313D Airflow and Duct Sizing 2

Question 1

What is the recommended maximum air velocity in a main supply trunk duct for a low-noise residential HVAC system?

Accepted Answer

900 FPM

Answer

600 FPM

Answer

1200 FPM

Answer

1500 FPM

Question 2

Which duct fitting generates the highest equivalent length of straight duct pressure loss?

Accepted Answer

90-degree square elbow without turning vanes

Answer

45-degree elbow

Answer

Straight tee

Answer

Reducing collar

Question 3

When using the equal friction method for duct design, what parameter is held constant throughout the system?

Accepted Answer

Static pressure drop per 100 feet

Answer

Air velocity

Answer

Total airflow CFM

Answer

Duct cross-sectional area

Question 4

A supply register is rated at 0.10 inches w.g. pressure drop at 150 CFM. If airflow increases to 200 CFM, approximately what is the new pressure drop?

Accepted Answer

0.18 in. w.g.

Answer

0.13 in. w.g.

Answer

0.22 in. w.g.

Answer

0.30 in. w.g.

Question 5

What is the purpose of a static pressure regain section in a duct system?

Accepted Answer

To recover pressure after a velocity reduction

Answer

To increase air velocity before a branch

Answer

To filter particles from the airstream

Answer

To add humidity to supply air

Question 6

For a residential system serving multiple zones, which device helps balance airflow between branches without mechanical dampers?

Accepted Answer

Balancing collar

Answer

Plenum box

Answer

Splitter damper

Answer

Duct board liner

Question 7

When calculating duct heat gain for a cooling system, which factor most significantly increases heat gain into supply ducts?

Accepted Answer

Duct location in unconditioned attic space

Answer

Duct color

Answer

Duct material thickness

Answer

Supply air temperature