HVAC Systems and Performance Flashcards
7 cards from real Certified Energy Auditor Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 HVAC Systems and Performance flashcards as text
When performing a duct leakage test, what does CFM25 indicate?
Answer: Cubic feet per minute of airflow at 25 Pa pressure differential
CFM25 is the measured duct leakage airflow in cubic feet per minute at a reference pressure of 25 Pascals.
What is the function of an economizer cycle in a commercial HVAC system?
Answer: Use outdoor air for free cooling when conditions allow
An economizer opens outdoor air dampers to use cool outdoor air for free cooling, reducing or eliminating mechanical refrigeration.
A building's HVAC system uses a pneumatic control system. What is a major energy-efficiency concern with this type of system?
Answer: Hunting and poor setpoint accuracy increasing energy use
Pneumatic controls are prone to hunting and calibration drift, leading to wider temperature swings and higher energy consumption compared to direct digital control.
In a hydronic system, what does 'delta-T' refer to?
Answer: Temperature difference between supply and return water
Delta-T (ΔT) in a hydronic system is the temperature difference between the supply water and the return water, indicating heat transfer effectiveness.
Which fan law states that fan power varies with the cube of the fan speed?
Answer: Third fan law
The third fan law (power affinity law) states that power varies as the cube of the speed ratio, which is why VFDs yield dramatic energy savings.
What does a high wet-bulb temperature relative to dry-bulb temperature on a psychrometric chart indicate?
Answer: High relative humidity
When wet-bulb temperature is close to dry-bulb temperature, the air is near saturation, indicating high relative humidity.
A facility manager reports that a VAV system's supply air temperature is constant at 55°F year-round. What energy savings opportunity does this represent?
Answer: Supply air temperature reset based on zone demand
Resetting supply air temperature upward when zone cooling loads are reduced allows the chiller to operate at higher suction temperatures, saving compressor energy.