Natural Science Forum / Physics / Acoustics / April 2006

    That's he basic way this has to be done. Sometimes it is sufficient to
only use a perimeter wall open to the sky, but that's for when only a
small reduction of noise is sufficient.

    Just use common sense in designing the cooling system.

    It is common to have sound attenuator installed across the face of a
large opening for inlet and exhaust cooling air. Those fans can provide
only about one inch of water static pressure to move the air through all
attenuators.

    This is described on this page in general. Vibro-Acoustics Co. supplies
attenuators that my work. There are many sizes and models to consider,
depending on the frequency range of gratest noise annoyance, the volume
of air flow and the static pressure available from the Caterpillar fans.

    This is a genral list of methods:

http://info@vibro-acoustics.com/HVACNoiseControl/Silencers/VASilencingProblemsAndSolutions/18CommonSilencingProblems.htm

    And a more pertinent solution; and arangement and design (if you have
plenty of money and time to do it right):

http://vibro-acoustics.com/HVACNoiseControl/Silencers/VASilencingProblemsAndSolu
tions/pr14main.htm

    That should basically work, depending on how large a plenum you can
make, and the space vailble for a second (dishcarge) plenum.

    It is helpful to know the sound level (octave band spectrum from 31Hz
to 4 kHz) of the sound that has arrived at the neighbor.

    Apart from that, the method you describe is a "plenum". This is
basically a room whose walls will stop the sound from escaping to the
outdoors, while the inside surfaces of those walls and ceiling are
covered with sound absorbing material. The air must then proceed to a
second chabler wwhich contans the louvers to discahrge the air and
remaining sound to the outdoors. It usually works to vrying degrees.

    If you have no acoustical equipment, then you have to try various
arrangements until both the neighbor complaints and the the equipment
overheats stop.

        Angelo Campanella

Five noise sources - air intake, exhaust, radiator noise, fan noise &
casing noise emission. The air intake and exhaust are obvious and easily
addressed. The fan and radiator noise appear easy to address until you
realize what they are there for.

The radiator is to get rid of the internal heat of the engine. If the
generator set is open to the air, the casing heat from the generator and
the casing heat from the engine are lost from the outside of the
generator and the engine by convection and radiation. The fan on the
radiator is only dealing with the air flow to remove the heat from the
engine cooling system. The exhaust will carry away the heat of the
exhaust gases but the exhaust pipe radiates heat as well.

You should contact caterpillar and find out what is the casing heat-load
for the 500 KVA unit. The air flow should be such that the air flow
around the the outside of the generator set increases by no more than 10
degrees above ambient temperature. The generator is designed so that the
 casing of the generator radiates enough heat (when unenclosed) that
the windings do not exceed 70 degrees above ambient. Any higher and the
insulation starts to break down, shorting out the generator. You need to
find out the heat load (radiator + casing), calculate the minimum air
flows and provide them OR else you will "cook" the electrics.

Hopefully the "acoustic booth" is adequately acoustically lined. and the
noise reduction compensates for the noise of the generator set, plus
internal reverberation within the "acoustic booth" (take your standard
calculations and add 10dB for the close fit of the "acoustic booth".

And be very wary of oil vapour. Unless the lining of the "acoustic
booth" is well sealed the acoustic lining will act like a sponge to any
oil vapour and you will end up with an oil soaked fire hazard.

The "open area" of the cooling air inlet area and the cooling air inlet
area should be 1 to 1.5 times the area of the radiator as a first
approximation, otherwise the restriction will push you to higher fan
speeds. The enclosure will need to be partitioned at the radiator to
stop recirculation of hot air. You need the fan curves for the radiator
fan and the static pressure drops for the radiator, the intakes louvres
and the exhaust louvres.

Radiator noise regeneration is the least of your worries.

This begs the question: why the "acoustic booth", when it might be
simpler to convert the room into a fully lined "plant room" with a fan
forced ducted, cooling air intake, acoustic louvered wall to let the
cooling air out and fully (thermally wrapped) muffler and engine exhaust
pipe ?

You need a mechanical/acoustical engineer to assess the situation and to
design this properly. If you can provide reasonably good engineering
drawings of the layout and noise requirements, the design could be done
remotely. The 1/3 octave band noise levels / sound power levels of the
500 KVA Caterpillar generator sets are readily available from Caterpillar.