Cleanroom Airflow Modeling to Determine the Required …cctr/seminar/seminar4.pdf · Cleanroom...

Cleanroom Airflow Modeling to Determine the Required Air Change Rate (Phase 1)

Engsysco

Principal Investigator

Wei Sun, P.E.Principal, Director of Engineering

Engsysco, Inc.Ann Arbor, Michigan, USA

Co-Investigators

Sponsored by TC 9.11ASHRAE Annual Meeting

(June 22, 2008, Salt Lake City, UT)

John Mitchell Particle Measuring Systems, Inc.

Boulder, Colorado, USA

Keith B. Flyzik Micro-Clean, Inc.

Bethlehem, Pennsylvania, USA

Shih-Cheng Hu, Ph.D National Taipei University of Technology

Taipei, Taiwan

Junjie Liu, Ph.D Tianjin University

Tianjin, China

Strategies of Cleanroom Fan Energy Conservation

During Operational PhaseUse Flow Demand Control to cut down unnecessary airflow over-supply

During Design PhaseUse Modeling to Determine the Airflow ChangeRate (AHR) to maintain the required cleanliness classification

Air Change Rate - Cleanroom vs. General-Purpose Room

Cleanrooms utilize much higher airflow rates than for general-purpose buildings, energy saving potential from airflow rate reduction is significant.

Type

of F

acili

ties

Air Change Per Hour (ACH)6

General Purpose Spaces – To Meet Heating & Cooling Loads

25 600

Cleanroom Spaces- To Mainly Dilute and Remove Particles

540

10%

15

Cleanroom Air Change Rate - Existing Guidelines

IEST Recommended Practices RP-12

Classification

ISO Class FS-209 Class

Air Change Per Hour

Range 8 100,000 5 – 48 7 10,000 60 – 90 6 1,000 150 – 240 5 100 240 – 480 4 10 300 – 540 3 1 360 – 540 2 360 – 600 1

This practice was based on old experience, in which air change rates were arbitrarily selected Solely based on room cleanliness classes.

High volume airflows have been utilized to meet FS-209 standard, and IEST (RP) for decades

IEST Recommended (RP-12) Air Change Rate For Cleanrooms

5

150

240

300

360360360

4890

240

480

540540

600600

600

100

200

300

400

500

600

700

0 1 2 3 4 5 6 7 8 9

ISO Cleanliness Class

Air

Cha

nge

Per H

our (

AC

H)

Cleanroom Air Change Rate,Existing Practices & Problems

Intuitively, ACR should be based on the required cleanliness class and the activities being performed in the space. Activities that generate higher level of dust would need higher ACH than those that generate at lower level.

Most design/operating engineers choose to obey the existing guideline to avoid being challenged. However, to have a scientific justification to save fan energy, modeling to have a quantitative toolis required.

Cleanroom Air Change Rate,Existing Practices & Problems

Cleanroom airflow rate should be provided “as needed” instead of “picking an arbitrary rate from the table”, a better approach should be similar as those of building heating/cooling load calculations utilized today.

Establish Mathematical Model –Configuration 1 (Conventional Primary Loop)

RA

EA

SA

Q

OAOA+RASA

Space ImpurityConcentration

ExhaustAir

LeakageAir

Particle Generation

Deposition

Cs

Space

D

G

Efficiency Ea

SupplyAir

ReturnAir

MakeupAirCo

CeCs

Cs

HC

FILT

ERCC

AHU Unit

HEP

A

Efficiency Eb

V = Space volume (ft3)OA = Rate of makeup airflow (volume/time)SA = Rate of supply airflow (volume/time)RA = Rate of return airflow (volume/time)EA = Rate of exhaust airflow (volume/time)Q = Rate of leakage airflow (volume/time)Cs = Impurity concentration in space

(parts/volume)Co = Impurity concentration in makeup air

(parts/volume)Es = Filter efficiency (mass basis)G = Rate of impurity generation in space,

averaged throughout the space (parts/volume/time)

D = Rate of impurity deposition from air to surface in space, averaged throughoutthe space (parts/volume/time)

T = TimeEa = AHU filters’ combined efficiency

[ = 1 - (1 - E2)·(1 - E1)]Eb = Ceiling HEPA filter efficiency


RA

EA

SA

Q

OAOA+RASA

Space Impurity Concentration

ExhaustAir

LeakageAir

Particle Generation

Deposition

Cs

Space

D

G

Efficiency Ea

SupplyAir

ReturnAir

MakeupAirCo

CeCs

Cs

HC

FILT

ERCC

AHU Unit

HEP

A

Efficiency Eb

Indoor Particle Balance Differential Equation

During Time Interval : dt

Room particle count change: dCS

= Supply air particle addition+ Room particle internal generation- Return air particle removal- Exhaust air particle removal+ Leakage air particle removal/addition- Particle deposition on surface

Indoor Particle Balance Differential EquationdtVDdtCQdCV S ⋅⋅dtCEAdtCRAdtVGdtEECRACOA ESHUSOS −⋅⋅−⋅⋅−⋅⋅−⋅⋅+⋅−⋅−⋅⋅+⋅=⋅ )1()1()(

SA = OA+RA, SA = EA+Q+RA

Room Mass Balance Equation

With basic operations, define:


ar)EEE(Em HUHU =⋅⋅−++

bACRC

DGmEEo

HU =⋅−

+⋅−⋅− )1()1(

Equation to Calculate Room Particle Concentration:

otACRa

oSOST CabeC

abCC ⋅⎟

⎠⎞

⎜⎝⎛+⋅⎟

⎠

⎞⎜⎝

⎛ ⋅⎟⎠⎞

⎜⎝⎛−= ⋅⋅−

Room Particle Concentration is a function of variables of:

If t→∞,


Room air change rate ACR,Room particle generation G, (data survey)AHU filters’ combined efficiency EU,Room HEPA efficiency EH,Particle deposition rate on exposed surfaces DOutdoor particle concentration CO,Outdoor air/supply air ratio m

)1()(

)1()1()1(

mEEEEmACR

GCmEEC

abC

HUHU

OHU

oST −⋅⋅−++

⋅−+⋅⋅−⋅−

=⋅⎟⎠⎞

⎜⎝⎛=

θ

oHUHU

oHU

oST CmEEEEm

ACRCDGmEE

CabC ⋅

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

−⋅⋅−++⋅−+⋅−⋅−

=⋅⎟⎠⎞

⎜⎝⎛=

)1()(

)1()1(

Effect of Internal Particle Generation Rate on Room Particle Concentration

Room Particle Concentration versus Air Change Rate (Steady State)

- Effect of Internal Particle Generation Rate

0.1

1.0

10.0

100.0

1,000.0

10,000.0

100,000.0

1,000,000.0

0 100 200 300 400 500 600

Supply Air ACH (Air Change Per Hour)

Con

cent

ratio

n (N

umbe

r of P

artic

les

Per F

T3 )

G=1

G=10

G=100

G=1000

G=10000

Condition:

OA/SA=5%CO=1x106

EU=95%EH=99.97%θ =5%

Internal Particle Generation Rate:G = Rate of impurity generation unit floor area, averaged throughout the space

Unit: Particals/FT3/Min.

Effect of Room HEPA Filter Efficiency on Room Particle Concentration

Room Cleanliness (Concentration) versus Air Change Rate- Effect of Final HEPA Filter Efficiency

0.1

1.0

10.0

100.0

1,000.0

1 10 100 1,000


Con

cent

ratio

n (N

umbe

r of P

artic

les

Per F

T3 )

EH=99.97%

EH=99.997%

EH=99.9997%

Condition:

OA/SA=5%CO=1x106

EU=95%G=10θ =5%


Unit: partIcals/FT3/Min.

Effect of Outdoor Air Intake Particle Concentration on Room Particle Concentration

Room Particle Concentration versus Air Change Rate(Steady State)

- Effect of Outdoor Air Intake Particle Concentration

0.1

1.0

10.0

100.0

1,000.0

0 100 200 300 400 500 600


Con

cent

ratio

n (N

umbe

r of P

artic

les

Per F

T3 )

Co=100,000

Co=1,000,000

Co=10,000,000

Condition:

OA/SA=10%EU=95%G=10θ = 5%EH = 99.997%


Unit: PartIcals/FT3/Min.

Effect of Outdoor Air Percentage of Supply air on Room Particle Concentration

Room Particle Concentration versus Air Change Rate(Steady State)

- Effect of Outdoor Air Percentage of Supply Air

0.1

1.0

10.0

100.0

1,000.0

0 100 200 300 400 500 600


Con

cent

ratio

n (N

umbe

r of P

artic

les

Per F

T3 )

m=5%

m=10%

m=15%

m=20%

Condition:

Co=1x105

EU=95%G=10θ = 5%EH = 99.997%


Unit: PartIcals/FT3/Min.

Model-Based ACH versus IEST RP-Based ACH

Model-Based ACH vs. Recommendation-Based ACH

1

10

100

1,000

10,000

100,000

0 100 200 300 400 500 600


Con

cent

ratio

n (N

umbe

r of P

artic

les

Per F

T3 )

G=100, ModelBased

G=1,000, ModelBased

G=5,000, ModelBased

ACH-Low, Rec.Based

ACH-High, Rec.Based

Condition:

OA/SA=10%CO=1x105

EU=95%EH=99.997%θ = 5%


Unit: particals/FT3/Min.

Research Experiments & Validations

Experiments to validate model-based ACR determination have being conducted in three research labs. Final data and conclusions will be published in November, 2008, supported by CEC. Real-world application and software development will start in 2010.Demonstrate cost-effective approaches to lower the Air Change Rate, to reduce fan energy waste.Propose new “Air Change Rate Recommendation” -Group of Charts, to replace existing over-simplified guidelines.

Selected Cleanroom Labs Description

Lab 1Floor Plan

Prep. RoomClass 1,000-10,000

Gown Room(Airlock)Class 100,000

Process RoomClass 1-100

2'x2' FanFilter Unit


30"x24' SidewallReturn Grille &Shaft


Symbol


Lab 1Airflow Diagram

1 2 3 4 5 6

7 8 9 10 11

Process RoomClass: 1-100Flow: 4,2874 cfm, 712 ACHSize: 96"x72"x90"(H)

Prep RoomClass: 1,000-10,000Flow: 1,641 cfm, 74 ACH Size: 143"x167"x96"(H)

Gown RoomClass: 100,000Flow: 601 cfm, 77 ACHSize: 96"x88"x96"(H)

AHU

MixingMixing

12

Selected Cleanroom Labs DescriptionLab 2Floor Plan

Testing Cleanroom Class 1-1,000




Symbol

AirlockClass 10,000



DCC DCC

OA

FFU

RA

Particles

MAU

ParticlesNon-unidirectional CleanroomClass: 1 ~ 1,000 Air Velocity = 60~100 FPMTemp.: 72±3°F, R.H.: 45±5%Pressure: +0 ~ 0.08 in.

RA

DCC DCC

OA

FFU

RA

Particles

MAU

ParticlesNon-unidirectional CleanroomClass: 1 ~ 1,000 Air Velocity = 60~100 FPMTemp.: 72±3°F, R.H.: 45±5%Pressure: +0 ~ 0.08 in.

RA

Selected Cleanroom Labs DescriptionLab 3Floor Plan

Research CleanroomClass 1,000-10,000ACH: 5-50

HEPA Supply

HEPA Supply

Return(Pattern 1)

Return(Pattern 1)

Return(Pattern 2)

Return(Pattern 2)

AirlockClass 10,000

Prep. RoomClass 10,000

ACH: 5-30 ACH: 5-30

2'x2' HEPASupply

Symbol

2'x2' Return(Ceiling)

2'x2' Return(Low Sidewall)

1'x1' HEPASupply

1'x1' Return(Ceiling)

Pass-Through



HEPA Supply

Ceiling

Supply Air

Return Air

Research CleanroomClass 1,000-10,000ACH: 5-50

HEPA Supply

Supply Air

Return Air


HEPA Supply

AirlockClass 10,000

Particle Concentration and Distribution under Various Flow Scenarios

A

B

C

E

HEPA Supply

Floor

Sensor Elevation Panes

Ceiling

Sensor Location Plan

12

3 4

5

6

9

10

8

7

13 15

12

14

11

ParticleGenerationPoint

Research CleanroomClass 100-10,000


Lab 3Particle Sensor Locations

Particle Concentration and Distribution under Various Flow Scenarios

Space Velocity Profile under Air Change Rate(Flow Pattern: Ceiling Supply & Ceiling Return)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

5 10 15 20 25 30

Air Change Rate Per Hour

Air

Velo

city

(m/s

)

01-A01-C02-A02-C03-B04-A04-B05-A05-B05-C07-C07-E08-C08-E09-E10-B10-E11-C12-A12-C13-B14-A14-C15-B

Sensor Location

Particle Migration Under Pressure Differential Between Rooms

Sealed Pass-Through

Generate Particles in Prep. Room (Contamination Source)

Measure Particle Migration to Cleanroom (Contamination Receiver)

ΔP

Pneumatic Air-Seal Door

12

3 4

65 7

9

8

Particle Deposition on Exposed Surface

Exposed Surfaces Areas (m2) Areas (F2)Unit Surface Particle Deposition Rate (counts/min·m2)

Walls 39.32 423.2 2.13E+03Ceiling 20.16 217.0 2.07E+03Window Glass 3 32.3 3.37E+03Floor 20.16 217.0 4.28E+03

Total 82.64 889.5 97.61%

Room Space Particle Generation Rate: 9,300,000 counts/min., Duration: 4.75 hours=285 min.

Percentage of Particles Removed through Return Air

0.45%0.11%0.93%

Surface Particle Deposition Rate (counts/min.)

8.38E+044.17E+041.01E+048.63E+04

0.90%

Surface Particle Deposition Percentage

2.39%

6.07E+055.90E+059.60E+051.22E+06

Surface Particle Deposition Rate (counts/m2)

Experimental Validations of Cleanroom Airflow Rate Modeling Approach

(Phase 2)

More Test Data

More Mathematical & Statistical Analysis

Conclusions & Recommendations

To Be Published in CEC Research Report In November, 2008, and Available in ASHRAE Chicago Meeting, January 2009.

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