Commercial HVAC Systems Flashcards
7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Commercial HVAC Systems flashcards as text
What is the main advantage of a water-cooled chiller compared to an air-cooled chiller?
Answer: Higher efficiency (lower kW/ton) due to lower condensing temperatures
Water-cooled chillers achieve higher efficiency because evaporative cooling in the cooling tower produces lower condensing temperatures than ambient air cooling.
In a commercial HVAC system, what does 'DOAS' stand for and what is its primary purpose?
Answer: Dedicated Outdoor Air System — provides ventilation air separately from sensible cooling
A DOAS handles ventilation (outdoor air) requirements separately, allowing zone equipment to focus on sensible load control.
What is the typical chilled water supply temperature range in a commercial central plant?
Answer: 44–48°F
Commercial chilled water systems typically supply water at 44–48°F to provide adequate dehumidification and cooling capacity at coils.
Which control strategy best describes 'demand-controlled ventilation (DCV)'?
Answer: Adjusting outdoor air intake based on CO₂ levels as a proxy for occupancy
DCV uses CO₂ sensors to modulate outdoor air dampers proportionally to actual occupancy, reducing ventilation energy waste in partially occupied spaces.
In a commercial building automation system (BAS), what is a 'setback' schedule used for?
Answer: Allowing space temperature to drift to a less conditioned setpoint during unoccupied hours
Setback schedules let space temperatures rise (cooling) or fall (heating) to unoccupied setpoints during nights and weekends, saving energy.
What is 'bypass factor' of a cooling coil?
Answer: The fraction of air passing through the coil that does not contact the coil surface
Bypass factor represents the portion of air that passes through the coil without making thermal contact, reducing the coil's effective heat transfer.
A commercial building uses a '4-pipe' fan coil unit system. What does this mean?
Answer: Separate chilled water and hot water supply/return pipes allowing simultaneous heating and cooling in different zones
A 4-pipe FCU system has dedicated chilled water and hot water circuits, enabling independent heating or cooling in each zone simultaneously.