Basic Documentation

and expectations in this regard. Since laboratory
clients probably won't know much about the
technicalities of sound, they aren't likely to provide
specific room NC sound level requirements.
However, client normally expect new labs to be
quieter than existing labs.
If there are existing laboratory rooms in a client's
facility it is advisable to get a feel for the room sound
levels. Ideally it is best to obtain room sound level
data, but this is seldom practical because it involves
considerable time and expense. As an alternative, it
is beneficial to determine how the present room
sound situation is perceived by the room occupants
and the client. Is the room sound level an issue? If
so, has any attempt been made to address it in the
past? Have any room sound level measurements
been taken?
If the present room sound level is objectionable, try
to determine the primary causes. Often this includes
a combination of factors including high airflows in
constant volume type systems, as well as the room
ventilation system design itself. Fume hoods sashes
left open also significantly add to the room sound
level. (More details on avoiding excess room related
ventilation sound are provided later in this
document.)
Table 2 lists acceptable ambient sound levels for
variou
s categories of new laboratory rooms with
chemical fume hoods. These dB levels are based
upon the 2003 ASHRAE Applications Handbook
Chapter: Sound and Vibration Control, and are
accepted with in the industry.
Equipment Sound Ratings
Manufacturers of ventilation components (air
terminals, diffusers, grills, etc.) provide certified
2
equipment sound ratings called sound power
ratings. These consist of the dB levels for the octave
band center frequencies at specific airflow rates and
static pressure drops. The industry standard for
providing equipment sound ratings only covers
octave bands 2 through 7 (125 to 4000 Hz).
Equipment sound ratings are normally provided in
terms of both discharge and radiated sound power
levels. Discharge sound is normally higher and
pertains to sound that is emitted into the connecting
ductwork. Designers are mostly concerned with
discharge sound since that sound can ultimately
enter a room via the ductwork.
Equipment radiated sound travels outward from the
source and is independent of the ductwork. Radiated
sound is of concern when rooms do not have a
dropped ceiling and equipment radiated sound can
enter a room without being attenuated (absorbed
and diminished) by the ceiling material.
One note of caution must be given regarding the
manufacturer’s equipment sound ratings. Some
manufacturers reduce their published equipment
sound ratings by a room absorption factor. Although
room sound absorption occurs and thus attenuates
some of the sound, the actual dBs that are
attenuated due to room absorption (space effect)
should be determined in the designer's analysis.
Therefore, carefully check the footnotes for this
when reviewing a manufacturer's equipment sound
ratings. If the manufacturer indicates that a room
absorption or space effect factor has been used to
reduce the equipment sound rating, it is advised to
add these dBs back into the equipment sound
ratings.
Page 4 of 12
Siemens Industry, Inc.
2. Most typically the certified data is obtained per ARI Standard
880.
Document No. 1
49-979