An old air cooled chiller had run its course in the Choctaw Building occupied by the Clinton School for Public Service and needed to be replaced. Meanwhile, 10-year-old inefficient Trane chillers were costing their neighbor next door, the William J. Clinton Presidential Library, a ton of money. Together they needed a solution that could provide chilled water for both facilities more efficiently as well as a better Building Automation and Controls System that could operate the chiller plant along with the entire facility.
In the pre-retrofit period, the Clinton Presidential Center facility used three (3) 300-ton Trane Centravac water cooled chillers to meet the cooling needs of the facility. The chillers were relatively inefficient with partially loaded constant-speed chillers and small temperature splits between chilled water supply and return. The Choctaw Facility’s air-cooled chiller, at more than 25 years of age, was beyond its useful life, an energy hog and less than reliable. A replacement solution was needed.
Powers began by upgrading the Trane chillers with new technology: frictionless chillers by Smardt. The new Smardt VFD centrifugal chillers have magnetic bearings and are oil-free. The VFDs allow the compressor to slow down due to lower lift requirements, caused by cooler condenser water temperatures. The existing cooling towers VFDs were optimized by decreasing the condenser water temperature as low as the wet-bulb and the cooling tower approach allow (in accordance with manufacturer specifications).
These new high efficiency chillers provided energy reduction and were able to carry the whole load, delivering chilled water from the main library’s central plant over to the Choctaw Facility via new piping. The diversity of the load and the new chillers' efficiency made the absorption of Choctaw into the Library system possible.
In addition to the chilled water plant optimization, a controls optimization took place in the main building with the following controls sequences optimized through the world class Siemens Building Automation and Controls System:
- Scheduling at the zone level (VAV scheduling).
- Closing the outside air dampers during pre-cool.
- Demand control ventilation (DCV), by monitoring CO2 levels.
- Air-Side economizer cooling.
- Isolation valves for chilled-water and condenser water.
- Zone temperature night set-backs at the zone level.
- Converting constant volume air handlers to variable volume (using zone temp for feedback rather than static pressure).
Upon completion of this project, the Clinton Presidential Center was recognized with a Silver LEED-NC Certification by the US Green Building Council (USGBC), two Green Globes by the Green Building Initiative (GBI) for best practices in energy and environmental design, and the Platinum LEED-EB Certification for Existing Buildings (USGBC). The Choctaw Route Station is now the oldest LEED Certified building in Arkansas.
Adding the kWh savings from Presidential Library and the Choctaw Facility resulted in total savings of 1,374,366 kWh. The kW Savings totaled 547 kW. Total incentives through the utility company were $522,123.