Lighting the Way

LED lighting coupled with occupancy-sensing controls have proved a winning and energy-efficient combination for Wal-Mart Stores. In a test, the system was installed in fall 2006 in the refrigerated cases of two stores near the chain’s headquarters in Bentonville, Ark. The energy savings proved so significant that the chain decided to retrofit cases in more than 450 existing stores in 2007.

The motion sensors, from WattStopper/Legrand, detect motion in the store aisles, turning the case lights on as a customer approaches the case. Soon after a customer leaves the area, the lights automatically turn off. The use of the sensors was made possible by switching from fluorescent lighting to LEDs (GE’s Lumination Refrigerated Display Lighting System) in the cases.

“Unlike fluorescent lights, LEDs can be switched on and off in cold temperatures without any loss of life expectancy,” said Ralph Williams, senior engineer, Wal-Mart Stores, who was in charge of the project.

In fact, he added, turning the LEDs off increases their lifespan so that the service life of the lighting will be as long as that of the refrigerated cases, virtually eliminating the need for maintenance. To maximize energy savings and LED life, the time delay for the sensors was set to the minimum of 30 seconds.

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Date loggers were installed in the two test locations to record on and off times over the course of six weeks. The results showed that the case lights remained off 44% of the time in one location, and 47% of the time in the second store. Based on the test, Williams concluded the chain could expect that by installing sensors, the LED case lighting would be off in excess of 40% of the time.

Energy savings: The total energy savings for the test installations was significant. Because the LEDs use far less power than the fluorescents, the connected load was reduced by 43%. Since the LEDs generate less heat than fluorescents, and no heat when turned off by the sensors, the compressors are not required to run as often to chill the cases.

The overall energy savings that resulted after switching from uncontrolled T8 fluorescent lighting to occupancy sensor-controlled LED lighting was 92%. The savings represent close to 3% of the total-energy usage of the supercenter.

As for customers, they have responded positively to the new lighting.

“Wal-Mart has experienced 100% acceptance of the sensor control of the LED glass-door lighting,”Williams said.

In addition, the new lighting has improved product visibility and the sensor control has added an element of theatricality that appeals to customers.

The cost of replacing the fluorescent lighting with LEDs and sensor controls will be paid back in approximately two years. The facilities will also benefit from reduced maintenance costs.

The new system has significant environmental benefits as well. By reducing energy usage, the new lighting helps lower greenhouse-gas emissions.

Supercenter Is Super Efficient

In January, in Kansas City, Mo., Wal-Mart Stores opened the first in a series of high-efficiency stores that will use 20% less energy than a typical facility (a second store has since opened, in Rockton, Ill.). The locations are designed to bring the retailer closer to achieving its environmental goals, which include opening a facility that is 25% to 30% more efficient by 2009.

The Kansas City store, a 197,000-sq.-ft. supercenter, is the first to bring some of the innovative technologies featured in Wal-Mart’s two eco-experimental stores in McKinney, Texas, and Aurora, Colo., from the preliminary testing phase to a practical-trial phase. The 20% reduction in Kansas City was achieved primarily by targeting two big energy-consuming units: the heating, ventilation and air-conditioning system (HVAC), and the refrigeration system.

Specifically, the HVAC and refrigeration are fully integrated so that 100% of the heat rejected by the refrigeration system is reclaimed into the HVAC. The reclaimed heat is then converted into usable energy. By incorporating a loop-piping design, the advanced refrigeration system also reduced the amount of installed copper and the total refrigerant charge required.

“For years, retailers have used air-cooled equipment for air conditioning and refrigeration,” said Charles Zimmerman, VP of prototype and new format design, Wal-Mart Stores, Bentonville, Ark. “In recognizing that water has four times the heat-carrying capacity of air, we realized it would be much more efficient as a conductor of energy in our heat, cooling and refrigeration systems.”

Wal-Mart is putting this idea to the test in Kansas City, Zimmerman added, by utilizing on-site resources to full capacity before applying secondary power resources. The store’s other energy-saving technologies include ultra-efficient case fans, a daylight harvesting system and glass doors on medium-temperature grocery cases.