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An alternative heating system saves thousands of dollars
By ROCKY WOMACK
(March 24, 2015) How would you like to save $30,000 or more a year on your greenhouse heating bill? Sounds enticing, yet you’re skeptical.
The good news is that it’s possible.
Growers Ryan Patterson and his father, Phil, of Broadway, N.C. have done just that in their tomato and tobacco greenhouses, and growers in Delaware, Maryland and Virginia may save too.
When the Pattersons started raising greenhouse tomatoes, they soon realized large LP gas payments were not in their future. So they took an old wood-fired stove and hooked the system up to the greenhouse.
They immediately noticed a difference in their heating bill. Then, they hooked the system up to their tobacco greenhouses and noticed an additional savings.
The only problem was they didn’t like the number of times they needed to wake up in the night to chunk wood in this small boiler. In addition, they also wanted to cure their tobacco with wood chips. So they needed a larger system.
They approached the engineering department at North Carolina State University to see what they could do. Engineer Grant Ellington helped the Pattersons determine the chip bin and boiler size they needed to cure their tobacco. “Based on his estimated green-leaf loading rates, the number of barns loaded weekly or daily, and total number of barns, we can estimate the maximum BTU per hour requirement to size this type of system,” Ellington said. “The curing barn thermal load is significantly higher than the greenhouse heating requirements. If the system capacity is adequate for his curing operation, then it would be more than adequate for this greenhouse operation.”
After all that was figured out, the Pattersons purchased a large Hurst boiler that would heat their two greenhouses and cure flue-cured tobacco in their 19 bulk barns.
They can move the boiler from the greenhouses to the barns since the boiler sits atop a tractor trailer. Outside the tomato greenhouse, the electrical system quickly connects from the boiler to a hot water circulator inside. Ryan estimates they fill up the chip bin every two or three days. The chip bin sits on top a scale so NCSU’s engineering department can monitor chip use. This allows them to correlate the amount of heat used to the tons of chips required, he says.
Just in case of system failure, Phil says they installed a backup monitor that allows the LP gas to come on, which he says is rarely needed.
The boiler is rated at 3.5 billion BTUs, Ryan says, but it puts out more than 4 billion. “We knew about how many chips it would take to get us through a 12-hour period,” he says. “We sized our chip bin accordingly. During tobacco curing, we have to fill it up once in the morning and once before dark. It will run for 12 hours without any problem. It’s definitely extra time—on a per week basis maybe six to eight hours more for just monitoring the system, but it’s got alarms on it. It’ll call us if anything happens. It pretty much takes care of itself.”
He says it takes about two tons of wood chips per barn to cure what would normally take 300 to 400 gallons of LP gas.
The wood costs $35 a ton and is produced from ground up scraps of furniture and pallets. The chips are moved by an auger system, similar to a grain auger, into the fire box of the boiler.
In heating the tomato and tobacco greenhouses, Ryan estimates they save $30,000 to $50,000 in one growing season by burning wood chips instead LP gas.
He saved on his tobacco curing bill too. Ryan says they would have paid $550 to $600 per barn cure in 2014. Using wood chips, that amount was only $70 per cure. He estimates they saved about $87,000 a year by heating with wood chips versus LP gas.
“That’s pretty good savings,” Phil says.