Air Duct Pressure Drop Formula |
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| \( \Delta P \;=\; f \cdot \left( \dfrac{ L }{ D } \right) \cdot \left( \dfrac{ 1 }{ 2 } \right) \cdot \rho \cdot v^2 \) | ||
| Symbol | English | Metric |
| \( \Delta P \) = Pressure Drop | \(lbf \;/\; in^2\) | \( Pa \) |
| \( f \) = Friction Factor | \( dimensionless \) | \( dimensionless \) |
| \( L \) = Pipe Length | \( ft \) | \( m \) |
| \( D \) = Pipe Diameter | \( in \) | \( mm \) |
| \( \rho \) (Greek Symbol rho) = Fluid Density | \(lbm \;/\; ft^3\) | \(kg \;/\; m^3\) |
| \( v \) = Fluid Velocity | \(ft \;/\; sec\) | \(m \;/\; s\) |
Air duct pressure drop is the reduction in air pressure that occurs as air moves through a duct system due to friction, turbulence, and resistance caused by the duct material, shape, fittings, and obstructions. As air flows, energy is lost when it encounters surface roughness, bends, transitions, dampers, or filters, which create drag and slow the airflow. This pressure loss must be overcome by the fan or blower in order to maintain the desired air distribution throughout the system.
The amount of pressure drop is influenced by factors such as air velocity, duct length, diameter, and smoothness, as well as the number of fittings and changes in direction. Properly managing duct pressure drop is needed in HVAC design, since excessive losses increase energy consumption, reduce airflow efficiency, and can compromise occupant comfort and system performance.
Air Duct Pressure Drop Formula |
||
| \( \Delta P \;=\; f \cdot \left( \dfrac{ L }{ D } \right) \cdot \left( \dfrac{ \rho \cdot v^2 }{ 2 } \right) \) | ||
| Symbol | English | Metric |
| \( \Delta P \) = Pressure Drop | \(lbf \;/\; in^2\) | \( Pa \) |
| \( f \) = Friction Factor | \( dimensionless \) | \( dimensionless \) |
| \( L \) = Pipe Length | \( ft \) | \( m \) |
| \( D \) = Pipe Diameter | \( in \) | \( mm \) |
| \( \rho \) (Greek Symbol rho) = Fluid Density | \(lbm \;/\; ft^3\) | \(kg \;/\; m^3\) |
| \( v \) = Fluid Velocity | \(ft \;/\; sec\) | \(m \;/\; s\) |
