What Is The Air Handling Unit?

An air handling unit, often referred to as an AHU, is a combination of components mounted in large, accessible box-shaped units called modules that accommodate the appropriate ventilation requirements for purifying, air conditioning or renewal of indoor air within a building or facility.

They are usually installed on the roofs of buildings and through ducts the air is circulated to reach each of the rooms in the building in question.

What Are The Primary Functions Of An Ahu?

In addition to managing the proper ventilation of the indoor space with outdoor air, the AHU performs other functions:

  • Thanks to air purification filters, the air that will reach the interior is filtered and its quality is controlled, and the air will be clean depending on the retention of these filters.
  • Control of air temperature, which regulates the air conditioning system as cold or hot, thus ensuring that the thermal feeling in the interior is at the desired level.
  • Relative humidity monitoring for greater indoor ease.

Field Of Applications Of An Ahu

The places where AHU is intended to be used are places where the human flow is high, where large numbers of people gather at the same time, and where natural ventilation is limited:

  • Airports and fairgrounds High flow rates for evacuating heating loads
  • Meeting rooms, schools, offices Evacuation of air pollution from people and partly from internal heating loads. Supply of conditioned replacement air.
  • Museums, art galleries Constant room conditions, small temperature ranges to protect against premature aging.
  • Data centers Reducing cooling loads by using and humidity minimum outdoor air and maximum recirculation air.
  • Hospitals and labs Constant temperature and humidity values. Low fine dust concentration. The system must meet the highest hygiene standards.
  • Pharmaceutical and chemical industry Defined clean room climate with relatively high demands on room air temperature and humidity.
  • Shopping centre Adjusting the desired temperature on different floors, ensuring fresh air circulation.
  • Public buildings Adjustment of temperature conditions of public. Spaces and constant fresh air intake.

As you see, AHU’s usage areas are quite diverse. Such as, hotel dining rooms, event rooms, restaurants, meeting rooms, indoor pools, etc. It is also an eligible option for areas with very high hygiene requirements: laboratories, clean rooms or operating rooms, etc. An air handling unit can also be used to ventilate spaces where air conditioning is provided by radiators or underfloor heating. Ventilation and air conditioning systems have become an integral part of our lives.

Air intake: air handling units collect air from outside, which is processed and distributed to rooms; and/or “recycled” indoor air.

What Are The Components Of An Ahu?

  • Filter: Depending upon air purity requirements, the applied filter will retain higher or lower levels of particles, viruses, bacteria, odors and other air pollutants.
  • Fan: It is an electromechanical system that drives the air from the AHU to the channels that circulate it to the rooms.
  • Heat ex-changers: Devices that transfer heat between two fluids (in this case, coolant and air) separated by a solid barrier.
  • Cooling coil: The air passing through this module is cooled. In this process, water droplets can be created, which collect in the condensation tray thanks to the built-in droplet separator.
  • Silencer: Coatings that importantly decrease the sound level of the installation.
  • Plenums: Empty spaces where air flow is homogenized.

What Are The Types Of Air Handling Unit?

Air handling unit types are generally divided into two: “blow-through” and “draw- through”.

1. Blow-through

The working principle of the blow-through air handling unit is as follows:

It has a fan which blows the air through the mixing box, cooling coil and filters before it goes to the ducting network.

2. Draw-through

Another types of air handling units is draw-through. They can be horizontal and vertical. Before the air enters the ducting network, it is pulled through the mixing box, cooling coil, and filters by a fan.

Furthermore, AHUs have a variety of sizes. Terminal units, also known as fan coil units or blower units, are compact, straightforward machines.

Air Handling Unit Selection Software

A machine that circulates and cleans the air in a home or building is called an air handling unit (AHU). “Box with a fan, coils, and filters that controls the air indoors” is a very basic definition of an AHU.  To elaborate, AHUs are units that are part of the HVAC system and are in charge of several functions like air conditioning, heating, cleaning, and humidity addition.

Though the fundamentals of AHUs may be covered by this brief explanation, this does not imply that all of them operate in the same manner or even possess the same features. Performance can vary depending on the parts and is frequently impacted by the climate where the AHU is located. While some systems may merely do air circulation, others may offer heating, cooling, and/or ventilation.

Building-specific air handling units are frequently designed to meet all specifications. Before making a purchase, it’s critical to comprehend the parts and operations of any AHU.

Ways to Select an AHU

There are a lot of factors to take into account when thinking about buying an AHU to make sure you’re getting the most effective and affordable unit for your needs.
Although we will dissect each part, it is crucial to assess each AHU’s individual features in addition to the unit as a whole.


The intended airflow that the AHU needs to manage comes first. Once you comprehend this, you should be able to determine the appropriate size and capacity for the AHU. Liters per second, or L/s, is the unit of measurement used to express how much air an air handler can condition and distribute.

The desired L/s can be determined by calculating the thermal load of the space that needs to be conditioned when thinking about an AHU. To start, figure out how big the area is that the AHU will be conditioning. Next, you need to determine how often the space needs to have its air changed. The Chartered Institution of Building Services Engineers (CIBSE) has guidelines for this.

Dimensions and modularisation

There are a few factors to take into account when determining the AHU’s size. The air handling unit’s dimensions must not only take into account the space that is available in the plantroom and comply with any building codes, but also allow for the filters, heat exchangers, and access sections for maintenance and fans. To make sure the AHU size is appropriate for the building, detailed 3D or BIM (building information modeling) representations of the unit are frequently used during the planning or design phase.

An AHU can be delivered in modules for easier transport and installation because they can be bulky. In this instance, the mode of transportation must be taken into account in addition to the destination building’s door and elevator sizes. An AHU with a modular design enables the system to be delivered in sections rather than requiring expensive special transportation.

Fans and energy recovery

Not only is size crucial when it comes to the fans inside the AHU, but proximity also matters. The fan efficiency may be affected by the location of the fan impeller inside the AHU. It’s crucial to take the fan’s style into account. Since the belt drive can wear out, belt-driven fans frequently require more maintenance than direct-driven fans.

Modern buildings must also take energy efficiency into account. For this reason, the internal specific fan power (SFPint), which calculates the relationship between the efficiency of the fan and the pressure drop over internal ventilation components, should be as low as feasible.

Selecting The Best Ahu

The most recent technologies are used to enhance the process of selecting the best AHU by ahuselection.com. It can fully operate on a local network or the Internet.

Features of ahu selection software:

User Friendly

Its simple interface will quickly get you used to using the program. Because all of the screens use the same standard logic, learning how to use one will make it much easier to understand and learn the others.


You can choose the AHU from anywhere in the world by using the Internet.

Common Database

The projects created by all users are saved in a common database, and users can access the projects based on their authorization.

Detailed Project Search

When the number of stored projects grows significantly, it will be difficult to find previous projects. Users can avoid this situation by searching for any value in the project. Users can, for example, list projects where the project name includes “ROCK” or where the AHU airflow is greater than or equal to 50.000 m3/h or where the “Klingenburg” branded rotary heat recovery module includes AHUs.

Vectoral Drawing

The design of the AHU can be seen from the sides, top, front, and back. During the AHU selection process, the AHU drawing on the screen is vectorial, and the entire AHU selection can be exported to Autocad in DXF format. The drawing you see on your screen while designing will be the same as the drawing you see in Autocad.

Technical Report

You can have the technical report customized with your own logo and company information. The technical report is available in PDF, Excel, Word, and HTML formats. The program also allows you to send the file in that format via e-mail.

Proforma Invoice

This program allows you to create a custom proforma invoice design and generate proforma invoices. You can also export the proforma invoice in various formats, such as a technical report, and send it by e-mail.

Copying Project

With a single click, you can copy and edit the previously prepared project / AHU and save it as a new project / AHU.

Heat Recovery

The heat recovery modules “Plate”, “Rotary”, and “Double Coil / Run Around” are available.

Turning Modules

You can design AHUs with two or more layers without using a heat recovery module by using 90° and 180° rotation modules. By using a 90° rotation module, an AHU in the shape of a maze can also be designed.

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