(1) Noise Control Standards
Under normal operating conditions: tall factory buildings ≤70dB(A); ventilation and air conditioning rooms ≤90dB(A); equipment and administrative rooms, excluding air conditioning rooms, ≤60dB(A).
The contractor-designed mufflers must ensure that the noise in the tall factory area and the equipment management buildings does not exceed the aforementioned standards. The test points are located 1.8 meters above the ground in the aforementioned areas.
Contractors must design silencers that meet the requirements of the "Environmental Noise Emission Standard for Industrial Enterprises Boundary" (GB12348—2008) for exhaust outlets and cooling towers. The sound environment functional area category outside the vehicle yard boundary is classified as Category 2.
(2) Silencer Design Requirements
Contractor provides silencers that meet the requirements of various systems for different air volumes, air pressures, and arrangement forms, while adhering to the needs of the project.
Contractors must design the acoustic attenuation system and select the appropriate attenuators based on the ventilation and air conditioning plan, system diagrams (electronic files), and corresponding parameters of the fans (such as air volume, air pressure, frequency noise values, speed, motor power, efficiency, blade count, etc.).
Contractors must provide operational muffler maintenance and cleaning plans.
Contractors must perform noise calculations on all ventilation towers and provide an integrated noise control plan that must meet the noise control standards for ground-level ventilation towers. In case of any modifications to the buyer's fan parameters or the design of the ventilation and air conditioning system during the project implementation, the noise attenuation plan should be promptly updated. It is also guaranteed that the implemented measures will meet the noise control standards.
After the construction project is completed, the contractor shall cooperate with Party A to complete the environmental protection acceptance. During the acceptance process, if the contractor fails to meet the national acceptance requirements due to technical or plan-related issues, the contractor must make corrections to pass the national acceptance.
f) The inter-blade wind speed in the silencer design should not exceed 12 m/s.
1) Material and Component Requirements
(1) Material Requirements
All materials used in the silencer must comply with the brand, specifications, and varieties as required by national or industry standards.
b) The material properties should meet the safety and lifespan requirements for the silencer's use.
c) The acoustic absorption materials used should comply with the requirements of JC/T469-2005 "Glass Wool Products for Acoustic Absorption," and should be ultra-fine glass wool. They must be certified by a nationally recognized acoustic testing laboratory, with detailed absorption coefficients and spectral characteristics, and complete data. The contractor should provide the diameter and filling density.
d) Absorptive materials shall have a tolerance of ±5% in capacity, moisture content not exceeding 5%, and impurity content not exceeding 3%.
Absorptive material surface structure
a) For silencers installed indoors, the protective facing of the sound-absorbing materials and the diffuser covers at both ends of the sound-decreasing panels should be made of hot-dip galvanized steel plate with a thickness of not less than 0.8mm. The thickness should ensure that after the protective facing is perforated, there is no deformation under normal service life, normal wind speed, and the compressive force of the sound-decreasing material. The galvanized layer thickness should be not less than 175g/m2. There should be measures and detailed scheme descriptions to prevent rust on the steel plate during operation due to perforation, along with corresponding usage case evidence.
b) The perforation rate of the acoustic material protective panels should meet the noise reduction performance requirements, and the flatness should not exceed 2/1000 (mm). The edges of the perforated plates should be smooth, with a surface free of burrs, dirt, or rust marks. The flatness of the perforated plates is to be executed according to GB1184 unnoted tolerance D grade accuracy, with a minimum distance of 5mm from the small periphery of the plate.
c) The protective layer of the perforated plate using glass cloth should be made of plain weave, alkali-free glass cloth, and it is not permitted to have any blocked holes.
d) The percentage of openings and the size of the apertures in the acoustic material facings should be carefully selected based on the specific acoustic characteristics of the project, with a detailed comparison of schemes and comprehensive explanations provided. The recommended opening scheme should ensure that the muffler is not easily penetrated by rainwater through the facing during operation, that the acoustic holes are not easily blocked by dust, and that the surface dust can be easily cleaned.
(e) The muffler sealing material should be made of rubber products or other materials with stable physical and chemical properties, high-temperature resistance, resistance to aging shock, non-corrosive, and non-polluting.
All standard parts, external components, and outsourced parts must have product inspection certificates or product qualification certificates.
(3) Framework Requirements
For the housing of the integral silencer, when the large side dimension of the duct connection section is ≥2000mm, it is manufactured from cold-rolled steel plate with a thickness of ≥3.0mm and is treated with reliable corrosion protection; when the large side dimension of the duct connection section is <2000mm, the thickness of the cold-rolled steel plate is increased by one size according to the national standard for duct thickness.
2) Silencer Elbow (Superfine Glass Wool)
The design incorporates an outer corner and inner circular structure to reduce resistance loss and minimize regenerative noise. The housing is made of steel plate (or equivalent), with an acoustic material consisting of glass cloth wrapped around ultra-fine glass wool, with a thickness of 50mm. The wood frame (or steel frame) serves as the skeleton, ensuring the stability of the acoustic material under adjusted airflow. When the flat edge length of the elbow is greater than 800mm, acoustic guidance plates should be added.
