Building Engineering Mechanical Engineering 4 — Questions and Answers
Question 1: What does the MERV rating system classify for HVAC air filters?
- Maximum rated energy recovery ventilation efficiency
- Minimum efficiency reporting value for particle capture efficiency (Correct answer)
- Manufacturer's endorsed resistance value for pressure drop
- Mean evaporative resistance value for humidity control
Correct answer: Minimum efficiency reporting value for particle capture efficiency
MERV (Minimum Efficiency Reporting Value) rates filters from 1–16 based on their ability to capture particles of specific sizes, with higher numbers indicating finer filtration.
Question 2: When sizing an expansion tank for a closed hydronic system, what is the primary variable the tank must accommodate?
- Diurnal pressure variation from the municipal supply main
- Volume change of water as it heats from fill temperature to operating temperature (Correct answer)
- Pump cavitation pressure spikes during startup
- Static head pressure from the building's top floor
Correct answer: Volume change of water as it heats from fill temperature to operating temperature
Water expands as it heats; the expansion tank provides a sealed air cushion to absorb this volume increase and keep system pressure within design limits.
Question 3: According to ASHRAE 90.1 energy code, what control is required for HVAC systems serving spaces with variable occupancy to reduce energy use during unoccupied hours?
- Demand-controlled ventilation (DCV) based on CO₂ sensors
- Occupancy scheduling with setback temperature control (Correct answer)
- Variable air volume (VAV) terminal units at every zone
- Economizer lockout when outdoor air exceeds 65°F
Correct answer: Occupancy scheduling with setback temperature control
ASHRAE 90.1 requires programmable setback controls that reduce heating and cooling set points during unoccupied periods, reducing energy consumption.
Question 4: What is 'hydronic balancing' and why is it performed on a new building's heating/cooling water system?
- Testing pipe welds for leaks using pressurized nitrogen
- Adjusting flow rates at each terminal to match design values so all zones receive adequate capacity (Correct answer)
- Flushing debris from piping before startup to protect equipment
- Setting relief valve pressure to match system design pressure
Correct answer: Adjusting flow rates at each terminal to match design values so all zones receive adequate capacity
Hydronic balancing adjusts balancing valves so each coil or terminal receives its design flow rate, preventing overflowing near terminals and starving remote ones.
Question 5: A mechanical engineer specifies 'low-leakage' dampers in a pressurized air system. Which AMCA rating class would meet the most stringent leakage requirement?
- AMCA Class I (Correct answer)
- AMCA Class II
- AMCA Class III
- AMCA Class IV
Correct answer: AMCA Class I
AMCA Class I dampers have the lowest permissible leakage rate, making them appropriate for critical pressurized applications like smoke control and clean rooms.
Question 6: In a steam heating system, what is the primary function of a steam trap?
- Regulate steam pressure entering the distribution system
- Prevent steam from passing while allowing condensate and air to discharge (Correct answer)
- Remove dissolved oxygen from the boiler feedwater
- Maintain constant steam flow to each heating terminal
Correct answer: Prevent steam from passing while allowing condensate and air to discharge
Steam traps automatically discharge condensate and non-condensable gases from the steam space while blocking live steam from escaping, maintaining system efficiency.
Question 7: What mechanical property is evaluated when specifying pipe hangers to prevent vibration transmission from pumps to a building structure?
- Hanger rod tensile strength rating
- Spring isolator static deflection (Correct answer)
- Clevis bolt torque specification
- Pipe clamp coefficient of friction
Correct answer: Spring isolator static deflection
Spring isolators for pipe hangers are specified by static deflection; greater deflection provides better isolation of low-frequency pump and pipe vibration from the structure.
Building Engineering Mechanical Engineering 4
What does the MERV rating system classify for HVAC air filters?