When Should I Turn the Fan On or Off? But Only have Temp Sensors

In the last blog, I talked about the ultimate controller that used moisture cables with temperature and relative humidity sensors.   But what if I don’t have this T/RH sensor cable — I only have temperature sensors?  Well, we can still do a pretty good job of turning the fan on only when the conditions are right for drying.  How, by using the grain drying calculator .  This calculator determines if conditions are right for drying, but it is subject to the accuracy of the EMC equations, whereas the ultimate controller does not require EMC equations other than to determine the MC of the grain.  Also the ultimate controller uses water balance to turn the fan off, whereas again this method requires the calculator to both turn the fan on and off.

Here is what you do; again it is important to get the fan going immediately upon filling the bin.  Then every hour one makes a calculation by entering the moisture content  (MC) of the grain, the temperature of the grain, and the temperature of the outside air.  The calculator returns a threshold relative humidity ( RHthres ) for several grains.  If the outside RH is less than this threshold, then we have drying conditions.  The greater this difference, the more drying will take place.  So we would turn the fan on.   If however the RHthres is less than the outside air RH, then the fan would be turned off.  Because conditions can change rather quickly, this calculation and  a decision should be made every hour or so.  This process would continue until  the average MC (as measured manually with a  sampling probe).  The bottom will as always dry first, but it is not necessary to continue the process until the top is dry, but only until the average is dry.  When the grain is pulled out, it will blend to give an overall dry.  The top, even if it is a bit tough, will not spoil because it will be cooled with this overall process and therefore be safe from spoilage.

After the process is terminated, the temperature of the grain should be monitored, and if the grain temperature begins to rise substantially, then the process should be restarted.  One might not have to do this all winter, but in the spring and summer the process may be used to keep the grain cool.

If one is not sure about the MC of the grain, then the dry level should be entered into the calculator.  For example, wheat may have been put into the bin, some being 14.2%  some at 15.1%  and another unknown quantity at 14.9%.  The dry level for wheat is 14.5%, so that is what should be put into the calculator, and it will do the calculations for drying the grain to this level.

This calculator is not quite as good as the ultimate control strategy, but it is pretty close.  It relies on the accuracy of the EMC equations, and it also requires manual measurements of the MC to determine the average MC and thus when the process can be terminated.