air and the layered ventilation is 12.96% and 11.06% respectively ( Figure 3 ), meeting the requirement of local thermal comfort with a sense of wind; the vertical air temperature difference between head and foot is 1.01℃ and 0.55℃ respectively ( Figure 4 ), meeting the local thermal comfort requirements of the temperature difference between the head and feet. The calculation method of the wind sensation refers to the thermal comfort standard ASHRAE55. The CO2 concentration in the work area based on the ventilation method based on the reverse double airflow of the supply and return air and the layered ventilation is lower than 1000ppm, and the air quality is good. Therefore, the ventilation method based on the reverse double airflow of the supply and return air and the layered ventilation both achieve a thermally comfortable and healthy work area environment; in this case, it is fair and meaningful to compare the air supply efficiency and energy efficiency of the two.

[0028] The air supply efficiency is characterized by Thermal Utilization Effectiveness. The calculation method of Thermal Utilization Effectiveness can be found in the literature: Zhang S, Lu Y, Niu D, Lin Z. 2022. Energy performance index of air distribution: Thermal utilization effectiveness. Applied Energy, 307, 118122. The Thermal Utilization Effectiveness of layered ventilation is 0.20. The ventilation method based on the reverse double airflow of supply and return air increases the Thermal Utilization Effectiveness from 0.25 to 0.30, which is 20% higher than that of layered ventilation ( Figure 5 ). Therefore, the ventilation method based on the reverse double airflow of supply and return air is used to use the return airflow to suppress the supply airflow from sucking air from the non-working area and force the supply airflow into the working area, thereby effectively improving the air supply efficiency.

[0029] The energy consumption of air return and fresh air treatment in layered ventilation is 243.1W. Since the ventilation method based on the reverse double airflow of supply and return air can create a thermal comfort and healthy environment in the work area with high air supply efficiency, the ventilation method based on the reverse double airflow of supply and return air reduces the energy consumption from 243.1W to 212.5W, saving 12.6% (compared with layered ventilation) Figure 6 ).

Claims

1. A ventilation system based on the reverse dual airflow of supply and return air, characterized in that: Applied to the ventilation environment driven by the momentum of the supply air, the supply air outlet is arranged at the height of the working area in the middle of the side wall, so that the supply air flow enters the working area; the exhaust air outlet is arranged at the top of the room, and the return air outlet is arranged between the supply air outlet and the exhaust air outlet, so that the return air flow creates a low-pressure area above the supply air flow, and the return air and the supply air form a reverse double airflow effect. The return air flow leaves the room from the non-working area in the opposite direction to the supply air flow. The return air flow suppresses the suction of the supply air flow from the non-working area, and enhances the suction of the supply air flow from the working area, forcing more supply air flow to enter the working area.

2. The ventilation method of the ventilation system based on the reverse dual airflow of supply and return air according to claim 1, characterized in that: The following steps are involved: Air is supplied through the air supply port, and the supply air flow enters the working area, and the return air flow leaves the room from the non-working area in the opposite direction of the supply air flow. Since the return air flow creates a low pressure area above the supply air flow, the pressure difference between the supply air flow and the space above the supply air flow, i.e., the non-working area, is reduced, thereby inhibiting the supply air flow from sucking in air from the non-working area; the reduction of the air suction from above the air flow makes the air suction from below the air flow, i.e., the working area, increase; since the amount of air sucked in by the supply air flow in the working area increases, the relative negative pressure in the working area increases, and more supply air flows into the working area, and finally leaves the indoor air through the exhaust port and is discharged to the outdoors.

3. The ventilation method of the ventilation system based on the reverse dual airflow of supply and return air according to claim 2 is characterized in that: The air leaving the room through the return air port is purified and heat-humidified together with the outdoor fresh air, and then delivered to the room through the supply air port.

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