Page 114 - Uninterruptible Power Supplies

Additional Information Relating to the Standby Supply Installation
112 Chapter Three

acoustic louvers or of splitter units. There will be an air pressure drop
across the louver or splitter dependent upon the face velocity, and sup-
ply (or extract) fans must be adequate for the duty.
Acoustic louvers are of the order of 300 mm deep and provide moder-
ate attenuation, typical performance is indicated by Table 3.7. Acoustic
louvers are normally weatherproof but cannot be closed so additional
pivoted weatherproof louvers will be required if the room is to be heated
in the winter.
Splitter units comprise a length of duct up to 2.5 m in length which,
as the name implies, is split into several vertical sections by barriers of
sound absorbent material. There is scope for design variation in the
length of the unit and the width of the vertical sections, and manufac-
turers offer a wide range of standard units; typical performance is indi-
cated by Table 3.8. Acoustic performance can be improved by narrowing
the width of the airway sections but at the expense of increasing the air
pressure drop. The acoustic performance of splitter units is slightly bet-
ter for air inlet units than for air outlet units; for air inlets the air and
sound are travelling in opposite directions. Splitter units are not pro-
vided with any weather protection and weatherproof louvres will be
required at the exposed end.

The Noise Level outside of the Engine Room
There will be noise breakout from the engine room to the outside and
this will be directly dependent upon the internal noise level. There will
be noise from the exhaust outlet and a small amount from the surface
of the exhaust pipe itself. If there is external machinery such as a
remote radiator and fan this will be a source of additional noise. The
noise breakout will be through the engine room walls and ceiling and
through any ventilating and cooling air inlet and outlet openings, or
any other services that pass through the wall. The breakout through
the walls and ceiling themselves depends on the sound reduction index

TABLE 3.7 Typical Performance for Acoustic Louvers
Center frequency Hz 63 125 250 500 1000 2000 4000 8000
Attenuation dB 4 4 6 11 17 20 15 15

TABLE 3.8 Typical Performance for a 2.5 m Splitter Unit

Center frequency Hz 63 125 250 500 1000 2000 4000 8000
Attenuation dB 9 19 30 40 40 21 15 11

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