The Standards and Other Basics of Cleanroom Design
Cleanrooms are an important component of industrial manufacturing and laboratories, used extensively within the technology, pharmaceutical and medical industries. Accordingly, a cleanroom design must be created according to exact requirements that are spelled out in internationally recognized standards. This blog is a first in a series discussing the design and construction of cleanrooms and will cover these standards, the utility matrix that guides the design process, and the equipment included in the mechanical systems that support the cleanroom. Future blogs will discuss mechanical equipment in depth, examine how to maintain the quality of the air within the cleanroom and review the protocols that must be maintained during construction to insure the integrity of the finished cleanroom.
Cleanroom Standards For many years individual countries set standards for cleanrooms, which created confusion and inconsistency. Today, cleanrooms are defined by the International Standards Organization under the standard ISO 14644. This standard defines a cleanroom as “A room in which the concentration of airborne particles is controlled, and which is constructed and used in a manner to minimize the introduction, generation, and retention of particles inside the room and in which other relevant parameters, e.g. temperature, humidity, and pressure, are controlled as necessary.”
As the definition implies, the standard contains several sections covering all aspects of cleanrooms, including classification of air cleanliness, testing, monitoring, evaluation, measurement and what constitutes an airborne molecular contamination. The following figure illustrates the scope of the standard.
ISO 14644 STANDARDS 14644-1: Classification of Air Cleanliness 14644-2: Testing and Monitoring to prove continued compliance to ISO-14644-1 14644-3: Methods of Evaluation and Measurement 14644-4: Design, Construction, and Start-Up of Facilities 14644-5: Operations 14644-6: Terms and Definitions 14644-7: Mini-Environments and Isolators 14644-8: Airborne Molecular Contamination
Cleanroom classifications are based on the number of particles equal to and greater than 0.5 per micron (µm) in one cubic foot of air. The task performed in the room dictates the standard of cleanliness required for the space, so the more susceptible the product produced is to contamination, the higher the standard. An ISO Class 1 cleanroom must have a particle concentration of no more than 0.01 per/cu.ft. @ 0.5 micron. Similarly, a Class 5 cleanroom could have as many as 100 particles per/cu.ft. @ 0.5 micron. The highest classification in the standard is a generous Class 9, allowing for one million particles per cubic foot. The standard also determines the type and frequency of testing, such as for particle count, air pressure and air flow, required to be in compliance. Finally, the cleanroom design must account for the equipment and finishes used because each contributes to the amount of particulate in the space.
ISO 14644-1 OVERVIEW
ISO 14644-1: Particle Concentration (#/cu.ft. @ 0.5 micron) ISO 1.0: 0.01 ISO 2.0: 0.1 ISO 3.0: 1 ISO 4.0: 10 ISO 5.0: 100 ISO 6.0: 1,000 ISO 7.0: 10,000 ISO 8.0: 100,000 ISO 9.0: 1,000,000
The Utility Matrix Successful cleanroom design begins with a high level of participation and involvement by the facility owner, the tool owner and the facility management team. The greater the cooperation, the easier to manage construction costs and, eventually, annual operation costs. Guiding the design process is the Utility Matrix (UM). Developed with the owner’s participation, this is the single most important document and you must get a sign off on this document before proceeding into design.
The UM can be developed directly by the owner, if the expertise exists in-house, or an outside consultant can be brought in to assist in development of a tool layout and process flow. Once this is completed, the tool list and UM is established and forms the baseline for design. The tool matrix lists all utilities that are to be used by the tool set and system designers will then take the information from the finalized UM to design the specific support systems. These will typically include:
Bulk gas and chemical source and distribution systems
Specialty gas storage area and distribution system
Industrial waste treatment plant
Exhaust air treatment and distribution systems
Make up air system
Cleanroom recirculation air cooling and filtration system
Support rooms recirculation air systems
Normal and emergency power systems
Process cooling water
Process vacuum system
Mechanical Systems in Cleanrooms The largest component of the construction cost of a standard cleanroom facility is the HVAC/Mechanical system and will be the primary focus of this and subsequent blogs. Constituting approximately 25 percent of the total facility cost, the HVAC/Mechanical systems consist of the following:
Recirculation Air Systems (cleanroom and support): 31% Chilled Water System ( chillers and dist piping): 31% Process Exhaust (scrubbers, VOC abatement, fans, ductwork): 18% Hot Water System (boilers and hw/steam dist piping): 13% Make Up Air System: 7% Total: 100%
Understanding the makeup air (MUA) and exhaust air requirements is necessary in order to determine the size and quantity of other elements of the HVAC/mechanical systems, so the design process for these systems starts there. Consult the UM to find the Exhaust (EXH) flow rates and then determine the MUA quantities needed to cover the air exhausted from the room plus surplus to pressurize the space. This is expressed as MUA=EXH+10%. The MUA requirement dictates the amount of chilled water and heating water required from the central plant, thus affecting the overall size and number of chillers and boilers. Likewise, the exhaust air quantity has impact on heat removal from the cleanroom and impacts the size of the sensible cooling coils and recirculation air system.
When it comes to designing the HVAC/Mechanical systems in a cleanroom, remember there is no single formula or right answer to an owner's specific requirements. Each project must be looked at individually and systems compared based upon cost, system type, owner sophistication and process requirements.
Our next blog will look into the specific details of the make-up and exhaust air systems and the filters required to maintain the purity of the air in the cleanroom.