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NEBB Testing, Adjusting and Balancing Certified Professional (CP) study materials
NEBB Testing, Adjusting and Balancing Certified Professional (CP) study resources

NEBB Testing, Adjusting and Balancing Certified Professional (CP) practice questions

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Question 1Testing, Adjusting and Balancing (TAB)

Before beginning any field measurements on a newly installed air-handling system, the TAB technician should first verify which of the following conditions?

  1. That the balancing dampers are locked in their final positions
  2. That the control contractor has finished all commissioning documentation
  3. That the system is clean, complete, and operating under design conditions Correct answer.
  4. That the owner has already accepted the building

Explanation

TAB work must start only after the system is mechanically complete, clean, and able to run continuously under design conditions. Premature balancing produces readings that cannot be repeated or certified, so readiness verification precedes all measurement.

Question 2Testing, Adjusting and Balancing (TAB)

A pitot tube traverse is being used to determine airflow in a rectangular duct. The velocity pressure readings are taken at which locations across the duct cross-section?

  1. At points of equal area in a grid pattern Correct answer.
  2. At the duct corners
  3. At randomly selected points along the duct length
  4. At the duct centerline only

Explanation

A proper traverse divides the duct cross-section into equal-area increments and measures velocity pressure at the centroid of each. This captures the velocity profile and yields an accurate average; a single centerline reading does not.

Question 3Testing, Adjusting and Balancing (TAB)

When measuring velocity pressure in a duct with a pitot-static tube, the total pressure port is connected to which side of the manometer?

  1. The high-pressure side Correct answer.
  2. The low-pressure (reference) side
  3. Neither side, because total pressure requires a separate probe
  4. Either side, since static pressure is independent of orientation

Explanation

Total pressure is the sum of static and velocity pressure, so the impact (total) port connects to the high-pressure side of the manometer while the static port connects to the low side. This arrangement reads velocity pressure directly.

Question 4Testing, Adjusting and Balancing (TAB)

A rotating vane anemometer is best suited for measuring air velocity at which location?

  1. At a supply diffuser face Correct answer.
  2. At the inlet of a centrifugal fan
  3. Inside a closed rectangular main duct
  4. Inside a lined round duct

Explanation

Rotating vane anemometers integrate velocity over their swept area, making them well suited to open plane surfaces such as diffuser and grille faces. They are less accurate in ductwork because the probe blocks a significant portion of the duct area.

Question 5Testing, Adjusting and Balancing (TAB)

The purpose of proportional balancing in a multi-branch duct system is to:

  1. Balance the system using only the main damper
  2. Set every terminal to its design airflow one at a time
  3. Establish correct flow ratios among branches before setting total flow Correct answer.
  4. Eliminate the need for a fan speed adjustment

Explanation

Proportional balancing adjusts branch dampers so that each branch carries its correct share of total airflow relative to the others. Once the ratios are correct, the total is set at the fan, and all terminals land on design simultaneously.

Question 6Testing, Adjusting and Balancing (TAB)

Which instrument is used to measure the rotational speed of a fan shaft during a TAB survey?

  1. A tachometer Correct answer.
  2. A velometer
  3. A hygrometer
  4. A manometer

Explanation

A tachometer measures shaft or wheel rotational speed, which is compared with fan curves to verify performance. Hygrometers measure humidity, manometers measure pressure, and velometers measure air velocity.

Question 7Testing, Adjusting and Balancing (TAB)

During a duct leakage test, the test pressure applied to a duct system is typically:

  1. Twice the design operating pressure
  2. Half the design operating pressure
  3. Independent of the design operating pressure
  4. Equal to the design operating pressure of the system Correct answer.

Explanation

Duct leakage testing is generally performed at the design operating static pressure, sometimes with a specified multiplier in the applicable standard. The measured leakage is compared against the allowable leakage class for the system.

Question 8Testing, Adjusting and Balancing (TAB)

A TAB report should record which of the following for each measured terminal?

  1. Only the design airflow
  2. Design airflow, measured airflow, and the instrument used Correct answer.
  3. Only the final airflow value
  4. The contractor's opinion of system performance

Explanation

A defensible TAB report documents design versus measured values and the instrument used so results can be verified or repeated. Recording only one value or opinions provides no traceable evidence of performance.

Question 9Testing, Adjusting and Balancing (TAB)

A technician measures a velocity pressure of 0.25 in. w.c. in a duct. What is the approximate air velocity? (Use V = 4005 × √Vp.)

  1. 1000 fpm
  2. 500 fpm
  3. 4000 fpm
  4. 2000 fpm Correct answer.

Explanation

Applying the standard formula, the square root of 0.25 is 0.5, and 4005 × 0.5 equals approximately 2000 fpm. The velocity is then multiplied by duct area to obtain airflow.

Question 10Testing, Adjusting and Balancing (TAB)

A round duct has a diameter of 12 inches and an average velocity of 1200 fpm. What is the approximate airflow?

  1. 1884 cfm
  2. 471 cfm
  3. 1200 cfm
  4. 942 cfm Correct answer.

Explanation

Area equals π times radius squared, which for a 12-inch duct is about 0.785 square feet. Multiplying 0.785 ft² by 1200 fpm gives approximately 942 cfm.

Question 11Testing, Adjusting and Balancing (TAB)

A technician observes that adjusting one branch damper changes airflow in an adjacent branch. This behavior is best described as:

  1. Fan surge
  2. Damper hysteresis
  3. System interaction Correct answer.
  4. System effect

Explanation

System interaction occurs when changing one component's resistance alters flows elsewhere in a shared network. It is the reason proportional balancing is performed in a defined sequence rather than terminal by terminal.

Question 12Testing, Adjusting and Balancing (TAB)

To measure the airflow of a small exhaust grille where a traverse is impractical, the most appropriate method is:

  1. A tachometer reading at the exhaust fan
  2. A static pressure reading at the fan
  3. A flow hood placed over the grille face Correct answer.
  4. A pitot tube traverse inside the branch duct

Explanation

A flow hood captures and straightens the air leaving a grille, allowing accurate volumetric measurement where duct access is unavailable. Pitot traverses require accessible straight duct, and fan readings do not isolate individual grille flow.

Question 13Testing, Adjusting and Balancing (TAB)

A fan delivers less airflow than its design curve predicts. Which condition most likely explains the shortfall?

  1. A fan with a larger impeller than specified
  2. Excessive system resistance from undersized or obstructed ductwork Correct answer.
  3. A duct system with less resistance than designed
  4. A fan operating at a higher speed than specified

Explanation

When actual system resistance exceeds the design curve, the fan operates further left on its curve and delivers less airflow. Higher speed, lower resistance, or a larger impeller would all increase airflow rather than reduce it.

Question 14Testing, Adjusting and Balancing (TAB)

The primary reason for recording initial (pre-balance) readings is to:

  1. Establish a baseline that documents existing conditions and identifies deficiencies Correct answer.
  2. Determine the contractor's payment schedule
  3. Satisfy the owner's aesthetic requirements
  4. Replace the need for final readings

Explanation

Initial readings document the as-found condition, revealing deficiencies such as incorrect fan rotation or blocked coils before balancing begins. They also protect the TAB technician from being blamed for pre-existing problems.

Question 15Testing, Adjusting and Balancing (TAB)

In a variable air volume system, terminal airflow is verified at which operating condition?

  1. Only when the fan is off
  2. Only at minimum airflow
  3. At both maximum and minimum design airflow Correct answer.
  4. Only at maximum design airflow

Explanation

VAV terminals must be verified across their full operating range, including maximum and minimum airflow setpoints. Checking only one condition leaves the other unverified and can mask control or damper problems.

Question 16Testing, Adjusting and Balancing (TAB)

A technician reads 0.50 in. w.c. velocity pressure in a duct with a 1.0 ft² area. What is the approximate airflow?

  1. 2000 cfm
  2. 1415 cfm
  3. 2830 cfm Correct answer.
  4. 4000 cfm

Explanation

Velocity equals 4005 times the square root of 0.50, or about 2832 fpm. Multiplying by the 1.0 ft² area yields approximately 2830 cfm.

Question 17Testing, Adjusting and Balancing (TAB)

Which practice best reduces measurement error when using a differential pressure manometer?

  1. Using the highest available range
  2. Ignoring temperature during measurement
  3. Reading with the instrument held vertically
  4. Zeroing the instrument before each reading series Correct answer.

Explanation

Zeroing removes offset errors and establishes a reliable reference before readings are taken. Proper orientation, appropriate range selection, and temperature awareness also affect accuracy, but zeroing is the fundamental step.

Question 18Testing, Adjusting and Balancing (TAB)

During balancing, a technician finds a branch with airflow far below design while the main is at design. The most likely cause is:

  1. A fan operating at excessive speed
  2. An oversized main duct
  3. A closed or obstructed branch damper or terminal Correct answer.
  4. A low total system static pressure

Explanation

A branch starved of flow while the main is at design points to localized resistance such as a closed damper, blocked coil, or faulty terminal. System-wide causes would depress flow across all branches, not just one.

Question 19Testing, Adjusting and Balancing (TAB)

The purpose of a duct static pressure profile taken during TAB is to:

  1. Measure the fan's rotational speed
  2. Determine the refrigerant charge
  3. Verify the building's electrical demand
  4. Document the pressure gradient along the system to locate excessive losses Correct answer.

Explanation

A static pressure profile plots pressure at points along the duct run, revealing abrupt drops that indicate restrictions or design deficiencies. It is a diagnostic tool for locating resistance problems, not for electrical or refrigerant verification.

Question 20Testing, Adjusting and Balancing (TAB)

In proportional balancing, the reference branch is typically:

  1. The branch with the highest measured percentage of design airflow Correct answer.
  2. The branch nearest the fan
  3. The branch with the largest duct diameter
  4. The branch with the lowest design airflow

Explanation

The branch already closest to (or above) its design percentage is used as the reference, and other branches are adjusted to match its ratio. This minimizes total damper pressure loss and avoids over-throttling.

Question 21Testing, Adjusting and Balancing (TAB)

A technician must balance a system where the fan delivers more total airflow than design. The correct first action is to:

  1. Throttle branch dampers until total flow matches design
  2. Reduce fan speed or adjust the fan to design airflow Correct answer.
  3. Add resistance by closing the main damper
  4. Accept the higher airflow as beneficial

Explanation

Excess total flow should be corrected at the fan by reducing speed or adjusting the drive, rather than by adding artificial resistance at dampers. Throttling branches first wastes energy and complicates proportional balancing.

Question 22Testing, Adjusting and Balancing (TAB)

The measured airflow at a diffuser is 380 cfm against a design of 400 cfm. Expressed as a percentage of design, and applying a typical ±10% tolerance, the result is:

  1. 105%, which is within tolerance
  2. 95%, which is outside tolerance
  3. 95%, which is within tolerance Correct answer.
  4. 90%, which is outside tolerance

Explanation

Dividing 380 by 400 gives 0.95, or 95% of design. A ±10% tolerance band spans 90% to 110%, so 95% falls comfortably within acceptable limits.

Question 23Testing, Adjusting and Balancing (TAB)

A technician measures a velocity pressure that produces a calculated velocity of 1500 fpm in a duct with 1.5 ft² area. What is the approximate airflow?

  1. 1500 cfm
  2. 2250 cfm Correct answer.
  3. 1000 cfm
  4. 3000 cfm

Explanation

Airflow equals velocity times area, so 1500 fpm multiplied by 1.5 ft² gives 2250 cfm. This straightforward multiplication is the final step after velocity is derived from velocity pressure.

Question 24Testing, Adjusting and Balancing (TAB)

Which condition would most likely invalidate a duct traverse reading?

  1. Traverse taken with a calibrated pitot tube
  2. Traverse taken at equal-area points
  3. Traverse taken in a straight duct section with several diameters of upstream length
  4. Traverse taken immediately downstream of an elbow Correct answer.

Explanation

A traverse taken just downstream of an elbow encounters a skewed, non-uniform velocity profile that produces a misleading average. Adequate straight duct upstream and downstream of the measurement plane is essential for valid results.

Question 25Testing, Adjusting and Balancing (TAB)

A balancing report shows a branch at 130% of design while all others are near design. The most defensible engineering conclusion is that:

  1. The measurement instrument is faulty
  2. The branch damper is likely fully open and requires adjustment or the branch is oversized Correct answer.
  3. The fan is undersized for the entire system
  4. The entire system must be rebalanced from scratch

Explanation

A single branch far above design while others are correct indicates localized excess capacity, such as a wide-open damper or oversized branch. System-wide causes would affect all branches, and instrument failure would not isolate to one terminal.

Question 26Testing, Adjusting and Balancing (TAB)

During a pitot-tube traverse of a rectangular duct, a technician records velocity pressure readings that vary widely across the cross-section. Which measurement practice yields the most representative average velocity pressure?

  1. Use only the reading taken at the duct centerline
  2. Use only the highest velocity pressure reading as the average
  3. Average the readings arithmetically and convert that average to velocity
  4. Convert each velocity pressure to velocity, then average the velocities Correct answer.

Explanation

Velocity pressure varies with the square of velocity, so averaging velocity pressures arithmetically understates the true average velocity. Each reading must first be converted to velocity using V = 4005√VP, and those velocities are then averaged. This procedure is standard for a duct traverse and gives a defensible average velocity.

Question 27Testing, Adjusting and Balancing (TAB)

A technician is preparing to measure airflow at a supply diffuser using a flow hood. Which condition must be verified before the reading is accepted?

  1. The air handler is off and the duct is at zero static pressure
  2. The flow hood is calibrated for water columns rather than air velocity
  3. The diffuser vanes are fully open and the hood is sealed to the diffuser face Correct answer.
  4. The diffuser is temporarily removed to expose the duct throat

Explanation

A flow hood measures airflow by capturing the entire discharge at the diffuser face. The hood must be sealed to the diffuser so no air escapes around the edges, and the diffuser must be in its normal operating position with vanes set as designed. Removing the diffuser or reading with the fan off would not represent design operation.

Question 28Testing, Adjusting and Balancing (TAB)

A technician is balancing a constant-volume system and finds that the total airflow at the air handler is 10% above design while all branch dampers are wide open. What is the appropriate first step?

  1. Record the excess airflow and proceed to balance the branches proportionally
  2. Close the branch dampers farthest from the fan to absorb the excess
  3. Reduce fan speed or add resistance at the fan to bring total airflow to design Correct answer.
  4. Increase the fan speed to make the excess airflow more measurable

Explanation

Total airflow must be set to design before branch balancing begins. If the fan delivers more than design airflow with all dampers open, the fan output must be reduced by speed adjustment, sheave change, or a balancing damper at the fan. Balancing branches against an incorrect total airflow will not produce a correct system.

Question 29Testing, Adjusting and Balancing (TAB)

A technician measures a static pressure of 1.2 in. w.c. in a duct and a velocity pressure of 0.16 in. w.c. at the same location. What is the total pressure at that point?

  1. 1.04 in. w.c.
  2. 0.16 in. w.c.
  3. 1.20 in. w.c.
  4. 1.36 in. w.c. Correct answer.

Explanation

Total pressure is the algebraic sum of static pressure and velocity pressure. Adding 1.2 in. w.c. static and 0.16 in. w.c. velocity gives 1.36 in. w.c. total pressure. This relationship is fundamental to interpreting duct pressure measurements.

Question 30Testing, Adjusting and Balancing (TAB)

A technician is measuring the airflow of a large return grille using a flow hood, but the hood is smaller than the grille opening. Which approach is most appropriate?

  1. Place the hood over one section and multiply the reading by the area ratio
  2. Seal the unused portion of the grille with cardboard and read the open section
  3. Record the reading as invalid and omit the grille from the report
  4. Use a velocity traverse with a thermal anemometer and average the readings Correct answer.

Explanation

When a flow hood cannot cover the entire grille, a velocity traverse across the grille face with an anemometer provides a representative average velocity. Multiplying that average by the free area gives airflow. Scaling a partial hood reading or blocking part of the grille changes the flow pattern and does not yield a reliable measurement.

Question 31Testing, Adjusting and Balancing (TAB)

During a TAB survey, a technician observes that the static pressure at the fan discharge is 0.5 in. w.c. lower than the design value. Which condition is most consistent with this observation?

  1. The fan is operating at a lower speed than design Correct answer.
  2. The fan is moving more air than design
  3. The filter bank is cleaner than design
  4. The duct system has less resistance than design

Explanation

Fan static pressure is generated by fan speed and absorbed by system resistance. A lower-than-design discharge static pressure at the fan indicates the fan is producing less pressure, which is consistent with reduced fan speed. Less system resistance would tend to increase airflow and reduce static pressure at the fan, but the direct cause of reduced fan pressure is reduced fan speed.

Question 32Testing, Adjusting and Balancing (TAB)

A technician is preparing to measure airflow in a duct using a pitot tube. Which condition would most likely cause an inaccurate traverse?

  1. The pitot tube is aligned with the airflow direction
  2. The duct has a straight run upstream of the measurement point
  3. The traverse is taken immediately downstream of an elbow Correct answer.
  4. The traverse is taken at a location with a uniform velocity profile

Explanation

A duct traverse requires a stable, uniform velocity profile, which develops only after a sufficient straight run. Taking the traverse immediately downstream of an elbow introduces swirl and non-uniform flow, making the average velocity unrepresentative. Proper traverse locations are typically several duct diameters downstream of disturbances.

Question 33Testing, Adjusting and Balancing (TAB)

A technician is balancing a variable air volume system and needs to verify the minimum airflow at a VAV terminal. Which condition should be established before taking the reading?

  1. The terminal is disconnected from the controller and manually held open
  2. The terminal is commanded to its maximum airflow setpoint and the fan is at minimum speed
  3. The system is operating in unoccupied mode with the fan off
  4. The terminal is commanded to its minimum airflow setpoint and the fan is at design static pressure Correct answer.

Explanation

Minimum airflow verification requires the terminal to be at its minimum setpoint while the system provides design static pressure. This confirms the terminal can control down to its minimum under normal operating conditions. Maximum airflow verification is a separate test, and disabling controls or shutting the fan off does not represent operation.

Question 34Testing, Adjusting and Balancing (TAB)

A technician is using a differential pressure manometer to measure duct static pressure. Which practice best reduces measurement error?

  1. Zero the manometer with both ports open to atmosphere before connecting Correct answer.
  2. Take a single reading and record it immediately
  3. Connect the high port to the duct and leave the low port open to the duct
  4. Use the longest possible tubing runs to reach the duct

Explanation

Zeroing the manometer with both ports at atmospheric pressure establishes a true reference before measurement. This compensates for sensor offset and ambient conditions. Leaving a port open to the duct or using long tubing can introduce errors, and a single reading may not be representative.

Question 35Testing, Adjusting and Balancing (TAB)

A technician is balancing a system with several branches and finds that adjusting one branch damper changes airflow in an adjacent branch. This behavior is best described as:

  1. System effect
  2. Interdependency Correct answer.
  3. Damper hysteresis
  4. Static regain

Explanation

When adjusting one branch affects airflow in another, the branches are interdependent. This is common in duct systems where dampers share a common plenum or main. Proportional balancing methods are used to account for interdependency and achieve a stable balance.

Question 36Testing, Adjusting and Balancing (TAB)

A technician measures a velocity pressure of 0.09 in. w.c. in a duct. What is the approximate air velocity?

  1. 1200 fpm Correct answer.
  2. 1500 fpm
  3. 900 fpm
  4. 1800 fpm

Explanation

Using the relationship V = 4005√VP, the square root of 0.09 is 0.3, and 4005 × 0.3 equals approximately 1200 fpm. This conversion is standard for pitot-tube measurements in air.

Question 37Testing, Adjusting and Balancing (TAB)

During a TAB investigation, a technician finds that a branch duct has airflow far below design while the main duct is at design airflow. Which cause is most likely?

  1. The main duct static pressure is lower than design
  2. The branch diffusers are oversized for the design airflow
  3. The fan is operating at a higher speed than design
  4. The branch damper is partially closed or an obstruction exists in the branch Correct answer.

Explanation

If the main is at design airflow but a branch is starved, the restriction is local to that branch. A partially closed damper or an obstruction such as debris or a collapsed liner would reduce branch airflow. Fan speed and main static pressure affect the whole system, and oversized diffusers would tend to reduce velocity but not necessarily airflow.

Question 38Testing, Adjusting and Balancing (TAB)

A technician is recording initial readings before balancing a system. What is the primary purpose of these initial readings?

  1. To verify that the building is ready for occupancy
  2. To determine the required fan speed for design airflow
  3. To establish a baseline for comparing final balanced conditions Correct answer.
  4. To calculate the system's total pressure loss

Explanation

Initial readings document the system's condition before any balancing adjustments. They provide a baseline that shows the effect of balancing and help identify problems such as closed dampers or obstructions. Final readings are compared against this baseline to confirm the balance.

Question 39Testing, Adjusting and Balancing (TAB)

A technician is balancing a system and needs to determine the airflow through a rectangular duct measuring 12 in. by 24 in. with an average velocity of 800 fpm. What is the approximate airflow?

  1. 2400 cfm
  2. 800 cfm
  3. 1200 cfm
  4. 1600 cfm Correct answer.

Explanation

The duct area is 12 in. × 24 in. = 288 in², which equals 2.0 ft². Multiplying area by velocity (2.0 ft² × 800 fpm) gives 1600 cfm. This is the standard airflow equation Q = A × V.

Question 40Testing, Adjusting and Balancing (TAB)

A technician is using a flow hood to measure airflow at a diffuser and obtains a reading of 250 cfm. The design airflow is 300 cfm. What is the percentage of design airflow?

  1. 83% Correct answer.
  2. 75%
  3. 133%
  4. 120%

Explanation

Percentage of design is calculated as (measured ÷ design) × 100. Here, 250 ÷ 300 = 0.833, or approximately 83%. This value indicates the diffuser is delivering less than design airflow and may require adjustment.

Question 41Testing, Adjusting and Balancing (TAB)

During a TAB survey, a technician notices that the airflow at a diffuser fluctuates significantly over time. Which condition is the most likely cause?

  1. The system is a variable air volume system modulating in response to load Correct answer.
  2. The duct static pressure is stable at the design value
  3. The diffuser is fully open and unobstructed
  4. The diffuser is located near a return grille causing short-circuiting

Explanation

In a variable air volume system, terminal airflow modulates in response to space load, so fluctuations are expected. Stable static pressure and an unobstructed diffuser would not cause fluctuation. Short-circuiting affects air quality but is not the primary cause of airflow variation over time.

Question 42Testing, Adjusting and Balancing (TAB)

A technician is preparing to measure the airflow of a fan using a pitot traverse in the fan discharge duct. Which location is most appropriate?

  1. At the center of the fan housing
  2. At a location with a straight duct run of at least several duct diameters downstream of the fan Correct answer.
  3. At a point just upstream of the fan inlet
  4. Immediately at the fan discharge flange

Explanation

A pitot traverse requires a stable, uniform velocity profile, which develops several duct diameters downstream of the fan. Measuring at the discharge flange or fan inlet is affected by turbulence and non-uniform flow. The fan housing is not a duct location for traverse.

Question 43Testing, Adjusting and Balancing (TAB)

A technician is balancing a system and finds that a branch damper must be nearly closed to achieve design airflow. What does this indicate about the system?

  1. The branch has excessive resistance and the fan is undersized
  2. The branch diffusers are undersized
  3. The branch damper is leaking air
  4. The branch has low resistance and the fan is delivering excess pressure Correct answer.

Explanation

If a damper must be nearly closed to reduce airflow to design, the branch is receiving more pressure than needed, indicating low branch resistance or excess fan pressure. This is common when a branch is short or oversized relative to the fan. An undersized fan would require dampers to be wide open to meet design airflow.

Question 44Testing, Adjusting and Balancing (TAB)

A technician is measuring the static pressure across a filter bank and finds a reading of 0.8 in. w.c. The filter manufacturer specifies an initial pressure drop of 0.3 in. w.c. and a final pressure drop of 1.0 in. w.c. What does the reading indicate?

  1. The filters are approaching the end of their service life Correct answer.
  2. The filters are clean and within normal operating range
  3. The filters have failed and must be replaced immediately
  4. The pressure gauge is out of calibration

Explanation

The measured pressure drop of 0.8 in. w.c. is between the initial 0.3 in. w.c. and final 1.0 in. w.c. values, indicating the filters are loading but not yet at the final setpoint. They should be monitored and scheduled for replacement before reaching 1.0 in. w.c. A reading above 1.0 in. w.c. would indicate replacement is due.

Question 45Testing, Adjusting and Balancing (TAB)

A technician is balancing a system and needs to measure the airflow at a terminal unit that is not equipped with a flow measuring station. Which method is most appropriate?

  1. Estimate airflow from the terminal's size and fan curve
  2. Use a pitot tube traverse in the flexible duct serving the terminal
  3. Read the terminal's controller setpoint and assume it matches actual airflow
  4. Use a flow hood at the associated diffusers and sum the readings Correct answer.

Explanation

When a terminal lacks a flow measuring station, the airflow can be determined by measuring at the diffusers served by that terminal and summing the results. A pitot traverse in flexible duct is unreliable due to turbulence and non-uniform profile. Controller setpoints and estimates do not provide measured airflow.

Question 46Testing, Adjusting and Balancing (TAB)

During a TAB survey, a technician measures the airflow at a supply diffuser and finds it is 20% above design. Which action is most appropriate?

  1. Adjust the branch damper to reduce airflow to design Correct answer.
  2. Increase the fan speed to balance the system
  3. Close the diffuser completely and reopen it halfway
  4. Record the reading and take no action

Explanation

If a diffuser is delivering more than design airflow, the branch damper serving it should be adjusted to reduce flow to design. Increasing fan speed would worsen the imbalance. Recording without action leaves the system out of balance, and completely closing the diffuser is not a controlled adjustment.

Question 47Testing, Adjusting and Balancing (TAB)

A technician is using a thermal anemometer to measure airflow at a grille. Which practice improves the accuracy of the measurement?

  1. Measure with the system fan off
  2. Hold the probe perpendicular to the grille face
  3. Take a single reading at the center of the grille
  4. Hold the probe parallel to the airflow direction Correct answer.

Explanation

A thermal anemometer measures velocity along the axis of the probe. Holding the probe parallel to the airflow ensures the sensor is exposed to the full velocity. A single center reading may not represent the average, and the fan must be operating to measure airflow.

Question 48Testing, Adjusting and Balancing (TAB)

A technician is balancing a system and finds that the total airflow at the air handler is 5% below design while all branch dampers are wide open. Which condition is most likely?

  1. The filters are cleaner than design
  2. The fan is operating at a lower speed than design Correct answer.
  3. The duct system has less resistance than design
  4. The branch dampers are oversized

Explanation

If all dampers are wide open and total airflow is still below design, the fan is not producing enough pressure or flow. A lower fan speed would reduce airflow. Less system resistance or cleaner filters would tend to increase airflow, not decrease it.

Question 49Testing, Adjusting and Balancing (TAB)

A technician is preparing a TAB report and needs to document the measured airflow at each terminal. Which information is essential to include for each terminal?

  1. The name of the installing contractor only
  2. The room temperature and humidity only
  3. Design airflow, measured airflow, and the date of measurement Correct answer.
  4. The terminal manufacturer and model number only

Explanation

A TAB report must record the design airflow and the measured airflow for each terminal so that the balance can be evaluated. The date of measurement provides traceability. Manufacturer, room conditions, and contractor information may be included but are not the essential airflow data.

Question 50Testing, Adjusting and Balancing (TAB)

A technician is balancing a system with a fan that delivers 12,000 cfm at design conditions. The system has two branches, each designed for 6,000 cfm. After adjustment, branch A reads 6,600 cfm and branch B reads 5,400 cfm. What is the percentage of design airflow for branch B?

  1. 110%
  2. 120%
  3. 90% Correct answer.
  4. 100%

Explanation

Branch B's measured airflow is 5,400 cfm against a design of 6,000 cfm. Dividing 5,400 by 6,000 gives 0.90, or 90% of design. This indicates branch B is 10% below design and requires further adjustment.