How is Airflow Managed in a Hardwall Clean Room?

How is Airflow Managed in a Hardwall Clean Room?

Airflow management in a hardwall Clean room is crucial for maintaining the desired cleanliness levels, controlling temperature, and ensuring product safety. This article provides an overview of the methods and standards used to effectively manage airflow in these controlled environments.

Air Change Rates

One key aspect of airflow management is the air change rate, which refers to the number of times the air within the clean room is replaced in one hour. According to ISO 14644-1, clean rooms typically require air change rates between 10 to 600 air changes per hour (ACH), depending on the cleanliness class. For instance, Class 100 Clean rooms usually operate at 30 to 60 ACH to minimize particulate contamination.

Ventilation System Design

The design of the ventilation system is critical in a hardwall clean room. High-efficiency particulate air (HEPA) filters are commonly employed to remove 99.97% of particles as small as 0.3 micrometers. The placement of these filters, often in ceiling-mounted units, is designed to create a unidirectional airflow pattern that directs Clean air downward while exhausting contaminated air from the room.

Airflow Patterns

Effective airflow patterns are essential for minimizing turbulence and ensuring uniform distribution of clean air. Typically, a hardwall clean room utilizes laminar flow, where air moves in parallel layers. This design reduces dead zones and recirculation, helping maintain consistent air quality. Computational fluid dynamics (CFD) simulations can be used to optimize these airflow patterns before construction.

Pressure Differentials

Maintaining pressure differentials is vital for controlling airflow and preventing contamination from adjacent areas. A hardwall clean room is typically maintained at a positive pressure of 0.05 to 0.1 inches of water column above adjacent spaces. This pressure difference ensures that air flows into the clean room rather than escaping, which helps keep contaminants out.

Related Standards and Guidelines

• iso 14644-1: This standard outlines the classification of air cleanliness in clean rooms and controlled environments based on particle concentration.

• iso 14644-2: This standard specifies the monitoring and control procedures necessary for maintaining cleanliness levels in clean rooms.

• ISO 14644-3: This standard provides guidance on the test methods to determine the performance of clean room systems, including airflow.

• FDA Guidance for Industry: This document outlines regulatory expectations for maintaining cleanroom environments in pharmaceutical manufacturing.

• FS209E: Although officially obsolete, this standard provided classification guidelines for clean environments and is often referenced in industry discussions.

What is the Air Flow Pattern in a Clean Room?

1. Unidirectional Flow

In a modular cleanroom, the airflow pattern is typically unidirectional, meaning air moves in a straight-line path. This design minimizes turbulence and prevents the mixing of clean and contaminated air, ensuring optimal cleanliness.

2. Laminar Flow

Laminar flow is a common pattern used in clean rooms, where air flows smoothly in parallel layers. This configuration helps maintain a uniform distribution of clean air, reducing the risk of particle contamination.

3. Turbulent Flow

While not preferred in clean rooms, turbulent flow can occur in certain situations. This pattern is characterized by chaotic air movement, which can lead to contamination if not properly managed and controlled.

4. Airflow Velocity

The velocity of airflow in clean rooms typically ranges from 0.3 to 0.5 meters per second. Maintaining this velocity is crucial for effective particle removal and to ensure that contaminants are swiftly exhausted from the space.

What are the Air Flow Requirements for a Clean Room?

• Air Change Rate

Clean rooms have specific air change rate requirements, generally ranging from 10 to 600 air changes per hour (ACH). The required ACH depends on the cleanliness class, with higher classes demanding more frequent air changes.

• Filtration Efficiency

High-efficiency particulate air (HEPA) filters are standard in clean rooms, removing 99.97% of particles 0.3 micrometers and larger. This level of filtration is essential for maintaining the high cleanliness standards demanded in controlled environments.

• Positive Pressure Maintenance

Clean rooms are generally maintained at positive pressure relative to surrounding areas. This is crucial for preventing outside contaminants from entering the clean space during door openings or other disruptions.

What is the Flow Rate of a Clean Room?

Definition of Flow Rate

The flow rate in A Clean Room refers to the volume of air exchanged within the space per unit of time. It is typically measured in cubic feet per minute (CFM) or liters per second (L/s).

Calculation of Flow Rate

Flow rate can be calculated by multiplying the air change rate (ACH) by the room volume. For example, a room with a volume of 1,000 cubic feet and an ACH of 20 requires a flow rate of 3,334 CFM.

Importance of Flow Rate

Maintaining the correct flow rate is essential for achieving the desired cleanliness levels in a clean room. An inadequate flow rate can lead to insufficient air exchange, resulting in increased particle concentrations and contamination risks.

What are the Guidelines for Clean Room Differential Pressure?

• Maintaining Positive Pressure

Modular clean rooms should be maintained at a positive pressure relative to adjacent areas, typically around 0.05 to 0.1 inches of water column. This ensures that air flows into the clean room, preventing contaminants from entering.

• Monitoring Differential Pressure

Regular monitoring of differential pressure is critical. Automated pressure sensors should be installed, providing real-time data to ensure that pressure differentials are maintained consistently, particularly during operational changes.

• Pressure Relief Valves

Pressure relief valves are essential in a clean room to prevent over-pressurization. These valves help maintain a balanced environment and protect the integrity of the clean room structure during fluctuations in air pressure.

What is CFM in a Clean Room?

1. Definition of CFM: CFM, or cubic feet per minute, is a measurement used to quantify the volumetric flow rate of air in clean rooms. It indicates how much air is supplied or exhausted per minute, essential for maintaining air quality.

2. Importance of CFM: CFM is critical for achieving the required air change rates in clean rooms. The proper CFM ensures that contaminants are effectively removed and that the environment remains within acceptable cleanliness levels.

3. CFM Calculation: To determine the necessary CFM, the clean room's volume and the desired air change rate must be considered. For instance, a clean room with a volume of 2,000 cubic feet and an air change rate of 30 ACH requires approximately 1,000 CFM.