AHU is an indispensable device in the air handling system for buildings. And if you don't know what AHU is, the working principle as well as the structure of AHU, let's find out with Vietnam Cleanroom Equipment through this article.

What is AHU?

AHU stands for Air Handling Unit, a heat exchanger and moisture heat treatment device that cleans the air and is often used in HVAC system.
AHU is a part of the HVAC system, it can be considered the brain of this system. And HVAC is widely used in factories, buildings, hospitals, hotels,...
AHU System is responsible for air treatment and air circulation in the entire building system. Air Handling Unit is usually designed for outdoor use, usually on the roof, also known as a rooftop unit (RTU).
In terms of form, AHU is a large metal box containing separate ventilators to supply and discharge air, heating coil, cooling coil, heat recovery / cooling system, rack or air filter chamber, sound attenuator, mixing chamber and shock absorber.
What is AHU?

Types of AHU - Air Handling Unit

Normally, Air Handling Unit is divided into 2 different types, which are Water AHU and AHU gas.
Each type has its own points, you can follow the following:

Water AHU

What is water AHU? Water AHU is also known as Water running AHU, it uses water including a heat exchanger that is often used to exchange heat in the middle of cold water passing through copper pipes. The air blows through the centrifugal fan, the control system includes humidity sensors, temperature, actuator triple valve and chiller…
When operating, if the temperature in the room is higher than the set temperature, at this time the 3-way valve will open for cold water to flow through the heat exchanger until the temperature drops to the set temperature, then the valve will close, then the cold water will flow through the Bypass line and finally to the water chiller.
AHU Gas - DX AHU
AHU Gas - DX AHU

AHU Gas - DX AHU

DX AHU is a type that includes a heat exchanger used to exchange heat between cold gases thanks to the suction of a centrifugal fan passing through copper pipes and blowing air through it thanks to the suction of a centrifugal fan.
Coarse filters and bag filters will filter through the air before entering the commonly used area. For high-cleanness environments such as clean rooms, we need to add a HEPA filter system, including G4 filter for AHU, bag filter and HEPA filter.
Air Handling Unit with a level fan is often used as a centrifugal fan. Particularly with the types of fans used in cleanroom with external static pressure up to 1000Pa.
This AHU will use VSD (variable speed drive) to accurately calibrate the amount according to the design for high-power fans.
The fan speed to control the output air temperature is controlled through the cold water valve.

AHU structure

Parts of an Air Handling Unit

The structure of the AHU system is usually assembled from many modules as follows: Mixing chamber, Air filter, heat exchanger and fan box. Especially on the mixing chamber, there will be 2 doors with adjustable valves, 1 door for fresh air, 1 door connected to the air return line. The main control system will include: thermostat, three-work actuator valve,.. Sound reduction and vibration reduction department, air supply pipe,...
Usually when choosing AHU, people will design it to suit the requirements of each project. However, it usually has a common structure including:
Parts of an Air Handling Unit

Details and Uses of each AHU part

AHU protective cover

The protective case is a profiled aluminum frame that helps create an insulation layer, which is usually designed to prevent external dust.

Blower

The fan used in the AHU System is usually a centrifugal fan. The structure of this type of fan will have two layers, including standard insulation. Especially with AHU installed outdoors, the fan will be equipped with a protective layer and anti-corrosion tape to suit environmental conditions.

Anti-vibration unit

Large-capacity fans will produce significant vibrations and noises during operation. Therefore, anti-vibration components help to operate more smoothly as well as avoid making noise during operation.
Airr Handling Unit

Heating system

The Heater, is the part that ensures the heat exchange work in the middle of cold water passing through the copper pipe and exchanging air through the AHU to create cold air.
Its structure consists of copper coils (or aluminum wire) for direct heat exchange in the airflow. This system of coils will be related to the supply environment and then make the heating or cooling appropriate.

Air filter

The AHU system will have coarse filtration, fine filtration and for environments that require high cleanliness, HEPA filtration will be necessary.

Filters will ensure the filtration of dust particles at different levels, helping to create clean air from the removal of dust particles and pollutants from the air outside the environment.

Heating resistor

The heating resistor is the part that helps treat moisture in the AHU system, and it will also take care of heat treatment.

Local condensation dehumidifier

This part will help with preliminary cooling, the air will be cooled and then preliminarily dehumidified and then moved into the main refrigeration unit.

Central control

This department has the role of transmitting control signals and receiving signals from feedback devices.

AHU working principle

So what is the process and operating principle of AHU?

AHU working principle

Below is the process and working principle of an AHU system:
  • The 3-way valve will open for cold water to flow through the heat exchanger to cool the air when the temperature in the area to be cooled is higher than the heat level degree of installation.
  • When the air causes the temperature in that area to be lower than the temperature level as originally set, this valve will close. After that, the cold water will flow along the Bypass line to the Chiller.
  • At the same time, the air before being put into the AHU chiller will be filtered through coarse filters and bag filters, we also call it the pre-filter unit.
  • For environments that require higher cleanliness, we will use additional HEPA filters.
  • The air after passing through the filtration system will be exposed to the heat exchanger inside the AHU system and then it will create cold air for the environment.
  • Next, the air will go to the circulation chamber, and finally, the cold air will be blown through the air duct of the HVAC system to go to the area that needs air treatment.
  • The temperature level of the output air will depend on the speed of the fan and be adjusted by cold water valve.
  • Usually, AHU air conditioning systems are mainly used for preliminary treatment for airflow, not absolutely accurate.
  • If you want to treat moisture in the most accurate way, people will use more FCU systems in each specific area that is necessary.

Necessary parameters when choosing AHU for HVAC system

Usually, air conditioning system suppliers will have a technical department to support customers to choose AHU equipment that best suits the specific requirements of the project given by the designer.
Designers play the most important role when choosing AHU for works. If they do not know all the parameters to choose available products, it will cause inappropriateness that reduces efficiency.
choosing AHU for HVAC system
You can refer to some specifications for the basic AHU System is as follows:
  • Total Capacity: kW
  • Sensible Capacity: kW
  • Supply Air Volume: 1/s
  • Coil Entering Air Temperature (DB-WB): ° C
  • Coil Leaving Air Temperature (DB-WB): °C
  • Fresh Air Volume: 1/5
  • Fresh Air (DB-WB): ° C
  • External Static Pressure: Pa
  • Cooling/ Heating Water Flow: 1/s
  • On-Off Coil Water Temp: °C
  • Main Filter Type: Panel/Bag/Hepa Filter
  • Supply Fan Power: KW

Installation location of Air Handling system Unit

AHU is often found in medium to large commercial and industrial buildings.
They are usually placed in the basement, on the roof or on the floors of the building. AHU will serve an area or designated area in a building such as the east, or floors 1 - 10 or perhaps just a purpose such as Toilets of buildings. It is very common to find many AHUs around a building.
Some buildings, especially old high-rise buildings, will only have one large AHU, usually located on the roof. They will provide the entire building. They may not have a return pipe, some old designs rely on air leaking out of the building. This type of design is no longer popular in new buildings because it is very inefficient. Currently, the most common is that there are many smaller airtight slots, so we need to have a return pipe to adjust the pressure inside the building.
In industrial factories, AHU or system HVAC will usually be placed on the technical ceiling.

Application of AHU

Functions of Air Handling Unit

The AHU will air condition and distribute the air in the installed building itself. They take in fresh ambient air from outside, clean, heat or cool it, even humidify and then conduct the air through some ventilation ducts installed around the designed areas in the building.
Most AHUs have an additional conduit to drain used air out of the room, back to the AHU, where a fan will discharge it back to the outside environment. Some of this circulating air can be circulated again into a fresh air supply to save energy, we will take a closer look at this in the next part of the article. Conversely, if it is not possible, the heat can be separated and put into the fresh air flow.

Where is the AHU system used?

Where is the AHU system used?

Air Handling Unit is used in many today, we can mention such as:
  • Tall building
  • Industrial workshops, manufacturing plants
  • Cleanroom
  • Hotels, high-class living facilities
  • Offices, schools, hospitals, Lab rooms,...
  • And in environments that need air treatment
AHU can be called an indispensable air handling equipment today. Through this article, hopefully it will help you understand what AHU is, its operating principle as well as how it is applied so that you can choose and apply it to your facility.

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