Georgia Elementary School

New Hybrid Coolingand Dehumidification SystemDelivers Comfort to Classrooms

School

Natural gas-firedIntegrated ActiveDesiccant Rooftopsystem

25 tons of cooling

Atlanta, Georgiaarea

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Students and teachers in one section of a Georgia elementaryschool are breathing clean, low-humidity air in their class-rooms, thanks to an innovative natural gas-fired hybrid coolingand dehumidification system developed by SEMCO.

The 25-ton Integrated Active Desiccant Rooftop (IADR) sys-tem, also known as the SEMCO RevolutionTM system, wasinstalled as a retrofit at an elementary school outside Atlanta. Itreplaced one of the larger air-handling units in an area of theschool experiencing serious indoor air quality problems. This10,000-sq.-ft. area includes eight classrooms, four teacherrooms, two hallways, two restrooms, and a storage room. Allwere previously cooled by a 30-ton conventional packaged vari-able air volume (VAV) system. For years, school staff com-plained about humidity issues in the building. To try solving theproblem, the outdoor air louvers in the original HVAC unitswere sealed, and commercial dehumidifiers were brought in to combat moisture on car-pets and ceiling tiles. However, the problems continued.

The school district decided to install a new cooling and dehumidification system to servethe area of the school where humidity problems were most severe. They obtained fundingfrom the Oak Ridge National Laboratory in Oak Ridge, Tennessee, and the U.S.Department of Energy to field-test the IADR system. Researchers from the Georgia TechResearch Institute and Georgia State University studied the air quality inside the schoolboth before and after the installation.

This new technology

gives schools a cost-

effective way to meet

the ventilation code

requirements, control

space humidity, improve

indoor air quality, and

reduce energy costs.

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Streamlined installation

Members of the school district’s maintenancestaff and SEMCO laboratory personnelinstalled the Revolution system during a singleweekend, using a custom curb adapter and theexisting gas and electrical connections. TheIADR is compact enough to be installed as adirect replacement for a conventional rooftopunit, re-using the same roof penetration andutility connections, ductwork, VAV boxes, andspace sensors.

Each of the 19 zones in the study area was fit-ted with a variable volume/variable tempera-ture (VVT) box. Each box contains a DDCbox controller and airflow monitor that com-municates with both the space thermostat andthe main control logic board installed insidethe IADR system mounted on the roof. Returnair enters the IADR system by way of a ceilingplenum on each floor of the two-story school.

Temperature and humidity control

SEMCO describes the Revolution as “the firstpackaged rooftop unit that can maintain bothtemperature and humidity, independently,while delivering any outdoor air percentagedesired and any sensible heat ratio (SHR)required by the space.” It operates as a totalconditioning system, handling all the outdoorair, space cooling and heating needs as well ascontrolling space humidity. It can also be applied as an effective dedicated (100%) outdoor air system.

The system matches the sensible and latentloads required by the space, rather than meet-

© Energy Solutions Center / May 2005 For more information, visit www.energysolutionscenter.org

ing just the sensible load. Research has shownthat occupants accept higher thermostat set-tings during the cooling season when humidityis controlled effectively. This greatly reducesenergy costs.

At the school, the system controls spacehumidity without the costly over-cooling fol-lowed by reheat required by conventional VAVsystems. During cool humid days, the IADRsystem can control moisture without the use ofcooling. By contrast, humidity remains a prob-lem in other areas of the school.

Other benefits of the new system include theability to utilize relatively inexpensive gas forwinter heating, and to operate in an energy-efficient “unoccupied mode” that still controlshumidity when school is not in session. Thismode protects against microbial problems at alow operating cost.

After a full year of operation, school officialspronounce the IADR system a success.

“It’s working great,” says the school district’sHVAC Supervisor/Energy Manager. “We haveexperienced excellent IAQ and comfort condi-tions at all times. Most importantly, the teach-ers are very happy with the new system.”

Lower operating costs

He says the new technology “enables schoolsto provide a cost-effective way to meet the ven-tilation code requirements, control spacehumidity, and minimize operating costs.”Data from the GTRI investigation confirmed asignificant improvement in IAQ, humidity con-trol and occupant comfort, according to theirreport.

“The teachers now have excellent control overtheir individual room conditions without thenoise, condensate management problems, andfluctuating supply air temperatures associatedwith heat pump or fan coil designs,” Dr. JamesSand, Program Director at Oak Ridge NationalLaboratory, states in the report.

Use of the heat recovery module in the IADRsystem makes it possible to eliminate approxi-mately 10 tons of cooling capacity. In winter,this recovered energy allows the building to beself-heated most of the time.

A conventional system without energy recov-ery would need 50 tons of cooling capacity tosupply the 47°F air required to reach desiredhumidity levels. A total energy recovery sys-tem would require 40 tons of cooling capacity.With the IADR and the integrated total energyrecovery module, only 25 cooling tons areneeded.

According to a cost analysis completed for theschool district by the design engineer ofrecord, “the IADR system was less expensiveto install than other, less efficient options,most of them unable to deliver the requiredventilation while maintaining the desired spacehumidity levels.” The Revolution systemoffered the lowest operating costs and besthumidity control of the three types. (See tableabove.)

Interest grows

The school district is seeking funds to installadditional units to serve other parts of thebuilding.

In part due to the success of the elementaryschool project, Revolution systems are beinginstalled in a new Rome, Georgia high schoolthat is scheduled to open in 2006. FourRevolution IADR systems will be combinedwith onsite power generation, using heat fromthe engines to regenerate active desiccantwheels. An additional seven Revolution unitsserved by traditional utilities will be applied tocondition classrooms, the cafeteria, the gym-nasium, band areas, and a large auditorium.

© Energy Solutions Center / May 2005 For more information, visit www.energysolutionscenter.org

Assumptions:1) Cost of RevolutionTM unit with FV provides the baseline analysis cost based on actual data from the school pilot study.2) Baseline case (school) is 10,000 square feel involving 19 zones, 8 classrooms, 4 teacher work rooms, 2 hallways, 2 restrooms,

and 1 storage room3) All other system cost estimates are based on 2002 Means data, reviewed by two separate mechanical consultants.

AGL Resources Inc. P.O. Box 4569 Atlanta, GA 30302-4569

SEMCO Inc.1800 East Pointe DriveColumbia, MO 65201

Energy Solutions Center Inc.400 N. Capitol Street, NW4th FloorWashington, DC 20001

Summary of Results from Installed Cost ComparisonSystem Approach Cost Per 10,000 sq.ft. Cost/sq.ft. Operating Cost/sq.ft. Hunidity ControlRooftop only (no recovery) $121,140 $12.1 Very High PoorRooftop and ERV $170,590 $16.6 Fair FairWS Heat Pump and DOAS $142,655 $15.1 Very High BestWS Heat Pump and ERV $130,055 $13.0 Fair FairRevolution and VAV $100,950 $10.2 Lowest Best