In a previous blog, I explained how condensation could be a problem in the fall with warm grain and cold outside air. The rough rule of thumb was that there was a potential for condensation on the roof if the grain was ten degrees warmer than the outside; but a more precise determination could be made with the grain drying calculator. The recommendation was not to turn your fan on if the RH from the calculator was above 100%.
There is another time, in the spring that condensation could be a problem. When the grain is very cold and the outside air temp is much warmer and holding a fair amount of water. This air enters the bin through the fan entrance, the top or vents; and it hits the cold grain — it will cool past its dew point and condensation may well occur. This will happen mostly on the poor old top layer, that may well have had water dumped on it from fall condensation, and it is the last layer in the bin to dry. No wonder the crust always forms on the very most top layer.
To prevent condensation in the spring, the best thing to do would be to not let the warm air in. The bin should be sealed. The top lid closed tight, the fan covered and all vents covered. Indeed, this is a time when vents will actually be the cause for grain damage. Sealing the bin in mid winter, after the grain has been cooled to its lowest possible temperature, will also keep the grain as cold as possible for as long as possible. Yes the grain will still warm up from conduction through the walls; but it will be a warming without adding water. At the end of the summer, when the grain has warmed up and the nights again are getting cold, the bin can be opened up and the grain again cooled. And this process could be done for years of very safe grain storage.