Running the aeration fan continuously has been the conventional wisdom since aeration fans came into existence. The truth is that no one really knew what was going on, and that eventually the grain would come down in moisture content. But there also was this lingering feeling that there must be times when drying was occurring and times when it was not.
I have also heard, many time, that one must keep their fans running because if you stop it, the moisture layer will collapse and a crust layer will form. So, maybe it is safer to just leave it on. And since we don’t really know when the conditions for drying are, maybe it is best to just leave it on. Let’s address this one first.
In all the data we have collected at Indian Head, since 2007, we have never seen a distinct drying layer, or moisture band. We have certainly see the bottom dry first, and in many cases at the end of the trial run, the top of the bin is still tough, while the bottom is over-dry. But there is no distinct layer, or even pockets of moisture. The change in moisture from one part of the bin to another, is a slowly changing continuum. And when the fan is shut off, the temperature and moisture of the grain more or less remain constant, or at the very least changing ever so slowly. Turning the fans off, is not the culprit reason for a crust forming.
Now for the other reason we leave the fans on: we don’t know when the conditions are right for drying. Well, now we do. We know the typical diurnal drying cycle and with the grain calculator one can exactly tell when there are drying conditions, and ever for conditions of condensation. So not knowing when we have a drying condition, no longer is a valid excuse for running the fans continuously.
So what’s the problem in running your fans continuously? In short more spoilage. Grain starts to deteriorate as soon as it comes off the combine. Storing grain can only slow down the spoilage process and there are two things that contribute to spoilage: higher grain temperatures and higher grain moisture. If you run the fan continuously during the day, there is a very good chance that you will be heating and wetting the grain — the exact things that contribute to spoilage.
To summarize, running the fan continuously will:
- Produce more spoilage
- Use more energy
- The Figure below is an example of a run done in 2009. In the first few hours of operation the amount of water being removed from the bin is quite high. It was not unusual to have one percent moisture removed from the grain on the first day. But at hour 21, we see something strange take place, the amount of water leaving the bin becomes negative; we are adding water to the bin. We are now into a well established 24 hour cycle of water being removed from the bin and then water added to the bin — almost equal amounts. After the first 21 hours, there is essentially no drying taking place. We are literally spinning our wheels, taking water out of the bin, and then putting it back in. And to make things worse we are adding the moisture during the day, as we heat the grain. Warming the grain, and wetting it at the same time are just the conditions necessary to promote spoilage.