HVAC Damper Pressure Loss

Overview

Engineering reference data for HVAC Damper Pressure Loss 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

Pressure Loss Formulas

The primary formula for calculating pressure loss across a damper is:

$\Delta P = C_v \frac{\rho v^2}{2}$

Where:

• $\Delta P$ is the pressure loss (Pa)
• $C_v$ is the dimensionless loss coefficient for the damper
• $\rho$ is the air density (kg/m³)
• $v$ is the face velocity of the air (m/s)

The relationship can also be expressed using the velocity pressure ($P_v$):

$\Delta P = C_v \cdot P_v \quad \text{where} \quad P_v = \frac{\rho v^2}{2}$

Factors Affecting Pressure Loss

1. Damper Type: Butterfly, parallel blade, opposed blade, and VAV box dampers all have different inherent loss coefficients.
2. Blade Design: Blade shape (e.g., airfoil, single-skin, double-skin) significantly impacts airflow resistance.
3. Position/Opening: Pressure loss is minimal when fully open and increases dramatically as the damper closes. The relationship is non-linear.
4. Airflow Velocity: Pressure loss is proportional to the square of the velocity.
5. Air Density: Affected by temperature and altitude; standard conditions are typically 1.2 kg/m³.

Calculation Example

For a standard opposed-blade damper at 100% open position:

As the damper closes to 50% open, the loss coefficient ($C_v$) increases significantly (e.g., to ~2.5), resulting in a pressure loss of approximately 24 Pa for the same airflow.

References

• Original Source