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The AHU From

The AHU From. INLAND EMPIRE CHAPTER. Hell. A Case Study Presented by David Sellers Portland Energy Conservation Inc. 1 - 2/27/2002. 2 - 2/27/2002. 3 - 2/27/2002. 4 - 2/27/2002. 5 - 2/27/2002.

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The AHU From

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  1. The AHU From INLAND EMPIRE CHAPTER Hell A Case Study Presented by David Sellers Portland Energy Conservation Inc. 1 - 2/27/2002

  2. 2 - 2/27/2002

  3. 3 - 2/27/2002

  4. 4 - 2/27/2002

  5. 5 - 2/27/2002

  6. At the time this was all going on, the clean room conditions were stable and within specifications; 68°F+1-1/2°F, 45%+3% relative humidity. 6 - 2/27/2002

  7. Leaving preheat coil Outdoor condition Leaving cooling coil, repaired condition; leaving humidifier, as found condition Space condition Leaving fans Leaving cooling coil, as found condition Leaving reheat coil The process as found was using $5,000 - $7,000 of unnecessary energy per month. 7 - 2/27/2002

  8. How Could This Be? • Clean room conditions were at spec • Fast track design build project • Specific clean room requirements • Non-specific HVAC process requirements • Clean room qualification based commissioning focus • The nature of the semi-conductor industry business cycle 8 - 2/27/2002

  9. Preheat Problems • Shut down steam when its not needed • Integral face and bypass type preheat coil • Valve in place, not control signal • Calibrate sensor • Add Alarms 9 - 2/27/2002

  10. Preheat Problems • Integrate control cycle • Eliminate multimode control approach • Operating cycles based on OAT rather than clean room • Inconsistent operation • Sequence with chilled water and reheat • Lock out when not required • Maintain an independent low limit 10 - 2/27/2002

  11. Cooling Problems • Calibrate sensor • A little tricky with an averaging element • Relative calibration more important than absolute calibration • Lock out when not required • Add alarms 11 - 2/27/2002

  12. Humidification and Reheat Problems • Eliminated by the other fixes • Improved space sensor calibration routine • Add alarms • Fan heat provided most of the reheat 12 - 2/27/2002

  13. The cost of correction is projected to be between $4,700 and $8,000. • Exact value depends on the hourly rate used. • Most of the cost was in facilities engineering labor. • Some modest costs were associated with hardware. 13 - 2/27/2002

  14. Educating the Operators Ensured Persistence • Diligent, talented operators • Lacking training in psychrometrics • Lacking training in clean room process • Informal training provided empowerment • Kept a psych chart by the operators console • Nature of engineering support requests changed • Acted on their own initiative 14 - 2/27/2002

  15. Systems Integration Problems 24 hour per day plant operating spec taken literally • No light switches in the clean rooms • No provisions for coordinated start-up and shut down Power failures and equipment failures caused severe pressure fluctuations in the fab • Contamination issue • Safety issue • Restart issue 15 - 2/27/2002

  16. Systems Integration Problems Multiple power sources on the same system • Controls on uninterruptible power supply • Drives on emergency power with different auto-restart options selected • Control interlock circuit on normal power 16 - 2/27/2002

  17. Power Coordination Coupled with an Assembly Problem for a DISASTER!!! 17 - 2/27/2002

  18. Fab Leakage = Energy Burden + Operational Danger Two parallel, redundant fans designed so: • Only one fan runs • Provides 27,000 cfm at 3.5 inches w.c. Clean room leakage resulted in running both fans to achieve pressurization required • 14,000 extra cfm of outside air to move and condition • Static requirement increased to 7 in.w.c. • Duct pressure class was 4 in.w.c.!! 18 - 2/27/2002

  19. Pressure Relief Doors Provide Protection • Protect from air hammer effects due to sudden damper position changes. • Protect over-pressurized ducts to the extent possible 19 - 2/27/2002

  20. Improved Damper Reinforcement Simply matched factory instructions • Reinforcing plate between sections • Bracing is an alternative approach 20 - 2/27/2002

  21. Permissive Interlocks and Better Quality Limit Switches • Start command opens dampers • Limit switches proving starts the fan • Wired to work in all selector switch positions • “Local” control mode on the drive disabled 21 - 2/27/2002

  22. HVAC Process/Efficiency Commissioning Benefits • Reduction in operating cost and improved performance and reliability in retrocommissioning arena. • Reduction in operating cost and first cost with improved performance and reliability in new construction. • Reduction in CO2 emissions. • Complements energy savings. • Potential for additional financial leverage. 22 - 2/27/2002

  23. Barriers to Moving from Qualification Based Approach • Rapid fluctuations in the semiconductor market cycle. • Short paybacks demanded. • Design innovations not embraced. • Drive to get on line and in production ASAP. • Production process tolerances. • Run on detection limits. • Extremely costly to ship bad product. 23 - 2/27/2002

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