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Clean / Precision Air Conditioning / Local Air Conditioning

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Clean booth selection

Following considerations are necessary in case of selection of Clean booth.

     1. Calculation of cleanliness factor for inside of booth
     2. Selection of wall material
     3. Selection of ventilation system
     4. Selection of air-conditioning within the booth

1. Calculation of cleanliness factor for inside of booth

Generally, it is determined on the basis of clean room regulations. The parameters considered are rate of circulation, filter type, flow system and ventilation system.

Reference table for rate of circulation

Class of clean room General numerical value USA209E standards Average air current speed
Class 100,000 20~30 rotations/h 20 .005-.041m/sec
Class 10,000 30~70 rotations /h 70 .051-.076m/sec
Class 1,000 100~200 rotations /h 150 .127-.203m/sec
Class 100 200~600 rotations /h 250~400 .203-.408m/sec

Rate of circulation per hour (rotations /h) =Average air current speed (m/sec) x discharge area (m2) x 3600sec ÷room capacity (volume) (m3)

Filter type

FFU

  Medium or high performance filter HEPA filter ULPA filter
Filtering Capacity Class 10~200000 Class 100~10,000 Class 1~10
Examples Usually office After IC Process Pre IC Process
Performance High trapping capacity as compares to coarse particle filter. Possessing a trapping of capacity up to 99.97 % for 0.3um size particles. Possessing a trapping of capacity up to 99.999% for 0.1um size particles.

The air flow capacity and units of FFU to be installed are selected on the basis of the volume of clean booth and the desired class.

Required air flow (m3/min) =targeted room capacity (m3) ×rate of circulation (rotations /h) ÷60

Example)
The FFU air flow for a clean booth with width 3m, length 2m, height 2m and desired class of 10000 is
 
(3×2×2) ×75÷60=15(m3/min)

*Single unit of PAU - A17FFU of our company is compatible.

FFU

2. Selection of wall material

Selection should be made on the basis of requirements related to ambient and internal space environment.

Type Sheet type Panel type Adiabatic type
Schematic diagram Sheet type Panel type Adiabatic type
Material properties Supports:Steel frame, aluminium, SUS or resin
Wall: Antistatic vinyl sheet
Supports: Steel frame, aluminium, SUS or resin
Wall: Resin (acrylic, polycarbonate etc.), aluminium composite sheet
Sandwich panel
Exterior: Coated steel panel, aluminium, SUS
Interior: Urethane foam material, Styrofoam etc.

Overall heat transfer coefficient
(W/m2/K)

Vinyl sheet t 0.3→18 Possessing a trapping of capacity up to 99.97 % for 0.3um size particles. Possessing a trapping of capacity up to 99.999% for 0.1um size particles.
Thermal insulating properties Low Moderate High
Cost Low Comparatively high High
Size Small ~ Medium Small ~ Large Medium ~ Large
Erection/Disassembly Easy Relatively simple Special operation required

3. Selection of ventilation system

  Down flow method Turbulent flow method Other generic methods
Summary Designing of Clean booth based on down flow method is necessary in case of in case of requirement of Class 100.The characteristic of this method is that uniform air flow circulation is caused in downward direction from the filters installed across the ceiling. Design of Clean booth is necessary in case of requirement of Class 1000. Air flow is caused from a restricted chamber and not from the ceiling. Causing air flow from part of ceiling or from section wall surface across the longitudinal direction of the Clean booth is a low cost method usually implemented for Class 10000 requirement.
Down flow method Turbulent flow method Other generic methods
Important points Uniform distribution of temperature, humidity and cleanliness factor. Occurrence of disproportionate zones at corners of the booth. The disproportionate zone problems do not arise near discharge sections.
Cost High Comparatively cheap Comparatively cheap
Cleaning/maintenance frequency Class 1~100 Class 1,000~100,000 Class 1,000~100,000
Cleaning/maintenance while in operation Very disturbance from the labour Disturbance from labour experienced Comparatively higher disturbance experienced from the labour as per the layout
Operational costs High Relatively low Low
Installation costs High Relatively low Very low
Cleaning frequency High Filter price cut is comparatively high Low
Maintenance Man hours required Easy Easy
Non-control zone Less All corners All areas other than discharge section
 

4. Selection of air-conditioning within the booth

As high density filter (HEPA, ULPA) in the Clean booth, high static pressure fan is used to discharge clean air in the targeted area. As this fan possesses high discharge capacity, the heat generated from this fan is uniformly mixed with the clean air discharged from the fan. Therefore, Clean booth occupied with humans should be air-conditioned. However, connection of AC points is not easy. Following 2 techniques are to be followed

EPDA filter EPDA filter

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