Air Handling Unit (AHU) in HVAC: Components, Working & Design Basics

An Air Handling Unit (AHU) is one of the most important components in an HVAC system. It is responsible for conditioning and circulating air as part of a heating, ventilation, and air conditioning system.

AHUs are commonly used in commercial buildings, hospitals, shopping malls, and industrial facilities where controlled indoor air quality is required.

What is an Air Handling Unit (AHU)?

An Air Handling Unit is a large metal box that contains components used to treat and distribute air. It is usually connected to ductwork that distributes conditioned air throughout the building.

Main Components of AHU

• Filters: Remove dust and contaminants from air.
• Cooling Coil: Reduces air temperature using chilled water or refrigerant.
• Heating Coil: Heats air using hot water, steam, or electric heater.
• Supply Fan: Pushes conditioned air into duct system.
• Return Air Section: Brings air back from space.
• Fresh Air Intake: Introduces outside air for ventilation.
• Mixing Chamber: Mixes return air and fresh air.

Working Principle of AHU

The AHU pulls return air from the building and mixes it with fresh outside air. This mixed air passes through filters to remove dust particles.

After filtration, air flows over cooling or heating coils to achieve the desired temperature. Finally, the supply fan pushes the conditioned air into the duct system for distribution.

Types of Air Handling Units

• Packaged AHU
• Modular AHU
• Rooftop AHU
• Custom-built AHU

AHU vs FCU (Fan Coil Unit)

An AHU handles larger air volumes and usually serves multiple zones. A Fan Coil Unit (FCU) serves smaller areas or single rooms.

Important Design Parameters

• Airflow (CFM or m³/hr)
• Static Pressure
• Cooling Capacity (TR or kW)
• Filter Efficiency
• Fresh Air Requirement

You can calculate airflow using our Air Velocity Calculator and design ducts using the HVAC Duct Sizing Calculator.

Applications of AHU

• Commercial buildings
• Hospitals
• Airports
• Shopping malls
• Industrial facilities

Conclusion

The Air Handling Unit is the heart of a centralized HVAC system. Proper AHU design ensures better indoor air quality, thermal comfort, and energy efficiency.

Disclaimer: This article is for educational purposes only. Final HVAC system design should be done by a qualified engineer.