Velocities over how many feet per minute through the return grill will produce noises and high static pressure drops?

The correct answer indicates that velocities over 600 feet per minute through the return grill are likely to produce unwanted noises and high static pressure drops. This threshold is significant in HVAC systems because high air velocities can create turbulence, leading to noise that may be disruptive in residential or commercial spaces.

When air moves too quickly through a return grill, it can also cause an increase in static pressure. This pressure drop can negatively impact the efficiency of the HVAC system, as it requires more energy to overcome the resistance created by the high velocity. Managing air velocities is crucial for ensuring system performance, maintaining comfort, and optimizing energy efficiency.

There are specific design considerations in HVAC engineering that dictate maximum airflow velocities to ensure quiet operation and minimize pressure losses. Typically, a standard range for acceptable velocities in return ducts is generally considered to be below 600 feet per minute, hence identifying this threshold is essential for effective system operation and occupant comfort.