An Air Handling Unit (AHU) is a central component of HVAC (Heating, Ventilation, and Air Conditioning) systems used in buildings to regulate and circulate air. AHUs are typically large metal boxes containing components for conditioning and distributing air to different zones or spaces within a building. They play a crucial role in maintaining indoor air quality, comfort, and temperature control.

Key components and functions of an Air Handling Unit include:

1. Filters: AHUs are equipped with air filters to remove dust, pollen, allergens, and other airborne particles from the incoming air. Filters improve indoor air quality and protect downstream components such as coils and fans from contamination.

2. Fans: AHUs contain fans or blowers that draw air into the unit, circulate it through the system, and distribute conditioned air to different areas of the building. Fans can be centrifugal or axial, depending on the application and airflow requirements.

3. Heating Coils: Heating coils, also known as heating elements or heat exchangers, are used to heat incoming air using various heat sources such as steam, hot water, electric resistance, or gas-fired burners. Heating coils raise the temperature of the air to the desired setpoint.

4. Cooling Coils: Cooling coils, also known as evaporator coils or chilled water coils, are used to cool incoming air by transferring heat to a refrigerant or chilled water loop. This process removes heat from the air, lowering its temperature and reducing humidity.

5. Humidifiers and Dehumidifiers: AHUs may include humidification and dehumidification systems to control indoor humidity levels. Humidifiers add moisture to dry air, while dehumidifiers remove excess moisture from humid air to maintain optimal humidity levels.

6. Mixing Dampers: Mixing dampers regulate the mixing of outdoor air and return air to achieve the desired ventilation rate and indoor air quality. They control the proportion of fresh outdoor air and recirculated air entering the AHU.

7. Controls and Sensors: AHUs are equipped with control systems and sensors to monitor and regulate various parameters such as temperature, humidity, air pressure, airflow, and air quality. Control systems adjust the operation of fans, heating and cooling coils, dampers, and other components based on setpoints and feedback from sensors.

8. Sound Attenuators: Sound attenuators, also known as silencers or acoustic panels, are used to reduce noise generated by fans and airflow within the AHU. They improve occupant comfort by minimizing noise transmission to occupied spaces.

AHUs are typically installed in mechanical rooms, equipment closets, or on rooftops, depending on the building layout and design. They are connected to ductwork to distribute conditioned air to different zones or rooms within the building. AHUs come in various sizes and configurations to accommodate different building types, occupancy loads, and HVAC requirements.