Cleanroom Air Management and Efficiency Improvement

Carl J. Peterson, Sandia National Laboratories

Objectives:

The 174,000 gross square feet (GSF) Microelectronics Development Laboratory (MDL) at Sandia National Laboratories in Albuquerque, NM, consists of 23 independent cleanroom bays and 26 chases, served by 27 vertical vane axial recirculation, and 4 each horizontal vane axial makeup air fans. The MDL includes over 12,500 sf of Class 10 cleanroom space (operating at Class 1), and over 21,800 sf of Class 10,000 chase space (operating at Class 1,000 in the chases). Cleanroom exhaust air consists of 80,000 cfm of scrubbed acid exhaust and 20,000 cfm of solvent exhaust. Both exhaust systems were originally designed as constant volume systems.

The original design basis of the cleanroom bays required a 92.5 feet per minute (fpm) velocity to achieve cleanroom certification. At that time typical laminar velocity design was at 90-120 fpm, and 540-650 air changes per hour (ACH). Throughout the years of operation since 1988, the facility has seen numerous tool changeouts, and bay and chase layout changes. Since the early 1990's money was never appropriated to annually certify the cleanrooms and adjust fan airflows to accommodate the changing conditions. During 1998 Energy Audit review by Rumsey Engineers of Oakland, CA, cleanroom bays were found to have laminar velocities that ranged from 50 to 130 fpm, with many exceeding 100. The acid and solvent exhaust systems were wasting up to 30% of their airflow capacities.

Sandia has been able to develop airflow management programs designed to maintain the air balance of the facility, seal cleanroom penetrations, reseal duct connections to HEPA filters, rebuild all of the 27 cleanroom fans, increase cleanroom chase airflow capacity while reducing ACH rates to most chases, reduce cleanroom bay laminar flow velocities down to 75 fpm and 450 ACH without decreasing cleanroom performance, install lower pressure drop scrubbers, and install a variable volume acid exhaust system controlling to a constant duct static. All of this was completed without the interruption of cleanroom operations, except for the standard annually scheduled 2-week building outage. The testing and implementation of these measures at the MDL has guided Sandia to specify specific performance metrics for the new 377,000 GSF Microsystems Engineering Sciences and Application (MESA) facilities recently designed and entering construction at this moment.

We will strive to educate other design professionals of successful cleanroom energy efficiency and capacity improvement measures implemented at the MDL, as well as lessons learned for the future. We will also strive to show how the success of these measures has led to the development of specific performance measures in the recently designed MESA buildings. If we can succeed in implementing these measures in existing cleanroom facilities without process interruption, we can do so in new facilities.

Findings:

Based upon the recent studies and implementation of the previously listed measures, we have been able to conclude the following:

1. Cleanrooms similar to the MDL can reduce their laminar flow velocities in bays down to at least 75 fpm, without affecting the cleanroom classification levels. In many instances, particulate count is improved.
2. The standard design practice of 90-120 fpm laminar flow velocities for Class 10 cleanrooms should be challenged.
3. Lowering system pressure drops in the exhaust and supply systems gains back capacity for the same size fans and scrubbers. The additional capacity regained is beneficial for the ever-increasing demands of the latest tool sets.
4. Installation of centrifugal fans with VFC's is more cost effective both in first cost and maintenance costs, than the old standard use of vane axial fans.
5. Effective engineering programs to calculate cleanroom airflows, and a good building HVAC controls system is beneficial for maintaining performance.

Labs21 Connection:

1. The adoption of voluntary goals by setting metrics to reduce cleanroom laminar air flow velocities from 90-100 fpm to 75 fpm, and to reduce the scrubber pressure drop by 50%.
2. Employing a range of energy consumption strategies.
3. Promote energy efficiency efforts by training others of successful implementations.
4. Expand beyond the laboratory building by implementing the same measures in the new MESA buildings.

Biography:

Carl Peterson has worked for the Facilities Organization at Sandia National Laboratories since 1989, performing such duties as Mechanical Design, Construction Management, Systems Engineering, Campus Chilled Water Plant and Cleanroom Systems Management, and Energy Efficiency Implementation in Cleanrooms. Mr. Perterson has been involved in the commissioning of a 1,000,000 gallon Thermal Energy Storage Tank System, design and commissioning of variable volume pumping and air systems, design and commissioning of Cleanroom airflow velocity reductions, design and commissioning of Cleanroom Water Recycle and Reclaim Systems, and other energy reduction measures. With his experience in construction and operation of building systems, Mr. Perterson brings an attitude of "let's try it and make it work" to the table in Facilities Engineering. Mr. Perterson works to implement good ideas outside of the "Norm" of engineering design.