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 primary purpose of an expansion tank in a closed hydronic HVAC system?
Answer: To accommodate the volume change of water as it heats and cools, maintaining safe pressure
An expansion tank absorbs the thermal expansion of water in a closed loop, preventing dangerous overpressure conditions.
In commercial HVAC controls, what does 'proportional-integral-derivative (PID) control' primarily improve over simple on/off control?
Answer: Control precision and stability by eliminating offset and minimizing overshoot
PID control continuously adjusts outputs based on error, accumulated error, and rate of change, producing stable, accurate control without the cycling of on/off control.
What is 'subcooling' in a commercial refrigeration circuit and why is it beneficial?
Answer: Cooling liquid refrigerant below its condensing temperature to increase system capacity and prevent flash gas
Subcooling liquid refrigerant prevents flash gas formation at the expansion device, increasing refrigerating effect and system capacity.
Which type of commercial chiller uses a screw compressor and is typically best suited for which capacity range?
Answer: Screw chillers for 100–500 tons
Screw (helical rotary) chillers are most efficient in the 100–500 ton range, filling the gap between reciprocating and centrifugal equipment.
In a commercial rooftop unit, what component is responsible for controlling the refrigerant flow rate to the evaporator coil?
Answer: Electronic expansion valve (EEV) or thermostatic expansion valve (TXV)
The expansion valve meters refrigerant into the evaporator, maintaining the correct superheat and preventing liquid flood-back to the compressor.
What is the function of an 'air separator' (air eliminator) in a commercial chilled water system?
Answer: To remove dissolved and entrained air from the hydronic loop, preventing corrosion and noise
Air separators remove dissolved air from hydronic systems, preventing air binding in coils, corrosion, and flow noise.
A commercial building's HVAC system is described as having a 'primary-secondary' chilled water loop. What does the secondary loop do?
Answer: Distributes variable flow to building loads while the primary loop maintains constant flow through chillers
In a primary-secondary arrangement, the secondary (distribution) loop provides variable flow to loads while the primary loop maintains constant flow through chillers for stability.