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Peng Xu, Philip Haves, James Braun, MaryAnn Piette January 23, 2004

A Case Study of Precooling with Zone Temperature Reset in a Commercial Office Building. Peng Xu, Philip Haves, James Braun, MaryAnn Piette January 23, 2004 Sponsored by the California Energy Commission and the California Institute for Energy Efficiency. Outline. Aim Test site description

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Peng Xu, Philip Haves, James Braun, MaryAnn Piette January 23, 2004

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  1. A Case Study of Precooling with Zone Temperature Reset in a Commercial Office Building Peng Xu, Philip Haves, James Braun, MaryAnn Piette January 23, 2004 Sponsored by the California Energy Commission and the California Institute for Energy Efficiency

  2. Outline • Aim • Test site description • Precooling and demand shedding strategies • Test results • Utility analysis • Conclusions and future work

  3. Aim Demonstrate the potential for reducing peak-period electrical demand in a moderate-weight commercial building using building structural mass.

  4. Executive Summary • Precooling and zone temperature reset can shift up to 100% of cooling power from on- to off-peak in a moderate-weight commercial buildings • Electricity peak demand reduced by as much as 2.3 W/ft2 • Potential for cost savings when combined with Critical Peak Pricing

  5. Case Study - Introduction • Started in August 2003 • Purpose - preliminary study to assess potential and need for further work • Potential demand reduction/load shifting in moderate-weight buildings • Effectiveness of precooling and zone temperature reset • Thermal comfort

  6. Test Site Description • Medium-sized government building • Santa Rosa, CA • 80,000 ft2 (40,000 ft2 office + 40,000 ft2 courthouse) • 3 stories • Relatively low mass building structure • 6 in. concrete floor, 4 in. concrete wall, medium furniture density, standard commercial carpet • High window-to-wall ratio • Floor to ceiling glazing on south and north façade • Typical internal loads • Number of occupants • ~100 (office side)

  7. South Facade

  8. North Facade

  9. Windows • Single glazing • Tinted glass • Internal blinds

  10. Cooling Plant • West wing: three 75-ton, 30-year old McQuay air-cooled chillers • East wing: two 60-ton, 10-year old Carrier air-cooled chillers • Constant-speed water pumps, one for each chiller • Two stage compressors

  11. HVAC Secondary Systems Five VAV air handling units (three single duct & two dual duct systems): • Variable-speed supply and return fans • 50-60 VAV zones • DDC control (Alerton) • No global rest of zone temperature

  12. Building Operation • 5 am - 8 am - start up • 8 am - 5 pm - occupancy • 2-3 hot/cold calls per month • No major faults, some modest problems: • One undersized cooling coil • Some air balance problems • Lack of reheat coils in single-duct systems causes temp control problems

  13. Precooling & Zonal Reset Strategies

  14. Monitoring • Existing: • Whole building power meters • Chiller power meters • Weather station • HVAC performance data from EMCS • ~500 data points • 15 minute intervals • Added: • AHU fans power meters • Operative temperature sensors

  15. Operative Temperature & Comfort Room Regular temperature sensor Radiant heat exchange screen Convective heat exchange Operative temperature sensor globe

  16. Peak OA Temperature vs. Peak Demand

  17. Classification of Weather Conditions Hot days Warm days Cool days

  18. Comparison of Baseline & Test Conditions

  19. Tests Performed

  20. Cool Days – Limited Precooling

  21. Warm Day – Limited Precooling

  22. Limited and Extended Precooling (warm days) baseline Limited precooling Extended precooling 4 3.5 3 1.4 W/sf shed 2.5 Whole building power W/sqft 2 1.5 1 0.5 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Extended & Limited Precooling

  23. Extended Precooling (Hot days ) Extended precooling 1 Extended precooling 2 baseline 5 4 2.3 W/sf shed 3 Whole Building power W/sqft 2 1 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Hot days – Extended Precooling

  24. Chiller Power: Limited Precooling 0.7 W/sf shed

  25. Results – Fan Power

  26. Results – Zone Temp

  27. Critical Peak Pricing (1 of 3) • Operating time • CPP high price: 3:00pm –6pm • CPP moderate price: 12:00pm –3:00pm • CPP days (12 days: 5/1 – 10/31) • Average of maximum outside air temperatures in San Francisco, San Jose, Sacramento and Fresno > 98 oF

  28. Critical Peak Pricing (2 of 3) • Current tariff: A-10S • Non CPP Day Rate • On-peak credit, $0.0559/kWh, (12 pm- 6 pm) • Part-peak credit, $0.0050/kWh, (8:30 am-12 pm) • CPP Day Rate • Moderate price, $0.24/kWh (12 pm – 3 pm) • High price, $0.82/kWh, (3 pm-6 pm)

  29. Critical Peak Pricing (3 of 3)

  30. Market Potential – Cooling in Office Buildings • State-wide peak demand ~50GW • Commercial cooling - largest contributor: 15%, ~7.5 GW

  31. Extended Precooling + DL Hot days Extended precooling 1 baseline 5 4 3 2.3 W/sf shed Whole Building power W/sqft 2 1 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (hour) Conclusions • Precooling & zone temp reset can shed up to 80 –100% of the cooling peak load, without comfort complaints, even in relatively high outside temperature conditions (90 oF) • Benefits of nocturnal precooling are unclear • Economic savings can be made if combined with CPP or similar DR programs

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