An Air Handling Unit (AHU) regulates temperature and humidity using a combination of cooling, heating, humidification, and ventilation strategies. These components work together under automated control systems to ensure a stable and comfortable indoor climate.
This guide explores how AHUs effectively control indoor temperature and humidity through precision airflow and advanced automation.
1. Temperature Control in AHUs
🔹 Why It’s Important:
- Maintaining consistent indoor temperatures is essential for comfort, energy efficiency, and process stability.
- AHUs achieve precise temperature control through modulating cooling and heating.
🔹 How It Works:
1.1 Proportional-Integral (PI) Control
✅ A temperature sensor detects actual room temperature.
✅ The PI controller compares it with the setpoint and adjusts heating or cooling accordingly.
✅ Cooling Coil (Chilled Water or DX Coil) – Activates when the room is too warm.
✅ Heating Coil (Hot Water or Electric Heater) – Activates when the room is too cold.
🔹 Benefits:
✔ Smooth, stable temperature regulation without frequent on/off cycling.
✔ Prevents overshooting, ensuring comfort and energy efficiency.
1.2 Dead Band & Interlock Control
✅ A dead band (temperature buffer zone) prevents frequent switching between heating and cooling.
✅ Interlock logic ensures heating and cooling do not operate simultaneously, reducing energy waste.
🔹 Example:
✔ Dead band set at 2°C: If the setpoint is 22°C, cooling starts at 24°C, and heating starts at 20°C.
2. Humidity Control in AHUs
🔹 Why It’s Important:
- Excess humidity leads to mold growth, condensation, and discomfort.
- Low humidity causes dry air, static electricity, and respiratory issues.
- AHUs maintain humidity between 40-60% RH for optimal comfort and health.
🔹 How It Works:
2.1 Dehumidification via Cooling Coils
✅ When humidity exceeds the setpoint, the cooling coil activates.
✅ Moisture condenses on the coil surface, effectively removing humidity from the air.
✅ The air may be reheated after cooling to maintain the target temperature.
🔹 Example:
✔ Setpoint = 50% RH → Cooling coil activates at 55% RH to remove excess moisture.
2.2 Humidification for Dry Air
✅ If humidity drops below the setpoint, a humidifier injects moisture.
✅ Types of humidifiers:
- Steam Humidifier – Uses heated water to generate steam.
- Ultrasonic Humidifier – Produces fine mist using ultrasonic waves.
- Evaporative Humidifier – Adds moisture by passing air over a wet medium.
🔹 Example:
✔ Setpoint = 50% RH → Humidifier activates at 45% RH to restore balance.
3. Fresh Air & Ventilation Control
🔹 Why It’s Important:
- Stale indoor air can cause poor air quality, CO₂ buildup, and odors.
- Proper ventilation helps control humidity, prevent contaminant buildup, and enhance occupant comfort.
🔹 How It Works:
3.1 CO₂-Based Fresh Air Regulation
✅ CO₂ sensors monitor indoor air quality.
✅ When CO₂ levels exceed 800 ppm, the AHU increases fresh air intake.
✅ This helps maintain oxygen levels and prevent indoor pollution.
🔹 Example:
✔ If CO₂ = 900 ppm, the AHU opens fresh air dampers to introduce more outdoor air.
3.2 Airflow Pressure Regulation
✅ AHUs use pitot tubes or airflow sensors to measure airflow.
✅ Adjustments are made to maintain a steady air supply, ensuring even temperature and humidity distribution.
🔹 Benefits:
✔ Prevents overcooling or overheating due to uneven airflow.
✔ Ensures balanced ventilation rates for comfort.
4. Variable Fan Speed Control (VAV & VFD Systems)
🔹 Why It’s Important:
- AHUs dynamically adjust fan speeds to optimize air circulation, pressure, and energy efficiency.
🔹 How It Works:
✅ VAV (Variable Air Volume) Systems – Adjust airflow based on cooling/heating demands.
✅ VFD (Variable Frequency Drive) Fans – Reduce fan power consumption during low-demand periods.
🔹 Benefits:
✔ Energy savings by reducing unnecessary fan operation.
✔ Maintains consistent air distribution across all areas.
5. Free Cooling (Economizer Mode)
🔹 Why It’s Important:
- Uses outdoor air for cooling, reducing the need for mechanical refrigeration.
🔹 How It Works:
✅ When outdoor temperature is lower than indoor air, the AHU increases fresh air intake.
✅ Reduces chiller or compressor load, saving energy costs.
🔹 Example:
✔ If outdoor air = 15°C and indoor air = 24°C, the system uses fresh air for cooling instead of activating the chiller.
6. Integrated Control Logic for Temperature & Humidity
🔹 Why It’s Important:
- Temperature and humidity influence each other.
- AHU controllers balance heating, cooling, and humidity to maintain an ideal indoor climate.
🔹 Example of Smart Control Logic:
✅ Winter: The system increases fresh air intake to reduce humidity.
✅ Summer: The cooling coil removes humidity, and reheating may be used to maintain temperature.
🔹 Benefits:
✔ Prevents excessive cooling or heating.
✔ Optimizes comfort while minimizing energy waste.
Conclusion: How AHUs Optimize Indoor Temperature & Humidity
AHUs use advanced control strategies to achieve precise temperature and humidity regulation.
✅ Temperature Control – Modulates cooling and heating coils with PI logic.
✅ Humidity Control – Uses dehumidification (cooling coils) & humidification as needed.
✅ Ventilation Optimization – Adjusts fresh air intake based on CO₂ levels.
✅ Fan Speed Control – Uses VAV and VFD technology for energy-efficient airflow.
✅ Free Cooling Mode – Uses ambient air when conditions allow, reducing energy use.
✅ Integrated Smart Control – Ensures temperature and humidity adjustments work together seamlessly.
By leveraging automated sensors, smart controllers, and efficient airflow management, AHUs create a comfortable, healthy, and energy-efficient indoor environment. 🚀