Analysis and selection of noise reduction equipmen

2022-08-17
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Analysis and selection of noise reduction equipment for Metro environmental control ventilation system

Abstract: Based on the research and analysis of the characteristics and causes of noise in Metro environmental control ventilation system, the selection of noise reduction equipment for Metro environmental control ventilation system is briefly analyzed

key words: subway ventilation; Noise control

1 introduction

with the large-scale construction and operation of the subway, the noise produced by the subway operation has also brought a certain impact on people's lives. The noise of the subway mainly comes from two aspects: one is the running noise of the subway train, and the other is the noise of the environmental control ventilation equipment of the subway. This paper mainly analyzes and studies the noise generation and control of the environmental control ventilation system of the subway

2 noise generation and characteristic analysis of environmental control ventilation system

subway environmental control ventilation system is generally composed of tunnel ventilation system, station ventilation and air conditioning system and air conditioning water system. The system function is mainly realized and completed through the operation of various types of fans, air conditioning units, chillers, water pumps, cooling towers and other equipment (Figure 1), The vibration and noise generated by these equipment during operation have become the main noise source of the subway environmental control ventilation system. The noise generated by the operation of air conditioning and ventilation equipment will spread to the public area of subway station, equipment management room and ground area through different ways, thus forming noise pollution. The noise generated by the ventilation and air conditioning equipment in the environmental control ventilation system of the subway during normal operation mainly includes mechanical vibration noise, motor operation noise and aerodynamic noise

(1) mechanical vibration noise and motor running noise of ventilation and air conditioning equipment. On the one hand, it radiates from the surface of the equipment body, on the other hand, it spreads outward along the structure through the foundation, hanger, etc. in the form of elastic waves. According to the field test data, the noise value reaches 80 ~ 110 dB (a), which has a great impact on the equipment room and the surrounding adjacent areas, and many measures are taken at the same time. The code for design of Metro clearly stipulates that "the noise in the ventilation and air conditioning machine room shall not exceed 90 dB (a); the noise transmitted by the ventilation and air conditioning equipment to each room shall not exceed 60 dB (a)". Therefore, in the layout plan of the building plane design and ventilation and air conditioning system of the metro station, the equipment generating noise should be set up in a centralized manner as far as possible, and an independent ventilation and air conditioning machine room should be set up, which is far away from the public area and management room of the station, At the same time, corresponding measures shall be taken to control the noise. For example, the wall of the machine room adopts concrete pouring structure or solid brick masonry to ensure that the sound insulation index ia of the enclosure structure of the machine room is greater than 50 dB (a). The machine room is equipped with closed sound insulation doors with a sound insulation loss greater than 30 dB (a). The inner wall of the machine room is equipped with sound-absorbing materials or sound-absorbing treatment according to the actual needs. Soft connections are used between the equipment and the pipeline to reduce the outward transmission of equipment vibration through the pipeline, Elastic materials such as damping springs or rubber are arranged between the equipment and the foundation and hangers to effectively control the vibration of the equipment and reduce the noise (Fig. 2)

(2) aerodynamic noise is mainly the noise generated in the process of gas flow, which is mainly caused by the unstable flow of gas, that is, the disturbance of gas flow, the interaction between gas and gas, and the interaction between gas and objects. From the mechanism of noise generation, it is mainly composed of rotating noise and eddy current noise. The aerodynamic noise of the subway environmental control ventilation system is mainly radiated from both ends of the inlet and outlet of the fan (Fig. 3), and spreads inward and outward through the connected air duct or air duct. On the one hand, it will affect the internal area of the station hall and platform, and on the other hand, it will cause noise pollution to the ground external environment adjacent to the wind Pavilion. The code for design of subway stipulates that "the noise transmitted by the ventilation and air conditioning system equipment of the subway to the station hall and platform shall not exceed 70 dB (a); the noise at the exit of the wind Pavilion (Figure 4) shall comply with the provisions of the current national standard environmental noise standard for urban areas". Because the tunnel fan in the tunnel ventilation system should be able to turn forward or reverse under different working conditions according to the functional requirements of the system, and in addition, the exhaust fan in the trackside area within the station platform will always be turned on during train operation, the air flow noise generated by the operation of the above fan has the greatest impact on the internal and external environment of the subway, which is the most prominent in the subway environmental control ventilation system, In the design of noise reduction, we must focus on the solution

since the subway tunnel fan is a reversible forward and reverse two-way fan, one end leads to the ground air pavilion through the connection with the air duct and air shaft, and the other end leads to the interval tunnel, it is an effective and reasonable noise reduction measure and method to set silencers in front of and behind the fan. In addition, the fans used in the subway ventilation and air conditioning system are basically axial fans, which are characterized by large air volume, high regenerative noise, low natural attenuation, relatively high total residual noise, and wide noise band, generally having high noise values in the range of 63 ~ 8000 Hz. Therefore, the selection of silencing equipment should be targeted and applicable to ensure the effective control and elimination of noise

3 analysis and selection of noise reduction equipment

according to the analysis and summary of the investigation of domestic metro, the noise reduction equipment of Metro environmental control ventilation system is generally divided into two categories: vibration reduction equipment and noise reduction equipment. Vibration damping equipment includes various vibration damping springs, vibration isolation pads, soft connectors, etc. these equipment have mature and finalized products for design and configuration. Silencing equipment includes various forms of silencers, silencing parts (such as air vents, louvers), etc. Mufflers and silencing components used in the air conditioning and ventilation systems of civil and industrial buildings have common standard products, which can be selected and matched according to equipment samples or standard atlas. However, for the subway environmental control ventilation system, its noise reduction equipment, especially the muffler, is restricted and affected by various factors. At present, there is no finalized and universal product, and the technical performance parameter standards of the products of various manufacturers are also different, which brings certain difficulties to the design

muffler is a kind of silencing equipment that allows air flow to pass through and effectively reduces the noise in the air flow. The basic requirements for silencers: first, acoustic requirements, which require good silencing frequency characteristics, that is, sufficient silencing volume within the required silencing frequency range; Second, the aerodynamic performance requirements require that the muffler resistance should be small; The third is the requirements of structure and processing, which requires small volume, economic and simple processing, so we should pay attention to the difference between joint oil leakage and cylinder plug oil leakage, and long service life. At present, the noise elimination equipment selected in the environmental control ventilation system of domestic metro is generally the resistive muffler that eliminates medium and low-frequency noise. However, when the resistive muffler cannot meet the design requirements due to the spectral characteristics of the system fan or the small natural attenuation of the system noise, the impedance composite muffler is usually used

resistive muffler uses porous sound-absorbing materials (often called resistive materials) laid in the air flow channel to absorb sound energy and reduce noise. Resistive muffler is one of the most widely used types of mufflers. Resistive chip muffler is a kind of resistive muffler, which has the characteristics of simple structure, excellent medium and high frequency noise elimination performance, low air flow resistance and so on. Therefore, its scope of application is very wide. The environmental control ventilation system of subway usually adopts metal shell sheet muffler and structural sheet muffler (Fig. 5). The former is mostly installed at both ends of the inlet and outlet of the fan, and is directly connected with the front and rear diffuser/reducer of the fan; The latter is mostly installed in the air duct of air intake and exhaust civil structure, as well as the piston air duct and air shaft. At the same time, according to the special requirements of the subway project, the interior of the silencing sheet should be made of non combustible sound-absorbing materials, and meet the operation requirements of 150 ℃ or 250 ℃ smoke passing every hour

through the acoustic test of 10 typical subway stations in 6 cities including Beijing, Shenzhen, Nanjing, Guangzhou, Chongqing and Tianjin, and the analysis and Research on the noise reduction design of subway environmental control ventilation system in various cities, the structure and performance of the resistive sheet muffler selected in the current subway environmental control ventilation system are summarized as follows

(1) perforated galvanized (plastic sprayed) steel plates with a thickness greater than or equal to 0.5 mm are generally used for the muffler panel to prevent corrosion, and a certain perforation rate should be guaranteed. The perforation rate is greater than 20%, and the aperture is 4 ~ 6 mm. The thickness of the silencer should be equal to the width of the air flow channel, that is, the percentage of the air inlet area is 50%, and the wind speed between the silencer blades is generally controlled at 10 ~ 12 m/s. The silencing sheet is filled with ultra-fine glass wool (wrapped with alkali free glass cloth) with a unit weight of 32 kg/m3 (or 48 kg/m3)

(2) because the tunnel fan operates reversely, the air flow flows in both directions, and both ends of the silencer may be windward, so both ends of the silencer body adopt wedge type or arc type to reduce the resistance. The thickness of the resistive slice muffler is generally 150, 200, 250, 300 mm, and 1/2 of the thickness of the slice is used for silencing the walls on both sides. Jiangxi Jinhui lithium industry has an annual 10000 ton lithium mica production line for industrial lithium carbonate, which was put into production in early September. The width of the air flow channel is 150, 200, 250, 300 mm, that is, the air inlet area ratio is 50%, and the resistance is the smallest at this time. For the metal shell sheet muffler, the shell of the muffler needs to use high-quality steel plate with a thickness of more than 1.5 mm due to sound insulation, and the four side connection is sealed with sealing strips and dense sealant

because of the complex and unique underground structure of the subway station, it is very different from the above ground civil and public buildings. At the same time, the special system functional requirements of the subway also determine that the environmental control ventilation system of the subway is different from the ventilation and air conditioning system of conventional buildings, Therefore, the silencing design (including the calculation of system silencing amount, the selection of muffler form and type, the determination of muffler length, etc.) needs to comprehensively analyze the actual composition of the system, determine the specific and reliable silencing and noise reduction scheme, and select the muffler with the best aerodynamic performance and acoustic performance through detailed silencing and noise reduction design calculation. At the same time, the selection of silencing equipment should also be based on fire prevention, corrosion prevention, purification, installation, project cost and other factors

4 conclusion

the noise control and analysis of subway environmental control ventilation system involves many aspects, such as acoustics, aerodynamics, and materials science, which can effectively avoid the pollution of hydraulic oil caused by metal corrosion. It is a complex system engineering. In the noise elimination design, we should pay attention to the relationship among sound source, sound transmission path and receiver. Therefore, it is necessary to analyze the specific composition and equipment composition of the subway system according to its different functional characteristics; Identify various factors and objects that produce noise; Understand the transmission route of noise; Determine the noise source and noise control standard of the impact (control) point; Relevant calculation methods and means are used to predict and analyze the noise and propagation of the system. Therefore, corresponding technical measures and schemes are formulated and adopted, and applicable auxiliary silencing facilities and equipment are selected. At the same time, effective detection means and calculation methods are used to measure, simulate, calculate, analyze and study the laws of various noises in existing projects and the actual effect of noise control, summarize and summarize the successful experience and lessons of failure in previous projects, learn from each other and improve each other, so as to continuously put forward reliable and accurate calculation and analysis methods and means, and develop more effective noise reduction products and equipment, Targeted

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