A Piggly Wiggly store in Columbus, Ga., using an NH3/CO2 cascade system has cut its energy consumption by 33% on average – for a total of $74,640 in savings – over a 13-month period compared to a similar store using HFC refrigeration.  

The savings derives, to a significant extent, from the ammonia/CO2 cascade system, according to Keith Milligan, CIO of JTM Corp., which owns the store. The system – only the fourth ever installed in a U.S. supermarket – has been used in the store since it opened in September 2015.

Milligan was a participant in a webinar hosted by the U.S. Environmental Protection Agency’s GreenChill Partnership on 6 December that provided an overview and update on the store’s NH3/CO2 cascade system. A profile of the system appeared in the September issue of Accelerate America magazine, published by shecco.

The period over which the store’s energy performance was measured covered October 2015 to October 2016. In an earlier analysis of the store’s overall energy consumption, conducted from October 2015 to April 2016, the Piggly Wiggly store consumed 23% to 33% less energy than the conventional HFC outlet, for an average energy savings of 28.5% ($33,170 in savings).

Milligan acknowledged in the webinar that “not all of the savings was from refrigeration” – some came from LED lights, skylights and other measures.

However, the energy savings from the refrigeration was found to be significant. In an analysis of the store’s NH3 rack and an HFC rack installed in the store for comparison purposes, Heatcraft Worldwide Refrigeration, manufacturer of the system, found that the NH3 rack consumed 22% less energy on average than the HFC rack, ranging between 18% and 25%, depending on ambient temperature; the analysis was done between February 2, 2016 and May 22, 2016.

“[This project was] an engineer’s paradise.”

Eric Nelson, CTA Architects Engineers

Eric Nelson, engineer and project manager, CTA Architects Engineers, who also participated in the webinar, explained the role CTA played in independently verifying the equipment installation and energy calculations made at the Piggly Wiggly store. CTA began its analysis about six months after the store opened.

CTA was given remote access to the system’s controller so that it could review measurements and set points. The combination of energy models and actual energy data from the store made this project “an engineer’s paradise,” Nelson said.

The store alternates using its NH3 rack and HFC rack every one to two weeks to allow energy measurements and comparisons to be made. However, there could be ambient weather differences and case load variations from week to week, which would detract from the “apples-to-apples” nature of the comparison. To compensate for these potential variations, CTA “normalized” the evaporator loads and ambient temperatures, said Nelson.