Page 28 - Uninterruptible Power Supplies

Standby Power Generating Sets
26 Chapter One

If the radiator fan is not engine driven, an equivalent amount of
additional power will be available from the generator output where it
will be required to supply an electrically driven radiator fan.
For sets rated up to about 800 kW the radiator and its associated
cooling fan are usually mounted, on the base frame, at the nondriving
end of the engine, the fan being belt driven from the crankshaft. Within
the engine room the set may then be positioned perpendicular to a
perimeter wall which is provided with an opening matched in size to
the radiator. This arrangement is convenient and ensures that the cool-
ing air passes over the engine in an efficient manner. To the purist it
has the slight disadvantage that the cooling air is extracted from the
engine room and will be above the outside ambient temperature and
hence the radiator is not used in the most efficient manner.
For larger sets the radiator is usually mounted outdoors in a horizon-
tal or vertical plane and uses one or more thermostatically controlled,
electrically driven, forced-draft fans. Horizontally mounted radiators
have the advantage of directing the warmed air upward where it is less
likely to cause a nuisance to personnel.
Whether the radiator is mounted in the engine room wall or outside
of the building the noise produced by the fan or fans will require con-
sideration and acoustic attenuators may be required. Wherever hot
water pipework is within reach of personnel, inside or outside of the
engine room, it is a source of danger and must be thermally insulated
to reduce the surface temperature to a safe value.
Lubricating-oil cooling is variously achieved: an oil/water or an oil/air
heat exchanger may be used or a section of the local radiator may be ded-
icated to oil cooling.

Direct Air–Cooled Diesel Engines
Up to ratings of the order of 100 kW direct air–cooled diesel engines are
available. For this arrangement the cylinders are provided with a
cladding having air inlet and outlet flanges. A fan forces air into the
spaces between the cylinders and the cladding where it absorbs the
engine’s rejected heat and is forced to the outlet opening. The route of
the air flow is necessarily contorted which leads to a large pressure
drop across the air flow passages and the air outlet flange will usually
be much larger than the inlet flange.
Within the engine room the set should be positioned so that the exit-
ing cooling air may be ducted directly to the exterior of the building by
a straight length of ducting of adequate cross section, say 125 percent
of the outlet flange area. The engine will normally be provided with an
engine-driven fan with some surplus power, but if any significant inlet

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