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NCSU studies wood-fired curing barn

By David Williams

North Carolina State University has been working on a new curing barn design using a wood-fired water boiler that creates heat through steam pipes. The demonstration barns – known as the Advanced Curing and Drying System Demonstration Barns – were set up by N.C. State’s Department of Biological and Agricultural Engineering. The barns were shown to visitors at the kickoff of the 2007 North Carolina Tobacco Tour in July at N.C. State.
While the buildings were carefully designed, a large number of the parts can be obtained at a local hardware store or lumber yard. The barns were designed to reduce heat loss and better control air flow during curing.
The structure has two barns sharing a common wall, sitting on a four-inch concrete pad that is slightly sloped to take water drainage away from the barns. The common wall reduces pad space by up to 50 percent by eliminating the space between traditional barns.
The pad also has a ¾-inch foam insulation panel that saves up to five percent of energy costs in heating loss.
The walls feature three and a half inches of foam sandwiched between ½-inch OSB plywood and common exterior sheathing. This gives the barns three times the insulation of standard barns. These common elements make the barns easy to assemble on-site and materials simple to find. The units have bi-fold doors that open vertically, allowing multiple barns to be loaded and unloaded without a conventional door creating a blockage. The top has a vinyl membrane similar to commercial buildings, and is readily available commercially.
The barns are ten-box size and large enough to get a forklift in and out easily. They can cure up to 35,000 pounds of tobacco on a regular 6-7 day cycle.
The heat is provided by a wood-fired Taylor Water Stove, which heats water to 200 degrees and rates at 500,000 BTU an hour. The water is pumped into the barns by a ¾ horsepower pump, which is controlled by the barn thermostat. A radiator in the barn, rated at 450,000 BTU per hour, extracts the heat.
A 15-horsepower,Aero-Vent direct-drive bladed fan is used in each barn, equipped with a variable-speed drive to allow variation in air flow through each barn.
Each barn has its own thermostat, and since water is circulated only when heat is needed, the risk of barn fire is negligible. The leaf is not exposed to the chemical smoke that requires oil-fired barns to use a heat exchanger.
The barns are still a research tool, and data on box weight, use of electrical power from the fans, heat to the barns and amount of wood required will all be monitored when the barn cures its first crop this summer. A curing controller is used to maintain the dry-bulb temperature needed and a wireless computer link monitors the barns and alarms when a parameter is exceeded.
Costs on the barns were estimated at $25,000 per barn.
The research team acknowledged the efforts and assistance of sponsors Insulated Component Structures of Mocksville, N.C.; Taylor Manufacturing of Elizabethtown, N.C.; Cureco of Seven Springs, N.C.; Hahn-Mason Air Systems, Inc. of Raleigh, N.C.; and Roof Construct, Inc. of Burlington, N.C.
Grants from The North Carolina Tobacco Research Commission, The North Carolina Tobacco Foundation and Philip Morris USA also helped to make this project possible.