Modular central plant helps library save energy, improve comfort
Installation of a modular central plant resulted in a 30% energy savings over a traditional plant for an Arizona library and recreation center.
The ability to meet a fast-track construction schedule and a 30% savings in electricity costs were critical factors in the selection of a Daikin McQuay modular central plant (MCP) for a new community library and recreation center in Queen Creek, Ariz. Those energy savings were in turn a contributing factor in the facility earning U.S. Green Building Council LEED Gold certification.
The Queen Creek Branch Library and Recreation Annex was designed and built through a partnership between the Town of Queen Creek and the Maricopa County Library District. The 47,000-sq-ft, one-story building houses a library, three meeting rooms, and a large recreation center with classrooms in a modern masonry and steel building. The MCP and cooling tower are situated in an enclosed service yard next to the building.
The Daikin McQuay MCP is a pre-engineered, pre-assembled module that combines a chiller, boiler, cooling tower, pumps, and interconnecting condenser water piping. This integral module is a low-cost alternative to a site-built central plant that reduces installation time and site assembly time.
Cost savings, flexibility
Lee Councilor, facilities manager with the Town of Queen Creek, was sold on the MCP after visiting an MCP installation nearby. Councilor says the energy savings of the Daikin McQuay MCP in kilowatt hours over traditional central plants has been impressive—at least 30% per month. He also noted the low start-up energy required for the magnetic bearing centrifugal chillers. The HVAC system at Queen Creek uses a four-pipe system. The Daikin McQuay MCP features a configuration of one Daikin McQuay Model WMC Magnitude chiller containing two 75-ton compressors. That means if one compressor happens to go down, the other one can keep cooling. In older systems, the whole chiller would have to be taken down.
The WMC chiller’s magnetic bearing centrifugal compressor also eliminates the need for oil handling equipment, offering savings on maintenance and repair costs compared to traditional centrifugal compressor chillers.
Without the loss of friction suffered in traditional centrifugal compressors chillers, the Magnitude chiller is very efficient. In addition, its frictionless magnetic-bearing compressors eliminate the metal-to-metal contact noise of conventional bearings, making the chiller relatively quiet, with sound power levels as low as 76 dBA per ARI Standard 575.
The MCP plant at the Queen Creek facility contains a sealed combustion boiler which, Councilor says, is a unique aspect of the installation that shows the flexibility in designing the plants. As a result of using hot-water heat instead of the electric-strip heating in air boxes typically found in many buildings, Queen Creek uses natural gas to the heat the building, further contributing to energy savings.
Ground broke on the Queen Creek library project in May 2007 and the MCP was installed in June 2008 within a couple of hours. During September 2008, Councilor says the required LEED blow-down was initiated to evacuate VOC (volatile organic compound) emissions from the new building in an intensive 10-day process. The system was fully commissioned in time for the grand opening of the building in November 2008.
The Queen Creek library building employs a number of advanced energy conservation techniques to achieve its low operating cost and improve comfort for its occupants, including air-side economizers, demand ventilation, daylighting, and variable air volume.
The building temperature is maintained between 74 and 76 F and back-set to 85 F at night. The air-side economizers bring in fresh air from the outside to cool the building. According to Councilor, the chiller runs at less than 20% load on a typical winter day.
Information provided by Daikin McQuay.