Working Principle of an Air Handling Unit
The main function of an Air Handling Unit (AHU) is to perform multiple air conditioning processes, including filtration, heating and cooling, and humidification/dehumidification, on outdoor fresh air or indoor return air to achieve the desired temperature, humidity, and cleanliness standards for the target area.
The basic working process is as follows:
- Air intake section: Intakes outdoor fresh air or indoor return air.
- Filtration section: Removes particles and pollutants from the air through primary, medium, or high-efficiency filters to ensure a clean air supply.
- Heat exchange section: Heating or cooling is performed through a condenser or evaporator to control the supply air temperature.
- Humidification/dehumidification section: Regulates air humidity to ensure that the workshop humidity remains within the optimal process range.
- Blower section: Powered by a high-efficiency centrifugal fan, it evenly distributes the treated air to the cleanroom.
- Silence reduction section: Reduces fan noise and improves environmental comfort.
The entire system is intelligently regulated by an automatic control system, ensuring stable operation around the clock while balancing energy conservation and environmental protection.
What are the different types of air handling units?
An AHU can be thought of as an enlarged version of a "fan + coil unit." The number of coil rows has been increased from 2-3 to 4-6, or even 8 or 10. This allows for deeper cooling, dehumidification, or heating of the air flowing through the coils. This not only provides high cooling capacity but also deep dehumidification. The corresponding fan also delivers higher air volume and pressure, meeting the needs of larger air volumes and longer ductwork.
Commercial air handlers are categorized by installation method as ceiling-mounted units or floor-mounted vertical and horizontal units in the computer room. They are also categorized by function as fresh air units (fresh air) and air conditioning units (including full return air units and mixed fresh air + return air units).
When a commercial air handler has more functions, it may combine cooling or heating coils, primary and secondary air filters, humidification, and supply or return air fans into multiple functional sections. This is a modular air conditioning unit.
Combined air handling units can be divided into single-tier unidirectional flow units and double-tier bidirectional flow units. Unidirectional flow units use a single supply fan to overcome resistance within the unit and the entire supply and return air ducting. Bidirectional flow units have separate supply and return fans to overcome resistance in the supply and return air equipment and ducting, respectively.
The selection of different types of Air Handlers needs to be precisely configured according to the on-site space layout, cleanliness level and process requirements.
Components of an Air Handling Unit
The functional sections of an AHU are generally designed to be freely combined based on the user's specific needs, and the order of combination varies between manufacturers. However, generally speaking, an AHU consists of the following functional sections:
Fresh Air Section
The fresh air section primarily receives fresh air from outside and settles any impurities in it. The fresh air valve is equipped with a damper actuator (switch) and is interlocked with the fan. It is recommended to install a temperature sensor in the shaded outdoor area for return air temperature compensation.
Filter Section
The fresh air is typically filtered by a primary (or coarse) filter, primarily removing larger impurities. The filter after the return air section is typically a medium-efficiency filter, which typically removes smaller impurities. Purifying air conditioners may also have sub-high-efficiency and high-efficiency filtration sections. Differential pressure switches should be installed before and after each filter to monitor filter cleanliness. If there are excessive impurities, an alarm will be issued.
Return Air Section
The return air section primarily mixes fresh air and return air. A damper actuator (analog) is installed at the return air inlet to adjust the return air volume. During hot or cold seasons, this maximizes return air utilization while maintaining a certain fresh air volume, thereby achieving energy savings. The exhaust air valve at the exhaust outlet is interlocked with the return air valve actuator, operating in the opposite direction. Temperature and humidity sensors are installed in the return air duct to monitor the return air temperature (thus determining the average indoor temperature and humidity), providing a basis for controlling the chiller, heating, electric heater, and humidifier valves.
Surface Cooling Section
The surface cooling section primarily cools the air delivered to the room and also performs cooling and dehumidification (optional), with dehumidification taking priority. A temperature control valve (T-way) is installed at the water inlet of the surface cooler. When the return air temperature and humidity reach the set requirements, the temperature control valve is lowered or closed, eliminating excess heat. Chilled water is returned through a third path to prevent excessive pressure differentials across the control valve when it is closed or closed, potentially damaging other pipes or the water pump and shortening the service life of the control valve. In addition, an antifreeze switch is installed on the surface of the air conditioner to protect the air conditioning equipment and is interlocked with the fan and damper.
Heating Section
The heating section is used in winter (or to generate heat after dehumidification and overcooling). Its operating principle is similar to that of the air conditioner. It is shared by the heating and cooling air conditioners of a two-pipe system.
Electric Heating
Electric heating is generally used when the heating section cannot meet heating requirements or when generating heat after dehumidification and overcooling.
Humidification Section
The humidification section provides humidification to prevent winter dryness or for special process requirements. The humidification method is generally wet film humidification or steam humidification.
Air Supply Section
The air supply section, also known as the fan section, supplies air to the room. The damper at the air supply outlet is typically equipped with an actuator (switch quantity, optional function) and interlocked with the fan.
FAQ
Q1: What industries are AHUs suitable for?
A: Our commercial air handlers are widely used in industries requiring constant temperature, humidity, and cleanliness control, such as:
- Pharmaceutical cleanrooms
- Semiconductor and electronics manufacturing plants
Q2: What is the difference between an AHU and an air conditioner?
A: Air conditioning systems primarily regulate ambient temperature, while air handling units (AHUs) not only regulate temperature but also perform air filtration and humidification/dehumidification functions. They are suitable for industrial or medical applications with higher requirements for air quality and cleanliness levels. The two can be integrated for precise air control.
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