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Energy Saving of Cleanrooms in Electronic Industries. Xu Han Tianjin University, China 2013 .01.11. Outline. Characteristics of cleanrooms Energy consumption of cleanrooms Identification of energy saving opportunities Commissioning. Characteristics .
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Energy Saving of Cleanrooms in Electronic Industries Xu Han Tianjin University, China 2013.01.11
Outline • Characteristics of cleanrooms • Energy consumption of cleanrooms • Identification of energy saving opportunities • Commissioning
Characteristics • Design or control ranges of key parameters for semiconductor cleanrooms Source: ISO 14644, R Schrecengost, 2004
Characteristics • Recommended air change rate • Empirical value1 • Wide range • Variation between standards Air change rate (1/hr) • 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. ISOcleanliness class Source: [1] R Jaisinghani et al., 2003 [2] IEST RP-12.1 [3] ISO 14644 [4] GB 50073
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
Energy consumption • Power use of different clean classifications • The power uses were estimated based on typical cleanrooms in CA, USA, by LBNL in 1993; +24.3% +94.9% +90.2% +28.9% • 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. Cleanrooms of higher cleanliness level consume much more energy than its lower level especially when the cleanliness level is 100 or 1000 Source: E Mills et. al,LBNL-39061 Report, 1996
Energy consumption • Power use in different countries/regions • 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; [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
Energy end use in cleanrooms Recir and Makeup Fans 17% Process Tools 39% Chillers and Pumps 21% Exhaust Fans 6% Figure 1 Fab energy flow Source: R Schrecengost, P Naughton, 2004
Energy end use allocation Taiwan China HVAC sector: 53.0% Water treatment Lighting Process Compressed air Figure 1 Average power consumption allocation of 9 fabsin Taiwan1 Air condition HVAC sector: 39.9% Chiller Figure 2 Powerconsumption allocation of a fabin China2 Source: [1] SC Hu, 2003 [2] PX Chen, 2003
Energy end use allocation CA, USA v HVAC sector: 58.0% HVAC sector: 64.0% HVAC sector: 36.0% Source: Report of LBNL HIGH TECH BUILDINGS PROGRAM,2001
Energy end use allocation USA HVAC sector: 46.0% Figure 1 Average electricity consumption in 12 example semiconductor fabs Source: LBNL benchmark project, 2001
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
Air change rate 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 Two cleanrooms of ISO Class-4 exceeded the upper limit recommended by IEST, Energy saving opportunities might well exist in the meanwhile Figure 1 Autual recirculation air change rates for ISO 5/4 cleanrooms.1 Source: [1] LBNL Cleanroom Benchmarking Study
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 Average 1.06 from International Sematech study Average 0.51 from International Sematech study Average 0.49 Average 0.91 Airflow efficiency (W/cfm) Airflow efficiency (W/cfm) Cleanroom ID Cleanroom ID Figure 1 MAU airflow efficiency Figure 2 RCU airflow efficiency 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 Average FFU:0.63 Ducted HPEA:0.58 Pressurized plenum:0.43 Source: LBNL benchmark database
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 Chiller plant efficiency (kW/Ton) Facility ID Source: LBNL benchmark database
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 70 60 50 40 30 20 10 0 22.2 21.1 20.0 18.9 17.8 16.7 15.6 RH (%) Temperature (℃) 3 10 11 12 13 14 18 23 17 24 Temperatures and humidity were not as tightly controlled as specified 3 10 11 12 13 14 18 23 17 24 Cleanroom ID Cleanroom ID Figure 2 Design and Measured Space Temperature Figure 1 Design and Measured Space Relative Humidity Source: LBNL benchmark database
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