Natural air grain drying: testing of an automatic controller for managing bin aeration fans
To determine if calculating the water holding capacity of the air as a function of its temperature and relative humidity can be used as a control point for the operation of aeration fans.
The recommended management strategy for natural air grain drying is to run the fan continuously after harvest until the temperature of the stored crop has been cooled down. However, producers are interested in knowing whether there is a more efficient way to cool and dry grain without running the fan unnecessarily. The objectives of this project were to develop a fan control strategy using natural air that 1) resulted in the safe storage of grain, 2) is efficient and results in less fan running time, and 3) dries the grain sufficiently for imminent sales. The study consisted of completing measurements of freshly harvested grain from different crops including field peas, barley, and spring wheat, in typical farm-sized bins equipped with sensors. The temperature and relative humidity of the air entering and leaving the bin, along with air flow into the bin were recorded on an hourly basis. The net mass of water leaving the bin was calculated for each of the trial runs. It was determined that the net water removal tended to be greatest during the night while water addition or hydration tended to occur during the day. It was also observed that the drying occurred when the grain was being cooled which led to a simple control management practice of only running the fan when the outside air temperature was less than the grain temperature. This was successful in keeping the stored grain cool, safe, and in reducing fan running time. The results of this study have provided valuable insight in determining the relationship between the ambient conditions and the drying rate of the grain with natural air.