Short Answer for Grain Aeration

I get asked this straight forward question about grain drying all the time.
My cousin Mark recently emailed me:
I was reading an article about grain drying with aeration that you worked on.
 You mentioned that it is best to run fans at night.
We have some peas that are dry but with some green kochia and other weeds.
We will have the same with some wheat that we will combine soon as the Kochia will get swathed but I suspect it will not dry down much as we will combine in probably 5 – 7 days.
What is the recommended drying – cooling times and what concerns should I have with Humidity and Temperature?
Thanks
Mark
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I replied:
Mark:
I don’t have a really short answer to question, but even if you didn’t know anything else, this would be a good rule to follow — even if your grain is dry.
1.  As soon as your bin is full (even before it is full) turn the fan on and run it until 9:00 AM the next morning.  The exception to this rule would be if it is raining or very high humidity.
2. Thereafter, run the fan every night until your grain is cooled down and dry.  This might be for a few nights, or it might be for several weeks if you have tough grain.  The cold clear nights will be the most effective for drying.  Again if it is raining, don’t run the fans.
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OK that’s the simplest; if you want to be more precise about drying conditions, you would only want to run the fan when there are conditions for drying and that is when the absolute humidity of the air outside is less than the absolute humidity of the air in the bin.  Absolute humidity is the actual amount of water in the air.  It is not the same as relative humidity; but relative humidity can be used to calculate the absolute humidity.  And they are kind of ugly equations that are tough to do even with a calculator.  So, I made an internet calculator that does the calculations for you. It can be found at  planetcalc.com/4959/   You can load it onto your cell phone and use it like an app.  You simply enter the moisture content of your grain, the temperature of your grain, and the temperature of the outside air.  It calculates, what I call, the threshold relative humidity.  If the relative humidity of the outside air is less than this you will have drying conditions and the fan should be turned on.  If the outside air’s relative humidity is greater than this, you will not have drying conditions and obviously you should keep the fan turned off.  If you really want to get up to speed on grain drying, read my blog at grain-aeration.com   It explains everything, even why you get condensation in a bin and why the bottom always dries first etc.

Another rule of thumb that mostly works (98% accurate):  You will have drying conditions when the outside air is at a lower temperature than the grain temperature and the relative humidity of the air < 85%   This is not as accurate as the calculator because it does not take into account the moisture content of the grain; however it does not require any calculations or calculators

I hope this helps, let me know if you have any other questions
rjp

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Thanks a bunch Ron.
As long as the relative humidity outside is less than 85 in the evening – I will run the fans and turn them off in the morning
Last night Environment Canada showed the Humidity at 90% so I should not run them at that point
Mark

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