Types of Aeration Systems: Which Type is Right for You?
Depending on the grain bin configuration and the structure use, the aeration system must be designed to move air through grain in the most effective and efficient way possible. Knowing the options for aeration system designs will help you make wise decisions when building a new bin or retrofitting existing bins for aeration. With proper design and management practices, aeration systems can help maintain the quality of your grain.
There are nine different types of aeration systems. Two are quite common, two are
a little less common and the remainder are found in “specific” applications.
Most common aeration types
Positive pressure (push) systems
It is speculated that these are the most often used aeration systems, particularly
in new steel bin installations in the U.S. Positive pressure or push systems consist
of fans blowing air into the bin at the bottom, either through ductwork or a perforated
false floor. The air is then exhausted with power exhaust fans on the roof, with passive
venting on the roof or with a combination of power exhaust fans and passive vents
or space in the roof (Figure 1). Air will heat a few degrees from friction as it goes
through the grain bulk, compared to negative pressure (see below) systems. But hot
air rises and the positive pressure system takes advantage of that natural warm air
movement. It is important to have the exhaust fans and the aeration fans wired separately
so the exhaust fans come on before the aeration fans. This helps reduce chances of
damaging the roof with differences in pressure.
Figure 1. Positive pressure aeration system.
Negative pressure (pull down) systems
For the negative pressure system, fans are located at the bottom and pull air down
through the grain bulk (Figure 2). No power exhausters are required, but proper design
of the passive vents is extremely important. Not having enough vents to let air into
the bin can cause a roof collapse. Maintenance of vents is extremely important in
a negative pressure system for the same reason. Adequate air intake is essential for
a negative pressure system to work correctly. Some experts report problems, such as
condensation at the top of the grain mass, is pulled down through the entire grain
bulk to the bottom. Therefore, managers must pay close attention to run time of the
fans so all of this extra moisture is moved completely through the grain and out of
the bin at the bottom. Also, small seeds, such as canola can pack more with a negative
pressure system and fine material and smaller seeds can be pulled through the perforated
flooring into the space below the floor. An advantage to a negative pressure system
is that the exhaust air can be easily monitored for temperature and CO2 at the ground
level, which makes determining if temperature fronts have been moved through the grain
much easier.
Figure 2. Negative pressure aeration system.
Less common aeration types
Pull-up systems
This system is commonly used on concrete tanks. The fans are located on top of the
structure and they pull air up through the bin (Figure 3). This system does not require
exhaust fans on the top but proper design of venting and duct work at the bottom of
the bin is important because this is where the air must enter the bin. Extra reinforcement
is necessary on the roof of the structure to accommodate the extra equipment weight.
One advantage to this system is that it is quieter than most aeration systems, which
can be a big plus in populated areas.
Figure 3. Pull-up aeration system.
Push-Pull (high air) systems
For this system, fans are located both at the top and the bottom of the bin (Figure
4). This application is for concrete tanks that have reinforced roofs much like that
designed for a pull-up system. This system can be especially helpful when storing
high-moisture grain. Static pressure is cut in half when compared to a negative or
positive pressure system. The amount of air provided by the fans can be much higher
than in other system designs.
Figure 4. Push-Pull aeration system.
Specific Aeration Design Applications
Turbocharged systems
Sometimes these positive pressure systems are considered “in-line” fan systems or
centrifugal fans in an in-line axial fan configuration. Contact fan manufacturers
about their company designs of this type of fan. Two fans are placed “in series” and
can increase pressure with the same capacity when needed. The exhaust from one fan
blows directly into the intake of another fan. Powered exhaust fans on the roof are
needed for these systems to remove moisture. These systems are more expensive, but
allow for higher moisture grain to be stored. They can be used in either concrete
or steel tanks.
Manifold systems
These systems use fans pushing air through manifolds in multiple bins (Figure 5).
There are fewer fans to maintain, which can save money, but the management of the
system is more difficult and the air distribution is harder to control.
Figure 5. Manifold aeration system on two bins.
Cross flow systems
Cross flow aeration systems (Figure 6) move air from one wall of the bin through the
grain bulk to the center of the bin or to the other side of the bin. Ducts run vertically
on the walls of a bin and air is blown sideways. The static pressure and the horsepower
of the fans are less in this design. However, the initial installation cost of these
systems is higher and maintenance of the equipment is more difficult.
Figure 6. Cross flow aeration system.
Air-assisted unloading (Kanal®) systems
These aeration systems are designed so they also aid in unloading the tank. The floor
has concrete channels that route the grain into the sump (Figure 7). Air assists the
grain along these channels, guiding it into the reclaim system.
Figure 7. Kanal® or air-assisted unloading aeration system.
Temporary Storage Aeration Systems
Temporary storage of grain can take on many different configurations. For aeration to be used in most of these configurations, ductwork is necessary. Flat storage structures are in this category as well as outdoor piles. The most common type of aeration in temporary outdoor piles uses ductwork around the sidewall perimeter. Some outdoor piles have a center fill tower. Air can be pulled through the grain pile and up through these towers by fans located on top of the towers. Aeration is almost always negative pressure for outdoor piles and can be either positive or negative pressure for flat storage. In the case of outdoor piles, negative pressure aeration not only provides air movement through the grain, but also holds tarps on the piles.
Important Considerations
Aeration equipment design is rather complex and must be considered as a “system.” An aeration system includes the fans, the ductwork or perforated flooring, the passive and/or powered vents, the grain, the air being moved through the grain and the controls (either electronic or manually operated). Careful attention must be paid not only to the design of this system, but also to the proper timing and control of the aeration system. Contacting a reputable aeration system contractor may be the best choice for purchasing and installing new aeration systems.
References and other sources of information
Bledsoe, P., Tiernan TriState Chapter: Geaps Preventive Maintenance and Safety Training. 2017.
Dietz, J., “Air Supply”, Ag Advance, Sep. 2014.
Miles, K., “All About Aeration, Lessons and Practical Uses for Best Results”, Grain
Journal July/August 2017: pp12-17.
Grain Drying, Handling and Storage Handbook, MWPS-13 Third Edition.
Dry Grain Aeration Systems Design Handbook, MWPS-29 Revised First Edition 1999.
BAE-1102, Aeration Systems for Flat-Bottom Round Bins, Oklahoma State University Extension
Service, Stillwater, OK.
BAE-1103, Aerations System Design for Cone-Bottom Round Bins, Oklahoma State University
Extension Service, Stillwater, OK.
BAE-1290, Grain Handling Automation and Controls, Oklahoma State University Extension
Service, Stillwater, OK
Carol L Jones, PhD, PE
Professor and Buchanan Chair
Stored Product Engineering