On average, grocery stores use about three times more energy per square foot than average retail spaces, with much of the use going to refrigeration. To help cut energy costs, future-proof against volatile energy markets and increase resiliency, Whole Foods Market is testing a Refrigeration Battery at a store in Los Altos, California.

“Thermal storage is not necessarily something new by any means but what [our supplier] has done is put together a very intelligent architecture to manage a significant load for grocery stores and other like facilities,” said Tristam Coffin, director of sustainability and facilities for Whole Foods Market.

“When we’re able to save our customers $30,000 in utility costs, that has the same bottom-line impact of $1.5 million in additional sales. That is like adding an additional month of sales to the calendar year.”

–Amrit Robbins, president and co-founder of Axiom Exergy

Whole Foods runs the system from noon until 6:00 p.m. on weekdays. So far, the system has demonstrated its ability to generate savings of 50 to 120 kilowatts during peak hours, and Coffin expects to see even greater savings going forward.

“Thermal storage solutions can make refrigeration systems smarter or able to respond to fluctuating grid conditions and electricity pricing, which can help refrigerated facilities avoid peak energy pricing. Grocery stores are being penalized for energy use and paying about five times more for power during peak periods of the day,” said Amrit Robbins, president and co-founder of Axiom Exergy, the company supplying battery storage to Whole Foods.

U.S. grocery stores operate on slim margins, with net profits after taxes of less than 1.5 percent, which makes reducing energy costs even more important, the Food Marketing Institute said.

“They are spending a tremendous amount on energy and most of that goes to refrigeration,” Robbins said. “When we’re able to save our customers $30,000 in utility costs, that has the same bottomline impact of $1.5 million in additional sales. That is like adding an additional month of sales to the calendar year.”

Even as the price of energy has fallen over the past few years, peak demand charges have increased. In California, for example, peak charges have increased by 8 to 12 percent per year in recent years, Robbins said.

THE TECHNOLOGY

During a recent webinar produced as part of EPA’s Green Chill program, Axiom said it offers a bolt-on retrofit that transforms existing refrigeration systems into low-cost, cloud-connected thermal batteries. “We make it possible for the first time to actively manage refrigeration systems,” Robbins said.

A standard, regular battery, either lithium ion or lead acid, stores electricity using electrochemistry. In contrast, Axiom’s Refrigeration Battery freezes tanks of saltwater at night when energy is inexpensive. It then uses the frozen tanks to supply cooling services when energy prices skyrocket during peak-use periods. As a result, supermarkets can turn off all their medium-temperature compressors and condensers for six-toeight hours at a time.

The system also has a proprietary cloud platform that intelligently manages fleets of assets using remote monitoring, data analytics, diagnostics and operational controls. “Rather than trying to sell our customers a big stack of batteries, we transform their existing refrigeration and air conditioning systems into low-cost, intelligent, cloudconnected batteries,” Robbins said.

Axiom said the battery can meet medium-temperature refrigeration needs. In an average store, the batteries can reduce peak electricity load by 40 percent.

The battery systems arrive on site fully pre-assembled. “The most timeconsuming part is installing the coolant loop between the system integrator and thermal storage tank,” Robins said.

EMERGENCY RESPONSE SOLUTIONS

During a power outage, perishable food can start to spoil in under two hours; Robbins said that Axiom’s Refrigeration Battery can keep food cold, which can mitigate the risk of food spoilage during a power outage.

“We found that some of our customers are even more excited about the backup cooling application than they are about energy cost reductions,” he said. “The holy grail for grocery stores when it comes to resilience is keep the doors open and keep selling groceries even after the power goes out. We get them 55 percent of the way there.”

Coffin agreed. “Resiliency is a very, very important conversation we need to be focused on more often than we are,” he said, referring to not only catastrophic events but also to brown-out and black-out situations.

The average grocery store contains about $368,000 worth of perishable goods at any time. “A single power outage can be very, very painful,” Robbins said.

Axiom Exergy’s batteries can provide hours of backup cooling, Robbins said. In order to function during a power outage, the thermal battery storage is paired with a small battery to power the pump, an Internet connection and the evaporator fans in display cases or walk-in evaporators.

THE FUTURE

Coffin said battery technology is gaining new relevance. “In California, our grid is becoming cleaner, but we’re still using carbon-based energy sources. Anytime you can reduce demands on the overall grid, there are environmental benefits,” Coffin said.

The grid is becoming more and more volatile over time, which is making energy storage solutions more valuable, Robbins said.

Whole Foods is looking at other locations to roll out and wants to include the refrigeration battery in new construction, and he said it could be used in stores with natural refrigerants. “Although the current refrigerant is a HFC refrigerant and that has been the focus to date, there is a lot of opportunity to pilot with natural refrigerants,” Coffin said.

The system currently works with HFC refrigerants, but Axiom plans to bring other refrigerants onboard.

Thermal storage could enable the use of CO2 in hot climates by relieving the stress on CO2 transcritical systems during higher-temperature days, Coffin said.

Axiom’s first fully-installed unit was at the Whole Foods location, and a second pilot is under construction at a Walmart in southern California. “Next year we plan to roll out another fiveto-10 units,” Robbins said, adding that the company is exclusively focused on supermarkets, but the technology is applicable to every step of the cold chain.

Certain states have more volatile energy pricing, and Axiom is currently focusing on 12 states. “California is the most obvious because it’s right in our back yard,” he said.

While Whole Foods experienced a 50-kilowatt reduction in use during peak times, Coffin and Robbins believe that could hit upwards of 125 kilowatts going forward.

During some of the testing, they weren’t maximizing the system’s potential. “This is a pilot for them and us. We understood going in that this was a pilot and there was going to be some lessons learned.”