HVAC Systems and Controls 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 Controls flashcards as text
Which metric best quantifies the overall efficiency of a chilled water plant including pumps, tower fans, and auxiliary equipment?
Answer: kW/ton of the entire plant
Plant-level kW/ton accounts for all energy consumers in the chilled water plant, providing a more accurate picture of total system efficiency than chiller-only metrics.
What is the purpose of a hot gas bypass in a refrigeration system?
Answer: Maintain minimum compressor load during light cooling loads
Hot gas bypass artificially loads the compressor by diverting discharge gas back to the suction side, preventing compressor shutdown during very light loads — though it wastes energy compared to variable capacity compressors.
An energy auditor finds that a building's AHU static pressure setpoint is fixed at 1.5 in. w.g. A better control strategy would be:
Answer: Reset static pressure down until one VAV box is fully open (trim-and-respond)
Trim-and-respond static pressure reset lowers the setpoint until the most-open VAV box is nearly fully open, minimizing fan energy while still meeting zone loads.
What is the significance of a high wet-bulb temperature when evaluating cooling tower performance?
Answer: It limits how cold the condenser water can get, reducing chiller efficiency
Cooling towers can only cool condenser water to approximately the outdoor wet-bulb temperature; high wet-bulb limits cooling tower performance and raises condensing pressure in the chiller.
When auditing HVAC controls, finding a 'deadband' of only 1°F between heating and cooling setpoints is a problem because:
Answer: It causes frequent short-cycling and simultaneous operation
A narrow deadband causes heating and cooling to compete — a small temperature swing triggers one system then the other, wasting energy and causing equipment wear.
Which control sequence in a dual-duct HVAC system would most reduce energy waste?
Answer: Reset hot deck temperature upward and cold deck temperature upward in winter
Resetting hot deck temperature up and cold deck temperature up in cold weather reduces the energy needed for both heating and cooling the respective air streams.
A retrocommissioning study reveals that a chiller is consistently operating at 110% of its rated capacity. The best corrective action is:
Answer: Increase chilled water supply temperature setpoint to reduce load
Raising the chilled water supply temperature setpoint reduces the cooling load the chiller must handle and may bring operation back within rated capacity without capital expense.