What is the required duct size for a duct system delivering 1,000 cfm with a pressure drop of 0.25 IWC and a friction rate of 0.095 IWC/100?

To determine the required duct size for a system delivering 1,000 cubic feet per minute (cfm) of air with a specified pressure drop and friction rate, we can use the duct sizing formulas and principles of air flow dynamics in HVAC systems.

The friction loss in the duct is calculated based on the duct size, airflow, and the friction rate. In this scenario, we have an airflow of 1,000 cfm and we need to achieve a maximum pressure drop of 0.25 inches of water column (IWC). The friction rate is given as 0.095 IWC per 100 feet of duct.

First, using the formula for calculating the required duct diameter, we can derive the size based on the airflow and the allowed pressure drop. This often involves estimating the velocity of air in the duct, as well as the cross-sectional area, to reach a point where the cumulative pressure loss matches the desired pressure drop.

In practical terms, the diameter of duct that allows 1,000 cfm of airflow while maintaining the friction loss at the specified rate leads us to the selection of a 14-inch diameter duct. This size effectively balances the airflow and friction loss to maintain the required 0.25 IWC pressure drop