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2001 ASHRAE Technology Awards: Hybrid Chilled Water Plant

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Journal Article by ASHRAE, 2001

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The central chilled water (CHW) plant was not meeting the needs of Capital University's 1.2 million-ft 2 (111 480 m 2 ) campus in Columbus, Ohio. Failure of one of the two 750-ton (2638 kW), 35-year-old single-stage steam absorption chillers caused the university to rent a chiller during summer 1998.

CHW loads were expected to increase due to a soon-to-be-built 126,000-ft 2 (11 705 m 2 )sports and recreation facility and the air conditioning of other campus buildings. The cooling towers and other ancillary equipment were degraded. The constant-flow CHW pumping system and lack of controls at each of the 10 buildings on the system resulted in wasted energy and comfort problems. The university's natural gas contract provided a monetary incentive for consuming 30% of the annual gas consumption during the summer months. An analysis showed that upgrading the central plant was the most cost-effective option. A life-cycle cost analysis was done to select the best central plant system. The design firm then designed and led the turnkey (i.e., design/build) replacement of the old central chiller plant with a new hybrid plant, consisting of the following:

  • Two 1,000-ton (3517 kW) electric centrifugal chillers,

  • Two 1,000-ton (3517 kW) cooling towers,

  • A 560-kW natural gas engine-generator set connectable to either chiller,

  • Variable-primary CHW pumping system,

  • An energy delivery station at each building to convert the campus system to variable flow,

  • Networked digital controls to monitor/control the entire system,

  • New electrical substation,

  • New plant roof and repainting of interior, and

  • Demolition of old equipment.
  • The entire system retrofit was completed by May 1, 1999 at a cost of $2.1 million and has been operating flawlessly since that time (almost two full cooling seasons).

    Citation: ASHRAE Journal, vol. 43, no. 7, July 2001

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