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Cleanroom Air Flow: Techniques, Pressure Control, and More

Picture a space where the tiniest particle is an adversary. This is not far from the truth, as in many industries, a single particle can cause serious damage to products. To avoid these dangers, cleanrooms must use cutting-edge air flow management strategies. In this article, we will discuss some common techniques for managing air flow, the effects of pressure on airflow, and additional factors that may influence it.

What is Unidirectional or Laminar Air Flow?

Unidirectional, or laminar air flow, is air that moves in a single direction at a consistent speed. The purpose of it is to remove particles from vulnerable areas quickly and efficiently.

When air moves in a single direction, particles are less liable to float around the room. Air will instead flow directly into air returns placed either in the floor or lower walls.

Unidirectional air flow systems are commonly used in ISO 5 cleanrooms and above, where high levels of cleanliness are required, such as in semiconductor manufacturing, pharmaceuticals, and biotechnology.

Industries that require pristine conditions need unidirectional air flow because, as we mentioned, some products can be ruined by a single particle, especially in electronics.

Standards and regulations, such as ISO 14644-1, provide guidelines for implementing and maintaining laminar air flow.

An illustration of laminar airflow.

What is Turbulent Air Flow?

Turbulent air flow, which is the opposite of laminar air flow, involves air moving in multiple directions at varying speeds. This method is the default and is often used in cleanrooms that do not require strict conditions, such as those classified as ISO 6 and below. Turbulent air flow systems are commonly used in industries such as food processing and general manufacturing.

While turbulent air flow can still dilute contaminants, it is much less effective in removing particles, as they can spread out in many directions and linger.

One of the main advantages of turbulent air flow is its lower cost (unidirectional air flow is significantly more expensive) and simpler installation process.

An illustration of turbulent airflow.

What is Mixed Air Flow?

Mixed air flow uses both unidirectional air flow and turbulent air flow. In other words, a mixed air flow cleanroom will have some areas that use unidirectional air flow, and others that do not.

Cleanrooms will typically use unidirectional or laminar flow in areas where products or processes are the most vulnerable. For example, in pharmaceutical manufacturing, the area where aseptic filling and compounding occur might use unidirectional air flow, while in packaging rooms, turbulent flow may be sufficient.

These mixed systems provide a good balance between cleanliness and cost.

What Role Does Pressure Play in Cleanrooms? What’s the Difference Between Positive and Negative Pressure Rooms?

Using positive and negative pressure in cleanrooms is important because it directly affects the direction of air flow. Depending on the type of pressure, air can either flow out of or into a cleanroom, in case of a breach or opening.

A positive pressure cleanroom has a higher air pressure compared to the surrounding areas, which causes air to flow out of the room upon a breach or door opening. Positive air pressure is commonly used in pharmaceutical cleanrooms and operating rooms, where it is important to keep contaminants out.

A negative pressure cleanroom, on the other hand, has lower air pressure relative to surrounding areas, which causes air to flow into the room. These cleanrooms are used to contain biological hazards or other dangerous materials. Common uses for them include biosafety labs, where dangerous pathogens are studied, and isolation rooms in hospitals, where patients with contagious diseases quarantine.

Managing pressure within cleanrooms protects both the environment and the surrounding areas from unwanted particles.

What are Recirculating Cleanrooms? What are Single Pass Cleanrooms?

Recirculating cleanrooms use a system where air is continuously filtered and recirculated within the cleanroom. Air is taken back through air returns, which are vents typically located near the floor or lower walls. From there, the air passes through a plenum—a space or chamber that acts as an air distribution pathway. The plenum helps to evenly distribute the air and guide it back to the filters. After passing through the plenum, the air goes through high-efficiency filters, such as HEPA or ULPA filters, which remove particles and contaminants. The filtered air is then reintroduced into the cleanroom.

This process of continuous filtration and recirculation makes the air consistent and high-quality, benefiting industries such as semiconductor manufacturing, pharmaceutical production, and aerospace engineering.

Single pass cleanrooms, on the other hand, work differently. A single pass cleanroom draws air from outside the cleanroom into the plenum where the HEPA fan filter units push the clean filtered air into the cleanroom. The air then travels to the floor and then exits the cleanroom through exhaust grills located on the walls.

Unlike recirculating cleanrooms, single pass cleanrooms do not have temperature control and rely on the cooling of the surrounding warehouse. They are also much cheaper to build and maintain.

The choice between recirculating and single pass cleanrooms depends on the specific requirements of each cleanroom. One will need to take into consideration factors such as the size of the particles that cause issues, energy efficiency, and costs.

Other Factors that Influence Air Flow in Cleanrooms

Many other factors can also influence cleanroom air flow.

For starters, the design and layout of the cleanroom may significantly impact it. Well-planned layouts, for instance, may reduce turbulence and improve overall circulation.

Similarly, thoughtful placement of air returns, grills, and other equipment may also improve air flow.

Further, regular maintenance, such as cleaning, inspections, and testing, are necessary in making sure that air is flowing properly. Checking that ducts, vents, and filters are free from unnecessary obstacles helps it stay optimal.

For those looking to upgrade or design a new cleanroom, Allied Cleanrooms offers expert solutions. Contact them today to get a free quote customized to your unique requirements.

The Bottom Line

Cleanroom air flow is an important part of making sure controlled environments stay clean of contaminants. Understanding the different types of air flow systems, pressure control methods, and cleanroom designs helps in selecting the right solution. As technology advances, cleanroom air flow systems will continue to evolve and provide even better contamination control.

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