Certified Energy Auditor Certification HVAC Systems and Controls 2 — Questions and Answers
Question 1: What is the primary purpose of an economizer cycle in an HVAC system?
- Reduce refrigerant charge
- Use outdoor air for free cooling when conditions allow (Correct answer)
- Increase compressor efficiency
- Preheat supply air in winter
Correct answer: Use outdoor air for free cooling when conditions allow
An economizer uses outdoor air for cooling when outside conditions are favorable, reducing or eliminating mechanical cooling energy.
Question 2: A chiller's coefficient of performance (COP) is defined as:
- Cooling output divided by electrical input (Correct answer)
- Electrical input divided by heat rejected
- Heating output divided by fuel input
- Total BTU capacity divided by tonnage
Correct answer: Cooling output divided by electrical input
COP equals the useful cooling energy output divided by the electrical energy consumed by the chiller.
Question 3: Which control strategy staggers the start times of multiple HVAC units to reduce peak electrical demand?
- Demand-controlled ventilation
- Optimal start control
- Load shedding / demand limiting (Correct answer)
- Night setback
Correct answer: Load shedding / demand limiting
Load shedding or demand limiting staggers equipment startups to avoid simultaneous peak demand spikes on the electric bill.
Question 4: What does a higher SEER rating indicate for a cooling system?
- Greater refrigerant capacity
- Higher seasonal energy efficiency (Correct answer)
- Faster cooling speed
- Louder compressor operation
Correct answer: Higher seasonal energy efficiency
SEER (Seasonal Energy Efficiency Ratio) measures cooling output over a season divided by electrical energy consumed; higher values mean better efficiency.
Question 5: In a variable air volume (VAV) system, reducing airflow to 50% of design typically reduces fan energy by approximately:
- 50%
- 75%
- 87.5% (Correct answer)
- 25%
Correct answer: 87.5%
Fan power follows the cube law: reducing airflow to 50% reduces power to (0.5)³ = 12.5% of full load, an 87.5% reduction.
Question 6: Which type of heat exchanger recovers energy between exhaust and supply air streams in an air handling unit?
- Shell-and-tube condenser
- Energy recovery ventilator (ERV) (Correct answer)
- Cooling coil
- Steam humidifier
Correct answer: Energy recovery ventilator (ERV)
An ERV transfers both sensible heat and latent moisture between exhaust and incoming outdoor air, reducing conditioning loads.
Question 7: What is the recommended minimum MERV rating for filters in commercial HVAC systems to balance IAQ and energy efficiency?
- MERV 1–4
- MERV 13–16
- MERV 6–8 (Correct answer)
- MERV 17–20
Correct answer: MERV 6–8
MERV 6–8 filters provide reasonable IAQ protection without excessive pressure drop that would increase fan energy consumption.
