Monitoring of Heat Exchangers Required by US Tobacco GAP
Checking the heat exchanger within all flue-cured tobacco barns (other than those using a boiler system with a liquid to air heat exchanger) is required at least once every three years according to the US Tobacco GAP Program guidelines. The intent of the heat exchanger is to reduce the tobacco specific nitrosamine (TSNA) levels found on tobacco. However, TSNA cannot be measured directly measured within the barn curing system. Fortunately carbon dioxide levels have been shown to be a good indicator of heat exchanger leaks that cause TSNA. Specific carbon dioxide meters, minimum equipment standards, manufacturing information and additional information for these meters can be found in a previous article, Monitoring Flue-Cured Tobacco Heat Exchangers
The requirement mandates that all tobacco curing barns used to supply tobacco to a company participating in the US Tobacco GAP Program and designated as being in service must have a properly functioning heat exchanger. It is the responsibility of the grower to arrange for testing and the grower will assume any cost. All barns must be tested collectively. Barns found to have a failing heat exchanger must be repaired and retested. Retested barns passing are considered functional. Any barns that continue to fail or cannot be repaired must be placed out of service by removing all utility connections. Barn testing records are to be kept by the grower and copies provided to participating contractor purchasers.
Only those that receive certification from a trainer certified by the US Tobacco GAP Program (currently NC State Extension within NC) may perform these tests. This may include independent third-party companies or individual growers. Those within NC interested in receiving this training should contact your local NC Extension office.
Specific information required as records include:
- Farmer or Farm name and address
- Location of barns
- Testing date
- Total number of barns to be tested
- Testing entity company name or individual name
- CO2 probe serial number and calibration information
- Barn ID numbers
If barns are tested at multiple locations, then separate reports should be completed for each location. All results of the barn testing along with a copy of the CO2 probe calibration information are to kept by the grower.
Generally, testing involves measuring the carbon dioxide within the empty barn (no tobacco) when the barn fan is on, air dampers are closed and heat is off compared to carbon dioxide levels within the same barn after the heat exchanger has run through several heating cycles (usually about ten minutes). The difference between these two numbers is used to determine a passing or failing status. If the difference measured is less than 200 ppm, the heat exchanger status is PASS. If the difference measured is greater than 200 ppm, the heat exchanger status is FAIL and must be retested after repairs.