308A HVAC Ductwork Systems 1 — Questions and Answers
Question 1: What is the primary function of a supply air duct in an HVAC system?
- To remove stale air from occupied spaces
- To deliver conditioned air from the air handling unit to occupied spaces (Correct answer)
- To drain condensation from cooling coils
- To house electrical wiring for the system
Correct answer: To deliver conditioned air from the air handling unit to occupied spaces
Supply air ducts deliver conditioned (heated or cooled) air from the air handling unit (AHU) to the occupied spaces throughout a building. They are a critical component of the air distribution system.
Question 2: What is the difference between a return air duct and an exhaust air duct?
- They are the same thing
- Return air recirculates air back to the AHU for reconditioning, while exhaust air is expelled outside the building (Correct answer)
- Exhaust ducts are always larger
- Return ducts are only used in summer
Correct answer: Return air recirculates air back to the AHU for reconditioning, while exhaust air is expelled outside the building
Return air ducts bring room air back to the air handling unit to be reconditioned and recirculated. Exhaust air ducts remove air from the building entirely, venting it outdoors.
Question 3: What is the purpose of a 'plenum' in an HVAC duct system?
- To filter the air
- To serve as a large distribution or collection chamber that connects to multiple branch ducts (Correct answer)
- To heat the air
- To measure airflow
Correct answer: To serve as a large distribution or collection chamber that connects to multiple branch ducts
A plenum is a large chamber or box that serves as a central distribution point for supply air or collection point for return air. It connects the air handling equipment to the duct system.
Question 4: What is the standard gauge for residential HVAC ductwork made from galvanized steel?
- 16 gauge
- 26 to 28 gauge (Correct answer)
- 12 gauge
- 30 gauge
Correct answer: 26 to 28 gauge
Residential HVAC ductwork is typically fabricated from 26 to 28 gauge galvanized steel. These gauges provide adequate strength for the lower pressures found in residential systems while being economical.
Question 5: What is the purpose of turning vanes in a rectangular duct elbow?
- To increase air velocity
- To reduce turbulence and pressure loss by guiding airflow smoothly around the turn (Correct answer)
- To filter particles from the air
- To support the weight of the duct
Correct answer: To reduce turbulence and pressure loss by guiding airflow smoothly around the turn
Turning vanes are curved airfoils installed inside rectangular elbows to guide the airflow around the turn with minimal turbulence and pressure loss, improving system efficiency.
Question 6: What is 'static pressure' in an HVAC duct system?
- The weight of the ductwork
- The pressure exerted equally in all directions within the duct, representing stored energy that pushes air through the system (Correct answer)
- The noise level of the fan
- The temperature of the air
Correct answer: The pressure exerted equally in all directions within the duct, representing stored energy that pushes air through the system
Static pressure is the force per unit area exerted uniformly in all directions on duct walls. It represents the stored energy available to push air through the duct system and overcome friction and other losses.
308A HVAC Ductwork Systems 1
What is the primary function of a supply air duct in an HVAC system?