Adapted from an article originally published in the July issue of Illuminate Magazine. Used with permission.
Project: Sears Distribution Center
Tenant: Sears Holdings Corporation
Location: Stockton, CA
Architect: Ware Malcomb
Lighting Design: Exposure Illumination Architects, Inc.
Electrical Engineer: ACIES
General Contractor: Big-D Pacific
Photography: Exposure Illumination Architects, Inc., Cooper Lighting
In 2006, Sears Holdings Corporation concluded a year-long study to produce an outline of the ideal built-to-suit facility to support its distribution network, and decided to replace five of its older facilities with new state-of-the-art centers.
In 2007, the company engaged ProLogis, a leading global provider of distribution facilities, to build a LEED-certified 780,400-sq.ft. distribution center in Stockton, CA, the last of the five. The new distribution center would be used to store and distribute big items such as washers, dryers and refrigerators. ProLogis, in turn, engaged Ware Malcomb, an architecture and design firm.
“Sears wanted a reliable, low-maintenance facility that met its standards,” said Jim Terry, Director, Commercial for Ware Malcomb. “ProLogis wanted to provide an energy-efficient, comfortable, functional environment that was of higher quality than typical distribution buildings. Ware Malcomb utilized unique architectural elements, including a suspended trellis canopy, bold entry articulation and consistent architectural treatment—paint, panel massing, clerestory windows—across the entire façade to bring a level of quality not typically seen in a large distribution facility.”
For the lighting, ProLogis and Ware Malcomb collaborated with Scottsdale, AZ-based Exposure Illumination Architects, Inc. In the RFP for the built-to-suit facility, Sears specified a maintained 30-footcandle light level, which it believed would support an environment conducive to safe and productive work among the 28-ft.-high product storage bins. ProLogis wanted these needs satisfied by a highly energy-efficient lighting system consistent with the company’s leadership in sustainable warehouse design.
The result was one of the most energy-efficient warehouse buildings in the country, with an effective lighting power density of 0.18W/sq.ft.—78% less than the maximum prescribed by California’s Title 24 energy code.
“For lighting designers focused on energy conservation, getting in early in the process is critical, allowing us to take responsibility not just for the lighting and controls, but also the total daylighting solution,” said Daniel S. Spiro, AIA, IES, president of Exposure Illumination Architects, Inc. “This involves educating the owner and design team at the front end of the design process about energy savings potential. Later in the process, once budgets are set, it’s very hard to make a change.”
In working on previous warehouse projects with ProLogis, Exposure Illumination Architects favored hi-bay fluorescent lighting as an alternative to more traditionally favored metal halide for a number of benefits, most notably high energy savings. For this project, Spiro envisioned integration of fluorescent lighting and daylighting using advanced lighting controls to dramatically maximize energy savings.
After receiving the product storage bin layout plan from Sears, which showed the fixed locations of the bins in the 600,000-sq.ft. storage space of the building, the lighting designers specified approximately 16,000 linear ft. of Cooper Lighting’s Metalux MB Series T5HO Micro-Bay luminaires in 360-ft. linear rows mounted 32 ft. off the floor. Select luminaires were specified with emergency battery backup, providing mandatory illumination throughout the warehouse in the event of a power outage without the need for a backup power generator.
“The Micro-Bay luminaire’s profile is extremely narrow, which increased design flexibility,” says Spiro. “The building code required obstructions wider than 2 ft. to be at least 2 ft. away from sprinkler heads. By being less than 1 ft. wide, we were able to place the luminaire within 1 ft. of the sprinkler heads. We gained valuable flexibility in placement. The luminaire could be as close as possible to the aisle center as a result.”
The luminaire’s narrow profile also enabled the electric lighting to integrate with the building’s daylighting strategy by minimizing blockage of daylight entering the space through a series of skylights also aligned over the center of each aisle. Except on cloudy days, these 4-ft. by 8-ft. double-dome skylights by manufacturer Bristolite, which are placed 40 ft. apart on center and cover 2% of the roof area, are able to meet target light levels without requiring any electric lighting during the daytime.
“Over 90% of the space has daylighting via skylights and clerestory windows,” Terry points out. “While not typical in industrial and distribution buildings, from past Ware Malcomb projects where we’ve employed extensive daylighting design, companies have noticed low employee turnover and increased productivity. Daylighting creates employee connection to the outside environment.”
One of the primary advantages of fluorescent over metal halide is its instant-ON operation, making automatic energy-saving switching strategies much easier to implement. This allowed the lighting designers to go beyond producing desired light levels for fewer watts, and look at what additional savings controls could bring to the table. By specifying luminaire sections adjoined in continuous runs, multiple circuits could be installed along the run, enabling granular zoning of sections in the row to support different control strategies such as daylighting control and occupancy sensing.
A Cooper Controls Greengate lighting automation system, which controls all of the building’s lighting at the lighting panels, turns the lights along critical pathways and aisle entrances ON before dawn. For example, in the bulk storage area, 16-ft. luminaire sections located at the head of each aisle are switched and kept ON all day for safety reasons. The rest of the lighting in each row is divided into 40-ft. sections, each controlled by its own integral occupancy sensor. In the late afternoon, as falling light levels are detected, the control system restores power to the lighting circuits; the lights remain OFF, however, unless occupancy is detected by the connected occupancy sensor, which turns the lights ON in the immediate area.
As daylight levels increase on the following morning, raising ambient light levels above a target threshold (as preset for local zone photosensors installed in select skylights), power to the non-critical lighting circuits is cut off. Multiple photosensors are used, dividing the lighting into nine daylight control zones, increasing sensitivity and flexibility based on an understanding that lighting conditions may vary in different parts of the building throughout the day.
“Stockton benefits from 310 days per year of clear skies, 55 days with semi-cloudy conditions, and only 16 with overcast conditions,” says Spiro. “On an average day, between 9 AM and 5 PM, most of the electric lighting is OFF in the building, saving energy.”
Meanwhile, in the other major space in the building, the 134,000-sq.ft. dock bay/staging area, 2×4 6-lamp T5HO luminaires provide general lighting, dual circuited so that two lamps provide 33% light levels for security purposes at all times. The circuit feeding the remaining four lamps is energized only if insufficient daylight is available, such as on cloudy days or at night, and then only if occupancy is detected.
Sears, which benefits directly from the operating cost savings based on their lease with ProLogis, is enjoying a projected 2.75 million kWh/year energy savings, which adds up to significant annual cost savings—$399,000—based on a local utility rate of $0.145/kWh (compared to a standard HID solution complying with Title 24’s requirement of 0.8W/sq.ft. maximum power allowance).
Monitoring to date [May 2009] has confirmed projected savings, measuring an average $0.0225/sq.ft./month electrical operating cost (lighting plus battery chargers) for the four winter months. Savings are expected to escalate during the summer—when the sun angle is higher, daylight hours are extended and utility rates typically increase—which are expected to reduce energy costs to as low as $0.0125/sq.ft./month, says Spiro. Annual energy costs are projected at $0.20-0.22/sq.ft. The next highest energy-performing building in all of Sears’ warehouses is $0.34/sq.ft./year (the worst is $0.58/sq.ft./year).
After an incentive provided by the local utility, PG&E, reduced the incremental labor, material and design costs, the energy savings is expected to recoup the net cost in less than eight months—a return on investment of 154%.
“A relatively small increase in initial construction costs for adding skylights and clerestory windows can quickly pay for itself in electricity costs and employee well-being,” says Terry.
“I would summarize this project with a simple statement,” says Spiro. “More costs less.”