Maintaining precise humidity levels in hospital operating rooms is essential for patient safety, infection control, and equipment reliability. Excess moisture can promote microbial growth and condensation on surfaces, while overly dry air can increase airborne particles and compromise surgical outcomes. Modern Air Handling Units (AHUs) use controlled cooling and reheating processes to ensure stable humidity and temperature, creating safe and sterile environments for surgical procedures.
Stable humidity — safer surgeries, cleaner environments, better outcomes.
Precise humidity regulation is essential in operating rooms, ICUs, and medical cleanrooms. Excess moisture in hospital environments can support microbial growth, cause condensation on surgical surfaces, and compromise sterile conditions. To prevent these issues, Air Handling Units (AHUs) use a controlled deep-cooling and reheating process to manage both temperature and humidity.
Why Outdoor Air Contains High Moisture
In warm climates, outdoor fresh air entering the AHU typically has a high temperature and a large amount of water vapor. Even if the relative humidity percentage varies, the absolute humidity remains high because the air contains a substantial mass of moisture.
How the AHU Removes Moisture
1. Cooling to the Dew Point
The cooling coil lowers the air temperature until it reaches its dew point. At this temperature, the air becomes saturated, and moisture begins to condense on the coil surface. This condensed water drains away, reducing the total moisture content in the air.
This is the dehumidification stage.
Note: Air reaching 100% relative humidity at the dew point does not contain more moisture. It simply means the air is fully saturated at that lower temperature and cannot hold additional water vapor.
2. Reheating the Air
Once dehumidification is complete, the air is too cold to supply directly to occupied medical spaces. The system reheats the air to the designed supply temperature. During reheating, no moisture is added back, so the air’s relative humidity decreases, creating cool, dry, and hygienic supply air suitable for critical healthcare environments.
Benefits for Hospitals and Operating Rooms
- Prevents bacterial and fungal growth
- Avoids condensation in sterile zones
- Helps protect medical instruments and electronic systems
- Provides thermal comfort for surgical staff and patients
- Maintains stable environmental conditions for surgical success
Process Summary
| Stage | What Happens | Humidity Condition |
|---|---|---|
| Fresh outdoor air | High temp, high moisture | High absolute humidity |
| Cooling to dew point | Moisture condenses and drains | Humidity removed |
| Reheating | Temperature rises without adding water | Low relative humidity |
Conclusion
Medical AHUs regulate humidity by cooling air below its dew point to remove moisture, then reheating it to the required supply-air temperature. This process ensures clean, dry, and controlled air — a critical requirement for sterile hospital environments and operating theaters.
Why does an AHU cool air below the dew point in hospitals?
Cooling below the dew point forces moisture to condense, removing humidity from the air. This is essential for stable humidity control in operating rooms and medical cleanrooms.
Does air become more humid when it reaches the dew point?
No. At the dew point, air reaches 100% relative humidity only because it is fully saturated at that temperature. Moisture is removed, so the total water content is actually lower.
Why is reheating used after dehumidification?
Reheating restores the supply air temperature without adding moisture back, reducing relative humidity further and ensuring stable, comfortable, sterile-room conditions.
What is the ideal humidity range for operating rooms?
Most operating theaters maintain 40%–60% RH to prevent microbial growth, condensation, and static electricity, while protecting medical equipment performance.
What problems does high humidity cause in hospitals?
High humidity can lead to microbial growth, condensation, corrosion, discomfort, and unsafe surgical conditions — especially in sterile environments like operating theaters.
