1.Overview
Air Handling Unit(AHU) is a key device in central air conditioning systems used for comprehensive processing of air, including filtration, cooling, heating, humidification, dehumidification and air supply.
When the AHU uses the ** Chilled Water System (Chilled water system) **, we call it the "water system air handling unit". This system is widely used in industrial plants, hospitals, shopping malls, office buildings and data centers and other places that require constant temperature and humidity or comfort air conditioning.
2.The composition structure of the AHU in the water system
A typical water system AHU is generally composed of the following main components:
Mixing Section: Mix fresh air and return air, and adjust the fresh air volume according to the set ratio. It is usually equipped with an electric damper or a regulating damper.
Filter Section: Used to remove dust particles from the air. Filters are available in primary, medium or high efficiency (selected according to the cleanliness requirements of the system).
Cooling Coil Section: It mainly conducts air cooling and dehumidification. The interior is equipped with finned heat exchange coils. The chilled water flows through the coils to absorb heat from the air, thereby cooling the air.
Heating Coil Section(Optional): In winter or when special processes require it, heat the air with hot water or an electric heater.
Humidifying Section(Optional): It is used to regulate air humidity, and commonly used types include spray humidifiers, steam humidifiers or electrode humidifiers.
Fan Section: Generally, centrifugal fans or forward-curved fans are used, driven by motors, to send the treated air into the air duct system.
Silencer & Air Outlet Section: Used to reduce the operating noise of the unit.
3.The working principle of the water system AHU
The working principle of the water system AHU is to regulate the air state through the heat exchange between the chilled water system and the air. The core process is as follows:
1)Air circulation path
The fresh air and return air from the outside are mixed in proportion in the air mixing section. The mixed air is processed in sequence through filtration, cooling, humidification (or heating) and other procedures. The treated air is sent into the room through a fan. A portion of the indoor air is returned to the AHU through the return air duct to achieve circulation.
2)Principle of heat exchange
The chilled water (typically with an inlet temperature of 7℃ and a return temperature of 12℃) is provided by the chiller and flows through the surface cooling coil of the AHU. When the air through the coil, between air and chilled water dish tube heat exchange:
Air cooling → The air temperature is decreased.
Air dehumidifying → Water vapor above the dew point condenses into condensate water and is discharged.
If it is in heating mode, hot water or steam flows inside the coil, and the air is heated.
3)Humidity control
When the air is cooled and dehumidified through the surface cooler coil, if the humidity is low, it can be increased through the humidification section to maintain comfort or meet the process requirements.
4)Air flow rate and temperature and humidity regulation
The fan frequency can be adjusted by a frequency converter (VFD) to match the system load.
Combined with temperature and humidity sensors and DDC/PLC control systems, automatic constant temperature and humidity control can be achieved.
4.System matching and energy circulation
The water system AHU usually works in conjunction with the following equipment:
Chiller unit: Supply chilled water;
Cooling tower + cooling water pump: Dissipate heat for the condensation system;
Chilled water pump system：Circulate and deliver chilled water to each AHU;
BAS / BMS: Monitor temperature and humidity, air volume, valves and fan operation
Energy recovery devices (such as heat recovery rotors, plate heat exchangers, etc.) can further reduce energy consumption and improve system efficiency.
5.The advantages of the AHU water system
1)Precise temperature and humidity control: It can achieve ±1℃ and ±5%RH precision control
2)High energy efficiency: The heat transfer efficiency of the water system is much higher than that of the fluorine system
3)wide range of application: It can be used in comfort air conditioning and industrial process sites
4)Can be managed uniformly: Multiple AHUs can be connected to a unified BMS system
5)Easy maintenance: The modular design of each section makes it easy to clean and replace the filter
6.Typical application sites
Hospital operating rooms and wards
Pharmaceutical, food and electronic factories
Shopping malls and office buildings
Data centers and laboratories
Constant temperature and humidity control system for industrial production lines
7.Summary
The water system air handling unit is the core equipment for achieving air quality control in central air conditioning systems. It achieves precise regulation of temperature and humidity through an efficient heat exchange process between chilled water and air, and combines modern intelligent control technology. It can not only ensure a comfortable indoor environment but also meet strict process requirements, making it an indispensable key link in modern buildings and industrial systems.
