NEBB Testing, Adjusting and Balancing Certified Technician (CT) cheat sheet

Fan law: airflow varies directly with fan speed (CFM2 = CFM1 × RPM2/RPM1); static pressure varies with the square of speed; brake horsepower varies with the cube of speed.

Velocity pressure is the difference between total and static pressure: VP = TP − SP; at standard air (0.075 lb/ft³) velocity in fpm = 4005 × √VP, with VP in inches of water column.

For nonstandard air, velocity = 1096 × √(VP/ρ), where ρ is actual density in lb/ft³; correct fan and duct readings to design density.

Airflow in a duct: CFM = A × V, with A in ft² and V in ft/min; for rectangular ducts, A = width × height ÷ 144.

Pitot traverse layout: use the log-Tchebycheff or equal-area method; NEBB requires enough points to keep each reading within the duct's stable velocity core.

Terminal airflow: CFM = K × √VP, where K is the terminal or hood calibration factor; verify K from manufacturer data or field calibration.

Proportional balancing: adjust branch dampers so each branch carries the same percentage of design airflow; start at the fan and work toward the terminals.

System static profile: record pressures at fan suction, fan discharge, filter, coil, and terminal; a rising profile locates restriction points.

Outdoor-air intake: measure OA cfm at the intake louver or flow station; minimum OA must meet design and ASHRAE 62.1 ventilation requirements.

Flow equation: GPM = 2.448 × d² × V, where d is inside pipe diameter in inches and V is velocity in ft/s.

Water horsepower: WHP = GPM × head (ft) × specific gravity ÷ 3960; pump brake horsepower = WHP ÷ pump efficiency.

Pump affinity laws: flow varies with speed, head with speed squared, and brake horsepower with speed cubed.

Sensible heat in water: Btu/h = 500 × GPM × ΔT for water near 60°F; use about 485 for 30% propylene glycol and correct for other concentrations.

Balance valve setting: measure differential pressure across the valve and convert to flow with the valve Cv or manufacturer flow curve; do not set by valve turns alone.

Reverse-return piping equalizes path lengths; direct-return systems require balancing valves at each branch to overcome unequal pressure drops.

Pump cavitation occurs when NPSH available is less than NPSH required; check suction pressure, water temperature, and suction line losses.

Coil flow check: low ΔT at design flow indicates fouling, air binding, or bypass; high ΔT indicates low flow.

Air elimination: locate air vents at high points and use an expansion tank; air in water systems causes noisy pumps and inaccurate flow.

Pitot tube: the impact port faces airflow and static ports are perpendicular; misalignment beyond about ±10° causes significant velocity error.

Pitot tube accuracy: below about 600 fpm, velocity pressure is too small for reliable readings; use an anemometer or flow hood.

Manometer: zero before use, use the correct fluid and range, and read at eye level; a differential manometer measures pressure drop across filters and coils.

Balometer or flow hood: match hood size to the grille, apply the manufacturer's backpressure correction, and avoid blocking the grille perimeter.

Anemometer: traverse the duct or grille face, keep the probe perpendicular to flow, and correct for temperature and pressure when the meter requires it.

Calibration: all instruments must have NIST-traceable calibration; record model, serial number, calibration date, and correction factors on field forms.

Psychrometer: wet-bulb and dry-bulb readings give relative humidity and dew point from a psychrometric chart; sling at proper velocity and keep the wick clean.

Tachometer: use reflective tape with a photo tachometer or a magnetic pickup; measure at the shaft, not the motor housing, and record actual RPM.

Temperature: contact sensors need good immersion or surface contact; infrared thermometers require correct emissivity and are unreliable on shiny metal.

NEBB TAB tolerances: air and water flows are typically balanced within ±10% of design; temperatures and pressures are recorded against design values.

Final TAB report includes design versus actual airflow, water flow, static pressure, temperatures, instrument list, calibration records, and a deficiency log.

Pre-balance checklist: verify fan rotation, belt tension, filter installation, damper positions, valve positions, and control sequence before balancing.

Specification precedence: written specifications, drawings, addenda, and RFIs are read in the order stated in the contract; the more stringent requirement governs conflicts.

NEBB certification requires a certified firm with a certified professional, supervisor, and technicians; recertification and quality assurance audits maintain status.

Field data must be recorded on approved NEBB forms, in ink, with corrections initialed and dated; do not overwrite or use correction fluid.

Non-conformance: document deficiencies that prevent design flow, notify the contractor in writing, and note the item in the final report until resolved.

Commissioning coordination: TAB is completed before functional performance testing; provide preliminary reports for commissioning review.

Fan operating point is the intersection of the fan performance curve and the system curve; system pressure varies with the square of airflow.

Centrifugal fan types: forward-curved for low pressure and high volume; backward-inclined for high efficiency; axial fans for high volume and low pressure.

Fan surge or stall occurs when a fan operates left of its peak pressure point; symptoms include noise, vibration, and unstable airflow.

Pump best efficiency point (BEP) is where flow and head produce maximum efficiency; operating far from BEP causes vibration and bearing wear.

Pumps in parallel add flow at the same head; pumps in series add head at the same flow.

Coil sensible heat: Btu/h = 1.08 × CFM × ΔT for dry air at sea level; latent heat uses 0.68 × CFM × Δgrains.

Opposed-blade dampers give nearly linear control; parallel-blade dampers have a higher installed pressure drop and are used for shutoff.

Valve flow: Q = Cv × √ΔP; a three-way valve modulates flow through the coil and bypass to maintain constant system flow.

Lockout/tagout: isolate and lock fan and pump disconnects before service; verify zero energy and allow fan wheels to stop completely.

VFD safety: wait the manufacturer's stated discharge time before opening the drive enclosure; capacitors retain dangerous voltage.

Confined space: test for oxygen, flammables, and toxics before entry; use a permit and attendant; never enter alone.

Fall protection: use guardrails, personal fall arrest, or travel restraint when working above the required height; inspect harnesses before use.

Ladder safety: maintain three points of contact, set the ladder at about a 4:1 angle, and do not stand on the top two rungs.

Jobsite coordination: schedule TAB after duct cleaning and before ceiling closure; coordinate with controls, electrical, and commissioning.

Daily reports: record weather, access, manpower, instrument use, and delays; communicate deficiencies to the general contractor in writing.

Electrical safety: use a true-RMS meter rated for the category, verify dead circuits, and do not work alone on energized equipment.

Housekeeping: keep test equipment and cords out of walkways; barricade open ceiling areas and floor openings.