Room Positive Pressure Air Balance Calculator (30Pa Example)

Maintaining a 30 Pa positive pressure in a room while accounting for both exhaust and return airflows is essential for environments requiring contamination control or specific air exchange dynamics, such as cleanrooms or hospital isolation areas.

Historical Background

The concept of positive pressure rooms became prominent in healthcare and semiconductor industries, where clean environments are crucial. Maintaining a pressure differential ensures that outside, potentially contaminated air does not enter the room. Over time, engineers developed models that relate pressure to airflow leakage, allowing for balance calculation.

Calculation Formula

Assuming air leakage through gaps behaves like orifice flow:

\[ Q_{\text{leak}} = C \cdot \sqrt{\Delta P} \]

Where:

• \( Q_{\text{leak}} \) is the leakage flow (m³/h)
• \( C \) is the leakage coefficient (empirical, typically 0.4–0.6)
• \( \Delta P \) is the pressure difference in Pa

Then: \[ Q_{\text{return}} = Q_{\text{supply}} - Q_{\text{leak}} = Q_{\text{supply}} - Q_{\text{exhaust}} \]

Example Calculation

• Supply Air: 1000 m³/h
• Pressure: 30 Pa
• Leakage Coefficient: 0.5

\[ Q_{\text{leak}} = 0.5 \cdot \sqrt{30} \approx 2.74 \text{ m³/h} \] \[ Q_{\text{return}} = 1000 - 2.74 = 997.26 \text{ m³/h} \]

Importance and Usage Scenarios

• Cleanrooms: Prevent particle ingress.
• Hospitals: Control infection spread.
• Laboratories: Maintain sterile environments.

Common FAQs

1. What if return + exhaust > supply?

   • That would result in negative pressure; you'd lose control of internal environment stability.

2. Can I just recirculate all the air?

   • Not if pressure or contamination control is required. Some air must exhaust to maintain pressure and remove contaminants.

3. How do I determine the leakage coefficient?

   • Based on construction standards or air leakage testing data (e.g., door gaps, wall integrity).

This tool offers a practical solution for HVAC engineers and facility managers to ensure controlled and safe air management in positive pressure rooms.