Decreasing Energy Use and Cost of Grain Drying by Extending Drying Period Using Ground-Stored Heat

Project Overview

FNC17-1080
Project Type: Farmer/Rancher
Funds awarded in 2017: $6,548.00
Projected End Date: 01/30/2019
Grant Recipient: Jellum Farm
Region: North Central
State: Iowa
Project Coordinator:
Eric Jellum
Jellum Farm

Information Products

Commodities

  • Agronomic: corn

Practices

  • Energy: energy conservation/efficiency

    Summary:

    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.

    Project objectives:

    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
    cfm/bu s.p. h.p. days Approx kWh
    0.25 0.52 0.35 210 1764
    0.5 1.22 1.63 105 4108
    0.75 2.1 4.2 70 7056
    1 3.13 8.35 53 10621
    1.25 4.3 14.36 42 14475
    1.5 5.62 22.49 35 18892
    1.75 7.06 33 30 23760
    2 8.64 46.13 26 28785

    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
        15%     14%    
      Temp, F EMC RH required temp increase   EMC RH required temp increase  
    15-Oct 51 67.68 1.7   61.07 5.0  
    1-Nov 43 63.84 3.6   57.31 6.8  
    15-Nov 36 60.48 5.3   54.02 8.5  
    1-Dec 27 56.16 7.4   49.79 10.6  
    15-Dec 20 52.8 9.1   46.5 12.3  
    1-Jan 16 50.88 10.1   44.62 13.2  
    15-Jan 14 49.92 10.5   43.68 13.7  
    1-Feb 16 50.88 10.1   44.62 13.2  
    15-Feb 21 53.28 8.9   46.97 12.0  
    1-Mar 26 55.68 7.7   49.32 10.8  
    average 27   7.4     10.6  
    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
    29-Oct 14 54.9 45.8 9.0 4.4 50.2
    12-Nov 28 51.1 35.0 16.1 7.2 42.2
    26-Nov 42 46.9 29.1 17.8 7.9 37.0
    10-Dec 56 43.9 27.4 16.5 7.4 34.7
    24-Dec 70 42.4 21.4 20.9 9.1 30.6
    7-Jan 84 39.9 10.1 29.8 12.7 22.8
    21-Jan 98 38.2 20.5 17.7 7.8 28.4
    4-Feb 112 37.6 13.9 23.7 10.2 24.1
    18-Feb 126 36.9 21.4 15.5 6.9 28.4
    25-Feb 133 36.7 19.5 17.2 7.6 27.1
    average   42.9 24.4 18.4 8.1 32.5
                 
    * 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%
    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.