TM 5-805-4/AFJMAN 32-1090
APPENDIX C
SOUND LEVEL DATA FOR MECHANICAL AND ELECTRICAL EQUIPMENT
C-1. Introduction.
c. A-weighted sound levels. In the tables and
figures that follow, A-weighted sound levels are
This appendix contains sound pressure and sound
also given. Where sound pressure levels are given,
power data for mechanical equipment commonly
the A-weighted sound level is in pressure; where
found in many commercial buildings. Where possi-
sound power levels are given, the A-weighted
ble, the noise data have been correlated with some
value is in sound power. A-weighted sound levels
of the more obvious noise influencing parameters,
are useful for simply comparing the noise output
such as type, speed, power rating, and flow condi-
of competitive equipment. For complete analysis of
tions. The noise levels quoted in the manual are
an indoor or outdoor noise problem, however,
suggested for design uses; these noise levels repre-
octave band levels should be used.
sent approximately the 80 to 90 percentile values.
d. Manufacturers' noise data. Whenever possi-
That is, on the basis of these sample sizes, it
ble, and especially for new types of equipment, the
would be expected that the noise levels of about 80
manufacturer should be asked to provide sound
to 90 percent of a random selection of equipment
level data on the equipment. If the data show
would be equal to or less than the design values
remarkably lower noise output than competitive
quoted in the manual, or only about 10 to 20
models or are significantly lower than the data
percent of a random selection would exceed these
quoted in the manual, the manufacturer should be
values. This is judged to be a reasonable choice of
asked to give guarantees of the noise data and to
design values for typical uses. Higher percentile
specify the conditions under which the data were
coverage, such as 95 percent, would give increased
measured and/or computed.
protection in the acoustic design, but at greater
cost in weight and thickness of walls, floors,
C-3. Packaged Chillers With Reciprocating
columns, and beams. On-site power plants driven
Compressors.
by reciprocating and gas turbine engines have
These units range in size from 15-ton to 200-ton
specific sound and vibration problems, which are
cooling capacity. The noise levels have been re-
considered separately in the manual TM
duced to the normalized 3 foot distance from the
5-805-9/AFM 88-20/NAVFAC DM-3.14.
acoustic center of the assembly. In terms of noise
C-2. Sound Pressure and Sound Power level
production, the measured compressors are divided
Data.
into two groups: up to 50 tons and over 50 tons.
The suggested 80- to go-percentile noise level
In the collection of data, most noise levels were
estimates are given in figure C-1 and in table C-1
measured at relatively close-in distances to mini-
for the two size ranges selected. Although major
mize the influence of the acoustic conditions of the
interest is concentrated here on the compressor
room and the noise interference of other equip-
component of a refrigeration machine, an electric
ment operating in the same area.
motor is usually the drive unit for the compressor.
a. Normalized conditions for SPL data. Note:
The noise levels attributed here to the compressor
All measurements were normalized to a common
will encompass the drive motor most of the time,
MER condition by selecting a distance of 3 feet
so these values are taken to be applicable to either
and a Room Constant of 800 ft.2 as representative.
a reciprocating compressor alone or a motor-driven
SPL data measured at other distances and Room
packaged chiller containing a reciprocating com-
Constants were brought to these normalized condi-
pressor.
tions by using the procedures of chapter 3 and 5.
b. Sound power level data. For equipment nor-
C-4. Packaged Chillers With Rotary-Screw
mally located and used outdoors, outdoor measure-
Compressors.
ments were made and sound power level data are
The octave band sound pressure levels (at 3 foot
given. To use these date, one may procedures of
distance) believed to represent near-maximum
chapter 3 and 5. Usually, more measurements and
noise levels for rotary-screw compressors are listed
a more detailed estimate of the measurement
in table C- 2. These data apply for the size range
conditions were involved in deriving the PWL
of 100- to 300-ton cooling capacity, operating at or
data, so they are believed to have a slightly higher
near 3600 RPM.
confidence level than the normalized SPL data.
C-1
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