Grain Storage: Considerations to Maintain Quality: Part 3 - When To Aerate Grain?, Aeration Rates, H

Aeration Rates

How much air is needed to aerate grain in storage? The most common measurement of air is in cubic-feet-per-minute. Typical ratios of air to grain range between 0.05 to 0.20 cubic-feet-per-minute per bushel of grain. This would be the equivalent of 0.054 to 0.222 cubic meters of air per minute for each metric ton of grain. It is most common to design for 0.10 to 0.14 CFM/Bu (0.114 to 0.162 m3/min/ton). If you receive a proposal for an aeration system designed to Imperial measurements, look for air volumes close to 0.10 (1/10) CFM/BU or higher. Each system manufacturer will try to determine the most efficient system, taking into consideration available equipment, the volume and depth of the grain, and the most cost efficient system to purchase and operate.

How To Aerate Grain

The amount of time required to aeration a grain mass will depend upon the volume of air and the volume of grain. Given 0.10 (1/10) CFM/Bu of grain, the time required to aerate the grain mass is 100 hours. In this time, the temperature of the grain mass will rise or fall to the same temperature as the outside air.

If the volume of air is reduced by one-half to 0-.05 (1/20) CFM/Bu., the time required will double to 200 hours. If the ratio of air to grain remains constant, the size of the grain mass is not important the amount of time is relatively fixed.

Aeration Front

Understanding how the air moves through a grain mass is important to understanding how aeration works. Typically, air is pushed into the bottom of the grain mass, and exits the top of the grain mass. As the air moves, it creates a "front" . Grain temperature below the front is equal to the outside air. The front collects temperature and moisture for transport through the grain mass. When the front completely passes through the grain mass, aeration is complete.