When it comes to clean room environments, achieving optimal cleanliness is not just about the air conditioning system; it’s a holistic approach encompassing technology, construction, and maintenance. In this article, we delve into the four essential conditions—air supply cleanliness, airflow trends, air supply volume and velocity, and static pressure difference—that are crucial to ensuring the effectiveness of clean room purification measures.
I. Air Supply Cleanliness
The Heart of Cleanliness:
The key to maintaining cleanliness in clean rooms lies in the performance and installation of the final filter within the purification system. Typically, high-efficiency or sub-high-efficiency filters are employed. The choice depends on various factors, including environmental pollution, exhaust air proportion, and the criticality of the clean room’s function.
Selecting the Right Filter:
- High-Efficiency Filters: When facing severe environmental pollution or when the clean room’s importance demands a significant safety margin.
- Sub-High-Efficiency Filters: Suitable for less critical scenarios with lower performance requirements.
However, selecting the appropriate filter isn’t solely based on its efficiency. Factors such as clean room characteristics and purification system specifics must also be considered.
Ensuring Clean Air:
Maintaining clean air goes beyond filter selection. To guarantee the cleanliness of the supply air, additional measures are essential:
a. Safe Transportation and Installation: Filters must remain undamaged during transportation and installation.
b. Quality Installation Structures: Installation tightness heavily relies on the structure’s quality and adherence to design guidelines.
- For single filters, unfolded installation types are recommended to prevent leaks into the room even if leakage occurs.
- The use of High-Efficiency Filter Terminal Housings (HEPA boxes) ensures tightness with ease.
c. Proficient Construction and Installation Personnel: Well-trained personnel with both knowledge and installation skills are vital.
d. Optimal Filter Seal: Consider using Gel seal or negative pressure sealing techniques to maintain the required tightness.
II. Airflow Trends
Guiding Airflow for Purity:
Clean room airflow organization differs significantly from standard air-conditioned rooms. Its primary goal is to deliver the cleanest air to the working area first to minimize and control pollution of the materials being processed.
Principles of Airflow Design:
- Minimizing Vortex Formation: Reduces the introduction of contaminants from outside the work area.
- Preventing Dust Resuspension: Minimizes the chance of dust particles settling on materials.
- Uniform Airflow: Ensures even air velocity within the working area, meeting technical and hygienic requirements.
- Appropriate Air Supply and Return Methods: Choose methods based on required cleanliness levels.
Different Airflow Configurations:
Clean rooms adopt different airflow organizations, each with unique characteristics:
1) Vertical Unidirectional Flow: Uniform downward airflow suitable for efficient equipment layout and self-purification.
2) Horizontal One-Way Flow: Achieves ISO5 cleanliness in the first working area but may lead to increased dust concentration as air flows across. Suitable for clean rooms with varying cleanliness requirements within a single space.
- Local distribution of high-efficiency filters can reduce initial investment but may result in eddy currents in specific areas.
Proper curtain installation is essential for correct airflow organization.
III. Air Supply Volume & Air Velocity
Diluting Polluted Air:
Adequate ventilation volume is necessary to dilute and remove indoor pollutants. The clean room’s height plays a role in determining the required ventilation rate, with different criteria for various cleanliness requirements.
Considerations for Ventilation:
- For Class 1,000 clean rooms, consider the high-efficiency purification system when determining ventilation volume. For other clean room classes, base calculations on high-efficiency systems.
- When high-efficiency filters are centrally placed in Class 100,000 clean rooms or when sub-high-efficiency filters are used, consider increasing ventilation frequency by 10-20%.
While the recommended ventilation volume provides a baseline, it’s crucial to ensure that the airflow velocity aligns with design specifications.
- For one-way flow clean rooms, the recommended airflow velocity is low, with vertical at ≥ 0.25 m/s and horizontal at ≥ 0.35 m/s.
- However, in some cases, achieving designed cleanliness levels in empty or static states may not ensure pollution interference prevention during operation. Therefore, it’s essential to fine-tune airflow organization.
IV. Static Pressure Difference
Maintaining Clean Room Integrity:
Maintaining positive pressure within a clean room is vital to prevent pollution and sustain the desired cleanliness level. Even negative pressure clean rooms must maintain a positive pressure relative to adjacent areas with lower cleanliness requirements.
Achieving Positive Pressure:
Positive pressure results from having the supply air volume exceed the return air and exhaust air volumes. Interlocking the supply air, return air, and exhaust fans ensures consistent positive pressure.
- When the system activates, start the supply fan first, followed by the return and exhaust fans.
- When shutting down the system, turn off the exhaust fan first, followed by the return and supply fans.
Static Pressure Requirements:
The US Federal Standard (FS209A~B) specifies a minimum positive pressure difference of 0.05 inches of water column (12.5Pa) between the clean room and any adjacent low-cleanliness area when all access points are closed.
Balancing Positive Pressure:
Maintaining an excessively high positive pressure can lead to operational challenges, such as difficulty in opening doors, noise issues, and discomfort for occupants. While many standards don’t specify an upper limit for positive pressure, maintaining a range of 10~30Pa is generally recommended.
In conclusion, achieving clean room purification success hinges on these four crucial conditions: air supply cleanliness, airflow trends, air supply volume and velocity, and static pressure difference. Ensuring each element aligns with your specific requirements is key to maintaining an environment that meets your cleanliness standards while maximizing operational efficiency.
1. What are the key considerations when selecting a filter for a clean room?
The choice of filter depends on factors like environmental pollution, exhaust air proportion, and the criticality of the clean room’s function. High-efficiency filters are suitable for severe pollution or critical applications, while sub-high-efficiency filters are used for less critical scenarios.
2. How can I ensure the proper installation of filters in a clean room?
To ensure proper installation, focus on safe transportation, quality installation structures, well-trained personnel, and tight filter seals. Consider using techniques like Gel seal or negative pressure sealing to maintain tightness.
3. What are the principles of airflow design in clean rooms?
Airflow design in clean rooms aims to minimize contaminants, prevent dust resuspension, maintain uniform airflow, and choose appropriate air supply and return methods. These principles help ensure optimal air quality.
4. Can you explain the difference between vertical and horizontal airflow configurations?
Vertical unidirectional flow provides uniform downward airflow, making it suitable for efficient equipment layout and self-purification. Horizontal one-way flow achieves ISO5 cleanliness in one area but may lead to increased dust concentration elsewhere, making it suitable for varying cleanliness requirements within a single space.
5. Why is maintaining static pressure difference important in clean rooms?
Maintaining a positive pressure difference ensures that the clean room remains uncontaminated and adheres to the desired cleanliness level. Even negative pressure clean rooms must maintain a positive pressure relative to adjacent areas to prevent contamination. Balancing positive pressure is crucial to avoid operational issues.