Heat Energy Content of Shelled Corn

 

The energy content of shelled corn is not a constant value because of biological variability and management factors. Generally, the energy content of corn is in the range of 8,000 to 8,500 BTUs per pound of dry matter. A BTU (British Thermal Unit) is a unit measure of energy. One BTU is the amount of heat energy needed to heat one pound of water one degree Fahrenheit. The factors that may influence the energy content of corn include variety of corn, soil fertility, weather conditions during growing season and at harvest, stage of maturity at harvest, drying method, and storage conditions.

 

It needs to be emphasized that the energy content of shelled corn is in the range of 8,000 to 8,500 BTUs per pound of dry matter based on bomb calorimeter studies. The term "dry matter" refers to material that is "bone dry." The standard moisture content of shelled corn is 15.5 percent moisture on a wet basis. This means that each pound of shelled corn will actually consist of 0.845 pound of dry matter and 0.155 pound of water. Using a median energy content value of 8,250 BTUs per pound of dry matter, the energy content of one pound of shelled corn at 15.5 percent moisture is then 6,971 BTUs (8,250 BTUs per pound dry matter x 0.845). The figure of 6,970 BTUs per pound is referred to as the higher heating value (HHV).

 

The HHV needs to be further reduced because of the energy required to vaporize the 0.155 pound of water in the shelled corn since this energy is unavailable for heating purposes. The energy needed to evaporate the water is approximately 163 BTUs (1,050 BTUs per pound water x 0.155 pound). The net available energy content of a pound of shelled corn with a moisture content of 15.5 percent is then 6,810 BTUs. This value of 6,810 BTUs per pound of shelled corn is known as the lower heating value (LHV), a reduction of nearly 17.5 percent when the moisture content is taken into account. The actual energy content of shelled corn would be even lower if pieces of cob, husk, or stalks are mixed in with the shelled corn.

 

The tradition in the United States is to compare the thermal energy content of various fuels on the basis of HHV, whereas in Europe the standard practice is to use the LHV. In the Energy Selectors on this Web site, the energy content for shelled corn is assumed to be of 6,970 BTUs per pound of shelled corn for all the analysis, along with an assumed overall seasonal thermal efficiency of 75 percent. Whenever reviewing commercial literature, be especially cautious of the recommendations and conclusions if the analyses are based on an energy content of the corn higher than 7,500 BTUs per pound of shelled corn and/or an overall thermal efficiency of 80 percent or higher.

 

Unfortunately, some manufacturers of corn stoves use the energy content figures of 8,000 to 8,500 BTUs per pound as though these figures were the energy content of the actual shelled corn itself. They frequently multiply energy content by the number of pounds in a bushel (56 pounds) and then report an energy content of 448,000 to 476,000 BTUs per bushel of shelled corn. Figures as high as 10,000 BTUs per pound or 560,000 BTUs per bushel have been used in some analyses. Whenever these exaggerated energy contents are used in any analysis, considerable distortion will occur in the results.