FREE 313D Airflow and Duct Sizing Questions and Answers

Question 1

A technician measures the total external static pressure (TESP) of a residential air handler and finds it to be 1.1 inches of water column (in. w.c.).
The manufacturer's data plate specifies a maximum TESP of 0.5 in. w.c.
What is the most likely consequence of this high static pressure reading?

Accepted Answer

Reduced airflow (CFM) and potential for evaporator coil freezing.

Answer

Increased airflow (CFM) and improved system efficiency.

Answer

Normal system operation with no adverse effects.

Answer

Overamping of the indoor blower motor due to reduced load.

Question 2

Which tool is most commonly used by an HVAC technician to quickly determine the required round or rectangular duct size based on a target friction rate and airflow (CFM)?

Accepted Answer

A ductulator (duct slide rule)

Answer

A psychrometric chart

Answer

A digital multimeter

Answer

A refrigerant charging scale

Question 3

In duct system design, which of the following best describes the concept of 'equivalent length'?

Accepted Answer

The pressure drop caused by a fitting, like an elbow or tee, expressed as the length of straight duct that would cause the same pressure drop.

Answer

The total linear measurement of all straight duct sections in the system.

Answer

The maximum recommended length for a flexible duct run before it requires support.

Answer

The length of duct required to achieve a specific velocity for proper air mixing.

Question 4

A technician is installing a new 3-ton (36,000 BTU/hr) residential air conditioning system. Using a standard industry rule of thumb, what is the target airflow the duct system should be designed to deliver?

Accepted Answer

1200 CFM

Answer

800 CFM

Answer

1050 CFM

Answer

1600 CFM

Question 5

Designing a residential duct system with excessively high air velocity is generally avoided primarily because it can lead to which of the following issues?

Accepted Answer

Unacceptable noise levels and increased friction loss.

Answer

Reduced heat transfer at the registers.

Answer

Air stratification within the conditioned space.

Answer

Condensation forming on the outside of the ductwork.

Question 6

A technician needs to verify the airflow (CFM) coming out of a specific supply register to help balance a system. Which of the following instruments is most suitable for this task?

Accepted Answer

An airflow capture hood (balometer)

Answer

A static pressure probe (manometer)

Answer

A combustion analyzer

Answer

A refrigerant leak detector

A technician measures the total external static pressure (TESP) of a residential air handler and finds it to be 1.1 inches of water column (in. w.c.).The manufacturer's data plate specifies a maximum TESP of 0.5 in. w.c.What is the most likely consequence of this high static pressure reading?

A technician measures the total external static pressure (TESP) of a residential air handler and finds it to be 1.1 inches of water column (in. w.c.).
The manufacturer's data plate specifies a maximum TESP of 0.5 in. w.c.
What is the most likely consequence of this high static pressure reading?