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  3. Precision air conditioning equipment Precision air conditioners PAU Series
  4. Precision air conditioners Technical Information
  5. 3-2. Precision air conditioners and clean rooms

Precision air conditioning equipmentPrecision air conditioners Technical Information

PAU Series

3-2. Precision air conditioners and clean rooms

This section describes the temperature and humidity control in precision air conditioning and cleanliness level of a clean room.

(1) Industrial air conditioning and conditions by process

As its name suggests, industrial air conditioning is air conditioning used for industrial applications. In the manufacturing processes of a factory, the purpose of industrial air conditioning is to maintain and improve the working environment of workers and the quality control of products. In the research and development field, its purpose is to stabilize product evaluation and analytical accuracy. Therefore, air conditioning conditions required in industrial air conditioning differ depending on the application. Recently, quality control of products is an important issue in the manufacturing industry. High-quality air conditioning control has attracted attention as one of the most effective measures for this purpose, and the scope of industrial air conditioning is expanding even further. Industrial air conditioning has become indispensable in the manufacturing processes of factories nowadays.

(2) Cleanliness level and clean room

Table 1 Temperature and humidity conditions by the industrial air-conditioning process

Industry Process Temperature condition Humidity condition
Semiconductor Photolithography  22~24℃±0.2℃ or less 45~50%±2~5% 
Dry etching 22~24℃±2℃ or less  45~50%±5% or less
Sputtering 22~24℃±2℃ or less  45~50%±5% or less
Pharmaceutical Powdered chemical storage  24℃±3℃ or less  30~50% 
Tableting  24℃±2℃ or less  20~40% 
Micro-analysis/blood serum  24℃±2℃ or less  50% 
Optical lens Grinding  25℃±2℃ or less  50±5%
Printing Printing 24~27℃±5℃ or less   50±2%
Cutting, drying, pasting etc.  21~27℃   45~50%
Foodstuffs Fresh bread   24~26.5℃   40~50%
Raw material storage   26.5~29.5℃   80~85%

*The list above serves simply as a general guide. Temperature and humidity conditions vary depending on the environment.

Cleanliness level

One effective measure to improve product yield and quality is to improve the environmental control accuracy. One of the important factors in environmental control is the management of the cleanliness level. The cleanliness level refers to the extent of air pollution inside a space based on certain criteria. The standard was originally established to quantify the level of the air cleanliness in a clean room, but together with the advancement in environmental separation technology, its use has expanded to spaces other than clean rooms where cleanliness needs to be controlled.

Clean room

A clean room is a special room to achieve and maintain the cleanliness of a space. Clean rooms can be divided into two types depending on the purpose of use. One type is the Industrial Clean Room ICR, which aims to control floating particles in the air used in industrial applications. The other type is the Biological Clean Room (BCR) used in the biotechnology, medical and food sectors to mainly control floating microorganisms in the air. Clean rooms are also classified by the air flow methods such as the “downflow method”, “turbulent flow method” and so on. Clean rooms achieve a high level of cleanliness by discharging or diluting floating particles in the air, which is an environmental factor of cleanliness, using clean air. In addition, where necessary, control of environmental factors such as temperature, humidity, and pressure etc. may be required.

Table 3 Type of clean room

Industrial Clean Room (ICR) Liquid crystals, semiconductors, LSIs, electronic components, precision instruments, printing, etching, deposition, printed circuit boards, lenses, optical disks, powder manufacturing, raw material manufacturing, etc.
Biological Clean Room (BCR) Chemicals, operating rooms, neonatal rooms, meat processing, mushroom cultivation, plant cultivation, brewing and cooking rooms, biotechnology, genetic testing facilities, etc.

(3) Cleanliness standards and class

The class (cleanliness level) prescribes the amount of particulate matter in a space according to the standards.
Although standards have now been unified to international ISO standards, US federal standard “FED-STD-209D”, which was often used in the past, is still widely used today.


The number of particles of size 0.1 μm or more per m3 of air is used to classify the cleanliness level into 9 classes from 1 to 9. The number of digits determine the class i.e. Class 1 if the number of particles per m3 of air is 10, and Class 2 if it is 100 or less, and so on.


Depends on the number of particulate matter with a size of 0.5 μm present in one cubic foot (1 foot = about 30 cm) of air in the target space. “Class 100” if the number of floating particles in one cubic feet of air is less than 100, and “Class 1,000” if it is less than 1,000.

Table 5 Measurement particle size and upper limit concentration according to the air cleanliness class

Cleanliness class Upper limit concentration (pcs/m upper limit concentration (pcs/m3))
International uniform standards
ISO 14644-1
US federal standards
Measurement particle size
0.1μm 0.2μm 0.3μm 0.5μm 1.0μm 5.0μm
Class 1   10 2        
Class 2   100 24 10 4    
Class 3 1 1,000 237 102 35 8  
Class 4 10 10,000 2,370 1,020 352 83  
Class 5 100 100,000 23.700 10,200 3.520 832 29
Class 6 1,000 1,000,000 237,000 102.000 35,200 8,320 293
Class 7 10,000       352,000 83,200 2,930
Class 8 100,000       3,520,000 832,000 29,300
Class 9         35,200,000 8,320,000 293,000


(4) Other items related to the cleanliness level

Air filter

Table 6 Type of filter

  Coarse dust filter High-performance filter HEPA filter ULPA filter Ultra-ULPA filter
Clean in use None in particular Class 100,000~200,000 Class 100~1,000 Class 10~100 Class 1~10
Example of use General office etc. General office etc. Semiconductor manufacturing
Post-processes etc.
Semiconductor pre-processes
Manufacturing line etc.
Ultra LSI manufacturing process
Capacity Foreign contaminant, dirt capturing capacity Higher capturing capacity than a coarse dust filter Possesses the capacity to capture 99.97% of 0.3 μm particles Possesses the capacity to capture 99.95% of 0.15 μm particles Possesses the capacity to capture 99.99% of 0.15 μm particles
Blowing method Turbulent ventilation Down flow ventilation

Table 7 Other filters

  Activated carbon filter Chemical filter
Description Absorption of ammonia, acetic acid, aldehyde gas and other VOC Chemical contaminants
Removal of molecular contaminants
Application Deodorization Semiconductor/liquid crystal manufacturing process

Ventilation frequency

Recommended ventilation frequency table

Class of clean room General value USA209E standard Average air flow rate
Class 100,000 20~  30回/h 20 .005-.041m/sec
Class 10,000 30~  70回/h 75 .051-.076m/sec
Class 1,000 100~200回/h 150 .127-.203m/sec
Class 100 200~600回/h 250~400 .203-.408m/sec

Air flow system

Table 9 Typical alert system

  Down flow system Turbulent flow system Other typical system

Cleanliness level Class 10~1,000 Class 1,000~ Class 10,000~
Features Easy to distribute the temperature, humidity and cleanliness level uniformly Installation is restricted because ducts are required on the ceiling and floor. Management is simple.
An non-uniform zone occurs in the four corners of the space.
Non-uniform zones tend to occur in direct proportion to the distance from the outlet.
Initial cost High Slightly high Low
Running cost High Slightly high Relatively low
Non-control zone Few Generated in the 4 corners Generated in the furthest venting areas


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