TM 5-805-4/AFJMAN 32-1090
Table C-10. Approximate Close-In SPLs (in dB) Near the Intake
limitless number of possible arrangements, this is
and Discharge Openings of Various Cooling Towers (3- to 5ft.
not handled in a general way, so the problem of
distance).
partially enclosed cooling towers is not treated
here. In the absence of a detailed analysis of
cooling tower noise levels inside enclosed spaces, it
is suggested that the close-in noise levels of table
C-10 be used as approximations.
f. Evaporative condensers. Evaporative condens-
ers are somewhat similar to cooling towers in
terms of noise generation. A few evaporative con-
densers have been included with the cooling tow-
ers, but not enough units have been measured to
justify a separate study of evaporative condensers
alone. In the absence of noise data on specific
evaporative condensers, it is suggested that noise
data be used for the most nearly similar type and
size of cooling tower.
g. Air-cooled condensers. For some installations,
an outdoor air-cooled condenser may serve as a
substitute for a cooling tower or evaporative con-
denser. The noise of an air-cooled condenser is
made up almost entirely of fan noise and possibly
air-flow noise through the condenser coil decks. In
general, the low-frequency fan noise dominates.
Since most of the low-frequency noise of a typical
cooling tower is due to the fan system, in the
absence of specific data on air-cooled condensers, it
is suggested that noise data be used for the most
nearly similar type and size of cooling tower.
h. Ejector-type cooling tower. This is a fanless-
type cooling tower that induces air flow through
the use of nozzles of high-pressure water spray.
Noise levels are generally lower for the ejector
cooling tower than for cooling towers using fans to
produce air flow. Adequate vibration isolation of
the drive pump, piping, and tower are necessary,
although the elimination of the fan reduces the
severity of tower vibration.
C-11. Pumps.
The overall and A-weighted 3 foot SPLs given in
table C-11. The pump power rating is taken as the
nameplate power of the drive motor. This is easily
determined in field measurements, whereas actual
hydraulic power would be unknown in a field
situation. For pump ratings under 100 hp, the
radiated noise increases with the function (10 log
hp), but about 100 hp the noise changes more
slowly with increasing power, hence, the function
(3 log hp). Octave band SPLs are obtained by
subtracting the values of table C-12 from the
overall SPLs of table C-11. Pumps intended for
high-pressure operation have smaller clearances
between the blade tips and the cutoff edge and, as
a result, may have higher noise peaks than shown
in tables C-11 and C-12 (by 5 dB, sometimes 10
C-9
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