308A HVAC Ductwork Systems 3 — Questions and Answers
Question 1: What is the purpose of a 'smoke damper' and how does it differ from a fire damper?
- They are the same device
- A smoke damper is motor-operated and controlled by smoke detectors, while a fire damper uses a fusible link activated by heat (Correct answer)
- A smoke damper is only used outdoors
- A fire damper handles smoke while a smoke damper handles fire
Correct answer: A smoke damper is motor-operated and controlled by smoke detectors, while a fire damper uses a fusible link activated by heat
Smoke dampers are motor-operated and close upon signal from a smoke detection system. Fire dampers use fusible links that melt from heat. Combination fire/smoke dampers provide both functions.
Question 2: What is the primary reason for insulating supply air ductwork?
- To make the duct stronger
- To prevent heat gain or loss and control condensation on cold duct surfaces (Correct answer)
- To reduce the weight of the duct
- To make the duct easier to install
Correct answer: To prevent heat gain or loss and control condensation on cold duct surfaces
Duct insulation prevents unwanted heat transfer between the conditioned air and the surrounding space, maintaining energy efficiency. It also prevents condensation from forming on cold duct surfaces.
Question 3: What is an 'air handling unit' (AHU) and what components does it typically contain?
- A single fan mounted in a duct
- A factory-assembled unit containing fans, heating/cooling coils, filters, and dampers for conditioning and distributing air (Correct answer)
- An outdoor condenser unit only
- A thermostat and controller assembly
Correct answer: A factory-assembled unit containing fans, heating/cooling coils, filters, and dampers for conditioning and distributing air
An air handling unit is a comprehensive assembly that conditions air before distributing it through the duct system. It typically includes supply and return fans, heating and cooling coils, filters, mixing dampers, and controls.
Question 4: What is the purpose of an 'economizer' in an HVAC system?
- To reduce the cost of ductwork materials
- To use cool outdoor air for free cooling when outside conditions are favorable, reducing mechanical cooling load (Correct answer)
- To speed up the fan
- To recirculate air without conditioning
Correct answer: To use cool outdoor air for free cooling when outside conditions are favorable, reducing mechanical cooling load
An economizer uses dampers to introduce outside air when outdoor temperature and humidity are suitable for free cooling. This reduces the energy consumed by mechanical cooling equipment.
Question 5: What is the code-required clearance between uninsulated HVAC ductwork and combustible materials?
- No clearance is required
- A minimum of 1 inch clearance from combustible materials (Correct answer)
- 6 inches clearance
- 24 inches clearance
Correct answer: A minimum of 1 inch clearance from combustible materials
Building codes generally require a minimum of 1 inch clearance between uninsulated supply ductwork and combustible construction. Greater clearances may be required for exhaust ducts or ducts carrying heated air.
Question 6: What is the difference between a 'diffuser' and a 'register' in HVAC terminology?
- They are the same device
- A diffuser distributes air in a spreading pattern and typically has no damper, while a register has a built-in damper for flow adjustment (Correct answer)
- A diffuser is for exhaust only
- A register is only used with return air
Correct answer: A diffuser distributes air in a spreading pattern and typically has no damper, while a register has a built-in damper for flow adjustment
A diffuser is designed to spread supply air in a specific pattern across a room, typically mounted in ceilings. A register includes an integral damper allowing the occupant or technician to adjust airflow volume.
308A HVAC Ductwork Systems 3
What is the purpose of a 'smoke damper' and how does it differ from a fire damper?