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Cleanroom Air Flow

Cleanrooms are designed to have vertical filtered air flow to keep the room as particle free as possible. The HEPA Fan filter units in the ceiling push the HEPA filtered air into the room where it travels down to floor and exits via low wall air returns.

A properly designed cleanroom will have laminar (think smooth river) air flow that sweeps contamination out of the cleanroom in the most effective manner. A poorly designed cleanroom may have turbulent (think raging rapids) air flow that just pushes contamination around the room.

GIF blue arrows red arrows, cleanroom air flow, recirculating cleanroom
Cleanroom air flow – recirculating
one pass cleanroom, cleanroom air flow, GIF blue arrows red arrows
Cleanroom air flow – one pass
Softwall cleanroom air flow

FAQs About Cleanroom Air Flow

Q: What Is a Recirculating Cleanroom?

A: In a recirculating cleanroom the air passes over and over thru the HEPA fan filter units. This makes the air cleaner and cleaner as well as extending the life of the HEPA fan filter units.

Q: What Are Advantages of a Recirculating Cleanroom?

A: Recirculating cleanrooms typically have their own air conditioning systems. This allows for temperature and humidity control. In a recirculating cleanroom the air passes thru the HEPA fan filter units over and over. This makes the air cleaner and cleaner as well as extending the life of the HEPA fan filter units.

Q: What Are Advantages of a One Pass Cleanrooms?

A: Typically one pass cleanrooms are lower cost than recirculating cleanrooms as they do not include air conditioning.

Q: What Are Disadvantages of One Pass Cleanrooms?

A: They cannot fully accommodate AC so you cannot control the temperature of your cleanroom. Workers inside that wear cleanroom suits can get very hot. Also one pass cleanrooms draw outside unfiltered air thru the HEPA fan filter units so they typically cannot achieve the same level of cleanliness as recirculating rooms. Finally, the HEPA fan filter units have significantly shorter life in one pass cleanrooms as they are constantly drawing dirt from the outside into the filter.

Q: What Is a Softwall Cleanroom?

A: Softwall cleanroom use clear vinyl curtains to form the walls of the cleanroom. They are almost always designed as one pass cleanrooms. The air exhausts underneath the curtain at the floor level to outside of cleanroom.

Q: What Is Laminar Air Flow and Why Is It Desired in a Cleanroom?

A: Laminar air flow in a cleanroom is when the air is uniform in both direction and velocity. Like a smooth-running river, the laminar airflow sweeps particles down to the floor and then horizontally to low wall air returns. This reduces particles in the cleanroom compared to turbulent air flow.

Q: What Is Turbulent Air Flow and Why Is It Bad in Cleanrooms?

A: Turbulent air flow creates unintentional swirls of air that swirl and deposit particulates inside a cleanroom. Like river rapids, the turbulent air flow carries particles all around the cleanroom as opposed to directing them to the floor and then to air return grills. Good cleanrooms rely on moving large volumes of clean air at low velocity. High velocity air causes turbulence. Turbulent air flow is much less effective than laminar air flow in removing particles.

Q: How Can I Ensure My Cleanroom Has Laminar Air Flow?

A: The cleanroom is typically designed with evenly distributed HEPA fan filter units in the ceiling and strategically placed low wall air returns to ensure an even uninterrupted flow of clean air. In larger rooms, air return walls are often added into the middle of the room to minimize the distance. Ceiling air returns should be avoided as it can result in short circuiting of the air flow between the ceiling mounted HEPA fan filter units and the ceiling air return.  

Q: How Can Equipment Placement Affect Cleanroom Laminar Air Flow and the Effectiveness of a Cleanroom?

A: Cleanroom users must be careful where they locate equipment to avoid blocking the air flow and creating dead areas. It is recommended that equipment be placed on open racks. Table and benches are often designed with perforated surfaces to allow open air flow. Equipment should never be placed in front of air return grills as this can significantly diminish air flow.

Q: What Cleanroom Design Gives the Best Laminar Air Flow Results?

A: 100% cleanroom HEPA filter ceiling coverage combined with raised cleanroom flooring will give the best results for cleanroom laminar air flow. It also allows for tightest temperature and humidity control. This type of design is common in semiconductor manufacturing class 100 cleanrooms.

Q: Why Are Rigid Wall (Modular or Conventional Construction) Cleanrooms More Effective Than Softwall Cleanrooms in Removing Particulates From the Air?

A: Rigid walls (modular or conventional) allow cleanrooms to maintain positive pressure to ambient. This means if there is a door opening or a leak in the cleanroom, the air flows from inside to outside the cleanroom pushing contaminants away from the cleanroom and reducing the amount that enters. Softwall cleanrooms (clear vinyl curtains) push the air to flow under the curtains to the outside of the cleanroom. There is rarely measurable positive pressure. Although they are overlapping, the strip curtain entrances also allow contaminants to enter the cleanroom.

Q: What Is Cleanroom Make Up Air?

A: A certain amount of air escapes from the cleanroom via door openings, cracks, and exfiltration thru walls. In addition, there is often equipment that exhausts to outside cleanrooms like chemical hoods. In order to maintain positive pressure, the cleanroom must have a source of sufficient makeup air to compensate for air that escapes.

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