Rectangular Air Duct Velocity Diagram

Overview

Engineering reference data for Rectangular Air Duct Velocity Diagram in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Practical Calculations

The following formulas enable direct calculation of air flow and equivalent diameter for rectangular ducts, complementing the velocity diagram:

Air Flow Rate

The volumetric flow rate $Q$ through a rectangular duct is calculated as:

$$Q = A \times v = (w \times h) \times v$$

where:

• $Q$ is the air flow rate (m³/s)
• $A$ is the cross-sectional area (m²)
• $v$ is the mean air velocity (m/s)
• $w$ and $h$ are the duct width and height (m)

Equivalent Diameter

For comparing rectangular ducts to round ones, the hydraulic equivalent diameter $D_e$ is:

$$D_e = \frac{4 \times A}{P} = \frac{2wh}{w + h}$$

where $P$ is the perimeter of the duct (m).

Application Note

The velocity diagram provides a quick visual estimation method for standard rectangular ducts. For precise engineering design, especially for noise-sensitive or high-velocity systems, use the formulas above with detailed loss calculations.

References

• Original Source