What is the recommended length of straight duct at a fan outlet measuring 18 x 26 with an air velocity of 6000 FPM?

To calculate the recommended length of straight duct at a fan outlet, you need to consider the specific parameters given: the size of the duct (18 x 26 inches) and the air velocity (6000 FPM). The purpose of determining the straight duct length is primarily related to achieving a proper airflow and reducing turbulence.

Using duct design principles, the proper length of straight duct allows for the airflow to stabilize and helps minimize losses due to turbulence, which can occur when transitioning from a fan to the ductwork. The recommended guidelines generally suggest that the straight duct following a fan should be adequate enough to allow the air to evenly distribute before entering any fittings or transitions, which can disrupt airflow.

The calculation or reference indicated in the context shows that 146 7/16 inches is based on standard engineering practices and airflow guidelines, ensuring that the duct's performance remains efficient at the specified air velocity. This length is essential for maintaining efficiency and reducing the chance of noise or other operational issues due to turbulent flow.

Achieving optimal airflow is critical for both comfort and system effectiveness, which is why the recommended length is carefully calculated to fit the given parameters.