- Agronomic: corn
- Energy: energy conservation/efficiency
Natural air grain drying can be a cheaper alternative to drying corn using LPG but is still energy intensive because of the limited drying season in the fall before declining temperatures prevent ambient air from drying corn to targeted moisture contents. Decreasing airflow rates by extending drying over a longer period in the fall and winter can save substantial amounts of energy for fan operation but can only be done if the drying air is heated to lower the relative humidity enough to meet targeted grain moisture contents. To be economically practical this would require an inexpensive energy source for heating the air. In this project, ground-stored (geothermal) heat was used to modify the drying air temperature and relative humidity to maintain optimum drying conditions throughout an extended drying period. Because ground heat was so inexpensive to deliver to the fan and cutting airflow rate resulted in much smaller fan horsepower requirements drying cost and energy use were substantially reduced. Results of the project were presented in an article published in the January, 2019 newsletter for Iowa State University’s Ag Decision Maker website. The successful results of this project can be replicated by farmers that have a good grasp of the principles of low-temperature grain drying.
Cutting drying airflow rates in half and doubling the drying period would move the same volume of air through a grain column but reduce the required fan to only 19% as large and would accomplish drying using about 40% of the energy for fan operation.
|Approximate kWh to move the same volume of air at different airflow rates|
During the winter soil temperatures remain warmer than air temperatures and closer to the average annual temperature. In early October air and soil temperatures are very close. But by late December soil temperatures 4 feet below the surface in northern Iowa are 15 to 20 degrees warmer than air temperatures. This project proposed to use ground-stored heat collected by circulating an antifreeze and water solution through buried polypropylene water lines through a heat exchanger in front of the drying fan to maintain optimum drying air conditions throughout a drying period that was extended into the winter for very little additional energy cost for pumping water. The objective was to use ground heat to maintain optimal drying conditions to substantially lower fan operation costs and energy consumption by using a smaller fan during the extended period. The objective of the second year of the project was to further reduce the required fan size by extending the drying season throughout the winter, thereby further decreasing drying cost and energy use.
|Average temperature in the fall for Osage and the temperature increase required for relative humidity to decrease enough to equilibrate with 15% and 14% moisture content corn|
|Temp, F||EMC RH||required temp increase||EMC RH||required temp increase|
|Hypothetical drying air temperature increase, based on average air and soil (52″ depth) temperatures at Nashua, Iowa over the period 2014 – 2018. The drying air T assumes heat recovery of 40% of the difference between soil T and air T and includes a small increase from fan operation (¾ degree F)|
|period ending||Cumulative days||50” soil T||ambient air T||difference||Drying air T increase||Drying air T|
|* Northeast Iowa Research and Demonstration Farm in Nashua, Iowa|
|** Relative humidity of ambient air during this period would average about 80%. The drying air temperature increase would reduce the relative humidity of the drying air to approximately 57%, which would equilibrate with corn at a moisture content just under 15%|