By Karl Ohm III
Solar heating scares off a lot of people…but here’s a simple system of collecting heat under a metal machine shed roof to dry the grain in an adjacent bin.
Not too many years ago, farmers dried their grain in the field – right on the stalk or stem – rather than in a storage bin.
Unknowingly, those farmers were already pioneering in what we now call “solar energy”. Little did they know that years later their early use of solar energy would make common such terms as “solar cells”, “solar heat collectors” and even “NASA”.
While there aren’t many people who look kindly on higher energy costs, those increasing costs can be given credit for sparking serious interest in solar energy from a bigger slice of agri-business people.
A couple of years ago, only agricultural engineers took its potential seriously. Now, many see the sun as an efficient means of supplying heat. In, fact they’ve now learned that heat can be collected to supplement gas or electric heaters in low-temperature grain drying operation.
How can it be done? Let’s take a look at a solar grain drying system that’s been in operation for over 2 years in Green Lake County, Wisconsin.
In 1974, Bernard Bauman and his sons, Barry and Kalton, decided their farm needed a new machine shed and grain bin They wanted a grain bin for drying shelled corn to support their hog finishing operation. But Barry, a University of Wisconsin agricultural engineer graduate, also thought that this would be an ideal time to put solar grain drying to the real test – a highly practical one, right on their farm.
The new grain bin was constructed adjacent to the machine shed. Then, by installing a false ceiling along with ducts under the machine shed’s metal roof, sun heated air could be channeled to the fan on the grain bin. These large volumes of warm air would be collected to supplement the electric heaters.
So with that in mind, the Baumans contacted Westra Agri-Builders, Waupun, Wisconsin which supplied them with a Butler grain bin and a Butler Farmstead building for a machine shed.
“When I talked with Don White at Westra, I specified two things in the shed’s construction,” explains Barry. “I wanted an unpainted galvanized metal roof along with purlin and I-beam framing.”
Galvanized Fluted Roof
Barry points out that he wanted a galvanized major ribbed or fluted roof because as it weathers it absorbs more solar heat than a smooth, shiny surface.
Barry also added that a ribbed surface tends to transfer the heat better, since this type of surface causes air turbulence when the fan is turned on. The purlins were necessary so that air ducts could be built directly beneath the roof.
The resulting machine shed measures 75 ft. long 60 ft. wide and 16 ft. high at the eaves with the roof tapering about 13 in. to the center peak. Its roof line lies in an east-west direction in order to maximize the hours of sunlight striking the roof.
The shed’s low profile roof was covered with channeled unpainted, galvanized metal with major ribs on 12-in. centers. Two pole I-beams were used in framing along with purlins, spaced 5 ft. apart, for the roof support.
The grain bin was then built next to the machine shed, near the southeast corner. The bin measures 27 ft. diameter by 18 ft.. high and holds 8,320 bu. of shelled corn.
Builds False Ceiling
About 11 ft. was provided between the bin and shed to make room for the drying fan, electric heaters and necessary duct transition.
But the heart of this solar drying system lies underneath the machine shed’s metal roof.
With the help of agricultural engineers Gene Shove, University of Illinois, and Marshall Finner, University of Wisconsin, the Baumans designed and built a false ceiling and air ducts. The false ceiling covers a 1,500 sq. ft. area on the easterly one-third of the building.
It was constructed by first bolting 2 x 4s (lengthwise) along the 8-in.-deep purlins. Then, 1 x 4s furring strips were secured (crosswise) on which 1/4-in.-thick, untempered 4 x 8-ft. masonite panels were nailed to cover the framing.
Along the east end, inside the machine shed, a common duct, 40 in. wide x 18 in. deep was built below the purlins. This duct serves to channel heated air from the false ceiling area into a vertical duct along the shed’s southeast corner.
This 4-ft.-sq. outlet duct extends downward from the false ceiling to the shed’s gravel floor line. Just above the floor line, there’s a 12 in. x 42 in. opening in the metal sidewall which heads the heated air into the bin’s fan duct.
Installs Fans and Heater
“The outlet duct to the bin should be larger than the grain bin’s fan duct,” says Barry. “The size is important, because if the outlet is too small, you restrict the air flow.”
To draw off the sun-warmed air inside the shed, a 27-in. vane-axial (10 hp) fan was installed, which can move about 15,000 cfm (cubic feet per minute) of pre-heated air below the bin’s perforated floor. When needed for added heat, a two-stage, 12/20 kw electric heater at the fan’s inlet can be used.
Barry also wired in thermocouples at various locations around the shed and bin which were used to record temperature changes during grain drying periods. Some thermocouples record outside air temperature, others record temperatures inside the bin ducts, as well as the roof. Kilowatt hour meters were also installed to measure how much electricity would be used by the fan and auxiliary electric heaters.
The system was completed in time for the harvest season. Barry recalls that it was a wet season, and one in which they started drying their corn later than normal.
“We started to dry our corn on November 3 after we had about 6 in. of grain in the bin,” says Barry.
“We added the last batch of wet, shelled corn on Nov. 25, and during this filling period we were able to stay ahead of the drying front with 1 to 3 ft. of corn. This seemed to work out well.
“Only the fan was used during the first 10 days of drying,” Barry adds. “If outside or bin exhaust air temperatures dropped below 32 degrees F., the fan was turned off. I can remember on Nov. 12 our corn started to freeze when temperatures dropped lower than expected. We plan to prevent this from happening next year by hooking up a thermostat to run the auxiliary heaters at about 35 degrees.”
Fans and Heater Used When Needed
The fan and electric heaters in the 20 kw stage were operated round-the-clock for only 2 days up until Nov. 24. From Nov. 24 to Jan. 10, the fan and electric heaters were used periodically to keep both the fan outlet and bin exhaust temperatures about 32 degrees.
On Jan. 10, when the outside temperature dropped below 32 degrees F., Baumans turned the fan on for 5 hours without any electric heat to cool the grain down. That concluded their drying period.
“We totaled about 672 hours in drying time,” Barry notes. “Our bin was about half full and on Jan. 13, I took moisture samples of grain at foot intervals.
“The moisture ranged from 13.6% at the floor to 18% at the surface, but including the other samples, the moisture averaged out to 14.7%. We did have some problems with re-wetting when the fan was run on very humid, cloudless days or nights.”
Barry estimates that the equivalence of 5752 kilowatt hours was supplied by the solar heat collected from the metal shed during the first season. He figures at 2.55 cents per kwh this represents $146.68 in electrical expenses alone that was saved for the first year’s operation.
“We only spent around $460 to modify our shed,” Barry says. “What we saved in electric bills has already paid for one-third of our total material costs.”
Report On Costs
During the 1975 drying season, Barry reported a $120 savings with their solar heat collector and their total electric costs (fan and heaters) were $10. This represents about 3720 kwh of electric energy at 3.23 cents per kwh.
However, last year the Baumans made a few improvements to their operation which helped reduce their drying time and costs.
Baumans added a time controlled 2-auger stirring device (David Mfg. Co.) in the grain bin. This increased the air volume delivered by the fan since the static pressure could be lowered inside the bin. They also installed a combination thermostat-humidistat to turn on the electric heaters when temperatures dropped below 35 degrees or when the relative humidity climbed above 65%. Along the south wall of the shed, Baumans put up 384 sq. ft. of paneling which was connected to vertical duct. Barry wants to find out how much added heat can be gained by using a portion of the south wall.
During the first year’s trial, Barry noticed that the south wall would warm up to 40 degrees on a sunny day when outside temperatures were 8 to 10 degrees. However, last year the roof absorbed twice as much heat energy. This occurred because the roof had a chance to weather.
Small Sidewall Heating
“The energy gain along the south wall last year wasn’t as great as I expected,” says Barry. “It appears that more work needs to be done on air inlets along this wall to maximize heat gains. I also think it’s possible to set up another adjacent bin, but we would have to extend our false ceiling farther to collect enough heat.”
“A stirring device and a thermostat-humidistat control makes a low-temperature operation more efficient,” Barry says. “Our drying time and costs have dropped considerably ever since we installed them.
“Last year, we only used 1677 kwh on the fan compared to 6720 kwh in 1974. And only 294 kwh were used for the electric heaters compared to 5760 kwh in 1974.”
Controls Save Operator’s Time
Barry feels that a thermostat-humidistat control helps reduce actual operator time. Without it, an operator must spend too much time checking weather conditions.
According to Barry’s figures, the total drying energy decreased from 0.399 kwh/bu. pt. of moisture removed in 1974 to 0.248 in 1975. This represents 1 cent per bu. pt. of moisture in 1974 compared to .8 cents per bu. pt. of moisture in 1975.
“I think this happened because no night time drying was done during our 1975 drying season,” he says. “Thus, we had very little or no re-wetting of the corn at lower levels like we had in 1974.”
The Baumans seem quite satisfied with their solar grain drying system. With just 2 years in operation, they have recovered 58% of their material costs used to install the ducts and false ceiling. And who really knows how much fuel costs will be 10 years from now?
In a sense, we may be turning back the clock. But this new approach to utilizing solar energy might just write another important chapter in United States agricultural history. And why not, since nothing would be possible without the most abundant resource we have – the sun. RB
