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Unidirectional Flow System Designs

This document discusses three types of unidirectional flow system designs for clean rooms: 1) single pass systems where filtered air enters and exits without recirculation, 2) recirculated systems where filtered air enters and exits through plenum walls to be recirculated through HEPA filters, and 3) ducted plenum systems where filtered air enters and exits through plenum walls to be recirculated through ducts directly to HEPA filters. It also discusses the importance of positive room pressurization between clean rooms to ensure air flows from cleaner to less clean spaces.

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67 views1 page

Unidirectional Flow System Designs

This document discusses three types of unidirectional flow system designs for clean rooms: 1) single pass systems where filtered air enters and exits without recirculation, 2) recirculated systems where filtered air enters and exits through plenum walls to be recirculated through HEPA filters, and 3) ducted plenum systems where filtered air enters and exits through plenum walls to be recirculated through ducts directly to HEPA filters. It also discusses the importance of positive room pressurization between clean rooms to ensure air flows from cleaner to less clean spaces.

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CIVIL
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© © All Rights Reserved
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www.PDHcenter.com PDH Course M143 www.PDHonline.

org

Unidirectional Flow System Designs

1) Single Pass System: Filtered air enters the room, exits through the louvers and is not re-

circulated. The system is ideal for 100% makeup air or when ambient temperatures are

favorable and acceptable.

2) Re-circulated System: Filtered air enters the room, exits through plenum walls and is re-

circulated through a sealed plenum using motorized fan modules with HEPA filters. This is

the most popular design.

3) Ducted Plenum System: Filtered air enters the room, exits through plenum walls and is re-

circulated through air ducts directly to the HEPA filters.

(Refer to the figures under part IV)

3
ROOM PRESSURIZATION
A clean room facility may consist of multiple rooms with different requirements for cleanliness.

Rooms in a clean facility should be maintained at static pressures higher than atmospheric to

prevent infiltration by wind. Positive differential pressures should be maintained between the

rooms to ensure airflows from the cleanest space to the least clean space. The only exception to

using a positive differential pressure is when dealing with specific hazardous materials where the

statutory health & safety agencies require the room to be at a negative pressure.

Ventilation Air
Ventilation air volumes are dictated by the quantity of air required to maintain indoor air quality,

makeup for exhaust and for building pressurization. This provides assurance that carbon dioxide

and oxygen remain in balance and that formaldehyde and other vapors given off by building

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