NEBB Testing, Adjusting and Balancing Certified Professional (CP) cheat sheet

Testing, Adjusting and Balancing (TAB)

• Airflow measurement: pitot tube traverse in duct; velocity pressure VP = (V/4005)^2 in in. w.c. for standard air (density 0.075 lb/ft³), where V is fpm.

• Fan laws: flow varies directly with speed, pressure with speed squared, power with speed cubed; density changes affect pressure and power proportionally but not flow.

• Pump laws: flow varies directly with speed, head with speed squared, power with speed cubed; affinity laws apply to geometrically similar pumps.

• Water flow: GPM = 0.002228 × Cv × √ΔP (ΔP in psi) for a valve or device with known Cv; for a coil, use manufacturer's pressure-drop curve.

• Balancing hood accuracy: capture hoods typically ±3% of reading; pitot traverse ±5%; use the correct hood for grille size and maintain a seal.

• Air density correction: actual density = 0.075 × (460 + 70)/(460 + T) × (Barometric/29.92); correct velocity and static pressure readings accordingly.

• Proportional balancing: adjust the terminal furthest from the fan first, then work back; use the ratio method (measured/design) to set dampers without repeated iterations.

• Fan static pressure: total static = discharge static minus inlet static (with sign convention); fan total pressure = discharge total minus inlet total.

• Duct leakage: test at 1.0 or 1.25 times design static pressure; leakage class (e.g., SMACNA Class A) defines allowable cfm per 100 ft² of duct surface.