AHU stands for Air Handling Unit. It is a device used for heat exchange and air processing to provide clean air into rooms. This equipment is commonly used in HVAC systems and is considered the "brain" of the system, responsible for processing and circulating air throughout the entire building. The Air Handling Unit is typically designed for outdoor use and is often located on the rooftop.

In terms of appearance, an AHU is a large metal box that contains separate ventilation fans for air supply and exhaust, heating coils, cooling coils, heat/cool recovery system, air filters, sound attenuators, mixing chamber, and dampers. AHUs are widely used in manufacturing plants, buildings, hospitals, hotels, and other applications. Classification of AHU - Air Handling Unit Currently, there are two main types of Air Handling Units on the market: water-cooled AHUs and direct expansion (DX) AHUs. Each type has different characteristics and specifications:

Water-cooled AHU: A water-cooled AHU, also known as a Water AHU, utilizes water, including a heat exchanger, typically used to exchange heat between chilled water flowing through copper tubes. Air is blown through a centrifugal fan, and the control system includes humidity and temperature sensors, three-way valves, actuators, and a chiller. When in operation, if the temperature in the room is higher than the set temperature, the three-way valve opens, allowing chilled water to flow through the heat exchanger until the temperature decreases to the set level. Then, the valve closes, and the chilled water flows through the bypass route back to the water cooling equipment. Direct expansion (DX) AHU: A DX AHU consists of a heat exchanger used to exchange heat between refrigerant gas and the air passing through copper tubes, driven by the suction force of a centrifugal fan.

Coarse and bag filters will filter the air before supplying it to the designated area. For environments requiring high cleanliness, such as clean rooms, a HEPA filtration system needs to be added. The AHU's supply fan is typically a centrifugal fan, while fans used in clean rooms can handle static pressure up to 1000Pa. Variable speed drives (VSD) are used to precisely adjust the fan speed according to the design requirements for high-capacity fans.

The fan speed is controlled by the chilled water valve to regulate the air temperature. AHU Construction: An AHU is constructed with various components, each serving different functions and tasks, including mixing chambers, air filters, heat exchangers, and fan housings. The mixing chamber typically has two doors with control valves, one for fresh air intake and one connected to the return air duct. The main control system includes temperature sensors, three-way valves, etc. Sound attenuators, vibration dampers, air supply ducts, and other elements are also part of the construction. Depending on the requirements and standards of each project, an AHU can be constructed with different components, but it typically includes the following main parts: supply fan, heating coils, cooling coils, air filters, and protective casing. Protective Casing of AHU: The protective casing is a formed aluminum frame that helps create insulation, usually designed with rounded corners to prevent dust accumulation on the exterior. Supply Fan: The fan used in the AHU system is usually a centrifugal fan. This type of fan construction includes two layers, with the inner layer meeting insulation standards. In particular, for AHUs installed outdoors, the fan is equipped with additional insulation and anti-corrosion coating to withstand environmental conditions. Vibration Isolation Components: Fans with high power can generate significant vibration and noise during operation. Therefore, vibration isolation components help ensure smoother operation and prevent noise generation. Heating Coils: Heating coils, also known as