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
Demand-controlled ventilation (DCV) uses which sensor to modulate outdoor air intake?
Answer: CO₂ sensor
DCV uses CO₂ sensors as a proxy for occupancy; when CO₂ rises above setpoint, outdoor airflow increases to dilute occupant-generated contaminants.
What is the purpose of a bypass factor in coil selection?
Answer: Fraction of air that bypasses the coil without being conditioned
The bypass factor represents the fraction of air that passes through a cooling coil without contacting the coil surface and therefore is not fully conditioned.
A two-pipe hydronic system serving both heating and cooling has what significant limitation?
Answer: Cannot serve heating and cooling simultaneously in different zones
A two-pipe system uses the same piping for hot or chilled water, so it can only provide one mode at a time — a problem in buildings with simultaneous heating and cooling needs.
What does the term 'integrated part-load value' (IPLV) measure for chillers?
Answer: Weighted average efficiency at multiple part-load conditions
IPLV is a weighted average efficiency metric that accounts for part-load operation at 25%, 50%, 75%, and 100% loads, reflecting real-world performance better than full-load ratings.
Which type of expansion device provides the best refrigeration system efficiency at varying loads?
Answer: Electronic expansion valve (EEV)
Electronic expansion valves precisely modulate refrigerant flow based on superheat and other inputs, providing superior efficiency across all load conditions.
In a direct expansion (DX) system, what does superheat indicate?
Answer: The temperature rise of refrigerant vapor above its saturation temperature
Superheat is the number of degrees the refrigerant vapor exceeds its saturation (boiling) temperature at a given pressure, ensuring no liquid enters the compressor.
What strategy can reduce chiller energy consumption by raising chilled water supply temperature during mild weather?
Answer: Chilled water reset
Chilled water reset raises the supply water temperature setpoint when loads are low, reducing the lift the compressor must overcome and improving COP.