by Sally Colby
Tom Childs was looking for an alternative method to heat his greenhouses, and the answer came in the form of a new building, a new tractor and a very large boiler equipped with electronic controls.
“I’ve always been interested in energy,” said Childs, of Twin Springs Fruit Farm in Orrtanna, PA. “Mike Palko, the biomass energy specialist for the Pennsylvania Department of Conservation and Natural Resources, told me that the project would take at least two years. In reality, it took about three years.” But after several years of planning, visits to other operations with wood chip boiler systems and many meetings with various specialists, Childs’ vision came to fruition.
The project was possible with the help of grants from the USDA Conservation and Innovation Grant (CIG) and the Pennsylvania Department of Community and Economic Development. Childs talked about the complex process of working through the various permits during the planning phase. “We had to put in a firewall because of the stored fuel,” he said. “It’s all one foundation, all under one roof; but part of the building is agricultural and the other section is commercial. There are very rigid definitions of an ag building because it’s taxed differently.” Because the large section of the building is used to store an agricultural product, it’s considered an ag building. However, even though the boiler is being used to heat greenhouses, it’s considered commercial.
Childs says he had originally planned to burn residue from tree service, but that turned out to be less than desirable source. “When you cut a tree down, it’s 50 percent moisture,” he said. “It will burn, but if you’re buying fuel that’s 50 percent moisture, for every ton, you’re buying 1,000 lbs. of water. That moisture has to come off before the fuel burns, and it takes energy to do that.”
“We’re hoping to end up in the $30/ton or less range for fuel,” said Childs. “That works out to about $4-$5 dollars per million BTU, whereas propane is around $30 per million BTU.” The system will operate efficiently with a variety of wood products including wood chip or wood pellets.
Fuel material will be kept in a newly constructed storage building. The natural, steep slope into which the storage building is constructed contributed to its efficient design. An overhead conveyer will move wood material into the building and distribute it evenly across the floor. “It has 60 ft. of track,” said Childs. “We can fill from end to end and side to side without ever driving on it. It’s an advantage to not have to drive over the fuel supply because it’s becoming compacted and that seals it in. But even with the wood chips from tree service trucks that have a lot of green material, after allowing it to sweat off and dry outside for awhile, it’s stable in a short time.”
Keeping fuel dry is a catch-21 — material dries better outside, but there’s a risk of it becoming wet if it’s rained on. Childs is hoping to avoid having to purchase a tub grinder that could process large chunks of wood, but is prepared to if his fuel source demands it.
When it’s time to fuel the boiler, Childs will use a yard-and-one-half bucket mounted on a tractor to scoop up chips. The chips go into a 70-yard hopper, which when full should last four days at 10 degrees F. That’s important because no one lives on the farm property. “It doesn’t happen often,” said Childs, “but if no one can get here, the supply will last long enough.”
Next, a vibratory screen sifts the material, then the material moves along on a series of conveyers that lead to the boiler. The boiler is separated from the storage area by a firewall. “It fills until it’s full,” said Childs, “then it shuts off. We put in new 480 volt electric service. The motor load of all the greenhouses and well pumps is about 10 hp. The system is 23 hp, and the material handling line is another 20 hp.”
The boiler has 3.5 million BTU output, and a highly efficient 10:1 turndown ratio. Turndown ration is the ratio of fuel used in the combustor between high-fire mode and pilot mode to maintain adequate combustion temperature without smoking. “My concern with a biomass system was whether it could shut down during the day, for extended periods, and I wouldn’t have to relight it all the time,” said Childs.
“This is the only one I could find with a 10:1 turn-down ratio, and it will run between 350,000 to 3.5 million BTU and anywhere in between at relatively the same efficiency. But the bigger thing is that it will go into indefinite idle. In spring and fall, we go into cooling phase soon after sunrise and just after sunset, so this has to sit here all day long without overheating — sometimes 14 to 16 hours.”
The system will heat three greenhouses that produce crops year-round for 17 markets in the Washington, D.C. and northern Virginia area, several of which are year-round markets. Another four-bay greenhouse that will soon be constructed will provide space for additional crops, and the heating system was designed with that in mind.
Once the new greenhouse is completed, Childs will be growing crops year-round in about 3/4 of an acre of greenhouse space. He also added a transplant house, which is used to start about 200,000 transplants/yr. New houses will have radiant floor heat, and Childs will eventually add radiant floor heat to existing greenhouses.
“We’ll be growing more of some of the things we already grow and adding several new things,” said Childs. “We can’t sell as many tomatoes once fall starts. People are tired of them from summer.” He’s considering adding nutrient film technique (NFT) lettuce, which will maximize production space for output. In one house, Childs is currently growing cucumbers and honeydew melons that will be ready to harvest the second week of November. “We grow cucumbers almost year round,” he said. “From seed to harvest, even in low light, is about 65 days. We had always shut down tomatoes but will now be growing them into spring and we’ll have eggplant growing and ready for spring.”
Is it economical? “One of the goals I had was that our bank payment would not cost us more than we were already using in fuel,” said Childs. “We won’t see the savings until the bank loan is done. But with what’s happening now with fuel, there will be a lot less volatility with my fuel source. Wood chips only change a percent or two every year, and that’s mostly for the trucking and processing cost. Propane and heating oil change a lot more.”
Twin Springs Fruit Farm will be hosting an open house to demonstrate and discuss the boiler system. The event is scheduled for Tuesday, Dec. 10th from 9 a.m to 11:30 a.m. at 936 Orchard Rd., Orrtanna, PA. Call 717-642-8988 for more details on the event.
Cutting greenhouse fuel costs with alternative energy
by Sally Colby