Energy Saving of Cleanrooms in Electronic Industries

1

Xu HanTianjin University, China

2013.01.11

Outline

• Characteristics of cleanrooms• Energy consumption of cleanrooms• Identification of energy saving opportunities• Commissioning

Characteristics

Parameters Ranges

Sensible internal heat loads

commonly high to 2152 W/m2 while typically 602-807 W/m2

Fresh air requirements to

replace process exhaust

51 L/s• m2 for some while typical industry averages 10.2-15.3 L/s•m2

Average air velocity typically 0.20 m/s to 0.51 m/s while 0.35-0.41 m/s most common

Temperature ±0.11°C to ±0.28°C

Relative humidity ±1% RH to ±2.5% RH

• Design or control ranges of key parameters for semiconductor cleanrooms

Source: ISO 14644, R Schrecengost, 2004

Characteristics • Recommended air change rate

Source: [1] R Jaisinghani et al., 2003 [2] IEST RP-12.1 [3] ISO 14644 [4] GB 50073

Note:– Unidirectional airflow type is

recommended for ISO Class 1-5, and non-unidirectional for ISO Class 6-8;

– Average airflow velocity is specified for unidirectional airflow type and air changes per hour for non-unidirectional airflow type.

– The average airflow velocity is transformed to air changes per hour related to a room height of 3.0 meter.

STANDARD\ISO CLASS 1 2 3 4 5 6 7 8IEST RP12.12 Maximum 600 600 540 540 480 240 90 48

Minimum 360 360 360 300 240 150 60 5ISO 146443 Maximum - 600 600 600 600 160 70 20

Minimum - 360 360 360 240 70 30 10GB 500734 Maximum 600 600 600 600 600 60 25 15

Minimum 360 360 360 360 240 50 15 10

ISO cleanliness class

Air c

hang

e ra

te (1

/hr)

Empirical value1

Wide rangeVariation between standards

Outline• Characteristics of cleanrooms• Energy consumption of cleanrooms

Comparison among different countries/regionsComparison among different cleanliness levelEnergy end use allocation

• Identification of energy saving opportunities• Commissioning

Source: E Mills et. al,LBNL-39061 Report, 1996

Energy consumption

The power uses were estimated based on typical cleanrooms in CA, USA, by LBNL in 1993;

• Power use of different clean classifications

Cleanrooms of higher cleanliness level consume much more energy than its lower level especially when the cleanliness level is 100 or 1000

0

100

200

300

400

500

600

700

800

0

2000

4000

6000

8000

10000

12000

1 2 3 4 5

Air C

hang

e ra

te [1

/hr]

Elec

trici

ty In

tens

ity [k

Wh/

m2 ·

yr]

Cleanroom Classification

Electricity intensityAir change rate

1 and 10 100 1000 10,000 100,000

+28.9%

+90.2%

+94.9%

+24.3%

Note:• Airflow velocity updates are taken from Chapter 7 (Class 1&10 to 90 fpm, Class 100 to 70 fpm,

Class 1,000 to 30 fpm, Class 10,000 to 10 fpm, and Class 100,000 to 5 fpm) Cleanrooms - 1992-2000, Rooms and Components Vol. Three.

• Outside air estimates for cleanroom make-up air (5 cfm/sq.ft. for both heating and cooling): Brown, W.K., PE. “Makeup Air Systems Energy-Saving Opportunities.” ASHRAE Transactions V. 96, 1990.

Energy consumption

[1] Power consumption range of 12 fabs in the USA, from LBNL report , 1999[2] Power consumption range in Japan, from Japan Mechanical Association, 1990[3] Power consumption average value of 9 fabs in Taiwan, from SC Hu et al., 2003[4] Power consumption range of 8” fabs in the USA and China, GM Lu and R Wang,2012

High power use in Taiwan and China;

Fabs in US decrease power use by about 27% within last ten years;

Fabs in China consume 15% more than that in US;

• Power use in different countries/regions

2.18

0

0.5

1

1.5

2

2.5

1 2 3 4 5

Pow

er co

nsum

ption

[kW

/m2 ]

Different countries/regions

Range

Average

USA19991 Japan1990

2 Taiwan20033 USA2012

4 China20124

Energy end use in cleanrooms

Figure 1 Fab energy flow

Process Tools39%

Recir and Makeup Fans

17%

Chillers and Pumps

21%Exhaust Fans

6%

Source: R Schrecengost, P Naughton, 2004

Energy end use allocation

Figure 2 Power consumption allocation of a fab in China2

Figure 1 Average power consumption allocation of 9 fabs in Taiwan1

Source: [1] SC Hu, 2003 [2] PX Chen, 2003

Chiller

Water treatment

Air condition

Lighting ProcessCompressed air

HVAC sector: 39.9%

HVAC sector: 53.0%

Taiwan

China

Energy end use allocation

Source: Report of LBNL HIGH TECH BUILDINGS PROGRAM,2001

v

HVAC sector: 58.0%

HVAC sector: 64.0%

HVAC sector: 36.0%

CA, USA

Energy end use allocation

Source: LBNL benchmark project, 2001

Figure 1 Average electricity consumption in 12 example semiconductor fabs

HVAC sector: 46.0%

USA

Energy end use• Observations: The HVAC systems account for 40-50% of power consumed in the fabs, while

the process tools account for 35-40%; Among HVAC system, chillers consume 20-35% of the total power used, and

fans consume 10-26% of total power used; HVAC efficiency influenced by:

Airflow system:• Air change rate;• Airflow system efficiency;

Water system:• Chiller plant efficiency;

Operation and Control;• Temperature and relative humidity control;

Outline• Characteristics of cleanrooms• Energy consumption of cleanrooms• Identification of energy saving opportunities

Airflow system:– Air change rate;– Airflow system efficiency;

Water system:– Chiller plant efficiency;

Operation and Control;– Temperature and relative humidity control;

• Commissioning

Figure 1: Measured air change rates for ISO 5 (Class 100)cleanrooms.1

ISO 5 facility could be operated with an air change rate of approximately 200 air changes per hour and still provide the cleanliness classification required

Source: [1] LBNL Cleanroom Benchmarking Study

Air change rate

Air change rate

Source: [1] LBNL Cleanroom Benchmarking Study

Figure 1 Autual recirculation air change rates for ISO 5/4 cleanrooms.1

Two cleanrooms of ISO Class-4 exceeded the upper limit recommended by IEST, Energy saving opportunities might well exist in the meanwhile

Air change rate • Observations: Air change rates vary significantly among different cleanrooms having the same

cleanliness classification; The ACR needed depends largely on the mount of contamination, which is not

necessarily well understood at design; thus the cleanroom may be designed/operating with more ACR than needed;

Air change rate can be optimized by: Use mini-environment to reduce area of clean zone; Measure actual ACR and compare with benchmark and Standard; Use CFD to model air flows, effects of convention from heat sources to identify

minimum downward velocity needed to overcome heat convection, movement of people;

Use distributed particle counters to monitor cleanroom conditions in the real time;

Demand controlled filtration, Automatic set-back, and Occupancy sensors were demonstrated

Airflow efficiency• Air flow efficiency was analyzed separately for the

recirculation units (RCU), make-up air units (MAU) Wide variation in air system performance Similar average results with International Sematech study

Cleanroom ID Cleanroom ID

Airfl

ow e

ffici

ency

(W/c

fm)

Airfl

ow e

ffici

ency

(W/c

fm)

Figure 1 MAU airflow efficiency Figure 2 RCU airflow efficiency

Average 0.51 from International Sematech study

Average 0.49

Average 1.06 from International Sematech study

Average 0.91

Source: LBNL benchmark database and International Sematech study

Airflow efficiency• Relationship between recirculation system efficiency

(W/cfm) and ceiling filter exit velocity

Source: LBNL benchmark database

Airflow efficiency• Relationship between recirculation system efficiency

(W/cfm) and filter coverage

Source: LBNL benchmark database

AverageFFU:0.63

Ducted HPEA:0.58Pressurized plenum:0.43

Airflow efficiency• Relationship between recirculation system efficiency

(W/cfm) and filter pressure drop

Source: LBNL benchmark database

Airflow efficiency• Observations: Benchmarking results showed wide variation in air system

performance; No necessarily strong correlation between airflow efficiency and

ceiling filter exit air velocity/ceiling filter coverage; Filter pressure drop shows more critical influence on airflow

efficiency, which varies with type of airflow system; Airflow efficiency influenced by:

System pressure drop;Fan and motor efficiency;Filter design;Other system design characteristics.

Water system efficiency• Chilled water system comparison

Source: LBNL benchmark database

Chi

ller p

lant

effi

cien

cy (k

W/T

on)

Facility ID

Water system efficiency• Observations: The Chilled water system efficiency varied, and was similar between water

cooled and air cooled systems, but the water system generated chilled water with lower temperature;

The Chilled water system generating 36 chilled water consumed 2.67 times ℉energy than that generating 43 to generated one ton chilled water; ℉

Water system efficiency can be improved by: Temperature reset may provide substantial savings opportunities; For

centrifugal-compressor-based chillers, a 1 change in chilled-water-℉supply temperature can increase efficiency by 1-2%.

Medium-temperature (55-70 )chilled water, which potential for “free ℉cooling”;

Optimizing Exhaust; VSD technologies;

Operation and Control• Temperature and relative humidity control

Figure 1 Design and Measured Space Relative Humidity Cleanroom ID

RH (

%)

70

60

50

40

30

20

10

0 3 10 11 12 13 14 18 23 17 24

22.2

21.1

20.0

18.9

17.8

16.7

15.6

Figure 2 Design and Measured Space TemperatureCleanroom ID

Tem

pera

ture

()

℃ 3 10 11 12 13 14 18 23 17 24

Source: LBNL benchmark database

Temperatures and humidity were not as tightly controlled as specified

Operation and Control• Observations: Cleanroom reheat energy usage can be significant when the

required space temperature and relative humidity requirements are very stringent ；

The temperature and RH measured were not as tightly controlled as specified;

Owners were unaware of actual conditions; Processes may not need tight control? Commissioning and monitoring are important; Energy efficiency opportunities abound

Outline• Characteristics of cleanrooms• Energy consumption of cleanrooms• Identification of energy saving opportunities• Commissioning

Verification – Cleanroom performance – HEPA filters– Other parameters

Commissioning – HVAC air system– HVAC water system

Verification • Cleanroom performance: Space Particulate level Room Recovery Space Pressurization Space Temperature Space Humidity Lighting Noise

Verification • HEPA filters performance: Efficiency; Air leakage; Air flow; Air velocity,

Verification • Other parameters: Cleanroom enclosure– Enclosure Leak Testing to Verify no contamination entering

and air leakage is not excessive; Process equipment– Exhaust air flow

Commissioning• Verification of HVAC air system performance: Total supply air flow Total return air flow MAU operating data

Commissioning• Optimization of HVAC air system : Optimizing Air-Change Rates– Actual measurement or CFD technology;– A 30% reduction in air-change rate may reduce power consumption by

66%1, and also improve cleanliness by minimizing turbulence Optimizing make-up air unit and exhaust– Makeup air requirements vary correspondingly, with an added amount for

leakage and pressurization; – Heat recovery in process exhaust/condensation;– Optimizing operating and control strategies.

[1] Source: a report of Industrial Energy Efficiency Workshop, 2007

Commissioning• Verification of HVAC water system performance: Design scheme and control strategies of chillers; History operation data Chiller-water-supply temperature; Operating parameters;

Commissioning• Optimization of HVAC water system : Feasibility study of optimization of operation and control strategy

of chillers– through history operation data or simulation to avoid long term part-load

operation of chillers with low energy efficiency; Feasibility study of application of variable frequency technology,

dual-temperature, cooling tower, free cooling, heat recovery;– For example, In a pilot project for a multiple-cleanroom-building campus, the

implementation of a dual-temperature chilled-water system was analyzed. The site had 2,370 tons of makeup-air cooling and 1,530 tons of sensible and process cooling. With 42-F (5.7C) water for low-temperature use and 55-F (12.8C) water for medium-temperature use, approximately $1 million was saved per year, with a payback of two years1.

[1] Source: a report of Industrial Energy Efficiency Workshop, 2007

Thank you!