You may be switching off more lights and turning up your air conditioner's thermostat this summer, but if you're really serious about saving electrical energy in your grocery store, then you need the facts. Ramin Faramarzi, project manager for Southern California Edison's Refrigeration and Thermal Test Center in Irwindale, has them. Faramarzi and his group conduct research into energy usage in grocery stores and supermarkets. Average grocery stores use up roughly 50 kilowatt-hours per square foot per year (a kilowatt-hour is the amount of electrical energy consumed when 1,000 watts are used for one hour). This consumption rate qualifies them as "high usage," Faramarzi says.
Refrigeration is the biggest electricity sucker, accounting for 50 percent to 60 percent of the electricity a grocery store uses, Faramarzi says. (The other major energy users: lighting, 25 percent to 30 percent, and heating, ventilating and air conditioning, less than 10 percent.) Faramarzi points out that refrigeration equipment is not governed by any uniform energy-efficiency standard, at either the state or federal levels. Instead, he says: "You have to reluctantly rely on the manufacturer's claims. So, if I approach you today and claim my display case is more efficient, you wouldn't have any way of knowing it. There's a big vacuum of information." At the same time, in 1993 the U.S. Food and Drug Administration required stores to reduce the core temperatures of certain food products—dairy, deli, meat, fish and cut produce—to 41 degrees in order to protect against food-borne illnesses. "Not only do [retailers] have to deal with their existing energy challenges, now they have to comply with FDA requirements," Faramarzi says.
About 50 percent of the electricity that's used for refrigeration is expended on compressors; 35 percent on display cases, which includes fans, lights and door warmers; 9 or 10 percent on condensers; and the rest on other uses, Faramarzi says. His group conducted tests that found that 80 percent of the cooling load on an open vertical-type display case comes from the infiltration of warm air from the sales area into the case. "By that token," he says, "any type of measure or technology that can reduce infiltration of warm, moist air into the cold zone of a display case will be really beneficial. If we didn't have to cool display cases as much, we wouldn't have big compressors, big condensers and so forth."
For the sake of explanation, Faramarzi groups his recommendations for how a small-to-medium-size grocery store or supermarket (under 12,000 square feet) can save energy into four tiers, each building off the one before it. The first step is to reduce the cooling load. The second step is to improve operational characteristics of the store (including proper product loading and maintenance of store's temperature and humidity). The next step could be the replacement of refrigeration components with more efficient equipment. Finally, the entire refrigeration system could be upgraded. He likens his process to what someone would do if smoke suddenly began pouring through his building. "You'd control the problem at the source, that is, remove it," he says. "Then deal with the rest of the building by opening windows on the top floor. Controlling cooling load is like that."
Energy efficiency starts with reducing the cooling load on display cases, Faramarzi says. One simple way to do this is to install glass doors on open vertical fixtures. When the RTTC added glass doors to a vertical deli/dairy display case, its compressor needed 87 percent less electricity to do its job. What's more, the temperatures of the products inside the case fell 14 percent. In another test, night covers were used on a 20-foot deli/dairy display case for just six hours. The result: a 9 percent savings on compressor electricity use.
Product over- or under-loading a display case also wastes energy big time. Too many products crammed together can block airflow from the return-air grill, which inhibits cooling efficiency. Similarly, "cavities"—the result, for example, of shoppers removing two side-by-side cases of a product at the same time—also disrupt airflow enough to tax the cooling system. Even signs or products hung in the path of the "air curtain" within a display case waste energy. One RTTC test showed that when products were loaded properly within the specified load-limiting zones of an open vertical display case, the compressor consumed 6 percent less electricity, while the temperature of the products inside fell 28 percent.
Turning up the air conditioning may not be as important as lowering the humidity inside the store. That's because, when the humidity is high, the compressors in display cases are essentially being asked to dehumidify the air as well as chill it. They aren't very efficient at this task compared with air-conditioning compressors that should be doing the job. An RTTC study showed that when relative humidity inside a store was lowered from 55 percent to 35 percent, demand on the compressor of an open vertical-type display case containing meat fell 18 percent. In addition, there was a 62 percent decline in the amount of ice caused by moist air entering the case at the end of the day. Less ice means less drag on the compressor, and less energy spent defrosting.
So far these suggestions by Faramarzi have been relatively simple ones any store owner could initiate. Until these root-cause, cooling-load issues with display cases and operational characteristics are addressed, he doesn't see much point in spending money on more exotic equipment. However, for store owners who have gone beyond the basics, Faramarzi has suggestions that are more technical and do involve new equipment in the form of evaporators, fan motors, compressors, condensers, lighting and display case door materials. At the system level, for instance, he suggests a high-efficiency "multiplex" configuration of unevenly sized display case compressors and their controls. Let's say your 10,000-square-foot store has 20 display-case lineups. Traditionally, that means you need 20 compressors, one per display case lineup. A multiplex system would employ unevenly sized compressors that would serve sets of display cases that share the same temperatures. That way, hundreds of feet of meat or dairy cases could be cooled by just four compressors, each sharing the same suction and exhaust manifolds.
Even the smallest amount of money saved on energy is critical. Faramarzi cites a study by the Food Marketing Institute that reported the average profit margin for grocery stores from 1995 to 1996 was 20 percent. "That means that from every buck of sales, they made about a penny point-two," he says. "In a typical store, the cost of energy equals or exceeds profit. If you can improve energy consumption, you're essentially improving profit margin." For more information about energy efficiency—specifically geared to grocery stores and supermarkets—visit Southern California Edison's Web site at www.sce.com. At the home page, type in "rttc" in the search section.
Natural Foods Merchandiser volume XXII/number 8/p. 18, 20, 24