World Grain - July 2011 - 55

GRAINOPERATIONS

at the sidewalls of the structure. Recalling that air follows the path of least resistance, the concern is that most of the air will ﬂow up the sidewall. However, keeping in mind that velocity and quantity of air will cause change in direction due to higher resistance, air will move throughout the grain mass with proper spacing. The vertical and horizontal distance should never be greater than 1.5 times the diagonal distance. Following these guidelines with proper tunnel size and surface area will ensure that air can get to all of the grain mass. There are, however, some additional factors that can inhibit the ﬂow of air. When the bin is ﬁlled without the use of a spreader, the course material ﬂows to the outside of the bin and the ﬁnes and trash accumulate in the center of the bin. There will also be a peak of grain in the center of the grain mass. These two factors create greater resistance to airﬂow and in some cases may totally block any air from aerating this area. It is important to eliminate this core blockage. After ﬁlling the bin, the center of the bin should be cored to eliminate this ﬁne buildup. Failing to do so will create an area for spoilage and insect activity that can cause the grain to form chunks or crusts that may block the discharge sump when starting to unload the bin. VENTING Proper venting of the roof area is also very important. I prefer to see at least one square foot of vent space for every 1,000 CFM of air. You should never exceed 2,000 CFM per square feet of vent space. The location of the gravity vents is a topic that will give almost as many answers as there are individuals questioned. In most steel bins there is almost always an opening between the sidewall and roof. With that in mind, I prefer the gravity vents to be about one-third of the way up the roof as this puts about one-half of the grain on each side of the vents. It is also important to have some venting near the peak of the roof as that it where the highest heat buildup will occur during the summer. When power vents are used, the location of the gravity vents can be low in the roof. The power vents will draw air through these vents and wipe the roof to reduce possible condensation. If the power vents cannot be located near the peak of the roof, there should also be gravity vents at this location. The goal is to keep from having heat buildup in the peak. The amount of air provided by the power vents should be equal to or greater than the amount of air provided by the aeration fans. Once the grain is cooled, the power vents can be used to keep the heat from building in the over space. STORAGE TEMPS During the fall and winter aeration time, the grain should be cooled to 38 to 40 degrees F. Cooling the grain any lower only uses up unnecessary energy. Once you start the fans
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World Grain - July 2011

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