CCP HVAC TAB & Functional Testing 3 — Questions and Answers
Question 1: A hydronic system's pump is producing design flow but inadequate head pressure. What does this most likely indicate?
- Pump impeller wear or incorrect impeller installed (Correct answer)
- Excessive pipe insulation
- Oversized expansion tank
- Incorrect water temperature
Correct answer: Pump impeller wear or incorrect impeller installed
When flow is correct but head is insufficient, pump impeller wear or an incorrectly sized impeller reduces the pump's ability to develop pressure.
Question 2: During functional testing of an economizer, what outdoor air condition triggers the changeover from economizer to mechanical cooling?
- When outdoor air temperature drops below 55°F
- When outdoor air enthalpy or temperature exceeds the high-limit setpoint (Correct answer)
- When building occupancy reaches 50%
- When supply air temperature drops below 60°F
Correct answer: When outdoor air enthalpy or temperature exceeds the high-limit setpoint
The economizer high-limit setpoint (enthalpy or dry-bulb) triggers changeover to mechanical cooling when outdoor conditions are no longer suitable for free cooling.
Question 3: What is the acceptable tolerance for air balancing of supply terminals per NEBB procedural standards?
- +/- 5% of design
- +/- 10% of design (Correct answer)
- +/- 15% of design
- +/- 20% of design
Correct answer: +/- 10% of design
NEBB procedural standards specify a +/- 10% tolerance for supply air terminal balancing as the acceptable variance from design airflow.
Question 4: During commissioning functional testing, a cooling tower bypass valve is tested. What scenario verifies correct control sequence?
- Valve stays fully open regardless of condenser water temperature
- Valve modulates to maintain condenser water supply temperature at setpoint (Correct answer)
- Valve closes completely when outdoor wet-bulb exceeds 70°F
- Valve position is fixed at 50% during all testing
Correct answer: Valve modulates to maintain condenser water supply temperature at setpoint
Correct cooling tower bypass valve operation modulates to maintain condenser water supply temperature at design setpoint across varying outdoor conditions.
Question 5: Which of the following best describes the difference between TAB and commissioning functional testing?
- TAB focuses on controls verification; commissioning measures airflow
- TAB quantifies and adjusts flows to design; commissioning verifies sequence of operations (Correct answer)
- TAB is performed after commissioning is complete
- There is no practical difference between the two activities
Correct answer: TAB quantifies and adjusts flows to design; commissioning verifies sequence of operations
TAB quantifies, adjusts, and documents fluid flow rates to match design; commissioning functional testing verifies that systems operate correctly through all control sequences.
Question 6: A dual-duct VAV system's hot deck is providing 10°F less than design heating supply temperature. What component should be investigated first?
- Supply fan motor amperage
- Heating coil control valve and actuator operation (Correct answer)
- Return air damper position
- Mixed air temperature sensor
Correct answer: Heating coil control valve and actuator operation
Insufficient hot deck temperature is most directly caused by a control valve not fully opening or an actuator failure limiting heating coil flow.
Question 7: When conducting a duct leakage test, what does a high leakage class (CL) value indicate?
- The duct system is well-sealed and efficient
- Greater allowed leakage per unit of surface area (Correct answer)
- Lower duct static pressure operating range
- Better energy performance than code minimum
Correct answer: Greater allowed leakage per unit of surface area
SMACNA leakage class (CL) values indicate maximum allowable leakage — a higher CL means more leakage is permitted per unit of duct surface area at test pressure.
CCP HVAC TAB & Functional Testing 3
A hydronic system's pump is producing design flow but inadequate head pressure.
What does this most likely indicate?