When Do I Turn On the Fans... And For How LONG??? Carol Jones, PhD. Stored Product Engineering Biosystems and Ag. Engr. Dept.

When Do I Turn On the Fans...

And For How LONG???

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

What’s the purpose?• Manage:

– Temperature– Moisture

• Properly managed..– Preserves quality – Helps to prevent insects

• 10% harvest lost every year– ½ due to poor storage procedures

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

What happens if we don’t aerate?

• Cool air outside

• Warm grain inside

• Convection Currents

• Move moisture

• Wet or spoiled grainat the top-center and/or on the cold wall

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

What does aeration do?

• Conditions grain and seed by– Lowering temperature in the grain– Equalizes temperature within the structure

• Prevents moisture migration and condensation

• Controls bacteria, insects, molds and mites

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

What does aeration do?

• Little insect reproduction occurs below 60F

• Eggs are controlled at 40F

• 40F is tough to do in some areas

• So fumigation is still required but can be reduced

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

When do we aerate?

• At Harvest:– Leave fans on continually until exhaust T is

close to same as (or less than) average air T– Usual day-night T difference is about 20°

• When outside air is 10° below grain temperature

• Ideal target is 40°, or as cool as possible

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

When do we aerate?• Cool in 15 to 20° stages

• Example:– If grain is 80°, wait for 55 - 65° weather and

cool until grain is cooled to that range– Then wait for the next drop of 15° to aerate

again.

• Monitor grain weekly to detect heat increases

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

How long will it take?• Goal: to move the cooling front through

the grain bulk.

• Depending on the season (1/10 cfm/bu):– Summer: 80 hours– Fall: 120 hours– Winter: 160 hours– Half that time if you use 0.2 cfm/bu

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

How do we know T?• Thermocouples throughout bin

– Permanently installed– Hung on cables

• Pipe with thermometers

• Temperature probe at least 3’ long

• CO2 monitor at exhaust of fan– Change indicates insect or mold activity

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

So what about RH?• Regardless of RH, harvest heat has to be

removed

• Then…– Equilibrium Moisture Content (EMC) RULES !– Point at which grain and air don’t exchange

moisture

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

So what about RH?• Example

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

RH at various Temperature

Grain MC 40F 60F 75F

13 54 61 65

12 47 53 58

11 40 45 51

10 33 37 44

So what about RH?• 1 – 2 days of rainy weather causes very

little change in MC

• Takes much longer to change MC than to change T

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

So what’s the plan?• Summary:

– Run fans night and day at binning until exhaust fan T is close to average daily T

– Then run fans only when air T is 10° less than grain until grain is about 40° if possible

– After desired T, operate a few hours each week to prevent musty odors

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Manual or Automatic?• Small grain storage: Manual

– Requires temperature and humidity information

– Thermometer and hygrometer

• Larger bins: Automatic

• Automatic will pay for itself by preventing shrink from over-drying and saving labor

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Automatic Controls

• Requires humidstat and thermostat

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Results of over-aeration• Grain shatter

– Grain is too dry– Temp. has dropped too quickly

• Excessive shrink

• Moisture can be added, but it’s slow and takes additional air capacity…careful monitoring

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Words of Caution• Make sure T front has moved all the way

through grain bulk

• Negative Pressure System: open vents before starting fans

• Positive Pressure System: watch for roof condensation…open vents

• Don’t cut corners on aeration…it never pays!

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources• EMC Tables

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources• EMC Tables (wheat, corn, soybeans)http://www.grainqualitycontrol.com/emc_drying.htm

• Temperature Probe

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources• Hygrometer

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources• Commercial controller

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources• Commercial controller (OPI System)

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Resources

http://biosystems.okstate.edu/Home/jcarol/index.html

Carol Jones, PhD.Stored Product EngineeringBiosystems and Ag. Engr. Dept.

Questions