Save Money Through Tobacco Barn Renovations

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When the month of September arrives, space in a tobacco curing barn becomes extremely valuable. The threat of hurricanes and the possible early departure of field workers can result in elevated blood pressure levels if you are a tobacco farmer. Given these possible adverse scenarios, tobacco farmers will often go to great lengths to identify available barn space in order to move their tobacco out of the field and into the curing barn.

Research that has been conducted at NC State by Dr. Grant Ellington, Extension Associate Professor in the Department of Biological and Agricultural Engineering, can possibly assist tobacco farmers in hastening the amount of tobacco that is moved through their curing barns. Through the installation of carefully installed pieces of sheet metal know as” turning vanes”, the total amount of time that tobacco is held in a tobacco barn can be reduced by 12-24 hours per cure.

turning vane installed in tobacco barn

Turning vanes installed in tobacco curing barns can reduce curing time from 12-24 per cure. (photo by Dr. Grant Ellington)

When green tobacco is placed in a curing  barn, having adequate airflow is critical to maximize the cured leaf quality and minimize the time required to complete the curing process. While most barns have enough fan power, the air circulation ductwork, particularly the air space under the barn called the “plenum” can sometimes be improved to increase the fan volumetric air delivery per unit of time. The space under the curing barn can range from 14 to 22 inches. As this space decreases, the more restriction that the fan must overcome in order to provide the desired amount of airflow.

A turning vane (Figure 1) is semi-shaped piece of sheet metal that is installed under the barn that potentially redirects air movement in a more efficient manner. The turning vanes that were  typically used in on-farm research were rolled out of 16 to 20 gauge sheet metal with a radius approximately equal to the existing plenum height. The vane width and length are slightly larger than the existing fan housing diameter (36 inches typically). Depending on the barn manufacturer, barns which have a lower plenum height of 17 inches or less were most likely to benefit from having a turning vane installed beneath the barn floor. A sheet metal turning vane usually costs less than $100 to be installed in a tobacco barn.

Listed below are more comments to be considered if tobacco growers are considering the use of turning vanes in their tobacco barns.

  • Tobacco barns which used a tube axial fan (prop fan) and have a plenum height of less than 17 inches would most likely benefit from the installation of turning vanes. Tobacco barns which use  a centrifugal fan (squirrel cage) would not be expected to benefit from the installation of turning vanes.
  • Turning vanes which are to be installed in a curing barn do not need to be the entire width of the barn. The turning vane fits just under the fan housing and needs to be only as wide as the fan housing or just slightly larger.
  • Before cutting the final turning vane, it is recommended to make a template from 20 gauge sheet metal which could be modified easier to create 16 to 18 gauge sheet metal for the final turning vane design.
  • For some turning vanes, a hole may be required to be cut in the metal in order to place a nozzle for ordering tobacco. An ordering boom which consists of several nozzles can be slid directly under the vane to emit the fine mist.
  • Refer to the chapter 10 “Curing and Mechanization” of the 2023 Tobacco Information Guide for more information on turning vanes.
  • Tharrington and the Long barn types are expected to benefit most from the installation of turning vanes. Turning vanes can be installed on any type of barn if the lower plenum is easy to access and installation is simplified. It will not take long to evaluate any airflow improvements.
photo by Dr. Grant Ellington

The turning vane simply needs to extend just beyond the fan housing of the barn. (photo by Dr. Grant Ellington)