A quiet learning environment, consistent comfort and energy efficiency topped the list of requirements at Northbrook Junior High School in selecting chillers as part of a $1.88 million life-safety improvement renovation project. The two-story, 135,000-square foot school was originally built in 1958 and now serves 650 students in grades six through eight in Northbrook, Illinois, north of Chicago. The renovation project included replacement of all heating and cooling system components. "We had a building with nine additions over the years and a severe overheating issue," says Russ Jensen, director of buildings and grounds for Northbrook School District 28.

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Quiet comfort a priority

With the priorities of quiet comfort and energy efficiency in mind, the project renovation team selected the Daikin WMC magnetic bearing compressor chiller with its industry leading efficiency and ultra-quiet operation.

"The biggest selling factor for me in selecting the two 170-ton Daikin WMC chillers was the noise factor. The chiller plant is located next to three classrooms in the lower level so the equipment had to be quiet," says Jensen.

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His views are echoed by John Kluber, partner with architectural engineering firm Kluber, Skahan and Associates in Batavia, Illinois. "You can't have noise and vibration in schools with classrooms so close to the chiller plant." Daikin WMC chillers have the quietest sound levels in the industry with sound pressure ratings as low as 77 dBA per AHRI Standard 575.

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The right technology for the job Kluber first saw the Daikin WMC chiller technology several years ago and knew it was right for the Northbrook project because Daikin WMC chillers effectively handle variable flow.

This capability was important because the school was converting from a primary-secondary pumping scheme to a more efficient variable primary pumping system during the renovation.

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"Variable primary systems can be problematic because of the limitations of typical chillers to handle the variable flow. But Daikin WMC chillers can go down to low flow as necessary."

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Jensen adds, "The technology of Daikin WMC chillers and the high level of Daikin service reinforced our decision to change the system design. We were able to proceed with a primary pumping system in a two-pipe configuration." He says the former system required more pumps with each new building addition that was constructed over the years. A total of 26 pumps were removed in the renovation since the new system requires only one main pump and a backup pump.

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As part of the retrofit the old natural gas direct-fired absorber was removed and replaced with the two electric Daikin chillers. The building's original boiler was replaced with two high efficiency condensing boilers. "The old system used a piping loop for the cooling system tied into the heating system at the plant. We had two sources of heat in every classroom with one source of control," Jensen says. 

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Complex control systems

The school renovation project also included the design and installation of a comprehensive building automation system which controls everything from the indoor air environment to outside parking lot lights.

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"One of the most challenging parts of the project involved integrating the building's various control systems to communicate with each other," says Chad Elliott, project manager with Premier Mechanical, Inc. in Addison, Illinois. The Daikin chillers, along with the cooling tower and pumps, are part of the chiller plant controller designed to optimize efficiency at different loading scenarios. The chiller plant controller in turn communicates with the building automation system from TAC.

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Jensen explains, "The chiller plant controller communicates with the chillers, boilers and pumps using Modbus® protocol. The building automation system communicates with the chiller plant controller and other building systems using either LonTalk® or BACnet® protocol."

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