Operating Room Air Changes (ACH) Optimization
In standard comfort cooling, CFM is dictated strictly by thermal load (temperature). In a Class B or C Operating Theatre, CFM is dictated by dilution physics. You must flood the room with enough HEPA-filtered air to literally wash skin squames, anesthesia gases, and bio-aerosols out through the low-wall return grilles.
The Laminar Array & Displacement Physics
Operating rooms do not use standard square ceiling diffusers. They utilize a Laminar Flow Array positioned directly over the surgical table. This creates a piston-like downward column of sterile, low-velocity air (typically 25 to 35 FPM).
To calculate the required Air Changes per Hour (ACH), engineers use the fundamental volumetric flow equation:
Where: CFM = Total Supply Airflow, 60 = Minutes in an hour, Volume = Room Length * Width * Height.
ASHRAE 170 Healthcare Ventilation Standards
| Space Designation | Min. Total ACH | Min. Outdoor ACH | Pressure Gradient |
|---|---|---|---|
| Operating Room (Class B/C) | 20 | 4 | Positive (+) |
| Procedure Room (Class A) | 15 | 3 | Positive (+) |
| AII Room (Infectious Isolation) | 12 | 2 | Negative (-) |
Diagnostic Gateway Challenge
You are commissioning a 20ft x 20ft x 10ft Operating Room (Volume: 4000 cu. ft.). The design blueprint demands exactly 20 ACH. What must the total supply CFM be calibrated to?