Study shows grain dryer fans should run mainly at night

Side-by-side trial conclusions Daytime drying ineffective because fan pushes warm, moist air into bin: researchers

Researchers say grain drying trials conducted this year have proven that aeration fans shouldn’t run continuously.

Instead, fans should run mostly at night, say researchers from Indian Head, Sask.

They held side-by-side trials in August and September, comparing continuous aeration to intermittent aeration of grain bins.

The results confirmed an earlier hypothesis that grain dries mostly at night, said Guy Lafond, an Agriculture Canada scientist at the Indian Head Research Farm.

“We now have the evidence to show that the drying occurs as the grain is cooling,” he said.

“Usually, we’re removing water during the coolest part of the day and adding water during the warmer part of the day.”

Lafond and Ron Palmer, a retired University of Regina electrical engineering professor, set up a grain drying system this summer that switched the aeration fan on or off, depending on the amount of moisture entering and leaving the bin.

They installed a sensor that measured the temperature and relative humidity (RH) outside the bin and another sensor to measure the temperature and RH near the bin exhaust. The fan would switch off if more water was entering the bin than exiting.

“The thing that told us to turn it on or off was the net amount of water coming out of the bin,” said Palmer, who is best known for developing auto steer for tractors and is doing the research on grain drying for the Indian Head Agricultural Research Foundation (IHARF).

In February, Palmer released the results of previous grain drying trials at Indian Head. The data indicated that grain dries mostly at night, a finding at odds with the long held assumption that grain dries when it’s warm outside.

“We’re putting water back in by continuous drying, pounds and pounds of it,” Palmer said.

He suggested that daytime drying was ineffective because the fan pushes warm and moist air into the bin. The cold grain inside the bin cools the warm air, transferring the moisture in that warm air to the grain.

In August and September, Palmer, Lafond and their IHARF colleagues compared their intermittent system to continuous aeration, drying wheat and barley in 2,000 bushel bins with five horsepower fans. The recent research confirmed their earlier results.

“Yes. This definitely validates our original suspicion that the best drying is at night,” said Palmer.

Running the fan during the day might heat the grain, which increases the risk of spoilage, he added.

“Not only (is it) more efficient, it’s a safer approach because your grain is cold,” he said.

“It’s the same reason we keep our food in the fridge so it doesn’t spoil. The same thing applies to grain.”

The researchers found that running the fan continuously dries grain faster, in terms of the number of days. However, running the fan intermittently, when conditions are suitable for drying, reduced the number of fan hours by 30 to 40 percent compared to the continuous system.

As well, the researchers observed significant differences in the air temperature of the grain.

“(Bins) with the continuous fans, the grain temperature would go up and down like a yo-yo,” Palmer said, mirroring the outside air temperature.

In contrast, the grain in the bins with intermittent aeration remained relatively cool.

“Whereas, the control bin, it might be sitting at 12 degrees and go up to 15 and then go back down to 11,” he said.

“The controlled grain was kept cold…. Cold and dry is the recipe for good storage.”

The temperature figures are an example, not actual data, he cautioned.

The recent trials may confirm the previous grain drying research at Indian Head, but farmers shouldn’t make the switch to nighttime drying just yet, said Joy Agnew, a project manager for agricultural research services with the Prairie Agricultural Machinery Institute (PAMI) in Humboldt, Sask.

Agnew and her fellow PAMI scientists have developed a grain drying system in which the fan turns on or off, depending on grain conditions inside the bin.

“We assessed how the moisture content was actually changing, rather than how much water was entering and leaving. And our results are the exactly opposite of what they’re finding,” she said.

“Our control strategy showed that the best time to dry the grain is during the day.”

The debate over drying at night or by day will likely continue into 2013. Agnew and Palmer will present their findings to producers and fellow scientists over the winter.

In fact, they will both speak in Saskatoon Dec. 13 at a meeting of Saskatchewan agronomists.

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