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Daylight Dividends Case StudyLocation ......................................... R. D. & Euzelle P. Smith Middle School

9201 Seawell School RoadChapel Hill, NC 27516

Completed .................................................................................................. 2001

Architect ................................................................Corley Redfoot Zack, Inc.

Consulting Engineer .......................................Reece, Noland & McElrath

Daylighting Design ........................................................ Innovative Design

© 2004 Rensselaer Polytechnic Institute. All rights reserved.

Daylight Dividends promotes the effective use of daylighting strategies innonresidential buildings. Part of this effort focuses on impartially evaluatingthe use of daylight in different building types, reporting those results so thatothers considering daylighting can see what works and what does not.

The Lighting Research Center and Daylight Dividends sponsors express theirsincere thanks to the principal, faculty, staff, and students of Smith MiddleSchool as well as the staff of Innovative Design for their assistance indeveloping this case study.

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In 2001, the R. D. & Euzelle P. Smith Middle School opened itsdoors, embracing not only a new student body, but also an environ-mentally conscious attitude. Part of the Chapel Hill-Carrboro CitySchool District in Chapel Hill, North Carolina, the Smith MiddleSchool exemplifies good daylighting practice. This case study docu-ments that good daylighting design incorporated at a building’s incep-tion yields positive results in energy savings (64% reduction in lightingenergy), comfort (teachers and students favor daylighting in the class-rooms), and a reasonable return on the added investment (4.2 years).

BackgroundThe progressive community of Chapel Hill lies within North Caroli-

na’s renowned Research Triangle—named for the triangle formed bythe area’s three major research universities: the University of NorthCarolina in Chapel Hill, Duke University in Durham, and NorthCarolina State University in Raleigh. This technology-focused businessregion is home to more than 140 organizations in a wide variety offields such as biotechnology, telecommunications, microelectronics,and information technology.

Education and environmental conservation are of paramountimportance to the Chapel Hill community. With those themes as aguide, the school district directed the design and construction of SmithMiddle School to include daylighting features and other environmen-tally friendly attributes. Green features include a solar water heatingsystem, 2-kilowatt photovoltaic panels, and a rainwater collectionsystem that provides sufficient filtered and chlorinated water for all thetoilets in the school, as well as the irrigation system for an adjacentathletic field. The water catchment system saves an estimated 2.6million gallons of water yearly.

Since the completion of the building, the school district has requiredevery new school to employ a daylighting strategy. This approach evenincludes performance goals for school principals to include sustainabil-ity in teaching and building performance.

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Design StrategyAll classroom corridors run east to west, maximizing the southern

exposure potential for the roof monitors. The design also minimizeseast- and west-facing walls and windows to reduce difficult to controlsun exposure.

Daylighting provides enough natural light into the single-storyschool to minimize the use of electric lighting without creating glare.Further, daylighting reduces the internal heat gains from electric lightsand reduces the overall cooling load. The key to successful implementa-tion of these goals was to incorporate daylighting in the initial designconcepts and integrate the daylighting strategy into the building’smechanical systems.

The building uses south-facing roof monitors to provide most of thedaylighting within the classrooms, media center, gymnasium and maincorridor. These monitors enable the electric lighting to be off most ofthe day, reducing peak cooling. Within the monitors are fire-retardant,UV-resistant, unevenly spaced cloth baffles that help distribute the lightuniformly while eliminating any potential glare problems. Clear,double-glazed glass is used in the monitor windows. This glass waschosen to allow the most light into the room with the least amount ofglass area. Optimizing the window size to distribute the correct amountof light across the room minimizes solar heat gain and reduces initialbuilding costs. The monitor allows hot air to stratify, keeping this airfrom entering the conditioned space of the room. This strategy wasincorporated in all larger classrooms, the media center, gymnasium,main hallway and the cafeteria.

Recessed windows on the exterior classroom walls are equipped withclear, low emissivity (low-e) double glazing. The south windowscontain anodized aluminum light shelves that reduce glare withouthaving to close the shades. The upper shelf surface reflects additionalsunlight into the rooms. North-facing windows do not have light shelves.

East- and west-facing windows were avoided in the design, and weremostly used in the hallways.

The windows have blinds that can be closed to darken a room; thescience rooms motorized shades on the roof monitor instead of blinds.

Triangular-shaped roof monitors provide most of the daylighting within the classooms.

Fabric baffles help ensure uniform lightdistribution while eliminating potentialglare from the roof monitors.

Light shelves and angled soffitsmaximize and redirect daylight upwardthrough the windows to light-coloredceilings.

classroom

translucentfabric baffles

roof monitor

Roof monitor scheme.

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Window blind usage is onlyrecommended when teacherspresent materials with overheadprojectors or video monitors.Teachers are encouraged toreopen the blinds following theirpresentations.

A white roofing membranereflects additional light upwardthrough the roof monitors.Light-colored walls and ceilingsdiffuse and reflect sunlight withinthe classrooms.

The daylighting strategy wasintegrated with the building’sHVAC systems. As a result oflower internal heat gains from theelectric lighting system, designerswere able to reduce the size of thecooling system by 78 tons (19%).The cost savings on coolinghelped to justify the additionaldaylighting installation cost.

Solar panels for the hot watersystem take advantage of north-facing roof monitors in thecafeteria because the slopingmonitor roof provides an idealpanel-mounting surface towardthe south.

Building plan view.

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gymnasium

auditorium/theater

cafeteria

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administration/guidance

mediacenter

classrooms

classrooms

classrooms

classrooms

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Electric Lighting StrategyThe classrooms employ two types of lighting fixtures. In each room,

eight fluorescent fixtures are installed on the monitor wall where itmeets the classroom ceiling. Each luminaire contains two T8, 4100 Klamps and a Lutron dimming ballast. Additionally, ten 2’ x 4’ fluores-cent fixtures are installed in the drop ceiling. Each recessed fixtureincludes three T8, 4100 K lamps in an 18-cell, 4” deep, parabolic trofferwith a Lutron dimming ballast.

The cafeteria, which also takes advantage of daylighting, uses thesame wall-mount, dimming fluorescent fixtures where the monitorsmeet the drop ceiling. Dimmable compact fluorescent downlights, eachwith two 18-watt lamps, are mounted in the ceiling. The cafeteria’sperimeter has non-dimming 2’ x 4’ fixtures with two T8, 4100K lampsin a 4” deep parabolic troffer.

- roof monitor

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The media center’s daylightingscheme employed the same typeof fixtures found in the class-rooms. In addition, compactfluorescent downlights are usedwhere supplemental light isneeded.

While the main hallway makesuse of roof monitors, the electriclighting is non-dimming andmay be switched on or off manu-ally. The gymnasium also isequipped with monitors, and likethe hallway, its 400-watt metalhalide fixtures cannot bedimmed.

Dual technology passiveinfrared and ultrasonic occupan-cy sensors enable classroomlighting in combination with amanual light switch. For theelectric lighting in the room tocome on, three conditions mustexist: the manual switch must beon; motion must be detected; andthe lighting level within the roommust be below the determinedsetpoint. Once these conditionsare met, the lights come on and aphotosensor adjusts the lightingdown to 10 percent in responseto daylight.

The media center and cafeteriause similar lighting controlschemes, except no motionsensors are employed.

Watt Stopper DT-200 energy-savingmotion and light sensors are installed inthe classsrooms.

Lighting controls installation diagram.

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Survey ResponseMore than 130 students, faculty and the school principal participat-

ed in a lighting survey conducted by the Lighting Research Center(LRC). The general summary can be proclaimed in three simplewords—they like it. A teacher wrote, “When I came to work at thisschool, I thought I had died and gone to heaven.”

Teachers favor the amount and quality of light provided by thedaylighting scheme and the electric lights. They like having the abilityto control the amount of light via the window shades and the lightingcontrols. Often the teachers do not even turn the electric fixtures on

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because their lighting needs are met by the daylight.Teachers believe the lighting at Smith Middle Schoolis much better than other schools where they havetaught.

Teachers and students alike experience a feeling ofspaciousness within the classrooms, caused by theadded volume of the roof monitors. They onlycomplain about too much darkness when viewingTV monitors. For this activity, all shades are closedand the lights are off. Most students rarely find theroom too bright; this only occurs on very sunnydays.

The principal uses the school building to attractprospective teachers to Smith. She gives tours of theschool to candidates. The building’s unique daylight-ing style and feeling of openness are factors inrecruiting new teachers.

The media center supplements daylighting with recessed andwall-mounted T8 fluorescent luminaires as well as CFLdownlighting.

Manually operated vertical blinds on theroof monitor windows can be drawn todarken rooms for audio-visualpresentations.

Maintenance IssuesThe LRC interviewed the maintenance staff at Smith Middle School

and from the school district. Some maintenance issues exist that shouldbe considered when integrating daylighting within a building.

Replacing failed dimming ballasts is expensive. When purchased insmall quantities, these ballasts generally cost approximately $90 each. Atypical instant-start, non-dimming electronic ballast may be replacedfor approximately $20.

Cleaning and maintenance of the additional windows is not aproblem. However, cleaning the cloth baffles in the roof monitors isdifficult. The chief electrician for the school district complained thatthere were too many parts to the lighting control system, making itharder to calibrate and maintain. Some teachers lodged minor com-plaints about the lighting levels on cloudy days.

Data LoggingTo understand the daylighting design effects on energy use at Smith

Middle School, the LRC installed data loggers to collect typical class-room lighting levels, indoor temperature, and lighting energy use. Datawas collected and recorded from March 3 to March 31, 2004.

Light loggers were placed on the teacher’s desk approximately fivefeet from the view window. Light levels and temperatures were record-ed at two-minute intervals. To collect lighting energy levels, a recordingammeter was placed on an electrical circuit which fed two classrooms:the subject classroom and a similar, adjacent classroom. The tworooms’ electric lighting was the only load on the circuit. The recordingintervals were six minutes apart, with the logger averaging the usageevery minute between recordings.

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Classroom Daylighting 101

1265 lux 1090 lux

996 lux

1128 lux

1330 lux

1385 lux

1235 lux

2070 lux2150 lux

1395 lux

28.0cd/m²

15.0cd/m²

11.8cd/m²

1185 lux

Illuminance and luminance informationwas recorded in a classroom with allelectric lighting off and window shadesopen, on a sunny day at 1:45 p.m. Theside windows face north. Measurementsreflect only daylighting contributions toambient light.

Illuminance measurements in lux (1 lux= 0.09 footcandle); luminancemeasurements in cd/m² (candelas persquare meter).

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A weather station was also erected outdoors to collect temperatureand solar intensity data. Researchers placed the station in a locationwhere nothing would block or shade the radiometers from sunlight atany time during the day. Solar intensity and temperatures were record-ed in one-minute intervals.

The chart, left, shows anaverage sampling of therecorded results. Three days ofsunny and three days of partlycloudy conditions, selectedrandomly, indicate significantlighting energy savings due tothe daylighting strategyemployed.

An awareness program uses postersreminding students, faculty, and visitorsof the school’s daylighting qualities.

* - Energy use based on connected lighting load.

Averaged Data, One Classroom

Energy Simulation ModelingPrior to construction, the schools’ designers used the DOE-2 energy

simulation model to estimate energy usage for a base case (no daylight-ing) and for the daylighting strategies employed. They estimated thatthe lighting energy reduction using daylighting was 64%. Data loggermeasurements confirmed this estimate by measuring 85% lightingenergy reduction on sunny days and 60% on cloudy and partly cloudydays. The energy simulation also predicted a peak cooling load reduc-tion of 19% (78 tons) due to the reduction of internal heat from thelighting system. Similarly, heating energy increases by an estimated20% when using the daylighting strategy as a result of the reduction inthe heat generated from the lighting system.

Cost DataDaylighting strategies are not cost-free. In the case of Smith Middle

School, the added cost of daylighting was estimated at $158,098, or$1.23 per gross square foot. Innovative Design, Inc., Smith’s daylightingdesign firm, provided these data based on detailed net cost estimatesand the actual bids for the work. This cost includes additional bracing,framing, wall and insulation for the roof monitors, additional glazing,lighting controls and dimming fluorescent ballasts, light shelves, andwall finishes and cloth baffles to eliminate glare. However, since thedaylighting design reduces the cooling load, a smaller air conditioningsystem helps to offset these costs. In addition, a reduced electrical costis attributed to the lower capacity chiller.

For daylighting to be considered economically viable, the energysavings must offset the additional cost in a reasonable amount of time.Although there may be other reasons to justify daylighting such ascomfort, productivity, and student learning ability, this analysis focuseson the more widely accepted justification for daylighting—energy costreduction.

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Results of energy simulation modeling in terms of energy reductionseem reasonable and acceptable when compared with actual findings ofdata logging and energy bill assessment. The simulation identified areduction in total electrical usage by 26% when using the daylightingstrategies. With daylighting, the annual electrical usage is 13.54 kilowatthours per square foot (kWh/ft²), compared to a base case (no daylight-ing) calculation of 18.30 kWh/ft². The cost for electricity at Smith is$0.07/kWh. By reducing the electrical usage, the annual cost savings is$0.33/ft²:

(18.30 kWh – 13.54 kWh) x $0.07/ft² = $0.33/ft².

The added energy necessary to heat the building slightly offsets thissavings. The energy simulation model indicates that it will take 20%more natural gas to heat the building, attributed to the reduction inheat gain from lower wattage of the dimmed lighting. The calculatedadditional energy required for heat is 0.048 therms/ft². With fuel costbased on $0.81/therm, the result is an additional $0.04/ft². Therefore,the total daylighting savings is the electrical savings minus the addi-tional heating energy cost:

$0.33/ft² (lighting + cooling) – $0.04 (heating) = $0.29/ft² (total savings)

Simple payback on the daylighting investment is 4.2 years.

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Summary of Lessons Learned• Fixed baffles in roof monitors are effective at direct sunlight

control (elimination of glare).• To reap the benefits and maximize the use of daylighting

while minimizing costs, daylighting design must be imple-mented from the start.

• Good daylighting design produces overall energy savings(lighting, cooling, and heating combined) while achieving ahigh degree of acceptance from school staff, teachers, andstudents.

• Dimming ballasts cost more to replace than expected.Maintenance budgets and financial analyses should incorpo-rate this additional cost for a daylit building.

• Although no empirical data from this study proves animprovement in student achievement or learning ability,anecdotal information from the instructors attributed fewerbehavioral problems to the quality of the light and a feelingof spaciousness brought forth by the roof monitors. Theprincipal concluded that the students respond to theirlessons better in the morning than in other schools she hadworked. One teacher remarked that the daylighting provideda “natural upper” for the students.

• South-facing, clear glass reduces the size of the windows inthe monitors, thereby reducing material costs.

• Reflective finishes on the ceiling, walls, and light shelvesincreases daylighting’s effectiveness.

• An administration effort to educate and encourage theproper use of daylight is an important element to success.

More information on this daylighting approach can be found in“Guide for Daylighting Schools,” developed for Daylight Dividends byInnovative Design.

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About the program...Daylighting, employed properly, reduces the need for electric

light by introducing natural light into a building. DDDDDaaaaayyyyyligligligliglighththththtDDDDDiiiiivvvvvideideideideidendsndsndsndsnds was established to build market demand fordaylighting as a means of improving indoor environmentalquality; to overcome technological barriers to effectively reapthe energy savings of daylight; and to inform and assist stateand regional market transformation and resource acquisitionprogram implementation efforts. More information can befound at:

www.daylightdividends.org

The following organizations sponsor Daylight Dividends:California Energy Commission

Connecticut Light and Power CompanyIowa Energy Center

Lighting Research CenterNew York State Energy Research and Development Authority

North Carolina Daylighting ConsortiumNorthwest Energy Efficiency Alliance

U. S. Department of Energy

Daylight Dividends is administered by:

Lighting Research CenterRensselaer Polytechnic Institute

21 Union StreetTroy, NY 12180(518) 687-7100www.lrc.rpi.edu

Principal Investigator .............................................................. Peter MoranteEditor, Graphic Design and Layout ......................................... Dennis GuyonIllustration ..................................................................Vasudha RamamurthyPhotography .................................................. Peter Morante, Nishith Pandya