Wall Mart Experience

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22 ASHRAEJou rna l a sh r ae .o rg Oc t obe r 2 00 7

About the Authors

PartTwo

The Wal-Mart

Experience

McKinney, Texas, Wal-Mart supercenter entrance vestibule showing sustainability objectives.

In 2005, Wal-Mart opened major experimental stores in McKinney,

Texas, and Aurora, Colo. These two stores incorporate several ex-

This article ocuses on the lighting

and renewable electricity generation ex-

periments. A related article by the same

authors in the September 2007 issue

develops a baseline and covers the HVAC

and rerigeration experiments.

Interior Lighting Systems

The typical Wal-Mart supercenter uses

standard two-lamp 4 t T8 uorescent

fxtures or sales area lighting, which are

By Michael Deru, Ph.D., Member ASHRAE, and Michael MacDonald, Member ASHRAE

Michael Deru, Ph.D., is a senior engineer at

the National Renewable Energy Laboratory in

Golden, Colo. Michael MacDonald is a staff

member at Oak Ridge National Laboratory in

Oak Ridge, Tenn.

The National Renewable Energy Labo-

ratory (NREL) is monitoring the Colorado

stores, and the Oak Ridge National Labo-

ratory (ORNL) is monitoring the Texas

stores. The construction and evaluation o

these stores are part o a commitment to

sustainability by Wal-Mart. The evaluation

also includes monitoring typical Wal-Mart

supercenters or a reerence case in close

proximity to the experimental stores.

In Texas, the experimental store and

the reerence comparison store are in

McKinney, north o Dallas. The Colorado

stores are in the Denver metro area, with

the experimental store in Aurora and the

reerence store in Centennial.

periments using recycled materials and energy-saving technologies.

Over the three-year period from 2006 – 2008, the performance of

the experiments will be evaluated and lessons learned generated.

The following article was published in ASHRAE Journal, October 2007. ©Copyright 2007 American

Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. It is presented for educational

purposes only. This article may not be copied and/or distributed electronically or in paper form without

permission of ASHRAE.



Octobe r 2007 ASHRAEJourna l 23

on dimming circuits. The same fxtures are used around the

perimeter o the sales oor but are not dimmed. Most o the re-

mainder o the interior lighting also is 4 t T8 uorescent lamps

with some incandescent and HID lights. Daylight harvesting in

the sales oor area is achieved with rectangular dome skylights

and an aggressive control strategy. Wal-Mart has about 300 mil-

lion t2 (2.8 million m2) o similar daylit space. In addition, the

peak lighting power is limited to 75% to 80% o the installed

capacity in the sales oor area, and the sales oor lights are

turned o during the day when there is adequate natural light.

Wal-Mart has started implementing the peak lighting powerlimit on a larger scale, but the typical store lighting energy in

Table 2 does not have this peak power limit in place.

The McKinney store uses the standard Wal-Mart skylights

and layout as shown in Photo 1. The interior lighting or the

sales oor and perimeter o the sales oor use single lamp 4 t

T5HO fxtures. In February 2007, a hybrid solar lighting (HSL;

www.ornl.gov/sci/solar) system was installed in the electronics

area. The rootop dish tracker-collector is shown in Photo 2. It

is too early to report results rom this experiment.

The Aurora store uses 5 t (1.5 m) T5HO lamps in the sales

oor area at a 15 t (4.5 m) spacing and 4 t (1.2 m) T5HO lamps

around the ront and side perimeters. The perimeter lights alongthe back o the store are eliminated in the design. In addition,

the perimeter lights are dimmed to 60% during the day.

The Aurora store incorporates a dierent strategy or collec-

tion o natural light with the addition o three large north-acing

clerestories (Photo 3) and skylights. The combination o the

large clerestory windows and skylights increases the aperture

area by 3.5 times the standard Wal-Mart design, which provides

more daylight but increases the envelope load on the building. In

addition, active solar tracking skylights and tubular daylighting

devices (TDD) are installed in the rear o the store. The TDDs

provide daylight to the break room and layaway areas, which

have drop ceilings and typically do not have natural light. The

active solar tracking skylights contain mirrors that track the

sun to reect the direct sunlight into the store. These mirrors

are rotated with motors in the skylight dome that are powered

by their own small solar electric panels. These skylights are

located in the receiving area at the rear o the store and mixed

with some o the standard Wal-Mart skylights.

Table 1 presents a summary o the experiments in the two

stores. Table 2 shows the measured energy data, and Table 3

lists some observed results and issues with the experiments.

Both stores show improved perormance over the typical Wal-

Mart store, with Aurora showing a 17% energy savings and

McKinney showing an energy savings o 13%. The Coloradoreerence store implements the peak lighting limit o 75% on

the sales oor lights and has annual energy consumption or the

sales oor and perimeter lights o 0.76 GWh/yr, which is better

than both experimental stores. The nighttime lighting energy

use in the Aurora experimental store is higher than in the typi-

cal Wal-Mart store because the lights in the high ceiling areas

o the clerestories must be kept on at a high level to maintain

even illumination on the oor.

Wal-Mart has been aggressive in reducing energy use or

lighting the sales oor area. It continues to adjust the control

strategies to improve perormance and reliability o the lighting

systems. The Aurora store shows Wal-Mart can save additional

Photo 1: McKinney supercenter uses the standard Wal-Mart skylights and layout. Photo 2: HSL collector and standard Wal-Mart skylights.

Photo 3: The Aurora store has our north-acing clerestories.




Aurora Experiments Description

T5HO lamps

5 t T5HO lamps are used in the sales oor area with 15 t spacing

between rows compared to the standard 12 t. Four oot T5HO

lamps are used around the ront and side perimeter area o the

sales oor.

Sawtooth Roo With

North-Facing Clerestory

Windows

Three large sawtooth structures provide north-acing clerestorywindows and sloped roo or photovoltaic panels.

Alternative Skylights

Tubular daylighting devices (TDD) provide daylight to the break

room and layaway areas. Active tracking skylights are installed

in the receiving area.

Focused Lighting

Over Produce

The ocused lighting over the produce was lowered and lower

wattage metal halide bulbs are used rom the standard design.

McKinney

ExperimentsDescription

T5HO lamps4 t T5HO lamps are used in the sales oor and around the pe-

rimeter o the sales oor.

Hybrid Solar LightingIn February 2007, a hybrid solar lighting (HSL) system was

installed in the electronics area.

Reduced Produce

Lighting

Overhead lighting was replaced with a lowered track lighting

system with low light levels (20 c) to reduce light intensity on the

produce and increase reshness and shel lie.

Table 1: Lighting experiment list.

ExperimentAurora McKinney Typical

GWh/yr GWh/yr GWh/yr

Sales Floor Lighting 0.71 0.65 0.76

Perimeter Lighting 0.08 0.18 0.19

Sales Floor and Perimeter Lighting 0.79 0.83 0.95

Table 2: Lighting energy results.

lighting energy by improving the lighting

systems and controls in the remainder o

the store.

LED Refrigeration Case Lights

The uorescent lighting in rerigerationcases have been replaced by 5000K LED

lighting. The McKinney store has frst

generation lights at about equivalent e-

fciency to uorescent lighting, while the

Aurora store has ourth generation LEDs.

While LEDs have a lower efcacy than

uorescent lamps, the ability to ocus the

lights directly on the products and the

better color rendering allows or about

hal the installed lighting power (Photos

4a and 4b). An additional experiment at

Aurora was to place a motion sensor on

one aisle, which turns on the case lights

only when the aisle is occupied. A ull-

scale test o the LED lights with motion

sensors was carried out by Wal-Mart at

a dierent supercenter and was so suc-

cessul that it is now part o Wal-Mart’s

standard design.

The LED case lights at McKinney

were not expected to have energy sav-

ings and no (or very small) savings have

been observed. The LED case lights at

Aurora have shown an energy savings

o 0.13 GWh/yr or 62% energy savings.An additional beneft to the LED lights

is the longer lie and associated lower

maintenance costs.

Renewable Electricity Generation

Both experimental stores have installed

photovoltaic (PV) systems and a 50 kW

wind turbine. The Aurora store has three

PV systems with a total installed capacity

o 135 kW and the McKinney store has

our PV systems with an installed capac-

ity o 57 kW. The PV systems at Auroraare typical roo mounted systems on the

sloped areas created by the sawtooth roo

structure (Photo 5).

One o the systems at Aurora is a ex-

ible thin flm that is adhered to the troughs

o the standing-seam metal roo. The PV

systems at McKinney provide experi-

ments with integrating the PV panels in

the architecture such as vertical mounted

(Photo 6 ) and glass integrated PV cells.

The wind turbines are mounted on 120

t (37 m) poles (Photo 7 ). A summary o

the systems with predicted and measured

perormance is shown in Table 4.

The PV systems at Aurora are perorm-

ing reasonably well with no maintenance

or intervention required over the last year.

Some problems occurred in the beginning

caused by an installation error that kept

two o the systems out o service or

several months until the problem was

corrected. The PV systems at McKinney

are also perorming close to the predic-

tions, except or the roo-mounted amor-

phous system, which is much lower than

expected. The wind turbines at both ex-

Photo 4a and 4b: While LEDs have a lower ecacy than fuorescent lamps, the ability to

ocus the lights directly on the products and the better color rendering allows or about hal

the installed lighting power.



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perimental store sites are, in a sense, frst-

o-a-kind, with the usual developmental

improvements that are ound necessary.

Electricity production has been reduced

by signifcant downtime, which has re-

sulted rom a range o issues, including

needing a stronger structural tower, highwind tilt-up mechanism malunctions,

and inverter ailures. An additional is-

sue at the Aurora store is that the wind

resource at the store is lower than what

was expected rom the designers.

Conclusion

Monitoring the experimental and pro-

totypical Wal-Mart stores has provided

several lessons rom systems that work

very well and systems that need improve-

ments. Lessons reinorced by these ex-

Photo 5: Aurora crystalline and thin lm

PV systems.

Photo 6: Crystalline PV array at McKinney.

Photo 7: 50 kW wind turbine.

Aurora Experiments Results

T5HO lamps

Incompatible lamp/ballast combinations were corrected with

relamping and dimming o the 5 t T5HO lamps. This is working

well. The revised perimeter lighting design and control strategy

saves 0.1 GWh/yr.

Sawtooth Roo With

North Facing Clerestory

Windows

Provides improved daylighting and more open eeling in some

parts o the store, but also introduces uneven lighting conditions.

Nighttime lighting energy use is increased because lamps located

in the high ceiling areas are required to be on at a higher level to

provide the same illuminance on the oor. The large clerestory

windows increase envelope loads.

Alternative Skylights

TDDs save 2.5 MWh/yr and provide natural light to the break

room and layaway spaces. The tracking skylights are placed

adjacent to standard skylights. No savings or other perormance

improvement estimations have been made.

Focused Lighting Over

Produce

The lower wattage lamps reduce energy consumption by 64%,

but do not spotlight the produce as well.

McKinney

ExperimentsResults

T5HO lamps

Ballast issues caused difculties or 4 t lamps (ballasts cause

coating boil-o at low power, which reduces lamp lie and

limits turndown i reasonable lamp lie is to be retained). The

workaround on the dimming limitation in McKinney means the

lamps are dimmed to 30% and held there until they can go o

completely. This means lamps are not dimmed below 30%, so

some savings are lost. The peak power limit is the primary reason

or the savings.

Hybrid Solar Lighting Testing on this system has not begun.

Reduced Produce

Lighting

The store manager, who has been there since the store’s opening,

indicates he receives regular comments rom customers about

produce being resher. However, other managers have indicated

they do not like how dim the produce area is.

Table 3: Lighting experiment issues and results.

Aurora SystemTotal Rated

Peak Power

Expected Annual

Production (MWh)

Measured Production

(MWh)

Front Roo-Mounted

Crystalline50 kW 63.0 56.2

Rear Roo-Mounted

Crystalline52 kW 61.0 60.3

Rear Roo Integrated

Thin Film33 kW 41.3 31.0

Wind Turbine 50 kW 94.6 7.18

McKinney System

Garden Center

Polycrystalline11.0 14.6

13.1

(However, metering prob-

lems have occurred.)

Roo-Mounted

Amorphous BIPV4.6 5.7 2.2

Curtain Wall Crystalline

And Amorphous

34.4 kW

Crystalline25.9 24.1

Flat Roo-Mounted

Thin Film6.8 8.3 8.3

Wind Turbine 50 kW 80.024 or irst 12 months

and 21 or last 12 months

Table 4: Renewable electricity experiment list.



Octobe r 2007 ASHRAEJourna l 27

periments or the lighting and renewable

energy systems include:

The standard Wal-Mart lighting and

skylight design or the sales oor area

is highly efcient, and the control sys-

tem works well, saving 0.27 GWh/yrin lighting energy compared with no

daylighting controls and no nighttime

dimming.

Further improvements in the Wal-

Mart lighting design are possible by

considering a redesign o the perim-

eter lighting around the sales oor, as

demonstrated in Aurora, and looking

at all the lighting in the other parts o

the store (the sales oor and perimeter

lighting energy are roughly 60% o

total interior lighting energy).

The use o T5HO lamps does reduce

the number o installed lamps by about

hal and can provide adequate lighting.

However, ballast/lamp combinations

still need some refnement. Energy sav-

ings over 4 t T8 lamps have not been

demonstrated with these experimental

stores, although the peak limit on

lighting power appears workable and

important to use or typical installed

lighting.

On-site electricity generation with PV

panels works well with little interven-tion once the systems are properly

commissioned. An automated moni-

toring system should be installed to

provide notifcations when the system

is down or when a ault is detected.

Nighttime parasitic energy use by

the inverter and isolation transormer

should be eliminated. This energy use

can total 5% to 10% o the energy

production rom the systems.

The wind turbine experiments have

not been successul due to severalmaintenance problems and a lower than

expected wind resource.

Wal-Mart has committed to improv-

ing the sustainability o their overall

operations. The work on the buildings

and sites is just one o 14 internal eorts.

The operation o the their buildings

represents two-thirds o the greenhouse

gas (GHG) ootprint, and they are

committed to making a large impact in

this area. Their goals or the building

operations is to reduce the energy use

•

•

•

•

•

and GHG emissions in existing stores

by 20% and by 30% in new construction

compared to their 2005 baseline. They

have made signifcant progress on both

goals, especially on new store designs.

The best part o all this is that they areactively sharing the lessons learned and

reaching out to work with other retail-

ers and expert groups like ASHRAE so

that everyone can reach the same level

o savings. Several initiatives between

Wal-Mart and ASHRAE are getting

under way. Wal-Mart is serious about

introducing more sustainable actions inbusiness and in the everyday activities

o their customers.

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Wall Mart Experience

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