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Two-year case study shows energy used for grain drying

pdf fileAgDM Newsletter
October 2015

With harvest time here, minimizing drying costs may be one of your goals. The field research conducted by the ISU Farm Energy team provides a benchmark to evaluate the amount of propane used for on-farm bin drying.

Mark Hanna, ISU Extension and Outreach ag engineer, led a team during the past two years to conduct field trials for bin drying. With support from the Iowa Energy Center, energy measurements during two drying seasons for 19 batches of corn in bin dryers with full perforated floors was collected.

mapWith assistance from our colleagues, measurements were collected in northeast, central, and southwest Iowa at the Northeast Research and Demonstration Farm, Nashua; the Ag 450 Farm, Ames; and the Armstrong Memorial Research and Demonstration Farm, Lewis.

Monitor drying conditions

As moisture leaves each corn kernel, the corn comes into equilibrium with the temperature and relative humidity of the drying air. The field trials confirmed that the amount of energy needed for drying is affected by incoming and final corn moisture, ambient air conditions during drying, and the degree of saturation reached by the drying air.

When total energy use was examined, propane accounted for 95 percent of the energy consumed for high-temperature bin drying. Electricity for fans and stirring equipment accounted for the remaining 5 percent. As expected, Figure 1 shows that wetter, incoming corn required more propane for drying.

textSpecifically, incoming corn at 23 percent moisture content required approximately 150 gallons of propane per 1,000 bushels (bu) of corn dried. However, incoming corn at 18 percent moisture content required only 75 gallons of propane to dry the same amount of corn to 15 percent moisture content.

Compare your crop

How can this information be used? If corn is being dried in bins, look up how many gallons of propane purchased for drying in each of the past two years. Then confirm the amount of corn dried with that propane and the average initial moisture content of that corn. How does it compare to Figure 1?

"The graph (Figure 1) illustrates a strong relationship between initial corn moisture content and propane use, which is useful for decision making," says Hanna. "For example, consider reviewing yield test reports for any full-season varieties you are using. Are they yielding enough to cover your costs to dry that corn?"

figure 1The graph suggests that approximately 15 extra gallons of propane, on average, will be needed to remove each point of moisture from 1,000 bu of corn. Yield trials conducted by the Iowa Crop Improvement Association show that full-season varieties adapted for each area are, on average, about 2.5 points wetter at harvest than adapted early-season varieties. Do the math and that adds up to 38 extra gallons of propane for every six acres of corn when drying is unavoidable. At a price of $1.50 per gallon for propane, this adds about $9.50 per acre to production costs.

For more information about the information found in this article, download the case study, "Energy consumption during grain drying," from the Extension Store at, or follow us on Twitter @ISU_Farm_Energy. Download other fact sheets, "Dryeration and Combination Drying for Increased Capacity and Efficiency" and "Managing High-Temperature Grain Dryers for Energy Efficiency." All publications are available free of charge.


Dana Schweitzer, Farm Energy Conservation and Efficiency Initiative, 515-294-5233,