All AHU Sensors & Their Uses
"If you work in HVAC or Building Management System, then AHU (Air Handling Unit) sensors are to you what senses are to humans — without these sensors, AHU will become blind, deaf and useless! Today we will deep dive into all AHU sensors – their functions, use, and why they are important for the efficiency and comfort of the system."
🏢 Role of Sensors in AHU
AHU is a system that filters, cools/heats and circulates air in large buildings, malls, hospitals, and offices. But it is smart only when it has the right sensors.
Sensors help:
Monitor temperature, humidity, and air quality
Increasing energy efficiency
Detecting faults
Maintaining comfort
📋 List of All Major AHU Sensors & Their Uses
1. Temperature Sensors (Supply, Return, Outdoor, Mixed Air)
Use:
Supply Air Temp Sensor: Monitors the temperature of the air leaving the AHU
Return Air Temp Sensor: Measures the temperature of the air returning to the AHU
Outdoor Air Temp Sensor: Measures the temperature of the outside air (for economizer control)
Mixed Air Temp Sensor: Measures the temperature of the mix of supply and return air
Example:
If the supply air is too cold, energy can be saved by adjusting the system.
2. Humidity Sensors (Relative Humidity Sensor)
Use:
Measures the percentage of moisture in the air
Controls comfort level and mold growth
Important for dehumidification and humidification control
Example:
Maintaining 50-60% RH in a hospital is important for infection control.
3. Pressure Sensors / Transducers
Types & Uses:
Static Pressure Sensor: Maintains air pressure in the AHU duct (for VFD control)
Differential Pressure Sensor: Installed across filters to detect clogs
Implanted across coils to monitor performance
Example:
If the pressure drop of the filter increases, it means the filter is clogged and needs to be changed.
4. Air Flow Sensors
Use:
They measure how much air is flowing in the AHU
Necessary for proper ventilation and energy optimization
Example:
If the airflow is low, then the fan speed or damper position can be adjusted.
5. CO₂ Sensors (Carbon Dioxide Sensor)
Use:
Monitors Indoor Air Quality
Adjusts fresh air supply according to occupancy (Demand Controlled Ventilation)
Example:
If there are more people in the conference room, the CO₂ level will increase, the AHU will automatically supply more fresh air.
6. VOC Sensors (Volatile Organic Compounds)
Use:
Detects chemical pollutants
Especially important in labs, hospitals, and manufacturing areas
7. Smoke Detectors / Fire Sensors
Use:
Shuts down fans in AHU as soon as smoke is detected
Critical safety feature to prevent fire spread
8. Filter Status Sensors (Differential Pressure Based)
Use:
Detects when the filter is clogged
Helps schedule preventive maintenance
9. Vibration Sensors (Fan Monitoring)
Use:
Detects abnormal vibration in fan bearings or motor
Gives maintenance alert before breakdown
10. Damper Position Sensors
Use:
Monitors exact position of outdoor, return, and exhaust air dampers
Helps in air mixing and economizer operation
11. Energy Meter / Power Sensors
Use:
Measures the power consumption of the AHU
Important for energy optimization and cost calculation
12. Chilled/Hot Water Supply & Return Temp Sensors
Use:
Monitors the temperature of water going to the coil and returning
Helps to check cooling/heating efficiency
🛠 Sensors + BMS Integration
Nowadays all sensors are connected to the Building Management System (BMS).
BMS:
Analyzes data
Automatically adjusts fan speed, damper position, cooling/heating
Gives fault detection and alarms
🔍 Real-Life Example – Hospital AHU
In a hospital AHU, temp, humidity, CO₂, and pressure sensors are critical because infection control is a priority.
If humidity becomes high, the BMS immediately activates the dehumidifier.
If CO₂ increases, the fresh air damper automatically opens.
🧠 Pro Tips for Engineers & Technicians
Get the sensors calibrated every 6-12 months
Faulty sensor can spoil the overall performance of AHU
Keep checking the wiring and BMS connectivity
Match the filters change schedule with the sensors reading
🎯 Final Words
AHU sensors are not just for monitoring but also act as a backbone to save energy, maintain comfort and ensure safety.
If you are in HVAC field, then understanding the working, location, and maintenance of all these sensors will take your career to the next level.
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