Typically used in manufacturing or scientific research, a clean room is a controlled environment that has low level of pollutants such as dust, airborne microbes, aerosol particles, and chemical vapors. To be precise, a clean room has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size.
The ambient air outside in a typical city environment contains 35,000,000 particles per cubic meter, 0.5 mm and larger in diameter, corresponding to an ISO 9 cleanroom which is at the lowest level of cleanroom standards.
OK, so “easy” may not be a word that comes to mind for designing such sensitive environments. Having said that, it doesn’t mean you can’t produce a solid clean room design by tackling issues in a logical sequence.
Many manufacturing processes need a strict environment condition provided by a clean room. Since clean rooms have complex mechanical systems and high construction, operating, and energy costs, it is essential to execute the clean room design in a systematic approach.
- Evaluate layout for people/material flow
- Determine space cleanliness classification
- Determine Space Pressurization
- Determine Space Supply Airflow
- Determine Space Air Exfiltration Flow
- Determine Space Air Balance
- Assess Remaining Variables
- Determine Mechanical System Layout
- Perform Heating/Cooling Calculations
- Fight for Mechanical Room Space
Cleanroom airflow principles:
Clean rooms maintain free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward in a constant stream. Laminar air flow systems are typically employed across 100% of the ceiling to maintain constant, unidirectional flow. Laminar flow criteria is generally stated in portable work stations (LF hoods), and is mandated in ISO-1 through ISO-4 classified cleanrooms.
Proper clean room design encompasses the entire air distribution system, including provisions for adequate, downstream air returns. In vertical flow rooms, this means the use of low wall air returns around the perimeter of the zone. In horizontal flow applications, it requires the use of air returns at the downstream boundary of the process. The use of ceiling mounted air returns is contradictory to proper clean room system design.
Points to consider by the clean room design contracting company:
The aim of the clean room design contractor must be to provide a complete facility with minimum participation by the customer or end user. The clean room contractor, with the responsibility to design and construct the clean room facility in a timely manner and at or below budget, must consider the following points:
- At what cleanliness level and in what locations are cleanliness levels required? This is highly dependent on the type of process which will be conducted in the clean room.
- What floor plan works best for the process being conducted? Does the process require multiple rooms and of what cleanliness level? Is a gowning room or ante room required?
- Where are the critical work areas located and how will they be affected by the location of the HEPA or ULPA filters and the airflow pattern in the room?
- What environmental conditions such as temperature and humidity are required in the clean space and will those requirements vary in the future?
- Is there a full understanding of the complexity of HVAC design to meet the tight temperature, humidity, and pressure specifications of a clean room?
- What are the heat loads due to number of people and equipment loads in the space?
- Are pass thru units or air showers required to isolate various areas from clean room to cleanroom or non clean room to clean room?
- Materials of construction for walls, ceiling, and floor and their compatibility with the process requirements must be evaluated. The output from your clean room could easily be directly related to the amount the materials out-gas or how well the materials dissipate static electricity.
- Is there sufficient space above the proposed ceiling for light troffers and HEPA or ULPA filter units and the required mechanical distribution system?
- Design and coordinate fire protection and any process requirements from electrical requirements to gas or liquid requirements.
- Design the wall system, taking into consideration material required and location and size of doors, windows, and other openings such as return grilles.
- Correctly identify the size and location of the filters, the air supply, and the air return to properly distribute clean air throughout the space.
- Light level must meet customer specific light level needs within the space and OSHA requirements.
- What are the requirements for process piping or electronic communications with the clean room?
- What temperature, humidity, and pressure controls, monitors and network connections are required?
Clean rooms are like race cars. When properly designed and built, they are highly efficient performance machines. When poorly designed and built, they operate poorly and are unreliable. Clean rooms have many potential pitfalls, and supervision by an engineer with extensive clean room experience is recommended for your first couple of clean room projects.