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Power Line shows supermarkets how to shop for energy savings

Editor's note: This is the first of two stories from the Power Line on energy efficiency measures grocery stores can use to control operating costs. Look for more tips for energy efficient grocery stores in the October Energy Services Bulletin.

For small rural electric cooperatives and municipal utilities, grocery stores can represent large key accounts, ones that are particularly vulnerable to fluctuating energy prices. A Western customer recently asked the Power Line, the Western-sponsored energy information clearinghouse, about ways to improve energy efficiency in a grocery operation. The Power Line responded with a wealth of suggestions, many targeting the food sales industry's single largest energy user.

Focus on refrigeration for big energy savings

The key to conserving energy in any business is knowing which operations consume the most energy. Like other businesses, lighting, heating and cooling and office equipment are a part of supermarkets' energy use profile. Typically, however, grocery stores use more energy for refrigeration than the other operations put together.

Several measures can reduce the cost of refrigeration. Some are inexpensive while others require a significant investment, but conservation in this area gives a double hit on savings. Cold air from refrigerated cases and walk-in coolers enters the store, increasing the energy needed to heat the building in winter so reducing refrigeration also translates to lower heat bills.

On the no-cost side, Energy Star offers the following refrigeration tips to help grocery stores save money and energy on refrigeration needs:

• Keep doors shut —Repeated fluctuations in temperature will damage food quality and cost money.
• Check temperature settings —If settings are lower than necessary, the system may be wasting energy. The most common recommended settings are between 14 degrees below freezing and 8 degrees below freezing Fahrenheit for freezers and between 35 degrees and 38 degrees Fahrenheit for refrigerators.
• Clean cooling and evaporator coils —Dirt accumulation impairs heat transfer and lowers the efficiency and capacity of refrigerators. Keep evaporator coils free of ice build-up. Don't forget the condenser coils, usually located on the building roof. Also, do not put a sprinkler on the roof to help cool the condenser coil, as domestic water contains mineral that can damage the coil.
• Check door seals —Tight seals and properly closing doors prevent warm air from entering the unit, which reduces cooling energy and prevents frost buildup. If a dollar bill slides easily into the seal, have the seal adjusted.
• Maintain equipment —Performing scheduled maintenance on any type of business equipment improves an operation's efficiency.

Simple changes prevent cooling losses

Taking common sense to the next level provides more refrigeration efficiency. Stores that do not operate 24 hours a day can save energy on their open-air cases by installing curtains to cover the case openings. This acts like a closed door on the case, sealing in the cold and significantly reducing the load on the refrigeration system.

When products are being moved to and from walk-in coolers, the doors are often left open for extended periods of time. Cold air flows into the store, creating a load on the heating system, while the refrigeration system tries to cool the space the heating system is warming up.

A simple solution is to add strip curtains. This minimizes the loss of cooling from the walk-in while the door remains open for staff and equipment to pass through. Since cold air sinks, the curtains should reach the floor to keep cold air from escaping at the bottom.

Automatic doors offer a more complete, but more expensive solution. The strip curtains should still be used with doors that close and open by a pull cord or button.

Lighting fixtures in older refrigerated cases can be big energy consumers. Many use high output ballasts because they work better at colder temperatures than regular ballasts. Try the new "cold weather" electronic ballasts that can be used with the lower wattage T-8 bulbs, measuring one inch in diameter, and 5/8-inch T-5 bulbs. These lower wattage bulbs often put out more and better quality light than older ones, and add less heat to the case. This savings potential could be as high as 10 percent.

System controls adjust energy use for operating conditions

Environmental conditions—ambient temperature, humidity, etc.—affect most electrical equipment and this is especially true of refrigerator units. Adding a variety of controller units to different system components can yield significant energy savings.

Refrigeration systems work by compressing and expanding a refrigerant. The pressure a compressor uses to develop is directly related to horsepower. So, the lower the pressure needed to cool to the desired temperature, the less energy used.

Most head pressure controls, as these are called, are set to a level that remains fixed regardless of the outside temperature. However, the system should not have to work as hard in cool weather since the condenser—the coil on the roof that cools the refrigerant—is in cooler air. By installing floating head pressure controls, the controller can automatically adjust downward as conditions allow for energy savings of 3 to 10 percent.

The condenser, which exhausts heat from the refrigeration system, and the evaporators that cool the walk-in cooler and product cases use electric motor-powered fans to cool the fins. High-efficiency motors do the same work with less energy. In the case of the evaporator, using less energy to move air generates less heat for the refrigerator to cool. Changing to energy-efficient motors can save between 5 and 13 percent per year.

Evaporator fans that operate continuously to mix cold air and distribute it to products also generate heat. Several manufacturers make controllers that reduce the fan motor's speed to minimize the heat when cooling is not needed. The fan continues running at a reduced speed until the thermostat calls for cooling. Then, it speeds up to blow air over the evaporator coils and cool the space. Contact the Power Line for more information about this equipment.

Many freezer cases have glass doors, which are excellent at saving energy and maintaining product quality. However, when the door is opened, moisture from the warmer store air condenses on the glass fogging it, so the product can't be seen. This is called sweating, and door manufacturers solve this by installing anti-sweat heaters to keep the door glass warm.

Glass fogs less during winter months and in dryer climates where the moisture content of the air is lower. Adjustable anti-sweat heater controls detect these differences in the environment and pulse the heaters on and off to save between 6 and 20 percent, depending on conditions. These controllers are relatively easy to install and can be adjusted automatically. In some cases, the refrigeration system may already have this feature and it just needs to be hooked up.

Western's Energy Solutions offers information specific to grocery stores and anti-sweat controls.

Refrigeration is only one area that offers grocery stores the opportunity for energy savings. In the October Energy Services Bulletin, the Power Line will focus on additional measures that can help utilities' large commercial customers cut costs and save money.