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High-Rise Office Building – Retro-Commissioning (RCx)

Duke Energy

This 20-story multi-tenant office tower in Charlotte, North Carolina, is served by six air handling units (AHUs) and nearly 200 fan-powered units and VAV boxes across a mix of leased and unleased floors. Michaels Energy conducted a Find-and-Fix study at the property as part of Duke Energy’s Retro-Commissioning (RCx) program, working with the building management team to identify operational improvement opportunities.

Challenge

Through the Find-and-Fix study, we found the building’s complexity had led to override creep:

  • AHU-1 through AHU-5 were stuck in occupied mode 24/7 because of BAS overrides, even on unleased floors.
  • Several floors’ VAVs remained in occupied mode after hours, preventing setback from taking effect.
  • Chilled water pumps ran at a constant differential pressure, and cooling tower/condenser water settings were not optimized for varying load.

These issues meant the tower was essentially “on” all the time, cooling and moving air for empty spaces.

Solution

The building management team implemented these recommendations to align controls with how the facility is actually used:

  • Scheduling fixes reduced AHU hours to 6:00 a.m.-6:00 p.m. weekdays and off on weekends, and restored unoccupied mode.
  • Pump differential pressure reset now modulates between 18 and 22 psi based on critical valve positions, trimming pump energy while maintaining comfort.
  • Temperature adjustments and VAV fixes allow night and weekend setup/setback to actually take effect on key floors.
  • Additional measures (DAT reset, cooling optimization, and economizer improvements) further reduced cooling energy and peak demand, and an optimal start strategy shortened morning warm-up/cool-down times.

Results

Together, the measures deliver verified annual savings of about $41,000 and more than 513,000 kWh, reducing peak demand by 94 kW. With schedules and resets now working for—not against—the building, the customer has a more efficient baseline and clearer visibility into which deeper capital upgrades (like equipment replacements) could deliver the next wave of savings.