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Energy savings. Lighting represents about 13 percent of the electricity consumption in a food sales establishment, not including its impact on cooling loads. Lighting retrofits can save 30 to 50 percent of lighting energy as well as 10 to 20 percent of cooling energy.
Best practices. Competition is pushing stores to create an inviting and exciting shopping experience, which is greatly enhanced by good lighting design. Products need sufficient illumination to attract the attention of shoppers, though care is needed to protect some products from being overheated.
A mixture of light sources inside a grocery store can create an attractive and comfortable environment that accentuates and visually enhances products, thereby driving up sales revenues. A blend of direct and indirect electric lighting can provide soft and uniform illumination. Diffused daylight is particularly attractive lighting for fresh produce and also creates a pleasant background for focused lighting on packaged products. Electric lighting should be coordinated with a daylighting scheme or adjusted in response to it.
The Illuminating Engineering Society of North America (IESNA) sets illumination standards by task. These standards focus on requisite lighting levels; therefore, they do not emphasize daylighting or other energy-saving opportunities. It is also of note that with a good daylighting design, the range of illumination levels can vary more widely than the levels recommended for electric-only scenarios, without negative repercussions.
Daylighting. For many years, grocery stores were designed to let in as little natural light as possible because of concerns that strong glare from sunlight would not only increase the interior cooling load and damage product but also interfere with bar-code scanners. However, properly diffused daylighting has been shown to avoid both of these negative results and offer many benefits. Rather than clear windows and skylights that introduce heat and glare into a supermarket, tints and glazes can be used to diffuse the natural light, creating a pleasant ambience. Combined with appropriate supplemental artificial light, daylighting can provide optimal illumination and color rendering for product displays. Products and people tend to look better under warm natural light, which has a higher color temperature than the artificial lighting usually used in supermarkets. Grocery store interior designers are changing their attitude about daylighting primarily to improve product appearance and customer experience, so energy savings is a welcome bonus.
Daylight offers two measurable benefits over electric lighting in grocery stores. First, it can save energy by reducing the need for electric lights. Of course, in order to reap those savings, artificial lights must be removed or turned off in response to daylight levels. For example, the supermarket chain Stop & Shop/Giant Food uses energy-efficient T5 fluorescent lighting that dims in response to daylight as one of its energy-saving strategies.
Second, there is some evidence that natural daylight can improve retail sales. A study published in 2003 and sponsored by the California Energy Commission looked at sales in 73 stores belonging to one retailer, 24 of which had a significant amount of daylighting. The study showed that the average effect of daylighting was to increase sales by up to 6 percent. It also found that stores with more hours of useful daylight per year are associated with a greater daylight effect on sales. Researchers concluded that daylighting could boost sales wherever color is among the key selection criteria for products.
Daylighting can be implemented as a retrofit with skylights and light pipes, a relatively low-cost solution that delivers light from roof- or exterior wall–mounted collectors through reflective tubes. Skylight fixtures and light pipes with diffusers can be designed to look like fluorescent fixtures. They can be laid out in a grid, similar to fluorescent lighting, to distribute illumination evenly. Giant Eagle, winner of an ENERGY STAR sustained excellence award, uses skylights for daylighting in its facilities.
Electric lighting. Because electric lights remain on for extended periods of time, substantial savings can be found by making improvements to lighting systems. Many supermarket owners have already upgraded their lighting systems at least once. But auditors continue to find new and overlooked lighting opportunities in supermarkets, even in regions where attention to energy savings has skyrocketed along with energy prices in recent years.
CASE STUDY: Stater Bros. Retrofits with Light Pipes
Concerned about rolling blackouts caused by California’s energy crisis in 2001, Stater Bros. retrofitted six stores with tubular skylights from Solatube to provide backup lighting. Recognizing the energy-saving benefits, the company later installed 164 Solatube light pipes in a new 43,000-square-foot supermarket in Chino Hills, California. During most daylight hours, this free lighting source replaces nearly all of the artificial lighting in the store. Integrated photosensitive controls modulate supplementary artificial lighting in zones throughout the store relative to natural light from the light pipes. This daylighting system is estimated to cut the store’s lighting energy costs in half.
For storewide ambient lighting, efficient linear fluorescent lighting, either T5 lamps or high-performance T8 lamps, can reduce energy consumption by 35 percent or more compared to T12 lighting (as discussed in Chapter 6). In high-bay areas and big-box stores with ceiling heights greater than 15 feet, high-performance T8 and high-output T5 lamps are the most efficient approaches. However, some grocery store owners prefer the look of semispherical metal halide fixtures. In those cases, ceramic metal halide fixtures with electronic ballasts are a good choice. They combine high efficiency with superior color quality.
Supermarkets can also save energy by reducing ambient lighting levels and using spotlighting to attract customers to product displays. Spotlighting can be done with energy-efficient compact fluorescent lights and spot reflectors to direct the light.
For parking and outdoor applications, high-intensity fluorescent (HIF) lighting is often a more efficient choice than high-intensity discharge (HID) lighting. HIF fixtures can provide more even illumination with fewer fixtures than HID lights. To maintain their light output, HIF lamps should be enclosed when used outdoors in cold climates.
Induction lamp technology is a good choice in areas where relamping and maintenance are difficult or hazardous, such as in high-ceiling stores, parking garages, and exterior pedestrian lighting. These products typically have long lifetimes (up to 100,000 hours, compared to 24,000 hours for HID lights), which means infrequent relamping. Moreover, they offer good lumen maintenance, compact construction, and vibration resistance. Induction lamps can start at temperatures as low as –40°F with no delay and operate at those temperatures without significant loss of lumens.
Light-emitting diodes (LEDs) are a good light source for several supermarket applications. In addition to the common exit-sign retrofit, LEDs are also an efficient alternative to neon lighting for grocery department signs.
LEDs additionally offer some advantages over fluorescent lamps for refrigerated-display-case lighting. The most important feature is that they perform very well in cold temperatures, unlike fluorescent lamps, for which light output drops appreciably with temperature. LEDs are directional in nature, allowing light to be directed just where it is needed inside the case. Also, with fluorescent lighting most of the waste heat is dissipated inside the case, whereas the heat sink for an LED can be moved outside the case entirely, resulting in reduced refrigeration energy needs. In addition, a study conducted by the Lighting Research Center at the Rensselaer Polytechnic Institute found that customers perceived LED illumination in freezers to be “brighter, more even, more appealing, and more comfortable” than fluorescent lighting, even when the LEDs operated at a lower average light level than the fluorescent bulbs. Wal-Mart has announced plans to use LED lighting in the refrigerated display cases of 500 stores. The LEDs will be integrated with occupancy sensors and will automatically dim when no customers are nearby.
A good option for accent lighting of perishable goods is remote-source lighting, in which a single high-efficiency light source feeds multiple remotely placed fixtures via fiber-optic cables. The systems can be costly, but the ability to keep infrared radiation away from produce while still illuminating the goods in an efficient, attractive manner is a big plus.
Controls. Occupancy sensors save energy but also help to reduce maintenance costs by lengthening the relamping interval. In storage rooms, break rooms, offices, and restrooms, ceiling-mounted ultrasonic occupancy sensors can be used to detect occupants, even around partitions and corners. Food Lion installed occupancy sensors in break rooms and storage rooms as one of its first energy-saving measures (see sidebar). For areas that use daylighting, automatic dimming controls can be used to ensure that minimum light levels are met while saving energy. A photocell control can instruct outdoor lighting to turn on and off based on light levels, or an astronomical clock can be used like a timer and set to adjust automatically to daylight saving time.
Since 2000, through lighting, refrigeration, and HVAC retrofits and company wide energy management efforts, Food Lion has reduced its energy use by 27 percent. This total savings is equivalent to eliminating energy use entirely at 457 of its 1,200 stores. Lighting is a big part of this grocery chain’s energy-saving efforts. Food Lion completed a major lighting overhaul in 2003, swapping T-12 with T-8 fixtures and lamps across the chain. Energy efficiency was just one goal of the relamping effort. The new lighting systems also improve the quality of light, work environment, and safety, according to a regional maintenance manager at the company. They have also helped the company achieve ENERGY STAR status for over 700 stores. As the chain progresses toward its goal of earning the ENERGY STAR for every store, lighting upgrades will include T-5 and LED systems.
Energy savings. Load reduction measures that reduce the operational time or intensity of HVAC equipment while still maintaining a comfortable shopping and work environment can offer substantial savings. Refrigeration is by far the largest load in a grocery store, representing an average of 43 percent of supermarket electricity usage. Significant energy savings can be gained not only from regular refrigeration tune-ups and maintenance but also through retrofits and cost-effective replacements of older refrigeration equipment.
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