Grain Storage Systems | University of Kentucky College of Engineering

# Grain Storage Systems

### UK Calculator for Stored Grain Capacity, Bin Sub-floor Volume and Wall Area

Dr. Sam McNeill, Extension Agricultural Engineer

As corn and soybean harvest approach, stored grain managers on farms, elevators, and warehouses are preparing different types of structures for service. This may include applying approved insecticides or grain protectants to guard against damage caused by insects during storage.

The recommended rate for most stored product protectants is based on either the volume of grain (bushels) or void space (cubic feet), or surface area of the grain or structure (square feet) to be treated.

The UK storage volume calculator has always included tables that show the capacity (in bushels) of conventional round bins, horizontal storage structures (such as machinery sheds and warehouses), large round piles/rings, grain bags and corn cribs. It now includes a new worksheet to calculate the surface area of bin walls and grain piles, as well as the volume of the space below perforated floors and air space above the grain surface.

### 2022 Decision Tool Updates for Grains

Equilibrium Moisture Content for Grains

Prepared by: Sam McNeill, PhD, PE

Moisture exchange between grain and the surrounding air is driven by differences in vapor pressure. An equilibrium state is reached when there is no net exchange of water vapor between the grain and air. This has important implications in grain drying and storage systems. As air is warmed, the relative humidity is reduced along with grain moisture (drying process). When dry grain is placed in storage and cooled, grain moisture remains constant and the relative humidity of the air surrounding it is lower.

Equilibrium moisture properties have been determined for different grains and are reported as a Standard by the American Society of Agricultural and Biological Engineers. In general, mold growth is suppressed during storage when the environment is maintained at a relative humidity level of 65% or lower, and insects are suppressed at temperatures below 60 F.

Implications for drying – Grain will reach the moisture levels shown in the tables when exposed to the corresponding temperature and humidity levels for a sufficient period of time, which depends primarily on temperature and airflow. This can occur in the field or a bin. In a bin, drying time will depend on the airflow rate through grain, which in turn depends on the depth of grain. The minimum drying rate for natural air drying is 1 cfm/bu, but this can take up to a month to dry the top layer depending on the grain and air conditions--during which time spoilage can occur.

Implications for storage – The stagnant air space between grain kernels in a bin or bag will have the humidity indicated at the corresponding moisture and temperature. For example, 15% corn at 60 degrees will generate a relative humidity in the air space between kernels of 70%, but when cooled to 45 degrees will have a relative humidity of 65% (Table 1). Similar data for soybean, soft red winter wheat and grain sorghum (milo) are shown in Tables 2-4, respectively. Additionally, a new calculator is available for twelve other grains and oilseeds that are grown in Kentucky, as shown in Table 5.

Temperature Relative Humidity (%)
10 20 30 40 50 60 65 70 80 90
C F Equilibrium moisture content, %wb
2 35 6.5 8.6 10.3 11.8 13.3 14.8 15.7 16.6 18.7 21.7
4 40 6.2 8.3 9.9 11.5 12.9 14.5 15.3 16.2 18.3 21.3
10 50 5.7 7.8 9.4 10.9 12.3 13.8 14.7 15.5 17.6 20.5
16 60 5.3 7.3 8.9 10.3 11.8 13.3 14.1 15.0 17.0 19.9
21 70 4.9 6.9 8.4 9.9 11.3 12.8 13.6 14.4 16.4 19.4
25 80 4.6 6.5 8.0 9.4 10.8 12.3 13.1 14.0 16.0 18.8
32 90 4.2 6.1 7.7 9.1 10.5 11.9 12.7 13.5 15.5 18.4

Source: ASAE Data D245.4 / Average of two prediction equations.

Temperature Relative Humidity (%)
10 20 30 40 50 60 65 70 80 90
C F Equilibrium moisture content, %wb
2 35 4.2 5.3 6.5 7.8 9.4 11.5 12.8 14.4 19.1 28.9
4 40 4.1 5.3 6.4 7.7 9.3 11.3 12.6 14.2 18.9 28.7
10 50 4.0 5.2 6.3 7.6 9.1 11.1 12.4 14.0 18.6 28.2
16 60 4.0 5.1 6.2 7.4 8.9 10.9 12.2 13.7 18.3 27.8
21 70 3.9 5.0 6.1 7.3 8.8 10.7 11.9 13.5 17.9 27.3
25 80 3.8 4.9 6.0 7.2 8.6 10.6 11.8 13.3 17.7 27.0
32 90 3.7 4.8 5.8 7.0 8.4 10.3 11.5 13.0 17.3 26.5
Source: ASAE Data D245.5 / Modified-Halsey equation.

Table 3. Equilibrium moisture content of soft red winter wheat (%wb) at different temperature and relative humidity levels.

Temperature Relative Humidity (%)
°C °F 10 20 30 40 50 60 65 70 80 90
2 35 7.3 8.9 10.2 11.3 12.3 13.4 14.0 14.7 16.1 18.2
4 40 7.1 8.7 10.0 11.1 12.1 13.2 13.8 14.4 15.9 18.0
10 50 6.8 8.4 9.6 10.7 11.8 12.9 13.4 14.1 15.5 17.6
16 60 6.5 8.1 9.3 10.4 11.4 12.5 13.1 13.7 15.1 17.2
21 70 6.2 7.8 9.0 10.1 11.1 12.2 12.8 13.4 14.8 16.9
25 80 6.0 7.5 8.7 9.8 10.9 11.9 12.5 13.1 14.5 16.6
32 90 5.8 7.3 8.5 9.6 10.6 11.6 12.2 12.8 14.2 16.3
Source: ASAE Data D245.4 / Average of two prediction equations.
Temperature Relative Humidity (%)
°C °F 10 20 30 40 50 60 65 70 80 90
2 35 7.3 8.9 10.2 11.3 12.3 13.4 14.0 14.7 16.1 18.2
4 40 7.1 8.7 10.0 11.1 12.1 13.2 13.8 14.4 15.9 18.0
10 50 6.8 8.4 9.6 10.7 11.8 12.9 13.4 14.1 15.5 17.6
16 60 6.5 8.1 9.3 10.4 11.4 12.5 13.1 13.7 15.1 17.2
21 70 6.2 7.8 9.0 10.1 11.1 12.2 12.8 13.4 14.8 16.9
25 80 6.0 7.5 8.7 9.8 10.9 11.9 12.5 13.1 14.5 16.6
32 90 5.8 7.3 8.5 9.6 10.6 11.6 12.2 12.8 14.2 16.3
Source: ASAE Data D245.4 / Average of two prediction equations.
Temperature Relative Humidity (%)
°C °F 10 20 30 40 50 60 65 70 80 90
2 35 6.5 8.6 10.2 11.6 13.1 14.6 15.4 16.3 18.5 21.7
4 40 6.3 8.3 10.0 11.4 12.9 14.4 15.2 16.1 18.3 21.6
10 50 5.9 7.9 9.6 11.1 12.5 14.1 14.9 15.8 18.0 21.3
16 60 5.5 7.6 9.2 10.7 12.2 13.7 14.6 15.5 17.7 21.0
21 70 5.1 7.2 8.9 10.4 11.9 13.4 14.3 15.2 17.4 20.7
25 80 4.7 6.9 8.5 10.1 11.6 13.1 14.0 14.9 17.1 20.5
32 90 4.4 6.6 8.2 9.8 11.3 12.9 13.7 14.7 16.9 20.2
Source: ASAE Data D245.6 / Modified Chung-Pfost prediction equation.

Similar tables for barley, canola, chickpea, ear corn, millet, oats, peanuts, popcorn, rough rice, rye, and hard red winter wheat and white corn are available at: www.uky.edu/bae/ext/grain-and-energy-calculators

Temp.°F RH % Grain EMC % wb

70 65 Barley 14.3
Canola 8.3
Chickpea 12.9
Corn-White 13.5
Corn-Yellow 13.6
Ear Corn 10.9
Grain Sorghum 13.6
Millet 17.8
Oats 12.2
Peanut 6.8
Popcorn 13.6
Rough Rice 13.1
Rye 10.5
Soybean 11.9
Wheat, HRW 14.0
Wheat, SRW 13.0