AFE Building Systems & Maintenance 3 — Questions and Answers
Question 1: A variable air volume (VAV) system reduces airflow to a zone when cooling demand drops. What risk does this create if not properly managed?
- Increased duct static pressure trips safety controls
- Inadequate outdoor air ventilation below ASHRAE 62.1 minimums (Correct answer)
- Excessive humidity in the supply duct
- Premature failure of the supply fan bearings
Correct answer: Inadequate outdoor air ventilation below ASHRAE 62.1 minimums
At minimum airflow positions, VAV boxes may supply less outdoor air than required, violating ASHRAE 62.1 ventilation standards and degrading indoor air quality.
Question 2: Which insulation material is most appropriate for a chilled water pipe operating at 42°F in a humid environment?
- Fiberglass with vapor retarder jacket (Correct answer)
- Calcium silicate
- Cellular glass
- Mineral wool
Correct answer: Fiberglass with vapor retarder jacket
Fiberglass with a continuous vapor retarder jacket prevents condensation on below-ambient piping by blocking moisture diffusion from the warm, humid surrounding air.
Question 3: What NFPA standard governs the inspection, testing, and maintenance of fire protection systems including sprinklers?
- NFPA 70
- NFPA 25 (Correct answer)
- NFPA 72
- NFPA 101
Correct answer: NFPA 25
NFPA 25 is the Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.
Question 4: A cooling tower's approach temperature is defined as:
- The difference between entering and leaving water temperatures
- The difference between leaving water temperature and ambient wet-bulb temperature (Correct answer)
- The difference between dry-bulb and wet-bulb temperatures
- The temperature of water returned from the chiller
Correct answer: The difference between leaving water temperature and ambient wet-bulb temperature
Approach temperature is the leaving water temperature minus the ambient wet-bulb temperature; a smaller approach indicates a more efficient tower.
Question 5: What is the correct torque sequence when retightening large flange bolts on a pressurized piping joint?
- Clockwise from the first bolt installed
- Sequential in a star or cross pattern to ensure even gasket compression (Correct answer)
- Random sequence to spread load
- Tighten to finger-tight then fully torque in one pass
Correct answer: Sequential in a star or cross pattern to ensure even gasket compression
A star or cross-pattern torque sequence distributes load evenly across the gasket, preventing leaks caused by uneven compression or gasket deformation.
Question 6: Which term describes the ratio of actual evaporation water loss to circulating water flow in a cooling tower, expressed as a percentage?
- Blowdown rate
- Drift loss
- Evaporation rate (Correct answer)
- Cycles of concentration
Correct answer: Evaporation rate
The evaporation rate (typically 1–2% of circulating flow) represents water lost to the atmosphere as vapor, which is the primary cooling mechanism.
Question 7: A facility's 480V three-phase distribution panel shows a voltage unbalance of 4.5%. What is the most likely consequence for connected three-phase motors?
- Increased motor speed above nameplate
- Reduced torque output and excessive heat in rotor windings (Correct answer)
- Tripping of motor branch circuit breakers only
- No significant effect below 5% unbalance
Correct answer: Reduced torque output and excessive heat in rotor windings
NEMA MG-1 states that a 3.5% voltage unbalance can cause a temperature rise of approximately 25%, significantly reducing motor life and torque output.
AFE Building Systems & Maintenance 3
A variable air volume (VAV) system reduces airflow to a zone when cooling demand drops.
What risk does this create if not properly managed?