World Grain - March 2016 - 76

GRAIN OPERATIONS

fans are less expensive and are normally used when static pressure
will not exceed 4 or 5 inches of water, Jones said.
Centrifugal type fans with backward-inclined blades give
more consistent air delivery over a range of pressures than
most axial type fans and, in special designs, can operate at 20
or more inches of static pressure.
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depth causes about a four-fold increase in power required.
In addition, different grain types have different resistance
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horsepower.
With light aeration systems, fractional horsepower fans are
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and grain depths of 20 feet or more, the power needs may exceed
1 horsepower for every 1,000 bushel of bin capacity. In large
bins, multiple fans of 20 or 25 horsepower may be required.
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from the manufacturer's rating tables or curves to deliver the
required air volume at the expected static pressure, Jones said.
OTHER CONSIDERATIONS
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"Y," or "U" patterns.
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power requirements reduce operating expense and capital costs.
Bins need adequate roof exhaust vents to minimize
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be a minimum of one square foot of roof vent opening for
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and access doors to allow air to escape.
Roof vents that are designed to open under pressure or
vacuum can remain closed between aerations to help reduce
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It is possible for aeration fans to suck rain and snow into a
grain bin. Short storms (three to six hours in duration) usually
do not create a moisture problem. But during longer storms or
continuous foggy weather, it is advisable to stop aeration until
the weather improves, Jones said.
The fans may be controlled by manual, semiautomatic or
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switch. Aeration fan controls include time clock or electric
eye for night operation, high- or low-limit thermostats and
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packages are available ranging from simple temperature and
humidity controls for a single bin to more elaborate controls
for multiple fan operation.
With semiautomatic or automatic controls, an elapsed-time
76

Figure 2 : Coring a grain bin to distribute foreign material.

clock should be placed in the circuit. If the aeration system is
not operating long enough to achieve temperature equalization
within the stored grain, then the control settings should be
changed to allow longer or more frequent operation.
During cooling seasons, aeration systems must be operated
several times, each time long enough to equalize temperatures
throughout the entire grain mass.
Small motors can be started and run by temperature and
humidity control switches if the contacts are rated for these
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of 0.5 horsepower or larger. Automatic aeration temperature
controllers using time delay to minimize inrush current and
peak power loads can control two or more larger fan motor
starters in sequence.
Thermostats and humidistats should be adjusted and
maintained according to the manufacturer's recommendations.
Controls should be cleaned at least once a year, and more
often if operated in dusty surroundings, Jones said.
AERATION PROCEDURES
A level grain surface is an important part of controlling
grain temperature and insect activity. Temperatures and
March 2016 / World Grain / www.World-Grain.com

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