Cleanrooms are designed to maintain strict control over environmental factors, but they’re only effective if they have an expertly designed airflow pattern to help them reach the desired cleanliness level and ISO classification standard. ISO document 14644-4 describes airflow patterns to be used in cleanrooms at the different classification levels in order to maintain strict airborne particle counts and cleanliness. 

Cleanroom airflow must allow the air within the cleanroom to be completely changed to remove particles and potential contaminants before they can settle. In order to do this properly, the airflow pattern must be uniform — ensuring every part of the space can be reached with clean, filtered air.

To break down the importance of cleanroom airflow uniformity, we need to start by looking at the three main types of airflow in cleanrooms.

3 Types of Cleanroom Airflow Patterns

Cleanroom airflow can be unidirectional, non-unidirectional, or mixed — a combination of both. The best cleanroom airflow type will depend on the cleanroom classification. Generally, cleanrooms of an ISO Class 6 or greater can use a mixed or non-unidirectional airflow pattern, while ISO Class 5 (or cleaner) cleanrooms rely on unidirectional airflow.

#1 Unidirectional Cleanroom Airflow

This type of cleanroom air moves in one direction across the room, either horizontally or vertically from fan filter units to the exhaust system that removes “dirty” air. Unidirectional flow requires as little disturbance as possible to maintain a uniform pattern.

#2 Non-Unidirectional Cleanroom Airflow

In a non-unidirectional airflow pattern, air enters the cleanroom from filter units located in multiple locations,  either spaced throughout the room or grouped together. There are still planned entrance and exit points for air to flow along more than one path.

Although air quality is less critical compared to unidirectional airflow cleanrooms, special attention should be paid to make sure air is changed thoroughly, minimizing the potential for “dead zones” within the cleanroom. 

#3 Mixed Cleanroom Airflow

Mixed airflow combines both unidirectional and non-unidirectional airflow. Unidirectional airflow may be used in specific areas to boost protection around working areas or more sensitive materials, while non-unidirectional airflow still circulates clean, filtered air throughout the rest of the room.

Why Cleanroom Airflow Uniformity Matters

Whether a cleanroom airflow is unidirectional, non-unidirectional, or mixed, having a uniform cleanroom airflow pattern matters. Cleanrooms are meant to be controlled environments where all systems should work to prevent areas where buildup of contaminants can occur — via dead zones or turbulence. 

What is Turbulent Air?

Turbulent air, or chaotic air, in a cleanroom is a serious threat to cleanliness. Turbulent air occurs when the airflow pattern is not uniform.

Think of a current moving through water. If the flow was uniform, all of the water would move steadily at the same speed. Obstructions or varying speeds, like rocks or rapids, impede the uniformity of the flowing water. Similarly, when you sweep your hand through water and see eddies and whirlpools form to the side of the current, that’s turbulence. 

Eddies in water may be harmless, but turbulence in cleanroom airflow can cause the uncontrolled movement of contaminating particles — or dead zones where no air is moving at all, where contaminants can build up and threaten sensitive processes in the cleanroom.

What Causes Turbulent Air in Cleanrooms? 

Turbulence in cleanroom airflow can be caused by non-uniform speeds of air entering the room or obstructions in the path of incoming or outgoing air. Airflow uniformity is about preventing unnecessary turbulent air so the cleanroom can perform at peak efficiency.

Minimizing Turbulence in Cleanrooms

You can minimize turbulence by designing the cleanroom airflow pattern to work with your layout, equipment, furniture, and personnel. The cleanroom should be removing air at the same or similar speed as it enters. This gives air a clear path to flow to prevent turbulence and dead zones.

Obstructions can also cause turbulent air, so make sure that no large furniture or equipment is blocking fan filter units or exhaust. Adjust equipment with aerodynamic attachments or design features to facilitate airflow, use perforated cleanroom tables to allow air to pass through uninhibited, or modify behavior of personnel to not block or impede airflow within critical zones.

Cleanroom Airflow and Pressurization

Another way to minimize contamination using a uniform airflow pattern to establish positive or negative air pressure. Cleanroom pressurization creates a natural barrier to protect or isolate cleaner or less clean zones, respectively. Using negative and positive pressure can be especially useful for sensitive applications such as the manufacturing of healthcare products, medical research, microelectronics, and more.

Custom Cleanroom Airflow Design

Cleanroom airflow patterns should be designed to work with each unique cleanroom layout and all the furniture, systems, and personnel in the cleanroom for optimal cleanliness during operation. 

A cleanroom engineer uses computational fluid dynamics to map out the cleanroom and place fan filter units and outlets appropriately to meet your classification requirements. This system allows the designer to visualize the pattern of air and make adjustments for cleanroom systems, equipment, and personnel in order to achieve uniformity. It also allows you to anticipate your energy requirements and make your facility as efficient as possible. 

As your ISO cleanroom classification gets lower, having an expertly designed airflow pattern becomes more and more crucial. Work with an expert to make sure your cleanroom airflow is as uniform as possible for your application.

Trust the Angstrom Technology Cleanroom Airflow Design Experts

Designing your cleanroom and need a little help establishing an efficient, uniform airflow pattern? Call the experts at Angstrom Technology. From cleanroom airflow design to HVAC and filtration maintenance, we can help you make the best choices for your budget and your classification. 

Pressurized cleanrooms are used in a range of industries and applications. Varying levels of pressure determines the way air naturally moves in a space. High and low pressure, or positive and negative pressure, can be used as a tool in cleanroom environments to help cleanrooms reach their cleanroom classifications and protect their products and people. Let’s explore air pressure in cleanrooms to discover how it works.

How Does Air Pressure in Cleanrooms Work?

It’s a well-known natural process for air to flow from high to low pressure. Examples of this are found around us every day. Wind and weather are formed from the uneven heating of the earth’s surface, which generates pockets of high and low pressure air. If you’ve ever witnessed the sudden closing of a door as air is sucked out of a room where no breeze was felt, what you experienced was the high pressure air moving to a low pressure area to achieve stasis. Air escaping from a balloon is traveling from a high pressure environment to the relatively low pressure of the surrounding air. 

What happens in all of these situations is that when air is moving in one direction, it’s not moving the opposite direction. When air is moving out of the balloon, there isn’t also air moving into the balloon, as long as the air inside the balloon is more pressurized. This concept can be applied to cleanrooms, to stop the flow of air into a cleanroom, or out of it, limiting particle transfer via the air and maintaining a cleaner environment.

To state this more plainly, higher pressure air within a cleanroom (compared to the air outside the room) blocks against contaminants entering the cleanroom, as air naturally wants to flow out. Conversely, lower pressure air within a cleanroom can trap contaminants and prevent them from leaving a cleanroom, as the natural flow of air wants to move in. 

Using pressure in cleanrooms, either higher pressure (positive pressure), or lower pressure (negative pressure) can be extremely useful in many cleanroom applications — but how do you implement it in the cleanroom design?

Using Pressure in Cleanroom Design

Positive and negative pressure in cleanrooms is achieved by controlling how much air is put into the cleanroom, and how much is withdrawn. 

In a positive pressure cleanroom, clean, filtered air is consistently pumped into the room through the HEPA filtration and cleanroom HVAC system. In the event that a door or window was opened in the cleanroom, air would rush out into the outside environment. 

This positive pressure ensures that in the event of a breach or leak in the cleanroom, the products and processes within the cleanroom are protected. Because the cleanroom has positive pressure, the air is forced out of the cleanroom, preventing contaminated or unfiltered air from seeping in. 

To achieve negative air pressure, external exhausts pull air from the cleanroom at a faster rate than air is introduced over a span of time. The resulting negative pressure means air will want to flow into the cleanroom to fill the low pressure area, effectively stopping contaminants from going against that natural movement in order to escape the cleanroom.

To maintain either positive or negative pressure in cleanrooms, adjacent spaces must be maintained at a lower or higher pressure than that of the cleanroom, respectively.

If you implement a pressurization system into your cleanroom design, having a pressure monitoring system is important to ensuring balance and consistency within your cleanroom. The monitoring system will check and maintain consistent pressure, which can be adjusted manually or automatically.

Positive Pressure Cleanroom Applications

High pressure, or positive pressure cleanrooms are extremely useful in applications where the slightest particle interference could disrupt processes within the cleanroom. Semiconductor cleanrooms, microprocessor cleanrooms, and aerospace and defense cleanrooms are just a few examples of industries that benefit from positive pressure cleanrooms, as they are extremely averse to contaminating particles. Many medical cleanrooms use positive pressure, to protect sensitive patients and maintain a controlled space.

Even when the stakes aren’t quite as high, using slightly positive pressure in cleanrooms can help reach cleanroom classifications and maintain a cleaner environment.

Negative Pressure Cleanroom Applications

Low pressure cleanrooms, or negative pressure cleanrooms, are ideal for applications that need to isolate substances, particles, or fumes inside the cleanroom environment to protect the space outside of the cleanroom. They are widely used in medical cleanrooms, for medical research, testing, and the development of treatments using sensitive substances. 

Pharmaceutical applications also use negative pressure in cleanrooms as part of a segmented layout. One room is kept at a lower pressure, while the ante room immediately outside it is maintained at a slightly higher pressure. This allows employees to transition into the negative pressure room with minimized disruption.

High and low pressure, or positive and negative pressure, can both be used as tools in cleanroom environments to protect against entering contaminants (in positive pressure cleanrooms) or contaminant leakage (in negative pressure cleanrooms). Using the natural movement of air due to pressure, we can build safer, more effective cleanrooms.

Think a negative or positive pressure cleanroom is right for you? Reach out to Angstrom Technology. Our cleanroom experts can design the best air flow patterns and containment systems for your application.