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Duct Sealing in Existing Nonresidential Buildings

Duct Sealing in Existing Nonresidential Buildings. Statewide Codes & Standards Program Prepared for CEC Workshop July 18th, 2002 Presentation by PG&E/HMG Jon McHugh, HMG. Existing Buildings - Duct Testing and Sealing upon Replacement .

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Duct Sealing in Existing Nonresidential Buildings

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  1. Duct Sealing in Existing Nonresidential Buildings Statewide Codes & Standards ProgramPrepared for CEC Workshop July 18th, 2002Presentation by PG&E/HMGJon McHugh, HMG

  2. Existing Buildings - Duct Testing and Sealing upon Replacement • Ducts that are outside of conditioned spaces or indirectly conditioned spaces … …..and attached to single zone AC or HP • Must be tested and sealed to maximum of 10% leakage, when … • More than 25% of Duct Surface is replaced, or • Attached HVAC unit is replaced

  3. Insulation of Ducts upon Duct Replacement • Outside of conditioned spaces and attached to single zone AC or HP  Must be insulated to R-8  If ducts are outdoors, they must have surface reflectance greater than 80%

  4. Duct Leakage in Existing Buildings • 350 Light Commercial Duct Systems tested for SCE • 85% of systems needed duct sealing • Average combined (supply + return) duct leakage of 36% • Some data indicates that duct leakage depressurizes buildings

  5. Opportunity to Plug the Energy Leaks • 140,000/year replacement HVAC units installed in light commercial buildings • LBNL study - 65% of ducts in locations where they should be sealed • 140,000 x 0.65 x 0.85 = 74,000 systems/yr • Replacing equipment affects the duct/air handler seal - opportunity to upgrade duct tightness.

  6. Prototypical existing building • 2,000 SF prototype office building • 9 ft ceiling height, 3 ft plenum height • Tilt-up wall construction • No economizer • 6 ton cooling system • R-4.2 duct insulation • Untested Ducts 36% leakage • Tested & sealed ducts 10% leakage

  7. TDV (Time Dependent Valuation) Savings Results • DOE2.2 simulation hourly energy results • Hourly energy multiplied by TDV energy factors • Higher TDV factors on hot weekday afternoons • Present value of savings: 30 year period of analysis, 3% real discount rate • TDV savings = TDVbase - TDVproposed

  8. Duct sealing vs alternatives, Plenum w/ R-19 Ceiling & R-0 Roof

  9. Duct Sealing & Alt - Unvented Plenum with Ceiling and Roof Insulation

  10. Unvented Plenum with Sealed Ducts: Increase Duct Insulation

  11. Average Costs/Savings Estimates • Costs based on: • Sealing $150/ton + $30 for 3d party verification • SCE duct sealing project • R4.2 to R-8 insulation incremental cost $122 • Owens-Corning Fiberglass • Weighted TDV savings based upon: • 60% vented plenum, ceiling only insulation • 40% unvented plenum, both ceiling and roof are insulated • Fans cycled in half of systems

  12. Prototypical Cost/Benefits

  13. Benefits from Duct Sealing Annual Energy Savings from Sealing Ducts • Natural gas savings 70,000 MMBtu/yr • Electricity savings 57 GWH/yr • Peak demand savings 43 MW 10 Years of Savings • 3.8 Million MMBtu natural gas • 2,685 GWH electricity • 430 MW Peak Demand

  14. Single Zone AC or Heat Pump Replacement • Ducts tested and sealed to 10% of fan flow IF • Ducts outside conditioned space, or • In vented plenum, or • Above insulated ceiling

  15. Alternatives to Duct Sealing upon Replacement of Single Zone AC • For buildings with no roof insulation • Insulate roof TO R-19 and seal roof vents, or • Insulate roof TO R-10 and apply “cool roof” coating to roof and any exposed ductwork • For buildings with roof insulation greater than R-5 • ADD R-10 roof insulation and “cool roof” coating to roof and any exposed ductwork

  16. New or Replacement Ducts Added to Existing Single Zone AC If outside of the conditioned space (above insulated ceiling, vented plenum etc): • Insulated to R-8 • Exposed (outdoors) ducts have a surface reflectance greater than 80% • Sealed and tested to <10% leakage, • If new or replacement ductwork is greater than 25% of duct system surface area

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