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!
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