Certified Energy Auditor Certification HVAC Systems and Controls 4 — Questions and Answers
Question 1: What is the primary energy disadvantage of a constant volume reheat HVAC system?
- High fan motor costs
- Simultaneous heating and cooling waste energy (Correct answer)
- Excessive outdoor air intake
- High refrigerant charge requirements
Correct answer: Simultaneous heating and cooling waste energy
Constant volume reheat systems cool all air to a low temperature then reheat it for zones needing less cooling, wasting both cooling and heating energy.
Question 2: A building automation system (BAS) data point showing 'chiller plant delta-T' refers to:
- Temperature difference between entering and leaving chilled water (Correct answer)
- Temperature difference between outdoor and indoor air
- Difference in refrigerant suction and discharge temperatures
- Supply and return duct temperature difference
Correct answer: Temperature difference between entering and leaving chilled water
Chilled water delta-T is the difference between the chilled water return temperature and supply temperature, which indicates how effectively the distribution system is transferring heat.
Question 3: What is the purpose of a cooling tower bypass valve in a chilled water plant?
- Prevent freezing of cooling tower fill in cold weather (Correct answer)
- Increase condenser water flow during peak load
- Reduce chilled water pump head pressure
- Maintain refrigerant subcooling
Correct answer: Prevent freezing of cooling tower fill in cold weather
A bypass valve diverts warm condenser water around the cooling tower during cold weather to prevent the tower from freezing and to maintain minimum condenser water temperatures.
Question 4: When auditing a pneumatic control system for energy savings opportunities, the auditor should look for:
- Opportunities to convert to direct digital controls (DDC) (Correct answer)
- Ways to increase pneumatic pressure
- Methods to reduce compressed air drying
- Opportunities to add more thermostats
Correct answer: Opportunities to convert to direct digital controls (DDC)
Pneumatic controls are typically less precise and flexible than DDC systems; conversion to DDC often enables advanced strategies like optimal start, reset schedules, and better diagnostics.
Question 5: Which HVAC system type is generally most efficient for buildings with highly variable zone loads?
- Constant volume single-zone system
- Multizone constant volume system
- Variable air volume (VAV) with DDC controls (Correct answer)
- Four-pipe fan coil with constant volume AHU
Correct answer: Variable air volume (VAV) with DDC controls
VAV systems with DDC controls modulate airflow to match zone loads, saving significant fan and conditioning energy compared to constant volume approaches.
Question 6: What does 'simultaneous heating and cooling' fault detection identify in a BAS?
- A cooling coil that is icing up
- A zone where heating and cooling systems are operating at the same time (Correct answer)
- Compressor short-cycling
- Supply air temperature sensor drift
Correct answer: A zone where heating and cooling systems are operating at the same time
Simultaneous heating and cooling is a common energy waste where a zone's heating and cooling operate concurrently, often due to control sequencing errors or faulty sensors.
Question 7: In evaluating HVAC efficiency, what does a low condenser approach temperature in a chiller indicate?
- Refrigerant undercharge
- Clean condenser tubes with good heat transfer (Correct answer)
- Excessive condenser water flow
- High ambient outdoor temperature
Correct answer: Clean condenser tubes with good heat transfer
A low approach temperature (small difference between condenser water leaving temperature and refrigerant condensing temperature) indicates clean tubes and efficient heat transfer.
Certified Energy Auditor Certification HVAC Systems and Controls 4
What is the primary energy disadvantage of a constant volume reheat HVAC system?