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Energy costs for corn drying and cooling

Grain needs to be dry to be stored through warm weather, but it takes energy to remove moisture from grain.

Fortunately, there are things growers can do to estimate the costs of drying and cooling corn and manage energy use.

Gas-fired drying

Energy use per bushel per percentage point of moisture removed for gas-fired drying varies widely among dryers. Plus, the percent of moisture to be removed varies widely from field to field and year to year.

However, energy use per bushel per percentage point of moisture removed is fairly consistent for a dryer that’s similarly managed from one year to the next.

The best source for energy use information about drying is actual records on the quantity of grain dried, amount of moisture removed and energy used to remove that moisture.

We encourage managers of gas-fired dryers to collect the information necessary for calculating annual drying costs. In some cases, you may want to install extra gas and/or electric meters to get the needed data.

If you don’t have information from actual records, use the following figures to roughly estimate energy use for gas-fired drying.

These figures do not factor in the energy savings that would result from recirculating part of the dryer’s exhaust air. Note that liquefied petroleum gas (LPG) is mostly propane.

Estimated energy use for gas-fired drying:

Burner: 0.02 gallons LPG per bushel per percentage point of moisture removed

For dryers that use natural gas, the equivalent number would be about 0.0184 cubic feet of natural gas per bushel per percentage point of moisture removed.

Fans: 0.01 kWh electricity per bushel per percentage point of moisture removed

Factors that affect gas-fired dryer energy use

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Natural-air drying

Energy use for natural-air drying – specifically, the electricity for operating natural-air drying fans – is very weather- and airflow-dependent, but can be predicted for given weather conditions and airflow.

Guidelines for natural-air corn drying in the Upper Midwest

The best information source about energy use for natural-air drying is several years of farm records for moisture removed, bushels dried and electricity used. The more years of records, the better, because energy use per bushel can vary greatly from year to year.

University of Minnesota drying studies, based on many years of weather data, indicate the following electric energy use values are reasonable averages for drying corn from 21 percent moisture to 16 percent. This assumes the drying bin is equipped with a fan that can supply 1.0 cubic foot of air per minute per bushel (cfm/bu) of grain in the bin.

Note that you can hold 16-percent-moisture corn through the winter, but you’d need 15 percent moisture or less for storage in warmer weather.

Average fan energy use – shown as kilowatt hours per bushel of grain dried (kWh/bu) – for natural-air drying corn in southern Minnesota, from 21 to 16 percent moisture at 1.0 cfm/bu:

  • Oct. 1 harvest: 0.75 kWh/bu

  • Oct. 15 harvest: 1.0 kWh/bu

  • Nov. 1 harvest: 1.25 kWh/bu

Factors that affect natural-air drying energy use

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Combination drying

Combination drying uses a gas-fired dryer to dry corn from high harvest moisture down to about 21 percent moisture, then uses a natural-air dryer to dry the corn to a safe storage moisture.

Use the energy values given earlier to arrive at a total energy cost for combination drying.

Cooling and aeration

The energy needed to cool hot grain from a gas-fired dryer or cooling grain for winter storage depends primarily on the fan motor’s size and the number of hours the fan operates. Note that hot corn transferred directly into storage should be cooled to outdoor temperatures within about 24 hours after it leaves the dryer.

The fan size, fan operation time and fan energy use required for changing grain temperature are much smaller than the fan size, fan operation time and fan energy use required for changing grain moisture.

Estimates

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Example energy cost calculations

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Other drying costs

Although energy costs for grain drying are very important, don’t forget to consider other grain drying costs when comparing drying systems.

The total for the other costs of owning and operating a grain dryer can sometimes be as much as energy costs. Other costs include things like:

  • Equipment costs for dryers.

  • Holding bins.

  • Conveyors.

  • Controls, such as depreciation, taxes, insurance, maintenance, and repairs.

  • Labor to operate drying systems.

Additional factors that might be harder to quantify include:

  • Quality of dried grain (quality is usually better for slower, lower-temperature systems).

  • Lost marketing opportunities for grain that’s not dried immediately after harvest.

  • The value of storage space you get with in-storage drying systems.

William Wilcke, emeritus Extension engineer

Reviewers

R. Vance Morey, emeritus agricultural engineer, College of Food, Agricultural and Natural Resource Sciences and Lizabeth Stahl, Extension educator

Reviewed in 2018

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