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For cleanrooms, environmental control is more stringent. Incredibly tiny particles are tracked in these spaces, even under 0.5 microns. For context, a human hair comes to around 100 microns wide, and the smallest thing our eyes can see is 50 microns. This is essential for the manufacture of computer chips, pharmaceuticals, and even spacecraft, where microscopic particles can wreak havoc to the production process. HVAC (Heating, Ventilation, and Air Conditioning) systems are at the heart of controlling the conditions in cleanrooms. How do they function? We’ll cover this and more here, including how advancements in technology are shaping their future.
Basics of HVAC Systems in Cleanrooms
It comes down to:
Temperature Humidity and Pressure Control: A lot of precision is needed here. Take semiconductor manufacturing, for instance, where tolerances are extremely tight. With the temperature, they can be as precise as +/- 0.02° C. Systems need to stabilize temperatures within this range otherwise results will be inaccurate. The setpoint temperature ranges typically between 19° C and 23° C. The relative humidity tolerances are similar, at +/- 0.5% RH and pressure varies from positive to negative depending the process. Such control tolerances are essential for processes such as semiconductor lithography, where photomasks require nano machining for defect repair.
Air Purity: HVAC systems use advanced filtration methods such as HEPA and ULPA filters to remove particulates and contaminants from the air. More on these shortly. The effectiveness of these filtration systems depends on the filters themselves, as well as establishing the proper airflow pattern and airchanges in the cleanroom for optimal filtration and cleanliness.
Advancements in HVAC technology have also led to more energy-efficient systems. For instance, the use of Variable Frequency Drive (VFD) for air circulation fan, ECM motors, etc, allows for precise control of air volume and temperature, leading to energy savings and improved environmental control. This improvement is not only beneficial for new installations but also for retrofits of existing systems.
Types of Cleanroom Ventilation Systems
Let's explore the types and their specific roles in cleanrooms.
Laminar Flow Systems
Laminar flow systems deliver air in a continuous stream. It involves a unidirectional flow of ultra-pure air without turbulence, which helps in removing contaminating particulate matter from the airstream in the critical zone. This technology is crucial in creating a Grade A or ISO 5 environment in cleanrooms.
Laminar flow systems are efficient in removing contaminants and particulate matter due to their uniform air direction. They are best suited for environments like semiconductor manufacturing and pharmaceutical compounding, where even the smallest particle can compromise the product quality. It is fundamental for producing sterile products and has evolved from being used at the whole facility level to more localized applications like Local Protection Zones (LPZs).
Turbulent Flow Systems
Contrary to laminar systems, turbulent flow systems distribute air in a non-uniform, mixed flow. While laminar systems direct air in parallel straight lines either horizontally or downwards, turbulent air flow systems are utilized in scenarios where the room's layout or equipment placement might create airflow dead spots with only laminar flow. Such systems use velocity filters in the ceilings or walls to mix the air and remove particles, effectively addressing these potential dead spots
Cleanrooms use far more energy than regular rooms, often up to 25 times more (1.25 kW/sqm vs. 0.06 kW/sqm). The HVAC systems in these rooms, crucial for meeting specific ISO standards, are big energy consumers. They can use 50-75% of a cleanroom's electricity because they need to move a lot of air. This heavy energy use underscores the need for solutions like turbulent flow systems that cut down on power consumption. These systems are more energy-efficient and cost-effective compared to laminar flow systems. They are suitable for general manufacturing and research facilities where a high level of air cleanliness is required.
Recirculating Air Handler System
The recirculating air unit (AAU) serves as one method for delivering air to a cleanroom. In this setup, a dedicated air handler unit is typically equipped with a fan, filter, and a sensible cooling coil enclosed within a cabinet unit. Positioned atop the cleanroom, this unit supplies air either through a ducted air distribution system or by being directly mounted on top of the pressurized Plenum unit, which acts as an integral part of the cleanroom ceiling and air distribution. The delivered air is filtered and tempered using HEPA or ULPA filters.
Return air follows a specific path, either directed through a raised access floor, returning unidirectionally from the ceiling through the raised floor and back to the return air (RA) chase unit, which is positioned along the side. Alternatively, it may be directed through the sub-fab and returned to the interstitial space.
Recirculating Air Handler System
Make-Up Air (MAU) is introduced from a dedicated Make-Up Air Unit providing humidity control and positive pressure and MAU required for process exhaust in the cleanroom.
Fan Filter Unit (FFU)
Recirculation air is provided with individual Fan Filter Unit (FFU) placed on cleanroom ceiling grille with HEPA/ULPA filters. Air is directed downwind towards the floor or side wall RA grilles, then directed upwards towards interstitial space and then mixed with the Make-Up Air, drawn into the intel of each FFU.
Fan Filter Unit (FFU)
Ducted Filter Distribution
Recirculation air is supplied through a dedicated Recirculation Air Unit (RAU), akin to the ones detailed earlier. This involves a ducted distribution from the RAU unit to each ducted filter (HEPA/ULPA). The return air (RA) pathway follows a pattern similar to the systems discussed earlier in this article. Additionally, Make-Up Air (MAU) is introduced through a dedicated Make-Up Air Unit, which is connected to each RAU unit for comprehensive air circulation.
Ducted Filter Distribution
So, when it comes to picking the right air system for a cleanroom, it's all about what you need – cleanliness, saving on power bills, or maybe a bit of both. Installation costs too. At DesignTek Consulting, we specialize in designing and implementing the most suitable HVAC solutions for your specific cleanroom needs.
HEPA and ULPA Filters 101
Let’s take a more comprehensive look at these two types of filters.
HEPA Filters: A Standard in Cleanroom Filtration
HEPA filters, made of a mat of randomly arranged fibers, remove microorganisms like bacteria and fungi through processes like impaction, interception, and diffusion. In high-grade cleanrooms, they are designed to remove approximately 99.97% of particles that are 0.3 μm in size or larger, depending on the grade of the filter. This makes them a key component in industries like pharmaceuticals and electronics. There are cases where they capable of capturing particles smaller than 0.3 μm, including viruses, which generally range from about 0.1 to 0.2 μm in size - a factor that became increasingly relevant during the COVID-19 pandemic.
In one particular published as part of the Journal of Nanoparticle Research, cleanroom-grade HEPA filters captured silver particles as small as 5 nanometers with a 99.99% efficiency. A NASA study had filters capturing particles under 0.01 micrometer in diameter.
ULPA Filters: For More Stringent Requirements
ULPA filters go a step further, capturing particles as small as 0.12 microns with an efficiency of 99.9995%. They are used in environments that require an even higher standard of air purity, such as semiconductor manufacturing, where the size of contaminants are on a nanometric scale. By 2029, the global market size for cleanroom ULPA filters is projected to reach USD 274.4 million, clocking a CAGR of 6.7% between 2023 and 2029.
Choosing between ULPA and HEPA filters? It depends on how clean your air needs to be. The technology itself continues to evolve. For instance, conventional HEPA/ULPA filters have used fiberglass paper as their standard media. However, filters based on expanded Polytetrafluoroethylene (ePTFE) and expanded Fluoro-Resin Membrane (eFRM) have now been introduced. These new materials are tougher, last longer, and even reduce the risk of media failure while maintaining filter integrity.
Regulatory Standards and Compliance
With cleanroom ventilation, designs need to align with regulatory standards to ensure you meet both legal requirements and industry best practices. For instance, the ISO 14644 standards provide a framework for classifying air cleanliness based on number of particles allowed per cubic meter of air, varying by particle size and cleanroom class. Adherence to ISO 14644 is critical for industries ranging from biotech to electronics manufacturing.
The design and maintenance of HVAC systems determines whether you comply with the ISO standards or not. Particle count, air change rates, and pressure differentials need to meet specified criteria. As reported by the International Organization for Standardization, these standards are continually updated to reflect technological advancements and industry needs.
Routine maintenance for these systems includes:
Regular Cleaning of HVAC components: This is your first line of defense, and is essential in preventing the buildup of contaminants that can compromise cleanroom standards. The ducts, filters, and vents should be cleaned.
Filter Changes: Over time, filters can become clogged with particles, reducing their efficiency. Changing the filters ensures the HVAC system operates optimally.
System Monitoring: Is the system operating within the required parameters? This includes temperature, humidity, pressure, and particulate levels. Real-time monitoring systems can provide alerts for any deviations, enabling prompt corrective actions. Plus, catching problems early saves you from headaches (and burning through loads of cash) down the line.
The Need for Energy-Efficient HVAC Design
Energy efficiency and sustainability are all the rage in today’s world – and this also applies to HVAC systems. For your business, you want systems that not only meet the stringent standards of cleanroom environments but also focus on reducing energy consumption and environmental impact.
HVAC systems usually account for 50-75% of the total electricity consumption in cleanrooms. This high energy demand is attributed to the necessity for maintaining high airflow rates to meet specific ISO class requirements. So, getting the design right is key to saving energy.
That’s why DesignTek Consulting’s engineers incorporate advanced technologies like Variable Air Volume (VAV) systems, which adjust the volume of air delivered to meet specific needs, thereby reducing energy use. Also, high-efficiency motors and smart controls keep everything running smooth and in a sustainable manner. This brings us to our next point.
The Journey Towards Eco-Conscious Cleanrooms
Sustainability in cleanroom design extends to using materials and processes that have minimal environmental impact. This includes selecting eco-friendly materials for construction and implementing waste-reduction practices during the operation of cleanrooms.
Large corporations are already doing this. One example is Contec's introduction of ReFIBE, a wipe used in cleanrooms. These wipes are made from 100% knitted standard weight polyester that have heat-sealed edges, sourced from recycled plastic water bottles. A single pack of these wipes equates to 35 plastic bottles being spared from landfills or ocean contamination. A full case of these wipes can divert as many as 840 bottles from harming the environment.
Going green with your cleanroom design is a win-win. You save cash for those day-to-day operations and ride the wave of being a responsible, eco-friendly player in the global scene – getting more consumers gravitating towards you. It's doing your bit for the planet while looking after your bottom line.
At DesignTek Consulting, we understand energy efficiency and sustainability are key considerations for modern cleanrooms, and are equipped to design and install HVAC systems that meet these criteria.
Reach us at (855) 203-2958 to explore solutions for your business.