US (VT): UVM students hone process to heat greenhouses with manure

To the untrained eye, Tad Cooke and Eric Crockenberg’s project at the University of Vermont Horticulture Research Center off Shelburne Road looks like a 15,000-pound pile of cow manure and used straw bedding next to a greenhouse, but to the UVM seniors the pile looks like a finely tuned heat and nutrient source for the greenhouse’s verdant tomato beds.

Their ultimate pile at the Hort farm, as the facility off Shelburne Road is known, comes as a result of some $56,000 in grants from the Clean Energy Fund.

Here’s how the system works.

A sturdy, three-sided wooden bin made of rough 3-inch lumber contains the manure and bedding trucked over from the Miller Farm, UVM’s dairy operation, a short distance away. Two sets of two perforated PVC drainage pipes lead from the bottom of the bin, where they’re encased in wood chips to keep air flowing, into two T pipes, each one hooked into shut-off valves.

An enclosed rotary fan in the greenhouse is hooked into a pipe that collects the air flow from all four pipes embedded in the compost pile. The fan pulls air from the pipes that has been heated by the natural decomposition process going on inside the pile.

Next, the heated air flows beneath two beds of tomatoes into more perforated PVC pipes, percolating heat and carbon dioxide created in the decomposition process directly into the soil surrounding the tomato plants’ roots.

As McCune notes, plants need carbon dioxide to grow.

“A plant is 99.9 percent carbon,” McCune said. “Carbon dioxide is part of that process. With more CO2 they can grow faster.”

The tomato beds also act as biofilters, eliminating odors from the decomposing farm waste. Indeed, stepping into the greenhouse brings only the pleasant scent of tomato plants. Green plum tomatoes hang from the profuse confusion of branches on the staked plants.

Cooke was hoping to take ripe, red tomatoes to the next meeting of the Clean Energy Fund committee on Oct. 16, when the pair will ask for a final $2,500 to build a cover over the compost pile so it’s not exposed, but he said it would probably another month or so before the tomatoes are ready.

“Whether or not they’re ripe, we’ll take pictures for the October meeting,” Cooke said.

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