NEBB Testing, Adjusting and Balancing Certified Technician (CT) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Fan law for airflow

Airflow varies directly with fan speed: CFM2 equals CFM1 multiplied by RPM2 divided by RPM1, at constant air density and system geometry.

Velocity pressure formula

At standard air density, velocity in feet per minute equals 4005 times the square root of velocity pressure in inches of water column.

Pitot tube traverse

A grid of velocity-pressure readings across a duct; the average velocity pressure is converted to average velocity and multiplied by duct area to obtain airflow.

Terminal K factor

A manufacturer-supplied multiplier that converts the square root of measured velocity pressure to airflow: CFM equals K times the square root of VP.

Proportional air balancing

Adjusting dampers so each branch carries the same percentage of its design airflow; the branch with the lowest percentage is used as the reference.

Outdoor air measurement

Measure intake airflow at the outdoor-air louver or flow station to confirm the minimum ventilation rate required by design and ASHRAE Standard 62.1.

Hydronic flow equation

Gallons per minute equal 2.448 times the inside diameter squared in inches times velocity in feet per second.

Water horsepower

Water horsepower equals gallons per minute times head in feet times specific gravity, divided by 3960; brake horsepower equals water horsepower divided by pump efficiency.

Hydronic sensible heat

For water near 60°F, Btu per hour equals 500 times gallons per minute times the temperature drop; glycol solutions require a lower constant.

Balance valve Cv

A valve's flow coefficient relates flow to pressure drop: flow equals Cv times the square root of differential pressure; use the manufacturer curve to set design flow.

Reverse-return piping

A piping arrangement that gives each terminal a nearly equal path length, reducing the need for balance valves compared with direct-return systems.

Pitot tube alignment

The impact port must face directly into airflow and the static ports must be perpendicular; misalignment beyond about ten degrees causes significant velocity error.

Flow hood backpressure

A balometer restricts grille airflow; apply the manufacturer's correction factor for hood size and airflow to avoid reading lower than actual.

Instrument calibration record

Record model, serial number, calibration date, and correction factors for every instrument; calibration must be traceable to a national standard such as NIST.

Sling psychrometer use

Wet-bulb and dry-bulb temperatures are read after slinging at proper velocity; the pair gives relative humidity and dew point on a psychrometric chart.

Infrared thermometer limits

Infrared meters infer temperature from emitted radiation; emissivity errors on shiny metal and distance-to-spot ratio can produce large errors, so contact sensors are preferred.

Anemometer traverse

Take multiple velocity readings across a duct or grille face, keep the probe perpendicular to flow, and average the readings to represent the area.

NEBB airflow tolerance

NEBB procedural standards typically require air quantities to be within plus or minus ten percent of design, with all terminals and branches measured and recorded.

TAB final report

The final report presents design versus actual airflow, water flow, pressures, temperatures, instrument calibration records, and a log of unresolved deficiencies.

Pre-balance checklist

Before balancing, verify fan rotation, belt tension, filter condition, damper and valve positions, and control sequence; corrections are documented and the system is rechecked.

Specification precedence

Contract documents state which document governs conflicts; addenda and RFIs modify the specifications, and the more stringent requirement usually governs.

NEBB certification

A NEBB-certified firm employs a certified professional, supervisor, and technicians, maintains instrument calibration, and undergoes quality assurance audits to keep certification.

Fan operating point

The intersection of the fan performance curve and the system curve; system pressure rises with the square of airflow, so the point moves as dampers change.

Pump best efficiency point

The flow and head at which a pump operates at maximum efficiency; operating far from this point causes vibration, cavitation, and bearing wear.

Parallel pump operation

Pumps in parallel add their flows at the same head; the combined operating point is found where the combined curve meets the system curve.

Opposed-blade damper

Blades rotate in opposite directions, producing a nearly linear airflow characteristic; parallel-blade dampers are used more for shutoff than modulation.

Coil sensible heat

At sea level, sensible Btu per hour equals 1.08 times airflow in CFM times the dry-bulb temperature difference across the coil.

Lockout tagout

Isolate and lock electrical, pneumatic, and hydraulic energy sources before service; verify zero energy and wait for rotating equipment to stop.

VFD capacitor hazard

Variable-frequency drives store dangerous voltage in capacitors; wait the manufacturer's specified discharge time before opening the enclosure.

Confined space entry

Test oxygen, flammable gas, and toxic gas before entry; use a permit, attendant, and rescue plan; never enter a confined space alone.

Ladder setup angle

Set an extension ladder at about a four-to-one ratio of working length to distance from the wall and maintain three points of contact while climbing.

Jobsite TAB coordination

Schedule balancing after duct cleaning and before ceiling closure, and coordinate with controls, electrical, and commissioning so systems are complete and operable.