AABC Test and Balance Engineer (TBE) flashcards

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

Sensible Heat Ratio

The ratio of sensible heat to total heat (sensible plus latent) for an airstream or coil load. Used to plot the room condition line on a psychrometric chart.

Apparatus Dew Point

The effective coil surface temperature at which the coil curve intersects the saturation line. Used with entering and leaving conditions to compute the coil bypass factor.

Coil Bypass Factor

Fraction of air passing the coil without contacting the surface. Computed as (entering DB minus leaving DB) divided by (entering DB minus ADP).

Sensible Heat Equation

For standard air, sensible heat in Btu/h equals 1.08 times cfm times the dry-bulb temperature difference. The constant 1.08 derives from air density and specific heat.

Total Heat Equation

For standard air, total heat in Btu/h equals 4.5 times cfm times the enthalpy difference in Btu per pound of dry air.

Velocity Pressure Formula

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

Pitot Tube Principle

Velocity pressure equals total pressure minus static pressure. The total-pressure port faces airflow; the static port is perpendicular to flow.

Expanded Uncertainty

Expanded uncertainty equals the coverage factor k times the combined standard uncertainty. k equals 2 gives approximately 95 percent confidence for a normal distribution.

Combined Standard Uncertainty

For independent error sources, combine by root-sum-square: the square root of the sum of the squares of each individual standard uncertainty component.

Percent of Full Scale Error

An accuracy stated as a percent of full scale yields a fixed absolute error. At low readings this becomes a large percentage of the measured value.

Calibration Traceability

An unbroken documented chain of comparisons linking the instrument to a national standard, with recorded as-found and as-left values at each step.

Equal-Area Traverse

Divide the duct cross-section into equal-area zones and average the square roots of the velocity pressures from each zone to obtain mean velocity pressure.

Traverse Location Rule

Locate the traverse at least 7.5 duct diameters downstream and 3 diameters upstream of elbows, transitions, or other flow disturbances where space permits.

Proportional Balancing

A method where the terminal with the lowest measured-to-design flow ratio is left fully open and other terminals are throttled to match that same ratio.

Airflow From Area

Volumetric flow in cubic feet per minute equals duct cross-sectional area in square feet multiplied by average velocity in feet per minute.

Pump Affinity Laws

Flow varies directly with speed, head with the square of speed, and power with the cube of speed. Used to predict performance at reduced speed.

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.

Valve Flow Coefficient Cv

Cv is the flow in gallons per minute of water at 60 F that passes through a fully open valve at a pressure drop of one psi.

System Curve

A plot of required head versus flow for a piping system. For turbulent flow, head varies with the square of flow; the operating point is where it crosses the pump curve.

Ventilation Rate Procedure

ASHRAE 62.1 method: breathing zone outdoor air equals people rate times occupants plus area rate times floor area.

Building Pressurization

Positive building pressure results when outdoor air intake exceeds exhaust and relief airflow. It limits infiltration but can cause moisture problems if excessive.

Hood Face Velocity

Average velocity at the hood opening, computed as exhaust airflow divided by hood face area. Used to verify capture and containment performance.

Stair Pressurization Test

Verify design differential pressure across the stair door with the door closed, and confirm the pressure holds under fire-mode fan and damper operation.

DDC Point Types

Analog input, analog output, digital input, and digital output. Each point is documented with range, units, and normal state in the point list.

Live Zero Signal

A 4-20 mA analog signal where 4 mA represents the minimum value. The nonzero minimum allows detection of a broken wire or failed transmitter.

Sensor Scaling Formula

Engineering value equals the fraction of signal span times the value span, plus the value minimum. Applied to convert raw analog signals to engineering units.

Functional Performance Test

A documented test confirming the sequence of operations under normal and failure modes, including forced outputs, trend review, and return to automatic control.

Balancing Report Contents

Design versus actual airflow, static pressures, fan speed, motor amperage, final damper and valve positions, calibration records, and a deficiency list.

Common Airflow Tolerance

A frequently specified balancing tolerance of plus or minus 10 percent of design airflow. The project specification governs the actual required tolerance.

AABC and NEBB Standards

Industry procedural standards that define balancing tolerances, instrument accuracy, report content, and certification requirements for test and balance work.

Confined Space Entry

Entry requiring atmospheric testing for oxygen, combustible gas, and toxics before and during entry, with an attendant stationed outside and a rescue plan.

Lockout Tagout

Isolation of all energy sources before servicing fans, pumps, or controls. Each worker applies a personal lock and verifies zero energy state.