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Friction Rate Formula:
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Friction Rate (FR) in ductwork represents the pressure loss per 100 feet of duct due to friction. It is a critical parameter in HVAC system design for determining fan power requirements and ensuring proper air distribution.
The calculator uses the Friction Rate formula:
Where:
Explanation: The formula calculates the friction rate by dividing the total pressure drop by the total equivalent length of the ductwork and multiplying by 100 to express the result per 100 feet of duct.
Details: Accurate friction rate calculation is essential for proper HVAC system design, ensuring adequate airflow, minimizing energy consumption, and preventing system inefficiencies or failures.
Tips: Enter pressure drop in inches of water column (in. w.c.) and total equivalent length in feet (ft). Both values must be positive numbers greater than zero.
Q1: What is a typical friction rate for HVAC ductwork?
A: Typical friction rates range from 0.08 to 0.15 in. w.c./100 ft, with 0.1 in. w.c./100 ft being a common design value.
Q2: How does duct material affect friction rate?
A: Different materials have different roughness factors. Smooth metal ducts have lower friction rates than flexible ducts or ducts with rough interiors.
Q3: What is included in total equivalent length?
A: TEL includes the actual duct length plus equivalent lengths for fittings, elbows, transitions, and other components that cause additional pressure drop.
Q4: How does air velocity affect friction rate?
A: Higher air velocities generally result in higher friction rates due to increased turbulence and surface friction.
Q5: When should I use this calculation?
A: This calculation is essential during HVAC system design, duct sizing, and when troubleshooting airflow problems in existing systems.