Phoenix Children's Hospital in Phoenix is projecting it will save $10.9 million in mechanical system costs over 15 years with a new "green" central plant that features an array of energy-efficient heating and cooling equipment.

The focal point of the central energy plant, which is being built as part of a hospital expansion, is a new 800-ton water-cooled heat pump chiller that cuts natural gas use by 70 percent and saves an estimated 5.6 million gallons of water annually. Instead of rejecting heat through the chiller condenser water to the cooling tower where it evaporates, the water is passed through the heat pump, which heats it for the hospital's hot water needs.

The water that's saved cuts costs for the hospital but also makes the system just that much more environmentally friendly, says Rick Rome, principal, CCRD Partners, the mechanical and electrical system firm that worked at the hospital.

The central plant also includes nine high-efficiency condensing boilers that feature a smaller footprint and variable-speed pumping systems to reduce hot water usage compared with conventional fire-tubed boilers, Rome says. Three 1,900-ton chillers with variable-frequency drives will supplement the cooling capability of the heat pump and will operate at optimum speed to reduce energy consumption. Three 2,000-kilowatt diesel generators are available for standby emergency power. The enhanced design was developed in partnership with Milwaukee-based Johnson Controls Inc.