1. Uniform Airflow Distribution
Achieving and maintaining uniform airflow throughout a bin of grain is an important factor in drying grain effectively and efficiently. Common problems seen with conventional aeration systems are as follows:
A) Conventional aeration systems that rest flat on the bin floor, straight tubes, and inverted "u" systems straddling hopper cones dry only from the bottom up. Although effective in drying the bottom half, these systems often fall short of drying grain in the center and top half of the bins.
B) As grain is augured into a bin, fine particles collect in the center and result in a dense packed core that is hard for air to penetrate. This can make the drying process frustrating - while the bottom is over dried, the top and center of the bin still remain wet.
Grain Guard systems overcome common problems by:
- Forcing air into the center of the bin
- Providing a drying front that conforms to the grain
- Reducing static pressure
- Increasing fan efficiency up to 20%
- Reducing drying time by up to 50%
C) By reducing drying time and drying grain uniformly, operation costs can be reduced. An independent test of 3,000 bushels of canola showed Grain Guard's Helfer duct system dried canola 17% faster and more uniformly than a conventional full floor aeration system.
2. Proper Cubic Feet of Air Per Minute (CFM) Air Flow Required Per Bushel
To dry grain: 3/4 - 1 CFM per bushel (8.5-17L/sec/tonne)
To aerate and condition grain: 1/10 CFM per bushel (2L/sec/tonne)
A) How can I successfully air-dry my grain?
Successful natural air drying requires the proper-sized aeration fan. The fan must force 3/4 - 1 CFM through the bin of grain in order for moisture to be drawn out and expelled from the bin. More air does not always mean faster drying, but not enough air can dramatically reduce the effectiveness of natural air drying.
B) How do I select a fan?
A general rule of thumb for selecting a full centrifugal fan is: 1 hp per thousand bushels to within 500 bushels of the maximum. Example: 1,200 to 2,500 bushels = 3 hp fan. For 2,500 bushels plus, you need to ask yourself the following questions:
1) Is the eave height of my bin over eighteen feet?
Taller bins create a higher static pressure.
2) Will I be drying small seeds such as canola or mustard?
Small seeds pack tighter and create a higher static pressure.
If you answered yes to any one of those questions above, you should probably move up one fan size. In the example above, you would increase the fan size to a 5 hp centrifugal fan.
C) Would a larger fan dry twice as fast? Example: A 7.5 hp fan on a 2,000 bushel bin.
No, power would be wasted, unwanted static pressure would be created, and the grain would not dry any faster than a fan properly sized for the bin of grain.
Airflow charts and fan specs can be found in the fans section under each fan type.
3. Warm Dry Air
A) It's the movement of warm, dry air through a bin that dries grain. Therefore aeration/drying is most effective when these low humidity (warm, dry air) conditions prevail. With these conditions present, combined with a proper sized fan and a Grain Guard rocket system, you can expect to draw out approximately 3/4 - 1% of moisture over a 24 hour period.
B) High humidity (cool, moist air) or night-time conditions reduce the effectiveness of natural air drying. For example, if outside humidity levels of 79% or higher are reached, the drying process of wheat at 16% moisture will stop.
At this point, the grain remains conditioned (unchanged) until humidity levels drop again for the drying front to proceed. The use of low temperature propane or natural gas supplemental heaters can be added to increase the outside air temperature by 10-12 degrees Celsius (18-20 degrees Fahrenheit) and lower humidity by up to 50%.
By adding the supplemental heater and allowing the drying process to continue during high humidity conditions (evenings and wet cool days) approximately 1/2 - 3/4% of moisture can be drawn out per day.
Propane and Natural Gas Low Temperature Supplemental Heaters
C) DO NOT shut your fan off at night when drying high moisture grain (16% - 20%), with or without supplemental heat use. Shutting the fan off can cause the drying front to stop moving, and can restrict air flow.