313D Air Distribution and Ducting 2

Question 1

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

Accepted Answer

To measure the pressure of air against the duct wall

Answer

A static pressure tap measures the pressure exerted by air against the duct wall, perpendicular to flow direction.

Question 2

Which duct shape provides the most efficient airflow per unit of material used?

Accepted Answer

Round

Answer

Round ducts have the lowest surface-area-to-cross-section ratio, minimizing friction losses and material use.

Question 3

A residential duct system has excessive external static pressure. What is the most likely result?

Accepted Answer

Reduced airflow and potential equipment damage

Answer

Excessive external static pressure restricts airflow, causing the blower to work harder, reducing CFM and potentially damaging the motor.

Question 4

When installing flexible duct, what maximum sag per foot of run is generally acceptable?

Accepted Answer

1/2 inch per foot

Answer

ACCA and SMACNA guidelines allow no more than 1/2 inch of sag per foot of flexible duct to prevent airflow restriction.

Question 5

What term describes the pressure loss caused by air changing direction in a duct fitting?

Accepted Answer

Dynamic pressure loss

Answer

Dynamic pressure loss refers to energy lost when air changes direction or velocity through fittings such as elbows and tees.

(313D) Residential Air Conditioning Systems Mechanic Certification Practice Test