Testing, Adjusting, and Commissioning
The Testing, Adjusting, and Commissioning domain tests whether you can prove a system performs as designed. Items cover TAB reports, static pressure and velocity measurement, duct leakage testing, fan curves, airflow verification, and commissioning documentation.
Core rules and concepts
- TAB is a sequence: test, adjust, then balance. Record initial readings, make damper adjustments, and record final readings.
- Measure duct velocity with a Pitot tube traverse or an anemometer; measure grille airflow with a flow hood.
- Convert velocity pressure to velocity with V = 4005 × √VP for standard air, then multiply by duct area for cfm.
- Compare measured fan airflow and static pressure to the fan curve; check motor amps against nameplate.
- Duct leakage tests follow the specified SMACNA leakage class and test pressure. Document the results.
Worked example
A Pitot traverse in a 2 ft² duct gives an average velocity pressure of 0.09 in. wc. The square root of 0.09 is 0.30, so V = 4005 × 0.30 = about 1,200 fpm. CFM = 1,200 × 2 = 2,400 cfm. If the design is 2,100 cfm, the tester investigates damper position, fan speed, and static pressure before recording the result.
Traps that cost marks
Taking a single Pitot reading instead of a traverse, using the wrong duct area, measuring at a turbulent fitting, and adjusting the fan speed before checking the design static. Another is submitting a TAB report with final readings only, with no initial readings or deficiencies noted.