HVAC Ductwork 3

Question 1

What ASHRAE standard primarily governs acceptable ventilation rates and duct design for commercial HVAC systems?

Accepted Answer

ASHRAE 62.1

Answer

ASHRAE 62.1 specifies minimum ventilation rates and indoor air quality requirements, including duct design criteria, for commercial buildings.

Question 2

A technician notices supply air temperature drops 8°F between the air handler and a distant register. What is the most likely cause?

Accepted Answer

Inadequate duct insulation allowing heat gain or loss

Answer

Significant temperature drop along supply ducts typically indicates insufficient insulation allowing heat transfer between the duct and surrounding unconditioned space.

Question 3

What is the recommended maximum air velocity in a residential supply trunk duct to minimize noise?

Accepted Answer

900 FPM

Answer

Residential supply trunk ducts are typically designed for 700–900 FPM to balance efficiency with acceptable noise levels; 900 FPM is a common upper limit.

Question 4

When installing flexible duct, what is the maximum sag allowed per SMACNA guidelines between supports?

Accepted Answer

1.5 inches per foot of length

Answer

SMACNA recommends flex duct supports no more than 5 feet apart, with no more than 1.5 inches of sag per foot of unsupported duct span.

Question 5

A VAV (Variable Air Volume) box modulates airflow by:

Accepted Answer

Adjusting a damper to control CFM to the zone

Answer

A VAV box uses a motorized damper to throttle airflow to the zone, maintaining zone temperature while the central AHU runs at constant temperature.

HVAC Practice Test

HVAC Practice Test

HVAC Ductwork 3