Air on the Cool Side: A BTU Captured is a BTU Earned By Bill Casady

The long warm fall seems to be finally coming to an end and not a day too soon for long term storage. It has been difficult to cool grain below 55 or 60 degrees until recently. Take advantage of naturally cool air now to increase storage life of grain. The cooling process is vital to slowing insect activity and keeps storage molds down as well. With recently higher costs for energy, it is also important to take the time to understand the energy resources used in the grain conditioning process. The differences in drying methods can be surprising.

It is usually estimated that it takes about 1200 BTU’s to remove a pound of water from moist grain. This value is known as the heat of vaporization. If you were to measure the amount of heat that is actually exchanged in the process of removing moisture from grain, you would consistently measure about 1200 BTU’s depending on just how wet the grain is to begin with and some other factors.

From experience, we know that to quickly dry grain can become rather expensive. We must buy more than 1200 BTU’s in order to remove each pound of water. There is obviously another factor that is just as important as the amount of heat energy that is required to remove a pound of water, and that is the energy efficiency with which the drying is accomplished. Drying efficiency explains what would be apparent exceptions to the 1200 BTU rule.

A hurried drying process that uses high temperatures and lots of air can require up to 2400 BTU’s or more to remove the equivalent of 1200 BTU’s of water. A slower more natural drying method without additional heat might get the job done with the purchase of less than 800 BTU’s of electrical energy per pound of water removed to run aeration fans. This is about a three to one ratio, but the difference can be as high as four to one at extreme ends of the scale.

We’re often taught that if something looks too good to be true, then it probably is too good to be true. In a comparative way to the use of heat pumps, there are often naturally occurring energy surpluses and deficits in ambient or natural air that we can take advantage of for the conditioning of grain for long term storage. We could say that there are two ways to capture the economy of ordinary or natural air in the grain conditioning process: drying with naturally warm and dry air in early fall, and cooling with naturally cool air in late fall.

The use of fans to dry a grain mass with naturally warm fall air effectively concentrates air movement around kernels and increases the speed of the natural drying processes that would occur if grain was allowed to sit out in a thin layer under the sun... or for that matter, if the grain remained in the field on the stalk. The latter two obviously require essentially no energy purchase at all.

The use of fans to cool a grain mass with naturally cool late fall air also concentrates air movement around kernels to cool the grain mass. Although it isn’t widely recognized in the north, chillers are sometimes used to improve the quality of some grains, such as rice, during the drying process and for long term storage. Naturally cool fall air avoids the need to pay for refrigeration of air.

Natural air is "energy efficient" plain and simple. It is no more efficient to wait and do all of the cooling all at once. In fact it is a bit risky. Grain should have already been cooled with a couple of aeration cycles to about 50 or 55 degrees by now. If that is the case, one more good aeration cycle will nail down additional storage safety. Always take advantage of the naturally protective cooling nature has to offer as soon as possible to maximize the protective benefit of cooling. The best part is that aeration is almost free.

Bill Casady
573 882-4370