Sam Nunn Atlanta

Federal Center

Atlanta, Georgia

One of the Largest Federal Office Buildingsn a unique combination of

traditional and contemporaryarchitectural elements, the Sam NunnAtlanta Federal Center houses 5,000employees for dozens of federalagencies. The center combines fourdistinct structural elements in a U-shaped configuration in centraldowntown Atlanta, near the GeorgiaDome and the recreational attractionUnderground Atlanta. Construction ofthe facility was completed in phases,with the first completed in 1996 andthe final phase in 1998. The facilitywas named the Building Owners andManagers Association (BOMA)Government Building of the Year forthe Southeast Region in 1999. Thebuilding is operated by the FederalGovernment’s General ServicesAdministration (GSA).

One Of The Largest Federal

Office Buildings

The facility, named for the formerU.S. Senator from Georgia, is one thelargest federal office buildings on theEast Coast. It encompasses 1.87million square feet of space. Thestructure straddles a busy downtownstreet. The building is also locatedatop an underground train tunnel ofthe Atlanta transit system, MARTA.

The building units include theremodeled 1924 department store,Rich’s, which was a downtown Atlantalandmark and an Atlanta institution.

I

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Now this renovated six-story buildingand its beloved clock are a visualcornerstone for the center. Otherelements are a 10-story mid-risesection, an eight-story bridge, sixstories over Forsyth Street and a24-story high-rise tower. Adjacent to the building is a 10-story parkinggarage. Construction of the buildingwas a joint urban redevelopmententerprise of the City of Atlanta andthe Federal Government. The designarchitect for the facility was theCalifornia firm of Kohn, Peterson, Fox and Associates. Newcomb &Boyd, a large Atlanta firm, waschosen as the project engineer.

Designed For 24-Hour Operation

Southeastern Facility Management,Inc., is contracted by GSA to operatethis facility. The system was designedfor 24-hour seven days a weekoperation to accommodate themission of the various agencieshoused in the facility. One or moreof the 1,310-ton chillers were tooperate, depending on the buildingload, between the hours of 6:00 a.m.and 6:00 p.m. After 6:00 p.m., the400-ton chiller was to carry allcomputer rooms and miscellaneousbuilding loads.

As a consequence, the facilitydesigners and engineers neededto plan for continuous occupancy.Atlanta has significant cooling loadsfor much of the year and highhumidity as well. The goal of the

©American Standard Inc. 2000

“The EarthWise™

system was designedfor 24-hour sevendays a week operationto accommodate themission of thevarious agencieshoused in the facility.”

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HVAC system design was to assurecomplete comfort in the buildingaround the clock, year-round. Toachieve this, significant emphasiswas placed on humidity control witha central chilled water plant, airhandlers for each area and a zone-controlled VAV air delivery system.Building designers also recognizedthat an important part of the officeenvironment is acousticperformance. For this reason,rigorous sound level standards wereset for occupied areas throughout thefacility. The air conditioning systemefficiency was extremely importantdue to the 24/7 operation.

The Trane Company was the supplierof chillers, air handling units and VAVterminal units for the facility. Bill Faulkner, sales engineer for theTrane Atlanta commercial salesoffice, worked extensively withNewcomb & Boyd, thecontracting/construction team, andwith the owners in specifyingequipment and systems that wouldmeet the rigorous efficiency,temperature and humidity controlstandards as well as meet acousticcriteria. The chilled water systemchosen was a central electrichermetic centrifugal chiller plant,with several large air handlers oneach floor and over 1,300 terminalunits—either fan-powered units (PIU)or variable air volume units (VAV)throughout the occupied areas.

Economizer Operation Attractive

The system uses four Trane ModelCVHF 1280 chillers rated at 1,310 tonsplus one smaller Trane Model CVHE500 machine rated at 400 tons.These EarthWise™ high-efficiency,low-speed, low-pressure, direct-driveHCFC-123 chillers are located in alarge basement mechanical room inthe tower section of the facility. In theinterest of system efficiency, the

plant also features a plate and frameheat exchanger to allow economizercooling without having to operatethe chillers when outdoor conditionspermit. The building is run ineconomizer mode with outdoorambient temperatures up to 46degrees. Because Atlanta has 1,643hours annually where the ambienttemperature is below 46 F and,because the building is in use aroundthe clock, this economizer option isvery attractive. The economizer’srange of operation is significantlyincreased by an upward reset ofsupply air temperature of as muchas 10 degrees during winter andmild weather.

Another chiller plant energyefficiency approach employed inthe Federal Center is the use of alow-flow design for the cooling towercondenser waterflow. The TraneEarthWise CenTraVac chillers wereselected with cooling waterflows of2.0 gpm per ton and still meet the

EarthWise™ system features

high-efficiency HCFC

CenTraVac® chillers and a

low-flow design for

optimum system efficiency.

government’s required maximumcompressor kW consumption. Thislow-flow design improves overallplant efficiency as well as allowingdramatically lower first cost incondenser piping, cooling towersand condenser water pumps. In theFederal Center design, forexample, the piping from thebasement chiller plant to the roof-mounted cooling towers 25 storiesabove could be reduced from24-inch to 18-inch pipe.

The facility managers strive tomaintain building relative humidityat 40 percent, even with theextensive mixing of outsideventilation air. To accomplish this,they rely on the ability of thecentrifugal chillers to deliver 42 Fchilled water for enhanceddehumidification. The building alsohas significant internal thermalloads. This is in part because of thehigh concentration of computerequipment. A recent surveyindicated two personal computersper building occupant. In addition,there are numerous agency dataprocessing centers. Themaintenance staff indicated theyhave found the lower relativehumidity level that they were ableto achieve has essentiallyeliminated any mold or mildewproblems in the facility.

Air Distribution To Meet

Acoustic Standards

Distribution of chilled air in thebuilding is accomplished with 100central station air handlers andassociated fan-powered VAVboxes. The air handlers are TraneModular Climate Changer® air

“They set a required sound performance level...This was an interesting design challenge.”

Heat exchanger allows operation in ecomomizer mode.

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handling units and the VAVequipment was also provided by Trane. Faulkner noted that theowner had set rigorous acousticstandards for the air handlermechanical rooms throughoutthe building. “They set a requiredsound performance level of NC40 just outside the mechanicalrooms and NC 35 elsewhere onthe occupied floors. This was aninteresting designchallenge.”

One acoustic solution wasto take advantage of themodular design of the airhandler. Trane teammembers worked with thedesigners at Newcomb &Boyd to configure the airhandlers in a blow-thrudouble-deck stackedconfiguration. Thatconfiguration delivers 48 Fsupply air with the fandrawing building airthrough filters at the lowerlevel and then turning the

airflow and moving it throughthe coil sections at the upperlevel. Turning the airflow withinthe air handler using dualdischarge plenums attenuatesthe low frequency fan soundenergy using a phenomenoncalled “end reflection” that reduces thetransmission of sound at the airhandling unit discharge as well

as radiated sound. The 48 F air temperature allowed lowerquantities of air, or fewer cubicfeet per minute, to be circulated.This dramatically increased theairside energy efficiency of thebuilding.

This design has been proven toreduce sound levels, particularlyin the lowest two octave bands.

“This design has been proven to reduce sound levels,particularly in the lowest two octave bands.”

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Generator set can power chillers during peak demand hours.

Literature Order Number

Date

Supersedes

Stocking Location

Since The Trane Company has a policy of continuous product improvement, it reserves the right tochange design and specifications without notice.

The Trane CompanyAn American Standard Companywww.trane.com

For more information contactyour local sales office ore-mail us at comfort@trane.com

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May 2000

New

La Crosse

“This is important,” says Faulkner,“because these low frequency‘rumble’ sounds are particularlydifficult to attenuate. Stacking theunits with the coil above the fanstiffens the whole assembly andreduces the rumble effect.”

Regular Cleaning An

Important IAQ Strategy

The building facility managementteam puts a high priority on indoorair quality and the design of themodular air handlers is an importantfeature in this strategy. The system in the Federal Center uses themechanical room itself as an inlet andmixing source for the air handlers.The air handlers have afree return. Building air first travelsthrough a four-ply pre-filter module,then through a bag filter sectionbefore going through the fanand coil.

The staff notes that this doublefiltration design allows the systemto capture particles down to thesmall-micron sizes. This is part ofGSA’s emphasis on maintaining goodindoor air quality. For the samereason, the facility management crewcompletely cleans the air handlers onan annual basis. “We remove the sidepanels to do this. Because of theirblow-thru double-deck stackedconfiguration, these units are easy toclean.” Faulkner indicates that the

cleanup crew vacuums and washesevery square inch of the air handlerinterior, including the coils. “It’salmost like a food service level ofcleanliness.”

According to the maintenance staff,now that the facility is up andrunning and the system is tuned,there are very few comfortcomplaints from building occupants.“Typically it’s eight to ten comfort-related trouble calls per month.For a facility this size and with thismany occupants, that’s phenomenal.”

Faulkner suggests that the reason forthe low complaint level is attentionby the facility staff to detail in thedesign and selection of equipment,in operation and in scheduledmaintenance of the facility tomaintain its high performance levels.“The performance and comfort of thefacility is not an accident. It’s a resultof good planning and great attentionto detail.”

The cleanup crew vacuums and washes every square inch of the TraneClimate Changer® air handler interior, including the coils.

Historic clock at Rich’sDepartment Store buildingportion of facility.

“The performance and comfort of the facility isnot an accident. It’s a result of good planningand great attention to detail.”