Grocery stores make good candidates for commercial and industrial (C&I) demand-response (DR) programs primarily because energy costs remain one of the highest expenses in these facilities. Grocery stores can earn financial incentives by shifting load to backup generators, curtailing HVAC and lighting systems, and shutting down refrigeration systems. Additionally, because DR events occur while customers are inside the store, grocery stores like to publicize their participation. Stores can announce it over the public address system and post signs around the store that explain the social and environmental benefits of the program. Grocery stores may boost customer retention by participating in a green initiative.
Grocery stores operate all day and into the late afternoon and evening. Utilities tend to peak later in the midafternoon during summer, so grocery stores will be active participants in DR programs because their loads, which will be at full capacity during the event, can provide curtailment.
The largest electricity users in grocery stores are, in decreasing order: refrigeration, lighting, space cooling, and office equipment. Grocery stores are at a slight disadvantage when participating in DR events compared to other commercial sectors because refrigeration is their largest electric load and they need to maintain proper temperatures to preserve their product. However, grocery stores are able to reduce refrigeration loads by reducing the number of compressor cycles that are run. Additionally, grocery stores can reduce HVAC and lighting loads through a building automation system (BAS). Large grocery stores may also have backup generation systems that facility operators may dispatch, although less than 10 percent of all grocery stores in the U.S. have backup generation.
A large supermarket in New York achieved a noticeable load reduction by participating in a DR program (Figure 1). From noon to 6:00 p.m., facility operators turned off anti-sweat heaters, raised thermostat setpoints, turned off one-third of the overhead lights, and dispatched backup generation.
Depending on local building codes, grocery stores have performance requirements that may limit their DR participation. For example, in some states grocery stores must monitor ventilation rates to meet indoor air quality requirements, such as ASHRAE Standard 62, “Ventilation for Acceptable Indoor Air Quality.” Their refrigeration units must also maintain proper temperatures because their products need to meet health-code and shelf-life requirements. Lastly, grocery stores have to balance the humidity in the store to control condensation: Excess condensation fogs refrigeration doors—preventing customers from seeing products—and can damage refrigeration equipment.
Grocery stores can use a number of load reduction strategies to reduce demand. These focus on lighting, thermostat setpoints, refrigerated cases, backup generation, load shifting, and employing a BAS.
Turning off lights. Although grocery stores are concerned about lighting their product, they can still use a couple of strategies to reduce lighting loads. First, the store can reduce lighting loads by turning off every other row of lights. Staff can also turn off lighting in special-purpose areas, such as window displays, stockrooms, offices, and other peripheral rooms. These strategies can be conducted either manually or through a BAS. Turning off lights can typically reduce a grocery store’s total peak load by 5 to 8 percent (Table 1). In New York, for example, a grocery store with a total peak load of 375 kilowatts (kW) reduced its peak load by 30 kW by turning off one-third of its lights.
In addition, grocery stores can significantly dim overhead lighting by using dimming ballasts. Studies conducted by the Lighting Research Center at the Rensselaer Polytechnic Institute show that building occupants usually cannot detect lighting level reductions of up to 20 percent. Turning off lights also reduces cooling and refrigeration loads, which can provide cooling and refrigeration demand relief during summer.
Adjusting the thermostat. During a DR event, facility operators can increase thermostat setpoints to decrease cooling demand. Some DR programs offer day-ahead notification of events, allowing facility operators to warn employees that indoor temperatures may be somewhat higher on the day of the event. However, building control designers claim that people can tolerate a temperature rise of up to 2° Fahrenheit (F) over a four-hour period without feeling inconvenienced and often without even noticing. Grocery stores can typically reduce their total peak load by 5 percent just by increasing the thermostat setpoint by 2°F.
Turning off anti-sweat heaters. Anti-sweat heaters are found in glass display doors and refrigerated cases to prevent condensation on the glass and ice buildup on door gaskets. Condensation on the glass obstructs product viewing. The latest anti-sweat heater controls can sense humidity in the store’s ambient air and reduce operation of anti-sweat heaters in low-humidity conditions. Turning off the anti-sweat heaters for short periods during a DR event may not cause display cases to fog. Demand savings can range from 5 to 10 kW for a grocery store that has 30,000 to 50,000 square feet of floor space. Note that if anti-sweat heaters are controlled with humidistats, this strategy will not be applicable in low-humidity climates or in grocery stores with dehumidification systems because the anti-sweat heaters will likely already be turned off.
Shutting off refrigerated cases. Store owners are likely to resist this strategy initially. However, in some situations, facility operators can completely shut down refrigeration fans, pumps, and compressors for several hours without damaging products. Thermal insulation in the walls of the refrigeration unit can prevent thawing and temperature creep. Facility operators need to monitor refrigeration equipment to ensure that temperatures remain below regulation levels and grocery store staff must be prepared to end curtailment if temperatures rise too rapidly. Additionally, staff can shift inventory to empty some of the refrigeration storage units in the back of the store—allowing the store to shut down those empty units.
Switching to on-site generation. Some grocery stores have on-site backup generation to keep refrigeration units running during power outages. These customers are good candidates for DR programs that allow shifting building loads onto backup generators. Switching to backup generation is usually immediate, so it causes no interruptions to service. The capacity of backup generators found in grocery stores typically varies from 15 to 25 kW.
Shifting processes off peak. Certain processes in a grocery store can be performed before a curtailment event or delayed until after the peak. For example, facility operators can schedule electric forklift charging and food preparation for off-peak hours.
Using a building automation system. A BAS uses sensors and controllers to monitor and optimize temperature, humidity, and lighting levels while minimizing the energy use of fans, pumps, HVAC equipment, lights, and refrigeration equipment. A BAS can be programmed to curtail predetermined loads upon notification from the utility (either day-ahead or early the same day), eliminating the need to manually adjust equipment. Most modern BASs are web-based—meaning that chain grocery stores can have one energy manager control loads in several stores remotely, rather than having one manager at each store. BASs are found in some grocery stores and they can typically reduce total demand by 10 percent. In addition to reducing demand, a BAS optimized for energy savings can also reduce a store’s overall energy consumption by 5 to 15 percent.
Albertsons, one of the largest grocery store chains in the U.S., installed automated DR systems in 264 stores throughout California. The average store size is just over 50,000 square feet. During the summer, the average peak demand is about 420 kW per store. The California Energy Commission provided $1.8 million in incentives to help cover the $3.3 million cost of installing the automated systems.
During a curtailment event, Albertsons’ corporate energy managers use web-based communications to send DR curtailment signals to each store’s BAS. The BASs then dim overhead lights by up to 50 percent (35 percent is typical), turn off refrigerated display case lighting, and turn off anti-sweat door heaters. Albertsons is able to achieve an average load reduction of 20 kW per store using these three load reduction strategies—providing an aggregate load reduction of 5.4 megawatts.
In addition to reducing demand on the grid, the upgraded automation systems provide Albertsons with some additional benefits. For example, the BASs provide comprehensive feedback about each store’s energy use, which helps the company track demand reductions during DR events and also track energy use throughout the year to reduce the overall energy consumption of a store. For example, Albertsons was able to reduce overall consumption by 60 megawatt-hours annually by upgrading lamps and ballasts and by adding motion detectors.
Facility Type: Supermarkets and Grocery Stores, (PDF) Energy Star Building Upgrade Manual, U.S. Environmental Protection Agency and U.S. Department of Energy
Managing Energy Costs in Grocery Stores, E Source Business Energy Advisor