“We challenged Hill Phoenix to come up with a design that would reduce our use of refrigerants by an amount that would allow us to meet GreenChill Platinum standards,” said Jerry Stutler, vice president, construction and facility engineering for Sprouts.

“Sprouts is on a quest not only to provide consumers with fresh and organic products in a unique shopping format, they also are working to reduce their global carbon footprint from every aspect,” said Tom McFarlane, regional sales manager for Hill Phoenix.

“The challenge was to reduce HFC emissions, increase energy efficiency, and control cost.”

Stutler further explained, “Before we got involved with GreenChill, we were averaging about 2,000 pounds of refrigerant in our systems. Then we reduced that by about 60 to 65 percent with our stores that are GreenChill Gold-certified. This new CO2 design yields an even more significant reduction in HFCs.”

He added, “The main goal at Thousand Oaks was to reduce the risk of leaking HFC into the atmosphere, and secondly, to reduce the cost of our initial refrigeration charge. And finally, we wanted to reduce our potential exposure to costly catastrophic leaks in our systems.”

According to GreenChill, most of the 35,000-plus supermarkets in the United States use centralized direct expansion (DX) systems to chill their products. Typically, these refrigeration systems are charged with 3,000 to 4,000 pounds of refrigerant and can leak more than 20 percent of their charge each year. Commonly used refrigerants include HCFCs and HFCs, both of which have issues related to global warming if a system is leaking.

GreenChill Platinum Award certification requires the use of only non-ozone depleting refrigerants, meaning no HCFCs. In addition, the store must achieve an average HFC refrigerant charge of no more than 0.5 pounds of refrigerant per 1,000 Btuh total evaporator cooling load and a store-wide annual refrigerant emissions rate of no more than 5 percent.

An Answer

In collaboration with Sprouts’ construction and facilities engineering team, Hill Phoenix designed and manufactured an R-744 (CO2) cascade system for both low-temperature and medium-temperature applications (branded as Second Nature MT2LX). The systems consist of two independent refrigeration systems that share a common cascade heat exchanger. The upper-cascade system is a reduced charge HFC system that cools the CO2 in the lower cascade. The HFC system rejects heat to ambient through the condenser, in this case an air-cooled, microchannel condenser.

According to the manufacturer, advantages of this condenser design include:

• Refrigerant charge reduction. “Microchannel coils offer a high primary to secondary surface area ratio, providing very efficient heat exchange while maintaining a low internal tube volume. As a result, the microchannel condenser reduces condenser refrigerant charge by over 70 percent.”

• Energy efficiency. “Microchannel air-cooled condensers feature very efficient variable-speed EC motors. These motors vary speed based on system requirements to provide optimal energy and sound performance.”

• Environmentally friendly. “Units feature 100 percent recyclable, all-aluminum coil.”

According to Tom Kilroy, inside sales engineer with Hill Phoenix Systems division, “It was really important that we were able to utilize air-cooled condensers. Nobody in the industry really thought that you could earn a Platinum Certification with air-cooled condensers. Otherwise you would need a separate condensing loop, pumping station, and an expensive fluid cooler on the roof.”

The design combines two systems into one unified system that is designed, manufactured, and installed specifically to meet the GreenChill Platinum requirements that Sprouts set for its Thousand Oaks store.

The system consists of a low-temperature CO2 cascade compressor system combined with a medium-temperature CO2 secondary coolant system. According to Hill Phoenix, benefits include:

• CO2 is considered a natural refrigerant with very low global warming potential (GWP=1).

• CO2 is an inexpensive, widely available refrigerant compared with HFC.

• A more than 70 percent reduction in HFC refrigerant charge can be achieved. The entire primary refrigerant charge is confined to the machine room and condenser to enable simple leak detection and servicing.

• The lines required for CO2 transport are typically one to two sizes smaller than traditional DX piping systems, reducing the weight of installed copper lines by 50 percent or more and reducing installation costs.

Each system (low temp and medium temp) within the cascade system uses a different refrigerant that is most suitable for the given temperature range. CO2 is used as a secondary coolant for the medium-temperature system and as a DX cascade refrigerant for the low-temperature system.

The advantages of a cascade system include a reduction in the refrigerant charge and a reduced carbon footprint. Since the HFC refrigerant is confined to the primary system located in the machine room, the total refrigerant charge and the potential for leaks are greatly reduced.

“Hill Phoenix’s project with fellow GreenChill Partner Sprouts is a perfect example of what companies can do when they take the GreenChill spirit and push the boundaries of the achievable,” said Keilly Witman, manager of EPA’s GreenChill Partnership.

“This store represents many firsts including the first CO2 cascade system to achieve platinum and the first platinum store west of the Mississippi.”

Energy + Emissions Savings

The Thousand Oaks location earned its GreenChill Platinum Award in May 2011. Current and anticipated energy and emissions savings include:

• The system uses 900 pounds of CO2 and reduces the total store HFC charge by 72 percent to 235 pounds.

• The expected total carbon footprint reduction is 2.4 million pounds over 10 years.

• The estimated reduction of HFC usage over 10 years is 1,155 pounds.

• The more energy-efficient system is expected to yield a 5 percent reduction in energy consumption.

• There is an 11 percent reduction in leaks over a standard DX system, saving more than 115 pounds of refrigerant per year. And HFC refrigerants have been eliminated entirely from the sales floor.

• The elimination of all mechanical thermal expansion valves (TXVs).

“It‘s tough to put a dollar value on the potential payback for this investment. If we had a catastrophic leak in our old system, we could have leaked 2,000 pounds of refrigerant. Multiply that by $10 per pound to recharge the system,” said Stutler. “With today’s system, we only have the potential to leak 235 pounds of refrigerant.

“Certainly we’re hoping to save money over the years, but how do you put a dollar amount on the value of being green, reducing your carbon footprint, and improving the overall system performance?”

Publication date: 11/07/2011