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An audit you'll like

02/04/2013 @ 9:48am

If you've wondered if swapping out that old dryer for a new energy-efficient unit would pay for itself, you can get paid to find out. The USDA, through its Rural Energy for America Program (REAP), offers grants to conduct an audit of drying systems.

“Energy audits determine if dryers are operating efficiently and economically,” explains Ken Hellevang, an agricultural engineer at North Dakota State University. “The audit will enable farmers to compare their energy use to what is typically expected and to dryers with energy-efficiency features.”

To qualify for a grant, REAP requires an audit by a certified energy manager or professional engineer. Specialists can be hired to conduct an audit. For more information, go to www.rurdev.usda.gov/BCP_ReapEaReda.html.

Conduct an unofficial audit

You can also conduct an unofficial audit of your dryer. But that requires extensive math. The first step in that process is to determine the amount of water removed per bushel. To do this, you need to know the weight of grain before and after it's dried and the initial and final moisture content.

If the weight of the grain before or after the drying process is unknown, use this equation to determine that figure: 100 minus the actual moisture percentage of the grain divided by 100 minus the base moisture percentage. Next, multiply this number by the measured quantity. This is the unknown weight.

The actual moisture percentage is the moisture content of the measured grain, and the base moisture percentage is the moisture content of the grain that was not measured. The measured quantity should be the weight of 1 bushel.

After initial and final weights are determined, subtract the final weight from the initial to determine the amount of water removed per bushel. Next, calculate the amount of propane or natural gas per bushel by dividing gallons of fuel used by the number of bushels of grain dried. This figure will help determine the energy per bushel. For example, propane uses 91,600 Btu per gallon, so multiply the amount of propane per bushel by 91,600 Btu. Finally, divide the energy per bushel by the water removed per bushel. This is the energy used per pound of water removed.

For example, say you harvest 240,000 bushels of grain at 25% moisture and dry it to 14% moisture content. The average bushel weighs 56 pounds after being dried, and you used 45,000 gallons of propane to dry the corn.

To calculate the amount of water removed, take 100 minus 14, which is 86. Next, take 100 minus 25, which equals 75. Divide 86 by 75, and this gives you 1.147. Now multiply 1.147 by the measured quantity, or 56 pounds. This means the grain weighed 64 pounds when it was harvested, and the amount of water removed per bushel was 8 pounds.

Next, take 45,000 gallons of propane consumed divided by 240,000 bushels. This calculation gives you .188 gallons of propane used per bushel. Multiply this by 91,600 Btu to determine that 17,221 Btu's of energy were used per bushel. Finally, divide this by the water removed, or 17,221 Btu divided by 8 pounds, to find the energy used per pound of water. In this case, it would be 2,153 Btu per pound.

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