Management of temperature and moisture content (MC) are key to successfully store grain. The most economical means to prevent spoilage and increase grain value is with aeration. This requires fundamental information and proper implementation for success:
|Grain MC||Ambient weather|
|Grain temperature||Goal (Target)|
|Airflow capacity||Current weather||Market prices|
|Frost damage||Airflow direction||Predicted weather|
|Transportation||Foreign matter||Grain depth|
|Time of year||Delivery date||Artificial drying|
Fan On/Off Frequency
A common recommendation has been to run a fan long enough to move a front all the way through the grain before shutting off the fan.
Diurnal (day and night) changes usually present a big swing in temperature and Relative Humidity (RH). As the temperature increases the RH drops. Selecting fan run times when these are near a TMC and a targeted temperature will introduce consistent conditions into the grain which will achieve better uniformity with fewer fan hours.
Chart 1 illustrates temperature and RH over a week. The gold targets show the limited conditions during this week for fan operation that will introduce consistent air. This policy achieves maximum progress toward the TMC and avoids run times that would start to move the grain away from your TMC so more is accomplished with fewer hours.
The sweet spot for aeration is reflected in this chart of T and RH.
The chart illustrates the large inverse swing each day between daytime and nightime weather conditions. It does not reflect actual conditions for a week.
The targets in Chart 1 show limited run time during these 7 days. Higher CFM per bushel airflow rates allow for being fussier on run times. This results in better uniformity quicker.
Fronts don’t present problems when they consist of small differences between the grain and the properties of the air – temperature and RH combination – being blown through it. Small fronts also average out because of the diurnal effect nearly each day.
There is no danger from shutting off fans if the next time the fan is activated the outside air conditions are near the conditions the last run time. It doesn’t matter whether it is off a few hours or a few days (assuming the grain is somewhat close to normal storage MC and not of high temperature).
Wet grain in a bin needs continuous air almost regardless of the outside conditions. This is because the drying front will leave the top of the grain sooner than if fans are shut off even though some rewetting may begin in the bottom. The bottom grain acts as a buffer and dries and re-wets to deliver a somewhat uniform MC above it. However once a drying (curing) front has moved through a grain mass so the top is within a 'safe' condition, stopping continuous fan operation saves energy.
A uniform temperature and MC will start to be achieved if the fan is activated when outside conditions are near a targeted temperature and MC combination. (An example: corn above 20% should not have fans stopped unless it is for a few hours at low temperature – < 40 F and confidence exists that the temperature is this low throughout the bin).