HVAC Ventilation and Air Distribution 2 — Questions and Answers
Question 1: What is the purpose of a Variable Air Volume (VAV) box in a commercial HVAC system?
- To mix outdoor and return air in variable proportions
- To vary the volume of conditioned air supplied to a zone based on its load (Correct answer)
- To recover energy from exhaust air
- To control the speed of the central air handling unit
Correct answer: To vary the volume of conditioned air supplied to a zone based on its load
A VAV box modulates the volume of air supplied to a zone by adjusting a damper, allowing independent temperature control of multiple zones from a single central AHU.
Question 2: What instrument measures air velocity in a duct or at a register?
- Manometer
- Psychrometer
- Anemometer or velometer (Correct answer)
- Combustion analyzer
Correct answer: Anemometer or velometer
An anemometer or velometer measures air velocity in feet per minute (FPM), which can be used to calculate airflow volume (CFM) when combined with the duct area.
Question 3: What does MERV stand for in relation to air filters?
- Maximum Efficiency Rating Value
- Minimum Efficiency Reporting Value (Correct answer)
- Mechanical Equipment Replacement Variable
- Motor Efficiency Resistance Value
Correct answer: Minimum Efficiency Reporting Value
MERV (Minimum Efficiency Reporting Value) is a standard scale from 1-16 that rates how effectively an air filter captures particles of various sizes.
Question 4: What is duct leakage testing used to determine?
- Whether the duct system can handle the required airflow
- The amount of conditioned air escaping through gaps and holes in the duct system (Correct answer)
- The static pressure of the duct system
- The air velocity at supply registers
Correct answer: The amount of conditioned air escaping through gaps and holes in the duct system
Duct leakage testing measures how much conditioned air is lost through unsealed joints, connections, and holes in the duct system, which wastes energy and reduces comfort.
Question 5: In HVAC, what does the term 'throw' refer to when selecting supply air diffusers?
- The volume of air delivered by the diffuser
- The horizontal distance the supply air travels before its velocity drops to 50 FPM (Correct answer)
- The angular spread of the air pattern from the diffuser
- The pressure drop across the diffuser
Correct answer: The horizontal distance the supply air travels before its velocity drops to 50 FPM
Throw is the horizontal distance that the primary air stream from a diffuser travels to reach a terminal velocity (typically 50 FPM) before mixing with room air.
Question 6: What is an economizer in a commercial HVAC system?
- A device that reduces refrigerant use in the cooling system
- A control system that uses cool outdoor air for free cooling when conditions allow (Correct answer)
- A variable-speed drive that saves motor energy
- A heat exchanger that recovers waste heat from the compressor
Correct answer: A control system that uses cool outdoor air for free cooling when conditions allow
An economizer uses outdoor air for free cooling when outdoor conditions (temperature and/or enthalpy) are favorable, reducing mechanical cooling energy consumption.
HVAC Ventilation and Air Distribution 2
What is the purpose of a Variable Air Volume (VAV) box in a commercial HVAC system?