19
NOTES ON LOW TEMPERATURE DRYING
LOW TEMPERATURE DRYING:
Low temperature drying is used to achieve a 25% drop in relative
humidity. Raising the outside temperature (ambient) by no more than 10 degrees, when using an axial
or centrifugal fan producing 2/3 to 3 cfm per bushel, and a Super –Low heater will achieve this. Keep in
mind, we suggest a grain spreader for your bin and this type of drying should be in a situation where you
are using your bin to dry one full bin per year (not for continuous flow drying). All super low heaters
come equipped with thermostat and under bin thermometer. Never exceed 15 degree temperature rise;
this can cause a number of problems like over drying, and cause a crusted condition resulting in bin
failure that is not covered by the bin manufactures warrantee.
Low Temperature Drying Depends On Several Important Variables;
Weather- Since little heat is used to control the relative humidity, operation of drying systems should
only take place when average daily temperature is between 30 and 50 degrees F. When temperature is
above 50 degrees F, allowable storage time may not be long enough to dry grain before it spoils. Below
30 degrees F, drying should be delayed until warmer weather because drying rates will be slow.
Airflow- Proper airflow levels must be maintained to dry grain before any spoilage begins. Insufficient
airflow will cause spoilage before drying is complete.
Moisture Content- The wetter the grain is, the faster the spoilage. More airflow is needed for wetter
grain because the grain dries more slowly and its allowable storage time is less. Typically, 1CFM is
required for 20% moisture corn, 2 CFM for 22%, 3 CFM for 24%, 4 CFM for 26%. Drying speed is
proportional to airflow. If airflow is increased 25%, then the drying rate also increases by 25%. The more
air delivered, the faster the drying front will move through the grain and greater the amount of water
removed and thus the more reliable the system.
Amount of Heat Utilized- The aforementioned (2-10 degrees F maximum) must be adhered to at all
times. When adding supplemental heat, the recommended airflow must not be reduced, nor should the
bin be loaded with grain wetter than recommended. The added heat helps to control the relative
humidity of the drying air to obtain the desired final moisture content and prevent rewetting during an
extended period of damp, cold weather. Heat should only be added when the relative humidity exceeds
70% to avoid over drying and minimize energy costs.
Managing A Low Temperature Drying System:
→ Use shorter season grain variePes to get lower harvest moisture content
→ Wait unPl average daily temperatures are between 30 degrees F and 50 degrees F.
→ Wait unPl harvest moisture contents are within the capabiliPes of your system.
→ Clean grain to reduce resistance to airflow and improve storability
→ Use a grain spreader to level grain, even distribuPon of grain is essenPal for uniform drying.
→ Start fans and open hatches when floor is covered.
Filling Procedures
On the initial fill, never exceed the maximum wet grain depth shown on drying guide table
(see page
21).
Exceeding the initial depth will result in spoilage. Refer to drying guide table for approximate drying
times for the initial fill. You may add additional layers of grain after initial fill dries. If the moisture
content of the second fill is equal to the initial fill, add one-half of the initial fill depth than the initial fill,
add two-thirds of the initial fill depth every 7-10 days until the bin is full. If moisture content of the
