313D Air Distribution and Ducting Questions and Answers

Question 1

A homeowner complains of a persistent whistling noise coming from a supply air register, which becomes louder when other registers in the house are closed.
What is the most probable cause of this issue?

Accepted Answer

The air velocity through the register is too high.

Answer

The return air filter is oversized.

Answer

The thermostat is located too close to the supply register.

Answer

The ductwork is oversized for the system's CFM output.

Question 2

In rectangular duct design, what does the term 'aspect ratio' describe?

Accepted Answer

The ratio of the duct's longer side to its shorter side.

Answer

The ratio of the duct's total length to its total CFM.

Answer

The ratio of static pressure to velocity pressure.

Answer

The ratio of supply airflow to return airflow.

Question 3

A technician is inspecting ductwork in an attic and identifies a type of duct constructed with a helical wire coil core, covered by a polymer plastic liner, a layer of insulation, and an outer vapor barrier jacket. Which type of duct material is this?

Accepted Answer

Flexible duct (Flex duct)

Answer

Sheet metal duct

Answer

Fiberglass duct board

Answer

PVC duct

Question 4

A technician measures the total external static pressure (TESP) of a residential air handler and gets a reading of 0.95 in. w.c. (inches of water column). The equipment's data plate specifies a maximum TESP of 0.5 in. w.c. Which of the following is a direct consequence of this high static pressure?

Accepted Answer

The blower motor will be strained, leading to reduced airflow and potential premature failure.

Answer

The system will provide excess airflow, overcooling the space.

Answer

The blower motor will work less, consuming less electricity.

Answer

The compressor will short-cycle due to rapid heat exchange.

Question 5

According to ACCA Manual D, what is the primary objective of the residential duct design process?

Accepted Answer

To size the duct system to deliver the correct CFM to each room with minimal pressure loss.

Answer

To calculate the total heating and cooling load for the structure.

Answer

To select the specific brand and model of HVAC equipment.

Answer

To determine the R-value of insulation required for the building envelope.

Question 6

Which of the following duct fittings will typically create the highest amount of friction loss (equivalent length) in an air distribution system?

Accepted Answer

A 90-degree square-throated elbow without turning vanes.

Answer

A 45-degree round elbow.

Answer

A 90-degree smooth radius elbow.

Answer

A straight 20-foot section of flexible duct.

A homeowner complains of a persistent whistling noise coming from a supply air register, which becomes louder when other registers in the house are closed.What is the most probable cause of this issue?

A homeowner complains of a persistent whistling noise coming from a supply air register, which becomes louder when other registers in the house are closed.
What is the most probable cause of this issue?