Northern Trust Company

Chiller Plant Upgrade, Design

Chiller Plant Upgrade, Design - Chicago, IL


After conducting an energy audit for this 584,000-square-foot commercial headquarters and banking facility, GBA designed recommended improvements to the chiller plant.


At the time of GBA’s 2009 energy audit, the chiller plant consisted of three chillers installed in 1964, each with a capacity of 884 tons and a cooling efficiency of 0.88 kW/ton. Upgrading to high-efficiency units would yield impressive cost savings and greater reliability; existing equipment was well past its estimated service life.

  • The new plant includes four Carrier 23xrv variable-speed screw chillers, each with a nominal capacity of 550 tons at AHRI conditions (518 tons with 25% ethylene glycol and project-specific flow rates and temperatures). Full-load efficiency is 0.555 kW/ton, with an IPLV of 0.329 kW/ton. N+1 redundancy is available even on peak days. Ozone- depleting refrigerants were eliminated.
  • New high-efficiency primary chilled water and condenser water pumps were added on a common header, allowing any combination of chillers and pumps to operate. Pump power (in terms of W/gpm) was reduced by 29% compared with the prior configuration, and additional reductions will be achieved through variable-primary control. Peak kW/ton for the property was reduced by 37%, and IPLV is estimated to be reduced by more than 50%.
  • GBA performed a life-cycle cost analysis to select chillers that would provide the best net benefit, considering energy efficiency, operational costs, and first cost of the machines. NTC then pre-purchased the chillers for installation by the contractor.
  • Overall, the project, which was completed in 2016, came in $240,000 under budget and also earned $219,000 worth of incentives from ComEd, the local electric utility.