HVAC Commercial HVAC Systems 2 — Questions and Answers
Question 1: What is the primary function of a cooling tower in a commercial HVAC system?
- To cool refrigerant directly
- To reject heat from condenser water to the atmosphere (Correct answer)
- To supply chilled water to air handlers
- To reduce indoor humidity levels
Correct answer: To reject heat from condenser water to the atmosphere
A cooling tower rejects heat absorbed by condenser water to the atmosphere through evaporative cooling.
Question 2: In a Variable Air Volume (VAV) system, what component controls airflow to each zone?
- Variable frequency drive
- VAV terminal box with a damper (Correct answer)
- Chilled water coil
- Return air plenum
Correct answer: VAV terminal box with a damper
A VAV terminal box contains a motorized damper that modulates airflow to maintain the zone's setpoint temperature.
Question 3: What does the term 'tons of refrigeration' measure in commercial HVAC?
- Weight of refrigerant in the system
- Heat removal capacity (1 ton = 12,000 BTU/hr) (Correct answer)
- Compressor mechanical output in horsepower
- Total weight of HVAC equipment
Correct answer: Heat removal capacity (1 ton = 12,000 BTU/hr)
One ton of refrigeration equals 12,000 BTU/hr of heat removal, derived from the heat needed to melt one ton of ice per day.
Question 4: Which refrigerant is most commonly used in modern large commercial chiller systems due to environmental regulations?
- R-22
- R-410A
- R-134a (Correct answer)
- R-11
Correct answer: R-134a
R-134a is widely used in centrifugal chillers as it is an HFC with zero ozone depletion potential, compliant with modern regulations.
Question 5: What is 'economizer mode' in a commercial air handling unit?
- Running the chiller at reduced capacity
- Using outdoor air for free cooling when conditions are favorable (Correct answer)
- Bypassing the filter section to reduce static pressure
- Modulating the heating coil to save energy
Correct answer: Using outdoor air for free cooling when conditions are favorable
Economizer mode uses outdoor air instead of mechanical cooling when outside conditions (temperature/enthalpy) are suitable, reducing energy costs.
Question 6: In commercial HVAC, what is the purpose of a 'chilled water reset' strategy?
- Resetting the chiller after a fault
- Raising chilled water supply temperature during low-load conditions to save energy (Correct answer)
- Draining and refilling the chilled water loop
- Lowering supply air temperature in winter
Correct answer: Raising chilled water supply temperature during low-load conditions to save energy
Chilled water reset raises the chilled water setpoint during part-load conditions, improving chiller efficiency (COP) significantly.
Question 7: A commercial rooftop unit (RTU) serving multiple zones typically uses which distribution strategy?
- Hydronic piping to each zone
- Constant volume ductwork with zone dampers (Correct answer)
- Dedicated outdoor air system (DOAS)
- Radiant floor panels
Correct answer: Constant volume ductwork with zone dampers
Multi-zone RTUs typically use constant or variable volume ductwork with zone dampers to distribute conditioned air to multiple spaces.
HVAC Commercial HVAC Systems 2
What is the primary function of a cooling tower in a commercial HVAC system?