design and renovation, the air handling system is the one
prominent noise source that is always in need of noise and vibration
control design. Two general types of noise occur:
- Fan generated noise,
which is caused by turbulence of the air handling unit (AHU) fan wheel
which propels the air.
- Vibration excited noise,
usually low frequency, which transmits through the building structure
to be felt and heard in adjacent and lower occupied spaces.
airborne noise reduction measures
include lined ducts and in-line sound attenuators. Design tools include
manual and computer spreadsheets or special software packages such as
Trane's TAP. We use all of these tools. We also go beyond them -
applying first principles to solve difficult situations where space is
limited or for very quiet installations such as in auditoriums, or to
remedy existing noisy installations. For instance, the acoustic plenum
makes maximum use of existing building space while providing maximum
low frequency attenuation. This is especially useful where circular
duct is favored for long distance air movement.
Common vibration reduction measures
include soft springs or strategic relocation of the rotating mechanical
systems. Additional attenuation is often needed for higher frequency
"vibration" in the form of motion harmonics and magnetostriction of
electromagnetic devices such as power transformers. The design
criteria, relating to tactile perception of vibration and the annoyance
of very low frequency sound (infra sound) are not well known, but we
have developed our own criteria which we have found to be appropriate
to office and residential occupancy. This was implemented in the top
floor of the Nalco Chemical executive offices building in Naperville,
IL decades ago.
Last updated 08-Jun-2012.
Original Web Site by Point
& Click Software, Inc.