Set-Point Drying: Drying to a Target Moisture Without Over-Drying

Grain that’s a little too wet for storage needs drying. Grain that’s dried too far loses saleable weight. The trick is to stop at exactly the right moisture — and that’s what set-point drying is for.

The over-drying problem

In-silo drying with ambient air works by moving a drying front up through the grain. The bottom dries first; the top dries last. Two things follow:

• If you stop when the bottom or the average looks right, the top layer may still be too wet.
• If you keep going until the top is dry, the bottom has been drying for longer and may now be well below target.

Without knowing what each layer is doing, most operators run fans “until it should be done” — and usually over-dry to be safe. Every point of over-drying is weight off the weighbridge.

What a set point means

Set-point drying turns the question around. You pick a target moisture — say 12% for wheat — and the system:

1. Measures moisture at every level of the silo.
2. Runs drying aeration when the outside air has drying power.
3. Judges progress on the wettest layer, not the average.
4. Stops when the wettest layer reaches the target.

You get grain that’s dry enough everywhere, and no drier than it needs to be.

Choosing air with drying power

Air dries grain when its equilibrium moisture — the moisture grain would settle at in that air — is below the grain’s current moisture. The bigger the gap, the faster it dries. Warm, dry afternoons have the most drying power; humid nights may have none, or may add moisture back.

A good set-point controller only runs on air that will make progress, and holds off when the air would undo it. (See Equilibrium Moisture Content Explained.)

You need drying airflow

Set-point drying needs fans that can actually dry. Typical cooling fans deliver around 2–4 litres per second per tonne — enough to cool, not to dry in a useful timeframe. Drying generally needs well above that. Check your airflow before relying on aeration to dry. (See Cooling Fans vs Drying Fans.)

Why the wettest layer matters

Judging drying by the average is the most common way to get caught out. A silo can average 12% with the top metre still at 13.5%. That top layer is where heating and mould start. Set-point drying watches that layer specifically.

How SiloSense helps

SiloSense IQ+ offers set-point drying for silos with drying airflow. Choose a target moisture and IQ+ dries to it, judged on the wettest layer, then stops. Its moisture guard keeps fans off whenever the air would push moisture back in, and a drying forecast estimates hours to target from the 7-day weather and your fan’s airflow and power.

Request a demo to see set-point drying on a live silo.