What is the velocity of air through a 24"x24" filter grill with 75% free area and an air volume of 2000 cfm?

• A. 600 fpm
• B. 666 fpm
• C. 700 fpm
• D. 750 fpm

Answer: (B)

To determine the velocity of air through the filter grill, first, it's important to understand how to calculate the effective free area of the grill and use it to find the velocity.

The filter grill dimensions are 24 inches by 24 inches, which yields a total area of:

[ 24 \text{ in} \times 24 \text{ in} = 576 \text{ in}^2 ]

Given that the grill has 75% free area, the effective airflow area can be calculated as follows:

[ \text{Free Area} = 576 \text{ in}^2 \times 0.75 = 432 \text{ in}^2 ]

Next, to work with consistent units, convert the area from square inches to square feet, since the air volume is given in cubic feet per minute (cfm):

[ 432 \text{ in}^2 \div 144 \text{ in}^2/\text{ft}^2 = 3 \text{ ft}^2 ]

Now, using the volume of air flowing through the grill (2000 cfm), we can calculate the velocity by using the formula:

[ \text{Velocity} = \frac{\