Air Handling Units Explained: The Heart Of HVAC Engineering

In the world of heating, ventilation, and air conditioning (HVAC), Air Handling Units (AHUs) play a crucial role in maintaining indoor comfort and air quality within commercial and industrial buildings. In this article, we will delve into the workings of AHUs, their components, and their significance in HVAC engineering.

Locating Air Handling Units

AHUs are commonly found in medium to large commercial and industrial buildings. They are typically situated in the basement, on the roof, or on various floors of the building. Each AHU serves a designated area or zone, catering to specific parts of the building, such as the east side, certain floors, or even individual spaces like restrooms. It is common to have multiple AHUs in a single building to efficiently control temperature and air distribution.

While older high-rise buildings may have relied on a single large AHU located on the roof to supply air throughout the entire building, newer constructions opt for multiple smaller AHUs. These distributed units offer enhanced efficiency and better pressure regulation, contributing to improved overall performance.

The Purpose Of Air Handling Units

The primary function of an air handling unit is to condition and distribute air within a building. The process begins with the AHU drawing fresh ambient air from the outside. The unit then cleans, heats, cools, and possibly humidifies the air before distributing it through a network of ductwork to different areas of the building. Additionally, the AHU collects used, or return air, back from the rooms, processes it, and discharges it outside. Some of the return air might be recirculated into the fresh air supply to conserve energy, a practice we’ll explore later in this article. In cases where recirculation is not possible, the thermal energy from the return air can be extracted and utilized in the fresh air intake.

Key Components Of Air Handling Units

1. Dampers: Dampers are movable metal sheets that regulate air intake and exhaust. They can fully close, open, or position themselves in between to control the flow of air.
2. Filters: Filters are essential in preventing dirt, dust, and other contaminants from entering the AHU and the building. Regularly monitoring the filters’ cleanliness is crucial, as a pressure drop across the filters indicates the need for replacement.
3. Cooling and Heating Coils: These coils heat or cool the air to achieve the desired supply air temperature. They act as heat exchangers and typically use heated or chilled water, refrigerant, or steam to control the air temperature.
4. Fan: The fan draws in outside air, passes it through the dampers, filters, and coils, and then distributes the conditioned air throughout the building. Energy-efficient EC fans are becoming increasingly popular for improved performance.
5. Ductwork: Ducts transport the conditioned air from the AHU to designated areas within the building. Return ducts carry used air back to the AHU for reprocessing.

Additional AHU Features And Energy Recovery

In regions with freezing temperatures, AHUs may be equipped with pre-heaters to protect the components from frost when the outside air is too cold.

Humidity control is crucial for some buildings, and humidifiers can be integrated into AHUs to add moisture to the supply air when needed.

Energy recovery systems, such as run-around coils, can be used to transfer waste heat from the extract AHU to the supply AHU, reducing the heating demand.

In some cases, a duct can be placed between the exhaust and fresh air intake to allow for recirculation of exhaust air to offset heating or cooling demands, contributing to energy conservation.

Conclusion

Air Handling Units are the heart of HVAC engineering, responsible for conditioning and distributing air in commercial and industrial buildings. By understanding their components and functionalities, engineers can design efficient systems that provide optimal comfort and air quality for occupants. From dampers to filters, cooling and heating coils to energy recovery systems, AHUs offer a versatile and sustainable approach to climate control. As advancements in HVAC technology continue, AHUs will undoubtedly play a vital role in creating energy-efficient and comfortable indoor environments for generations to come.