Basic Documentation
Table Of Contents
- Getting a Handle on Decibels
- The Frequency Component
- The Octave Bands
- Sound Curves
- Now Come the Complications and Confusion
- NC Sound Curves
- Attaining Acceptable Ventilation Related Sound Levels in Laboratory Rooms
- Equipment Sound Ratings
- Fume Hood Sound
- Attaining an Acceptable Room Sound Level
- Example Analysis of a VAV Research Laboratory Room Supply Air System
- Item 1: Supply Air Sound Level
- Item 2: Space Effect Sound Attenuation
- Item 3: Multiple Sources of Sound
- Item 4: Allowable Supply Air Sound at Diffusers
- Item 5: End Reflection Sound Attenuation at Supply Diffuser Inlet
- Item 6: Supply Air Terminal Duct Attenuation
- Item 7: Duct Division
- Item 8: Allowable Supply Terminal Discharge Sound
- Allowable Room Sound Level
- Room General Exhaust Terminal
- VAV Fume Hoods
- Suggestions for Reducing Excess Room Related Ventilation System Sound
- Conclusion
Product or comp
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Building Technologies Division Document No. 149-979
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2. Use multiple large laminar flow room supply
air diffusers. This lessens the airflow per
diffuser and lowers the individual diffuser
sound. Ensure that the airflow volume is
equally divided among the diffusers.
3. Keep all diffuser throttling dampers fully
open. If necessary, add throttling or
balancing dampers upstream and closer to
the supply air terminal.
4. Use a sound attenuator or lined flexible duct
between the supply air terminal and the
diffusers. Specify a type of duct lining that
will not release fibers into the supply air or
allow moisture to be retained that could
result in mold growth.
5. Use larger size supply air terminals to
lessen the airflow velocity and pressure drop
through the air terminals.
Avoiding Excessive Room Exhaust
Air Sound
1. Ensure that the duct that connects to the
exhaust grill is vertical for 1 to 2 duct
diameters immediately above the exhaust
grill collar.
2. Use a larger general exhaust grill to ensure
the pressure drop is less and the air velocity
entering the grill is minimized.
3. Use the lowest practical static pressure in
the exhaust system to prevent excessive
pressure drops. No more than 0.5 inches of
water above the minimum required static
pressure level is recommended.
4. Ensure that the exhaust system ducts are
well sealed to minimize the additional airflow
caused by leakage into the exhaust system.
Reducing airflow always lowers the sound.
5. Ensure the fume hood baffles are adjusted
for maximum containment since improper
baffle adjustment can adversely affect fume
hood containment and increase fume hood
sound.
Conclusion
Due to the relatively high airflow rates in laboratory
rooms, it is generally not possible to achieve a
sound level comparable to a conference room or
office area. However the laboratory occupants
should not be subjected to unnecessarily high
ventilation system sound. Whether a new laboratory
project or a retrofit, much can usually be done to
lower the ventilation related sound in the room.
Constant volume laboratories will usually have
considerable excess ventilation airflow, and if the
airflow can be reduced the sound level will also be
reduced. A VAV system is usually the most effective
way to minimize room and fume hood airflow for new
laboratory projects and thus will minimize the room
ventilation related sound.
For more detailed information on this topic, request
the following document from your Siemens Building
Technologies, Inc. representative:
Minimizing Excessive Sound in Ventilation System
Design Application Guide (125-1929)