Wal-Mart experiment showcases sustainability for retailers
A 50-kW wind turbine is one of 50 sustainable measures being tested at Wal-Mart's SuperCenter in Aurora, Colo.
A retail chain best known for its low prices has launched a project to make its name synonymous with sustainable operations. Wal-Mart opened an experimental SuperCenter in Aurora, Colo., Nov. 9, and it boasts 50 different tests of environmentally friendly building materials, energy-efficient systems and renewable energy.
The 206,000-sq. ft. department and grocery store is intended to evaluate the cost-effectiveness of those measures in a working setting. It is the second such facility the company has built. The first, located in McKinney, Texas, has 26 sustainable features and is 10 percent more efficient than a typical Wal-Mart SuperCenter. The Aurora store is designed to be 20 percent more efficient.
"The company's goal is to make its operations to build a prototype that is 25 to 30 percent more efficient and reduces green house gas emissions by 30 percent within four years," said Aurora Store Manager Charlie Harris. "The experiments at this store will help us figure out how to get there."
Laboratories monitor results
The National Renewable Energy Laboratory believes that other big box retailers can benefit from Wal-Mart's experience, too.
NREL installed data acquisition systems in the Aurora store and a conventional SuperCenter nearby in Centennial, Colo. For the next three years, the laboratory will collect and compare information on energy and water use in each store to find out how much energy the measures are really saving. Oak Ridge National Laboratory is doing a similar study on the McKinney store.
"It's one thing to want to build a green facility, another thing to actually get it built and something else again to run the building," said Senior Engineer Paul Torcellini, project leader for NREL. "Part of our involvement is to close that loop, to help others beyond Wal-Mart."
Ron Judkoff, director of NREL's Buildings and Thermal Systems Center, added, "What makes this project especially interesting to us is the potential for large-scale replicability of the energy-saving features."
Wal-Mart hired a team of consultants to help the company take energy efficiency to a new level, and approached NREL afterward to monitor the results. The NREL team helped with researching some of the proposed measures, but was otherwise not involved in the building design. "That way, we could be totally objective in our evaluation," explained Senior Engineer Michael Deru, project manager.
Lighting technology offers many benefits
The lighting experiments are probably the measures that shoppers—and other retailers—are the most likely to notice.
The saw-tooth roof design creates three rows of clerestory windows, bringing natural light into the shopping area. Several different types of tubular skylights such as Solatube and So-Luminaire on the roof redirect sunlight down a highly reflective tube, through a diffuser that spreads it around the interior space. A dimming system adjusts the lighting to supplement the natural light. At night, the system reduces artificial light levels at the entrances and in parts of the main floor to help customers’ eyes adjust to the change of light when going in and out of the store.
An existing facility would require extensive retrofits to duplicate the SuperCenter’s use of daylighting. However, some of the other lighting strategies could increase efficiency and improve marketing for a smaller investment. The main store lighting system uses smaller, more efficient T5HO lamps. One of the high-output, linear fluorescent lamp replaces two of Wal-Mart’s standard T8 lamps and uses about 15 percent less energy. Its light more closely resembles natural daylight, improving customers’ ability to see the merchandise.
The store’s lighting fixtures have been placed 12.5 feet above the produce, instead of the usual 18 feet, and use lower wattage lamps that illuminate the fruits and vegetables in truer colors. LED fixtures light the grocery and jewelry cases, saving electricity and maintenance and improving the product displays. The lighting energy savings for the Aurora SuperCenter are projected to be between 350,000 and 450,000 kWh annually.
Store runs on conventional, renewable energy
Wal-Mart is testing power supply technologies that may find wider use once other retailers start seeing the results. Although the systems focus mainly on efficiency, a 50-kW Bergey wind turbine will provide about 1.25 percent of a typical SuperCenter's annual electricity needs.
The passive solar wall on the SuperCenter's south face boosts the store's heating system by warming outside air before drawing it into the ventilation system.
Additional electricity is generated by three types of photovoltaic panels—single crystalline, edge film growth and amorphous—mounted on the roof and on parking lot signs. Also, the building’s south face is covered with perforated metal siding that warms outside air by 10 to 20 degrees. The air rises to the top of the passive solar wall to be drawn in by the ventilation system.
A grid-tied, natural gas-fired cogeneration plant generates electricity, provides backup power and recovers and re-uses waste heat. The highly efficient system includes six 60-kilowatt microturbines, an absorption chiller plant and a cooling tower. The designer chose indirect evaporative cooling instead of energy-intensive air conditioning to cool the store.
In cold weather, a radiant floor will keep customers and employees comfortable. Water from two waste oil boilers and heat recovered from the cogeneration system heats the floor. The boiler uses cooking oil from the store’s deli and motor oil from the automotive center for fuel. The efficiency of radiant floor heating made it a good choice for the auto center, the cash register aisles, and the refrigerated grocery section.
Systems protect comfort, air quality
Another reason shoppers won’t catch a chill in the refrigerated foods aisle is that most of grocery cases have doors. First tested in the McKinney store, the measure keeps cold air in and reduces energy use. “One of our vendors was concerned that doors would make his product less accessible,” said Harris. “It turned out that refrigerated food sales actually rose 22 percent at that store.”
Also, the refrigeration system in medium temperature cases uses 35-percent propylene glycol. The use of this secondary low-pressure refrigerant cuts the amount of greenhouse gas-producing, high-pressure refrigerant in the system by half. The technology also reduces the chances of leaking high-pressure refrigerant into the atmosphere.
DuctSox are another innovation that adds to comfort and protects air quality. Perforated fabric tubes mounted 11 feet overhead disperse air all along their length, instead of through a single register. When the airflow is cut off, the tubes deflate and the dust that usually accumulates on hard ducts settles to the ground where it can be swept up. Designers chose white tubes to reflect the daylight cascading through the clerestory windows.
Project includes consumer education
All this efficiency comes with a cost, but the company did not release the figures. “The SuperCenter is more of a lab where we can look at as many different measures as possible and see what offers the best return,” explained Harris.
Wal-Mart plans on sharing the learning experience, too. Large green signs on the floor tell customers about the store’s many experiments, while kiosks at the main entrances reports on how much electricity the systems are generating and saving.
Interested individuals in other parts of the country won’t have to wait for the NREL report. Wal-Mart has posted an interactive Web site for the Aurora view2.fatspaniel.net and the McKinney walmartfacts.com stores, where visitors can follow the progress of the experimental SuperCenter and monitor its systems.
Not all of those systems will make the cut—that's why it is called an experiment. However, Wal-Mart officials say that the technologies that prove to save energy and money and are good for the environment could start showing up in future stores and retrofits as early as next year.
Whatever the results, the SuperCenters have already taught Wal-Mart and other retailers one lesson: How building owners, scientists, engineers, architects, contractors and landscape designers can work together to create stores that appeal to shoppers and protect the environment.
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