Simple Aeration Fan Controllers for Hard Red Winter Wheat in North America

Air Relative Humidity | Instructions for Electricians | HRWW Aeration Guide

Aeration Fan Management

The grain aeration fan is a simple, dumb device. It does but one thing - move air - and has but one control - the “on-off” switch. The success of grain aeration depends completely on the knowledge and accuracy of the fan operator. Several companies sell devices that automatically activate or de-activate the fans, depending on the objective of the aeration.

• Hold the tarp in place: Some fans on covered grain bunkers are controlled by a wind-speed monitor. The objective is to turn some fans off on calm days to reduce cost while ensuring that all fans are operating when the wind is strong and maximum suction is needed to hold the tarp in place.
• Condition grain to a target moisture and temperature: Programmable fan controllers operate aeration fans in an attempt to condition the grain to the moisture content and temperature selected. Air temperature and humidity have to be measured constantly while a computer program computes the relative usefulness of the air to condition the grain to the programmed moisture.
• Cool with minimum cost: Simple fan controllers use a common, dry-bulb thermostat to operate the fan only when the air is cooler than the level chosen by the operator. These devices are much less expensive than the programmable controllers, and are useful when the objective is to cool grain at minimum cost.

The simple (non-programmable) fan controller often is cost effective in the hard red winter wheat belt of North America where wheat is harvested at the beginning of the warm season. Wheat usually arrives from the field with a temperature of 90ºF to 110ºF (32 – 43 ºC), which makes it vulnerable to deterioration by molds and insects during storage. Research has shown that cooling it to a more moderate temperature (85ºF or lower) within a few days of harvest greatly reduces the rate of quality deterioration. Cooling to 60ºF or lower would, of course, provide greater protection, but the ambient air is not cold enough until late fall.

The grain manager who wishes to efficiently cool HRWW under this scenario (early summer and hot, dry grain) must insure that only cool air is passed through the grain. To do this, the manager must select the appropriate “target air temperature”, the upper temperature limit. Reviews of historical weather data have demonstrated that 70 - 75ºF, depending on the latitude, is the appropriate “target air temperature”. That is, in most parts of the HRWW production area, the ambient air will be cooler than 75ºF long enough in the three-week period immediately after harvest that cooling can be completed in most bins. However, the ambient air is likely to cool to the “target temperature” after business hours, and may warm to above the “target temperature” before time to go to work. Under these conditions, a thermostat-based, mechanical device operates the aeration fans more efficiently than a human being could.

Simple (non-programmable) aeration controllers can be purchased - or built - with or without a humidistat. Immediately after wheat harvest, air that is cool enough to use for aeration is likely to be moist. High relative humidity air does not retard the process of aeration, although it leaves the wheat slightly warmer than would dry air of the same temperature. Happily, moist air provides a huge benefit in this situation because it dries the wheat less than would dry air. Moisture loss, or “shrink”, is a major cost of wheat cooling, and is directly related to the value of the grain. When wheat prices increased in 2007 and 2008, so did the cost of each tenth of a percent of shrink. At $10/bushel, each 0.1% shrink costs 1¢ per bushel, leading to immediate pay-back on technologies that increase efficiency in elevator operations (i.e., precision grain management, automated aeration fan control, modern personnel management techniques, etc.). Because high-humidity air is beneficial and low-humidity air is unlikely, I don’t recommend humidity control for this application.