After 35-plus years of operation, the two chillers and the boiler system on the 60-acre Desert Vista campus of Pima Community College in southwest Tucson, Ariz., had become inefficient and were starting to develop reliability problems, with associated increased maintenance costs.

The college chose McQuay's Modular Central Plant (MCP) to serve two main buildings across approximately 28,998 sq ft of classroom and facilities space.

"The project was approved on the basis of the advantages of a packaged central plant vs. a site-built central plant for installation-cost savings and minimal disruption to the facility while maintaining a fast-track schedule," William Ward, assistant vice chancellor of facilitates for the college, said. "McQuay demonstrated phenomenal cost savings over other solutions."

The MCP is located in an enclosed service yard just off the northwest corner of the Pueblo building, the larger of the two buildings on campus.

"The elimination of the chiller and boiler rooms in the Pueblo building allows us to expand our science lab and classroom space by about 1,850 sq ft," Ward said.

The MCP was delivered to the campus in pre-engineered, pre-assembled modules. Two of the modules included two magnetic-bearing, 300-ton-capacity McQuay Magnitude chillers and two cooling towers to replace the chilled-water central plant. The third module included energy-efficient sealed-combustion boilers to provide heating and domestic hot water. The system also incorporates solar panels to supplement domestic-water heating. The solar panels are located on top of the domestic- and heating-water module.

Ward was impressed by the Magnitude chiller's magnetic-bearing frictionless centrifugal compressors, which operate efficiently at a variety of load capacities. He also was impressed by the elimination of an oil-handling system, which results in reduced maintenance and repair costs compared with traditional centrifugal-compressor chillers.

Pima Community College selected NTD Architecture of Tucson to oversee the entire project.

"The approval process started in mid-summer 2009, and the main challenge was the tight timeframe under a qualification-based procurement system," Michael Harris, an architect with NTD Architecture, said.

Meeting the Tight Timeframe
Larry Borges, a sales engineer for Climatec, the McQuay representative in Tucson, said the project moved quickly.

"The entire demolition, installation, and startup of the new system had to occur over the holiday break in time for classes to start the third week of January," Borges said.

"Changing out an old central plant to a modular system is the way to go because you have significant site time labor savings," Jim Brown, vice president and chief executive officer of Tucson-based Mechanical Systems Inc., the installing contractor, said. "… The project brought a tremendous amount of labor, material, and time savings to Pima Community College because thousands of hours of on-site work were eliminated. The McQuay Modular Central Plant contains all the interconnecting piping work between the pumps, chillers, and towers. It's all done within the modules."

Work by Mechanical Systems included demolition, fabrication of piping in the interior buildings, connection to the MCP unit, and commissioning of the new system. Demolition of the old equipment began after the conclusion of the fall semester, on Dec. 21, 2009, and occurred in phases, allowing the campus to maintain heat until the MCP was installed in January.

"We extended the existing building piping to the new McQuay central plant outside the main building, and the old piping came out in the boiler and chiller rooms," Brown said.

When the semester commenced on Jan. 19, 2010, the heating system was operational. By early February, the entire system was operational. The MCP is integrated with an Alerton building-automation system using BACnet communications and run remotely from Pima Community College's centralized campus control system in Tucson. The McQuay chillers inside the MCP have unit controllers that offer a choice of LonWorks, Modbus, or BACnet communications.

Energy Savings Multiply
The upgrade to high-efficiency chiller technology qualifies for an incentive program from Tucson Electric Power. The new MCP reaps a significant reduction in electrical-power costs over the college’s traditional central plant. Natural-gas costs are reduced because of the energy-efficient boiler, aided by the solar panels.

"I'm expecting our overall energy costs associated with heating and cooling will be greatly reduced, up to 40 percent or more," Ward said.

Changing the existing chilled-water system from constant flow to primary variable flow also contributed to significant energy savings. The existing air handler's chilled-water control valves were changed from three-way to two-way.

"Changing the central plant from constant to primary variable flow increases the temperature rise through the system, making the water temperature far more efficient and at times can reduce pump horsepower by up to 80 percent," Stan Adams, principal with Adams and Associates Engineers PLLC of Tucson, the firm that designed the new HVAC system, said.

Ward said the McQuay chiller technology and hot-water heating contained in one unit is a win-win for Pima Community College and that the college will consider the technology for future replacement projects.

Information and photograph courtesy of McQuay International.