| Summary: | 碩士 === 國立勤益科技大學 === 冷凍空調系 === 98 === The aim of the thesis is to take the noise control of a parking lot ventilation system at basement floor as an example to investigate the noise absorption effect on the ventilation machine room. In this thesis, the acoustical louver installed at the airflow entrance of the machine room is to allow air ventilation but reduce the noise to reach the purpose of noise elimination as well as to reduce the noise at the parking lot. In order to avoid internal reflect sound, the ceiling and walls in the machine room have been installed sound-absorbing materials for acoustic treatment to absorb the reflected sound so as to avoid the louder sound inside the machine room and reduce the sound from outside of the room simultaneously.
In the example study, the Sound Intensity Method is firstly applied to measure the ventilation room at the basement parking space and determine the sound power of the sound and noise sources. The major noise source is determined by the sound power after analyzing the noise generated from the operating centrifugal and axial fans. As the frequency range is between 250Hz and 500Hz, the acoustical silencers are selected and installed at the inlet and outlet of the fan to allow air ventilation and reducing the sound. Such could reach the purposes of sound elimination.
After determining the major noise sources, namely, the work would continuously proceed the research of noise control in the machine room. In this thesis, the 90cm~300cm length acoustical silencers in the fan equipments are seleced to conform to the field environment. The 30cm~60cm thickness acoustical louvers are installed based on the opening area at the air inlet and outlet. The machine room ceiling and the wall has been installed by the sound-absorbing mineral fiber ceiling of 2 inches with the density of 110kg/cm3 sound-absorbing material. The measurement results indicate the best noise control effect since the acoustical silencers installed in the fan machine, the installed sound-absorbing material, and the acoustical louver installed in the partition wall opening. The overall noise value at the one meter away the outside of the machine room can be reduced less then 70 dBA and the noise above 1.5 meters from the pipeline outlet can be reduced less then 60 dBA . Both values would comply with the noise control standard.
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