Energy Saving of Cleanrooms in Electronic Industries 1 Xu Han Tianjin University, China

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

Characteristics ParametersRanges Sensible internal heat loads commonly high to 2152 W/m 2 while typically W/m 2 Fresh air requirements to replace process exhaust 51 L/s m 2 for some while typical industry averages L/sm 2 Average air velocity typically 0.20 m/s to 0.51 m/s while 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 [4] GB 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 IEST RP Maximum Minimum ISO Maximum Minimum GB Maximum Minimum ISO cleanliness class Air change rate (1/hr)  Empirical value 1  Wide range  Variation between standards

Outline Characteristics of cleanrooms Energy consumption of cleanrooms Comparison among different countries/regions Comparison among different cleanliness level Energy end use allocation Identification of energy saving opportunities Commissioning

Source: E Mills et. al,LBNL 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 % +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 , 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

Energy end use in cleanrooms Figure 1 Fab energy flow Process Tools 39% Process Tools 39% Recir and Makeup Fans 17% Recir and Makeup Fans 17% Chillers and Pumps 21% Chillers and Pumps 21% Exhaust Fans 6% Exhaust Fans 6% Source: R Schrecengost, P Naughton, 2004

Energy end use allocation Figure 2 Power consumption allocation of a fab in China 2 Figure 1 Average power consumption allocation of 9 fabs in Taiwan 1 Source: [1] SC Hu, 2003 [2] PX Chen, 2003 Chiller Water treatment Air condition Lighting Process Compressed 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

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 Airflow efficiency (W/cfm) 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 Average FFU:0.63 Ducted HPEA:0.58 Pressurized 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 Chiller plant efficiency (kW/Ton) 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 (%) Figure 2 Design and Measured Space Temperature Cleanroom ID Temperature ( ℃ ) 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 years 1. [1] Source: a report of Industrial Energy Efficiency Workshop, 2007

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