| Wal-Mart's Experimental Store Offers Futuristic Peek at Retail HVAC Systems
Wal-Mart’s new experimental Supercenter in McKinney, Texas, proves American ingenuity is not dead. Some of the nation’s best engineers produced state-of-the-art innovations when the 3,720-store chain challenged them to create what is perhaps the most environmentally conscious and energy efficient retail store on the planet.
The store boasts many emerging technologies ranging from bioswales for naturally cleaning parking lot rainwater, to wind turbine and solar energy generation. However the HVAC and refrigeration systems are expected to produce some of the store’s greatest energy savings, according to a Wal-Mart spokesperson.
The HVAC system, which consists of a fabric duct system from DuctSox, rooftop units by AAON Inc., and make-up air dehumidification by Munters Corp., is estimated to save approximately 600,000 kwh of electricity per year or enough to power about 60 single family homes for an entire year.
The system utilizes displacement ventilation concepts to efficiently heat and cool the store, according to Sean Timmons, P.E., principal, Timmons Design Engineers, a San Francisco-based engineering firm that team-engineered the store’s mechanical, electrical and plumbing (MEP) innovations with Shaun Landman, P.E., associate principal, ARUP Electrical & Mechanical Engineers, San Francisco. ”Wal-Mart came to us (engineers associated with the design) with a request to push the envelope in energy conservation and environmental consciousness,” said Timmons, whose 11-year-old firm specializes in sustainable MEP design.
Typical Wal-Mart Supercenter HVAC systems in southern states require approximately 450 tons of cooling and the air is distributed through with metal duct/register systems mounted near the ceiling. The McKinney store’s cooling is 380 tons. Much of the 70 tons of reduced cooling tonnage is a result of displacement ventilation on the sales floor made possible by fabric duct, according to Timmons, because mounting the one linear mile of DuctSox fabric duct only 11 feet above the sales floor cools the bottom half of the store where it’s needed most.
The DuctSox have a linear array of holes that deliver supply air at a draft-less low velocity and moderate temperature of 65-68º F. After gently falling to the floor and mixing with air warmed by occupants and other heat sources, the air rises slowly to the upper levels of the store. Ceiling mounted return registers recycle the air back to the rooftop units where it is mixed with outdoor air and conditioned again.
“We were attracted to the DuctSox product as it gave us a relatively inexpensive air delivery for an overhead displacement ventilation system without the inclusion of expensive displacement diffusers,” said Timmons. Following a CFD analysis, we determined the ideal height and supply air temperature to maintain a 72º F comfort temperature within the main sales floor areas. Supplying air at 65º F allows us to increase the amount of free cooling during the swing months.”
The fabric duct also makes an environmental impact because hundreds of tons of metal weren’t used for the duct system. Additionally, energy usage and labor during construction was reduced by half because the ductwork required half the man hours needed for metal duct installation, according to Michael Schloeman, vice president, CBS Mechanical Inc.
The store utilizes other innovations as well. Heat is recovered from the parallel compressor racks supplying refrigeration to the freezer and refrigerated cases by Hill-Phoenix. The process provides free water heating via a Bryan Boilers 1.2-mbh boiler that supplies domestic hot water for the bathrooms and an Uponor Wirsbo 93º F in-floor radiant heating system for comfort in the refrigerated/freezer aisles, entrance vestibule, cashier stations, and tire/lube area.
Waste cooking oil from the kitchen and waste motor oil from the tire/lube area is recycled, filtered, stocked in a storage tank, and used to power a 500,000-BTU EnergyLogic boiler which provides supplemental heating through reheat coils in the store’s make-up air handlers.
The energy-saving innovations go well beyond HVAC. The McKinney store is projected to save up to 300,000 kwh per year by using an ample amount of skylights and clerestories combined with light sensors and dimming controls that provide electric lighting only when needed. The reduction in electric lighting results in a lesser heat load for the air conditioning system to overcome.
Additionally, store lighting consists of smaller, more efficient, and optically superior T5HO high output linear fluorescent lamps. Instead of conventional fluorescent strip lighting, refrigerated case interiors use cooler LED lighting.
All store energy usage is monitored and controlled by a Novar Controls building automation system.
With the McKinney store and a second experimental store scheduled to open in fall 2005, Wal-Mart hopes to inspire the retail world to improve environmental sustainability. “These two stores will change how the industry looks a big box super centers,” according to Timmons. “Wal-Mart is challenging the industry to think outside the box. With the advent of self-power generation, stores will become grid independent in the future along with lower cooling, heating, refrigeration and lighting loads. These stores will have an immediate impact on the industry as rival stores will need to keep pace with Wal-Mart’s innovativeness in reducing the impact of super centers on the local environment and reducing operating costs over the long term.”
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