Do high daytime headspace air temperatures in steel bins tend to reheat the grain in steel bins during suction aeration?
Steel bin headspace air does get very hot from solar radiation absorbed by bin roofs. Air temperatures of 120-130F are common during the warmest part of the day. This temperature starts dropping late in the day. During the night, headspace air temperatures usually drop to within a few degrees of outside air temperatures. The top 2-3 inches of the grain surface will tend to cycle up and down. However, suction fans dilute and replace headspace air within the first 2-3 minutes of fan operation. For example, a 10,000 bu bin may have a total air volume of 15,000 cu ft and a headspace volume of 2,500 cu ft (1 bu = 1.25 cu ft, so 10,000 bu = 12,500 cu ft of grain). If the aeration fan generates 1,000 cfm (0.1 cfm/bu), it will take 2.5 minutes to replace the headspace air volume. Within 5-10 minutes (dilution time) and during the remainder of the time the suction aeration fan operates, the temperature of air moving through the headspace and into the grain surface will be outside air temperatur
