>> Application of Outdoor Sound Field Evaluation on Noise Influence of Exhaust Fan System of Semiconductor FAB on Neighborhood Residents
If a new FAB near residents will be built by you and the exhaust fan systems should be located near to your neighborhood residents based on the concerning of prevention of cross contamination between makeup air and processing exhaust, how will you do the potential estimation on the influence of noise on your future neighbors?
In this issue, a practical case study would be provided here for your reference.
>> Preface
Preface
The story was started from one FAB was already built with bad experience of exhaust fans noise and another side by side new FAB was going to build. Due to the prior noise experience, we found the importance of noise control in the newly planned FAB.
In this case study, we would like to introduce how we did the evaluation for the influence on neighborhood residents if both of exhaust fan systems running.
>> Stituation Description
Stituation Description
The situation of this case is as shown below, the area with inclined hatched lines is already built and operating and the portion with white color is newly planned FAB. As you can see, a high residents occupation is just located at the direction of north-east of future new FAB. And the worst, they are very near.
And this is what we cared about the noise effects on residents.
>> Fundamental Assumptions for Calculations
Fundamental Assumptions for Calculations
For implementation of calculations, following assumptions are made,
1. Neglect the outdoor air temperature gradient effect on barrier reduction.
2. No wind so that the building G barrier effects could be considered at best conditions.
3. 5mm thickness and 50% opening for the aluminum screen.
4. The exhaust fan will be regarded as a point source related to receiver at ground due to long distance.
5. The sound power of exhaust fans are based on the data from supplier.
6. Neglect the influence of noise from stack outlet.
7. Exhaust fans will be assumed as full capacity to simulate the worst case and the running status as shown below. (the dots in the figure indicate the locations of fans)
8. Six points of receivers are assumed based on 150m, 200m, and 250m as shown below,
>> Calculation Procedures and Some Concerning
Calculation Procedures and Some Concerning
The fundamental approach is the calculation should be based on the sound power of noise emission source. Followings are what should be concerned for the calculations.
1. Fan directivity
2. Aluminum screening effects
3. Building barrier effects
4. Distance reduction
As for the distance effects, the distance effect is more easier based on the theory of relationship of 1/r2 for point source but the directivity is related to source area and relative angles of receiver.
As for the building barrier effects, due to lower height of Building F of FAB 1, the building barrier effect will be neglected as shown below,
Although the height of Building F barrier effects for FAB 1 will be neglected, the Building C will also play a similar attenuation effects but for horizontal plane not vertical as shown below,
However, due to high and also long enough height and length of Building G of FAB 2, the building barrier effect will be considered as shown below,
>> Calculation Results
Calculation Results
A sound level value is summarized as below,
And the spectrum of 1/1 octave band for each 6 points of receivers is also shown below,
>> Site Measurement and Validation
Site Measurement and Validation
We did site measurement to validate the feasibility of our calculation schemes before the construction of FAB2. The measurement locations are as shown below and the deviation between calculation and measurement of location 4 and 5 could also be found below,
Basically, the calculation method will impose overestimation, especially for high frequency (>125Hz) but better prediction for low frequency (<125Hz) if distance is long enough.
However, an overestimation is good for future judgment as a safety factor.
>> Conclusions
Conclusions
Based on the requirement of engineering problem, we tried to develop our outdoor sound field evaluation method and validate with site measurement.
We expect a diverse engineering service could be provided for our future engineering service.