HVAC Ductwork Systems Flashcards

What is the equal friction method of duct sizing?

Answer: A design method that maintains a constant friction loss rate per unit of duct length throughout the system

The equal friction method sizes each duct section to maintain the same friction loss per unit length (typically inches of water gauge per 100 feet). This helps balance the system naturally.

What is the function of a fire damper in a duct system?

Answer: To automatically close and prevent the spread of fire and smoke through duct penetrations in fire-rated walls and floors

Fire dampers are installed where ducts penetrate fire-rated walls and floors. They contain fusible links that melt at a specific temperature, causing the damper to close and maintain the fire barrier.

What is the recommended maximum air velocity in a main supply duct for a commercial HVAC system to minimize noise?

Answer: 1,200 to 1,500 FPM

Main supply ducts in commercial systems are typically designed for 1,200 to 1,500 FPM to balance energy efficiency with acceptable noise levels. Higher velocities increase noise and friction losses.

What is the purpose of a balancing damper in an HVAC duct system?

Answer: To adjust airflow to individual branches or outlets to achieve the designed air distribution

Balancing dampers are adjustable dampers installed in branch ducts to regulate airflow. They allow technicians to fine-tune the air distribution so each zone receives its designed volume of air.

What is a 'flexible duct' commonly used for in HVAC systems?

Answer: To connect rigid duct branches to diffusers and registers in locations where rigid duct is impractical

Flexible duct is primarily used for short final connections between rigid branch ducts and supply outlets (diffusers/registers). It accommodates misalignment and vibration but should be kept short and straight.

What SMACNA duct pressure class is typically specified for a standard commercial supply air system?

Answer: 2 inch WG

Standard commercial supply air systems typically operate at 2 inch water gauge (WG) pressure class. This determines the construction standards including gauge, reinforcement, and sealing requirements.