Certified Energy Auditor Certification HVAC Systems and Performance 4 — Questions and Answers
Question 1: What is the typical minimum outdoor air ventilation rate for office spaces per ASHRAE 62.1?
- 5 cfm per person plus 0.06 cfm/ft² (Correct answer)
- 10 cfm per person with no area component
- 15 cfm per person plus 0.12 cfm/ft²
- 20 cfm per person for general office use
Correct answer: 5 cfm per person plus 0.06 cfm/ft²
ASHRAE 62.1 requires 5 cfm/person (Rp) plus 0.06 cfm/ft² (Ra) for general office spaces under the ventilation rate procedure.
Question 2: A cooling tower's approach temperature is defined as what?
- Difference between entering and leaving water temperature
- Difference between leaving water temperature and ambient wet-bulb temperature (Correct answer)
- Difference between ambient dry-bulb and wet-bulb temperatures
- Difference between condenser and evaporator temperatures
Correct answer: Difference between leaving water temperature and ambient wet-bulb temperature
Approach temperature is the difference between the cooling tower's leaving (cold) water temperature and the ambient wet-bulb temperature — a smaller approach indicates better tower performance.
Question 3: What is 'demand-controlled ventilation' (DCV)?
- Reducing outdoor airflow during peak electrical demand periods
- Modulating outdoor air intake based on measured occupancy or CO2 levels (Correct answer)
- Increasing ventilation to flush contaminants after high-demand processes
- Fixing ventilation at design maximum to meet worst-case conditions
Correct answer: Modulating outdoor air intake based on measured occupancy or CO2 levels
DCV uses CO2 sensors or occupancy data to adjust outdoor airflow rates dynamically, providing required ventilation only when spaces are occupied.
Question 4: An energy auditor measures a chiller's kW/ton as 0.55. A newer model offers 0.48 kW/ton. If annual chiller run-hours are 2,000 and the facility has 400 tons of cooling, what is the annual kWh savings?
- 28,000 kWh
- 56,000 kWh (Correct answer)
- 14,000 kWh
- 112,000 kWh
Correct answer: 56,000 kWh
Savings = (0.55 – 0.48) kW/ton × 400 tons × 2,000 hr = 0.07 × 400 × 2,000 = 56,000 kWh.
Question 5: What is the purpose of a building's static pressure control in a VAV system?
- Maintain duct static pressure at a setpoint to ensure terminal boxes can deliver required airflow (Correct answer)
- Prevent duct leakage by keeping pressure below rated duct class
- Equalize pressure between supply and return plenums
- Control outdoor air volume entering the air handling unit
Correct answer: Maintain duct static pressure at a setpoint to ensure terminal boxes can deliver required airflow
Duct static pressure control ensures enough pressure is available at the most remote VAV terminal so it can open and deliver design airflow.
Question 6: Which refrigerant replacement is commonly used as a low-global-warming-potential (GWP) alternative to R-410A in air conditioning?
- R-22
- R-32 or R-454B (Correct answer)
- R-134a
- R-407C
Correct answer: R-32 or R-454B
R-32 (GWP ~675) and R-454B (GWP ~467) are leading low-GWP alternatives to R-410A (GWP 2,088) for air conditioning applications.
Question 7: In a heat pump system, the reversing valve is used to do what?
- Bypass the compressor during defrost cycles
- Switch refrigerant flow direction to change between heating and cooling modes (Correct answer)
- Regulate refrigerant superheat at the evaporator outlet
- Control refrigerant charge between indoor and outdoor units
Correct answer: Switch refrigerant flow direction to change between heating and cooling modes
The reversing (four-way) valve redirects refrigerant flow so the indoor coil acts as a condenser in heating mode and an evaporator in cooling mode.
Certified Energy Auditor Certification HVAC Systems and Performance 4
What is the typical minimum outdoor air ventilation rate for office spaces per ASHRAE 62.1?