Cleanrooms and Air Filtration


One of the main things that makes a cleanroom “clean”, is the air distribution & filtration system. The Pharmaceutical, Medical, Hospital and Food industries all share a similarity in that they require cleanrooms to properly operate to maintain their hygiene levels. A cleanroom is an enclosed space or area where the environment is controlled to prevent contaminants. Dust, airborne particles, chemicals vapours, water vapours, and microbes are all examples of pollutants /contaminants that a cleanroom environment prevents.

By using HEPA and ULPA filters, cleanrooms can prevent contaminants from entering the “Clean” space and compromising the integrity of the cleanroom. But it is not just about the filtration used, it is equally important to establish a proper airflow pattern in the cleanroom for optimal filtration.

Air Distribution Strategies for Cleanroom

The cleanest air environment can be achieved with a unidirectional (laminar) air flow pattern. Low level return air flow creates a unidirectional flow pattern in the cleanroom. Unidirectional (Laminar) air flow means the air in a designated space is blowing in a uniformed pattern, in terms of velocity and direction.

It makes the air inside an enclosed space (such as the cleanroom) move safely and free from contaminants. Particles which enter a room with laminar airflow will only stay in the room for a short time and be filtered out quickly through HEPA filters.

When primary existing air mixes with the induced room without any proper directional flow, it is classified as turbulent air flow. This air flow is best used when concentrating clean air in select points of the cleanroom. Turbulent airflow keeps the air in a cleanroom in constant motion.

Benefits of Low-Level Air Return

Achieving Unidirectional (Laminar) Air Flow

Since the unidirectional air flow pattern is used to achieve the cleanest air classes, it is understandable that a low-level air return is important to have in any cleanroom. To achieve a unidirectional air flow pattern, you would need to have an air supply on the ceiling and a low-level air return towards the bottom of the room. Airflow would come down from the ceiling and would be pushed down to the floor and into the low-level air return, resulting in a unidirectional air flow pattern.

Maintain Equal Temperature

The suggested temperature of a cleanroom should be 21°C in most applications, unless specified otherwise.  Sometimes a fluctuation of 2°C is acceptable. Maintaining and controlling cleanroom temperature is important for your own comfort and the integrity of the cleanroom.

Low level air return will help maintain equal temperature in the room. Naturally, cold air is heavier, and it typically settles towards the bottom of the room. While hot air is lighter and gradually rises to the top of the room. A low-level air return grill will maintain balance between the hot and cold air, resulting in an equal temperature, no matter where you are in the cleanroom.

Balanced return air is an advantage of a low-level air return duct. Air balancing is important for added comfort when working inside the cleanroom.

A good return air flow keeps the room at a maintained temperature. It makes people breathe easier and the room feels warmer. It also keeps away contaminants that can potentially compromise the integrity of the cleanroom.

Better Air Quality

Air return ducts installed on a low level or somewhere on the wall promotes better air quality. The air is cleaner, fresher, and cooler if the air return in your cleanroom is installed and working properly.

Air returns installed up in the ceiling tend to produce low-quality air due to poor air distribution. Poor air circulation attracts contaminants which defeat the purpose of a cleanroom. Air quality is important in an enclosed space such as the cleanroom. Not only does it prevent contaminants, but it also provides a more comfortable setting for cleanroom workers.

Improved Air Distribution

Low-level air return is more efficient than high-level air return if we are talking about air distribution. Hot and cold air mixes when the air return duct is up in the ceiling, making the room feel hotter.

The air pushes in and out of the air supply efficiently when the air return duct is at a low level. It helps achieve equal air distribution inside the cleanroom which allows good ventilation. Poor air distribution can contaminate the cleanroom.

HVAC Efficiency

Without the help of low-level air return filtration, you may find that the HVAC unit may become compromised. MERV rated filtration integrated in the low-level air return prevents biological or product related impurities from going to the HVAC unit. This aids in improving HVAC usage and efficiency.

Why Return Air Filtration

Low Level Air Returns come equipped with filters that prevent any contamination from going out of the room. You might be wondering, what is the point of filtering air that is leaving the cleanroom? There are a couple of reasons that make this important to consider.

Filtration for Hazardous Products (Such As Pharmaceuticals)

Some cleanrooms are used to manufacture hazardous products, particularly in the pharmaceutical industry. Without the proper protection, these products can be harmful for people working in and around the cleanroom. When working with pharmaceuticals, it is common for powder to be spread around the room, naturally settling on the floor. With a laminar air flow and low-level air return, these hazardous chemicals are trapped in the air return filtration.

Easy Maintenance

Since low level air returns are found at the bottom of the room, it is extremely convenient to replace the filters as part of your regular maintenance of the cleanroom. Modular cleanroom panels can be manufactured with prefab low-level returns in the wall and space for grill integration.

Importance of Keeping Cleanroom Air Returns at “Low-Level”

  • Low level air returns assist in creating a laminar air flow pattern.
  • Laminar airflow patterns are used to achieve the cleanest air classes.
  • Filtration for low level air returns is important to have, especially when working with hazardous materials.
  • Low Level Air Return filters are easy and convenient to replace.
  • Low Level Air returns provide a more comfortable workspace for cleanroom workers.


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