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Understanding the Air Handling Unit (AHU) – Step-by-Step Air Treatment Process

Understanding the Air Handling Unit (AHU) – Step-by-Step Air Treatment Process


Step 1 - Air Inlet Section


Outdoor fresh air enters the AHU through the air inlet and dampers. Dampers regulate the quantity of fresh air entering the system according to ventilation requirements and pressure control strategy.


Step 2 - Pre-Filter Section


The incoming air first passes through the pre-filter where large dust particles, fibers, and airborne contaminants are removed. This stage protects downstream components and improves equipment life.


Step 3 -Fine Filter Section


After pre-filtration, air moves through the fine filter section which removes smaller particulate matter and improves indoor air quality (IAQ) as per HVAC and ASHRAE filtration standards.


Step 4 - Cooling Coil Section


The filtered air then passes across the cooling coil where sensible heat and latent heat are removed. This process cools and dehumidifies the air to achieve the required supply air conditions.


Step 5- Heating Coil Section


In winter operation or reheating applications, the heating coil increases the air temperature to maintain indoor thermal comfort and accurate supply air temperature control.


Step 6 - Humidifier Section


The humidifier adds moisture to the air whenever indoor relative humidity falls below the design requirement. This section is critical for hospitals, laboratories, clean rooms, and comfort applications.


Step 7-Supply Fan Section


The supply fan is the heart of airflow movement inside the AHU. It generates the required static pressure to overcome duct losses, filters, coils, dampers, and terminal devices throughout the HVAC distribution system.


Step 8 - Drain Pan Section


During cooling and dehumidification, condensate water forms on the cooling coil surface. The drain pan collects and safely removes this condensate to prevent water accumulation and microbial growth.


Step 9- Access Door & Maintenance Section


Access doors are provided for inspection, filter replacement, coil cleaning, fan servicing, and preventive maintenance to ensure long-term operational efficiency.


Step 10 - Air Outlet Section


Finally, the conditioned air leaves the AHU through the supply outlet and is distributed through the duct system to maintain the required indoor comfort conditions.


Key Engineering Objective:


An efficiently designed AHU ensures proper ventilation, energy efficiency, temperature control, humidity regulation, occupant comfort, and healthy indoor air quality for commercial and industrial buildings.



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