HVAC (heating, ventilation & air conditioning) is vital for enclosed environments. It ensures the consistent circulation of fresh air with the addition of warmer or cooler air where required.
Cleanroom ventilation requires meticulous levels of precision to meet regulations required for usage. Particles as low as 0.3 microns can cause contamination, so the highest ventilation standards must be met for cleanrooms.
What is Cleanroom HVAC?
Cleanroom HVAC is a specialized system designed to maintain clean and controlled conditions within a specific environment. Cleanrooms need a higher level of air filtration in comparison to regular HVAC systems. Here are some key features of cleanroom HVAC systems:
Precise Temperature and Humidity Control
Cleanroom HVAC maintains strict control over temperature, humidity, airflow patterns, and air filtration to meet the required standards. Temperature must remain within ±1°F and humidity within ±5% RH.
Air Filtration
Cleanroom filtration is much higher compared to regular rooms. They can remove particles down to 0.3-0.5 microns for critical manufacturing, as in the case of semiconductors.
This is achieved by using high-efficiency particulate air (HEPA) and ultra-low penetration (ULPA) filters, which remove 99.97-99.999% of particles ≥ 0.3 microns.
Air Circulation and Flow
Cleanrooms havehigh rates of air circulation. The air in the room gets replaced multiple times an hour in critical areas to flush contaminants out.
The flow is designed to move from the cleanest areas to less clean areas via positive pressure to prevent contaminants from entering the room.
Fan Positioning
Fans and air handling systems are typically present outside the cleanroom and air ducted in via the ceiling plenum.
This is to maintain optimum cleanliness by preventing any dust that may accumulate on the fans from entering the room.
Importance of Ventilation
Here’s why proper ventilation is paramount in cleanrooms:
Contamination
Particles like dust, bacteria, and chemicals can have disastrous consequences in cleanrooms. Even trace amounts can compromise product quality or disrupt a delicate manufacturing process.
HEPA or ULPA systems present in cleanrooms act as a first line of defense, capturing and removing nearly all airborne particles.
This ensures a safe environment for personnel, products, and manufacturing processes.
Temperature
Cleanroom processes are susceptible to temperature fluctuations. The slightest changes can affect product consistency and working performance which can cause contamination.
Cleanroom ventilation systems are equipped with precise temperature control capabilities. Heating and cooling systems provide a stable, desired temperature within the cleanroom.
This ensures optimal conditions for sensitive processes maximizing product quality and process efficiency.
Humidity
Much like temperature, too high or low humidity can adversely affect cleanroom processes like electronics and semiconductor manufacture. It can also facilitate the buildup of static charge.
The humidity control mechanisms within cleanroom HVAC systems provide adequate humidity levels to prevent these issues.
Airflow and Air Pressure
Cleanrooms require high rates of filtered air circulation, as well as positive pressure differentials relative to surrounding less clean areas.
This ensures particulate contaminants only flow from clean to dirty areas, ensuring contaminants are efficiently swept toward filtration units.
Positive pressure, where the cleanroom air pressure is slightly higher than the surrounding environment, prevents unfiltered air from entering, further safeguarding the controlled space.
Venting
Even within a cleanroom, air is bound to be contaminated at one point, either due to the manufacturing process or through any air that escapes into the room.
This stale, contaminated air needs to be removed from the cleanroom before the next manufacturing process begins.
Proper venting mechanisms are essential for expelling such contaminated air. This continuous removal allows fresh, filtered air to be introduced, maintaining the desired air quality within the controlled environment.
Ducting
Ducts are responsible for transporting air in and out of the cleanroom. However, if not designed and maintained properly, they can become breeding grounds for contaminants and disrupt airflow patterns.
Cleanroom ventilation relies on specialized ductwork, made from non-shedding materials to minimize particle generation.
Additionally, regular maintenance of such ducts ensures that they remain clean and free of dust and potential contaminants.
Best Practices for Cleanroom Ventilation
Here are some of the best practices to ensure optimum ventilation:
- Install instrumentation like magnehelic gauges, anemometers, and data loggers. This is to continuously monitor differential pressures between cleanroom zones, airflow velocities, laminarity, temperature, and humidity.
- Follow the standard operating procedures for routinely checking critical ventilation parameters at defined intervals and locations. Utilize industry standards like ISO 14644.
- Make sure that air systems and emergency backup systems are adequately sized to handle rapid drops in pressure from contamination incidents or accidents — all without allowing uncontrolled infiltration from surrounding dirtier areas.
- Implement a regular inspection, testing, and cleaning regimen for ductwork and ventilation systems. Check for any leaks or breaks, and remove any accumulated interior dust to prevent microbial growth.
- Adequately position supply and exhaust points based on the equipment layouts and anticipated personnel movements. This allows for the optimization of unidirectional vertical airflow and air change rates in critical areas.
- Utilize separate air handling systems for the highest-risk areas in the cleanroom. However, you should still maintain the desired pressure cascades while doing so.
- Strategically locate fan filter units to minimize dead zones and areas of restricted flow. Use computational fluid dynamics simulations to optimize room airflow during design.
Cleanroom Ventilation Systems
Here are some common cleanroom ventilation systems:
Fan Filter Units
These units are mounted overhead and supply 100% conditioned outside air. Air is passed through HEPA or ULPA filters to remove >99.97% of particles ≥0.3 μm.
Airflow capacities range from 100 cfm in small environments to 100,000+ cfm in large, complex cleanrooms.
These fans are also equipped with electronically commutated (EC) variable speed motors for optimum airflow control.
They can also provide vertical laminar or non-unidirectional airflow depending on the space function. Placing these fans strategically provides zone control of contamination and optimized airflow.
Chilled Beams
Chilled beams are ceiling-mounted devices containing a cooling coil. They could either induce room air over the coils (passive type) or use a dedicated air supply passing over the coil before being discharged (active type).
Pairing the cooling coil with an integrated HEPA/ULPA filter in the air supply makes chilled beams useful for cooling and particulate control. They also require no ductwork, lessening the chance of hidden contaminants.
Automated Logic Controllers
These are central computerized cleanroom control systems tied into a network of sensors, variable frequency drives, actuators, humidifiers, and various other devices.
They allow programmable regulation of temperature, humidity, and pressure cascades, as well as airflow velocities.
These controllers also provide automated alarms for out-of-spec conditions and data logging for verification and troubleshooting.
Exhaust Risers
Exhaust risers are vertical ducts placed over cleanroom equipment that generate substantial airborne contamination like wet benches and coating tools.
They capture vapors, fumes, and particulates near the source before they disperse widely in the clean room.
These rises must pass through HEPA filters before being released outdoors to prevent expelling contaminants outdoors.
Air Showers
Air showers are vestibules with multiple HEPA-filtered air nozzles that blow particulate contamination off personnel and equipment before entering the room.
They also help maintain airlocks at positive pressure and reduce the introduction of “passenger” contamination. Some designs recirculate filtered air, while others use 100% exhausted air.
Desiccant Systems
Desiccant systems use a solid drying medium like silica gel that absorbs moisture to independently control humidity without overcooling.
They are particularly useful when processes require warmer temperatures but low relative humidity. The desiccant wheel or other medium is regenerated with heat. They can be tied into a cleanroom HVAC system or be used as standalone units.
Partial Recirculation Loops
Recirculation loops blend fresh filtered makeup air with up to 30% recirculated existing cleanroom air. The primary purpose of this is to improve the energy efficiency of heating/cooling systems.
The recirculated air must pass through additional filtration stages before blending to maintain low particular levels.
This allows cleanrooms to partially benefit from the cooling/heating effect of conditioned recirculation air while still supplying sufficient fresh air for contamination control.
The ratio of fresh to recirculated air can be modulated based on real-time particle count data.
TL;DR
- Cleanroom HVAC maintains precise control of temperature, humidity, airflow patterns, and high levels of air filtration to meet cleanroom standards.
- HEPA and ULPA filters are used to remove 99.97-99.999% of particles ≥ 0.3 microns.
- High rates of filtered air circulation flush out contaminants. Airflow goes from clean to less clean areas.
- External positioning of fans and air handlers prevents internal cleanroom contamination.
- Proper ventilation controls contamination, stabilizes temperature/humidity for sensitive processes, maintains airflow/pressure cascades, and vents point source emissions.
- Best practices include monitoring instrumentation, standard operating procedures, proper sizing of backup systems, and duct inspection/cleaning.
- Common systems include fan filter units, chilled beams, automated control systems, exhaust risers, air showers, desiccant dehumidifiers, and partial recirculation loops.