AABC Test and Balance Engineer (TBE) key terms

The temperature of air measured by a thermometer exposed to the air but shielded from radiation and moisture. It indicates sensible heat content and is the temperature most people mean when they say 'air temperature.'

The lowest temperature air can reach through evaporative cooling, measured with a wetted wick and moving air. It combines temperature and moisture content and, paired with dry-bulb, fixes a point on the psychrometric chart.

The ratio of water vapor actually in the air to the maximum the air could hold at that temperature, expressed as a percentage. It changes as temperature changes even when the moisture amount stays the same.

The temperature at which air becomes saturated and water vapor begins to condense. Air cooled below its dew point produces condensation on surfaces, which matters for coil design and duct insulation.

The mass of water vapor per unit mass of dry air, usually given in grains or pounds of moisture per pound of dry air. It does not change when air is simply heated or cooled.

A graphical plot of air properties including dry-bulb, wet-bulb, dew point, humidity ratio, and enthalpy. Technicians use it to predict coil performance, mixing conditions, and supply-air states.

The total heat content of air per unit mass, combining sensible heat and latent heat of the moisture it carries. Enthalpy difference across a coil indicates total cooling or heating delivered.

Heat that changes the temperature of air without changing its moisture content. It is associated with dry-bulb temperature change and is measured in Btu per hour for airflow calculations.

Heat absorbed or released when water changes phase, such as evaporation or condensation, without a temperature change in the air. In HVAC it represents moisture removal or addition.

The fraction of total coil load that is sensible, calculated as sensible heat divided by total heat. A low ratio means the coil is doing substantial dehumidification work.

A reference density for air, commonly about 0.075 pounds per cubic mass at sea level and 70 degrees Fahrenheit. Corrections for altitude, temperature, and pressure are applied when converting measured airflow.

A probe with a forward-facing total pressure port and side-facing static ports that measures velocity pressure in a duct. Velocity pressure is converted to velocity using density and a standard equation.

The difference between total pressure and static pressure, representing the kinetic energy of moving air. Its square root is proportional to velocity, so small errors matter at low velocities.

A systematic set of velocity pressure or velocity readings taken at multiple points across a duct cross-section to estimate average flow. Point spacing follows a log-linear pattern for accuracy.

A calibrated capture device placed over a supply or return grille that measures volumetric flow directly. It must be sized and corrected for the grille type and backpressure effects.

An adjustable blade or vane installed in ductwork or at a terminal to regulate airflow during balancing. Its position is locked after adjustment so the setting remains stable.

A method of adjusting branch dampers so that airflows are corrected in proportion to design, converging quickly on the branch needing the most correction. It reduces repeated readjustment compared with trial-and-error balancing.

A factory-engineered duct section with pressure taps or sensing arrays that provides a repeatable airflow signal. It is calibrated and often used for continuous verification of system airflow.

Relationships showing how fan airflow, pressure, and power change with speed and diameter. Airflow varies with speed, pressure with speed squared, and power with speed cubed for a fixed system.

A plot of the pressure required to move various airflows through a given duct system. The operating point is where the system curve meets the fan curve.

The outward pressure exerted by air against duct walls, independent of flow direction. It is used to diagnose restrictions, filter loading, and fan performance.

An instrument that measures pressure difference, often using a liquid column or electronic sensor. Digital manometers are common for duct static pressure and filter pressure-drop readings.

The process of comparing an instrument's readings with a known reference and adjusting or documenting the difference. Traceability to a recognized standard is essential for valid measurements.

The range within which a true value is expected to lie, accounting for instrument accuracy, technique, and environmental effects. Reporting uncertainty clarifies how much confidence a measurement supports.

An unbroken chain of comparisons linking an instrument's calibration to a national or international standard. It documents that measurement results are defensible and reproducible.

A gradual change in an instrument's reading over time or with use, independent of the measured quantity. Regular calibration and field checks detect and correct drift before it affects results.

A graph of a pump's head or pressure versus flow at a given speed. The intersection with the system curve defines the actual operating point.

Relationships describing how pump flow, head, and power change with impeller speed or diameter. Flow varies with speed, head with speed squared, and power with speed cubed.

The formation and collapse of vapor bubbles in a pump when local pressure drops below vapor pressure. It causes noise, vibration, and damage and is avoided by maintaining adequate net positive suction head.

The margin of absolute pressure above a liquid's vapor pressure at the pump suction. Insufficient margin leads to cavitation and loss of performance.

A hydronic valve with a calibrated measuring port and adjustable setting used to set and verify design flow in a circuit. Its setting is recorded and locked after balancing.

The difference in pressure between two points in a system, used to infer flow across coils, valves, or filters. It is a key measurement for verifying hydronic balance.

The intentional pressure difference between indoor and outdoor spaces, controlled by balancing supply and exhaust air. Positive pressure limits infiltration; negative pressure controls contaminant migration.

The natural pressure difference caused by temperature-driven density differences between indoor and outdoor air. It makes buildings act like chimneys and shifts pressurization between floors.

The number of times the volume of air in a space is replaced per hour, calculated from supply or exhaust flow divided by room volume. It is used to verify ventilation and exhaust adequacy.

Confirming that exhaust systems move design airflow and maintain intended pressure relationships in spaces such as restrooms, kitchens, and laboratories. It includes hood capture and make-up air checks.

An electronic controller that varies motor speed by changing supply frequency and voltage. It enables airflow or flow modulation and interacts with the fan or pump laws.

A microprocessor-based control system that reads sensors and commands actuators through programmed logic. Technicians verify sensor calibration, setpoints, and sequences during commissioning.

A written description of how equipment and controls are intended to respond to conditions and commands. It is the basis for functional performance testing during verification.

A recorded time series of sensor or control values used to analyze system behavior over time. Trends support verification of sequences and diagnosis of intermittent problems.

A documented procedure that demonstrates a system operates as designed under specified conditions. Results are recorded and compared with the design intent and sequence of operation.

A quality-focused process of verifying and documenting that systems are installed and perform according to design intent and owner requirements. It spans design, construction, and acceptance phases.

The formal record of measured air and water flows, setpoints, and adjustments compared with design values. It documents deficiencies, corrections, and final balanced conditions for the owner.

The airflow specified by the designer for a terminal, zone, or system under stated conditions. It is the reference against which measured values are compared during balancing.

A volumetric airflow expressed at a defined reference density, allowing comparison of flows measured under different conditions. It differs from actual volumetric flow at field conditions.

The real airflow measured at the prevailing temperature, pressure, and moisture conditions. It must be converted to standard conditions when comparing with design or rating data.