Overhead cost containment is critical to the profitability of food stores; however, properly refrigerating food products is at least as important. As ambient temperatures rise, refrigeration systems must run longer to reject heat, which increases energy usage. Furthermore, the cooling capacity falls, sometimes to the point where it may become inadequate to satisfy the load.
Roche Bros. is a high-end food store chain based in Wellesley, Massachusetts. Recently, in the chain’s Westwood, Massachusetts, store, management upgraded its older air-cooled condensers to hybrid Baltimore Aircoil Co. Inc. (BAC) Trillium Series Condensers. The goal was to improve the peak ambient performance of the store’s refrigeration systems and lower its energy use. Trillium Series Condensers are particularly well-suited for food stores, which have a continuous need for refrigeration and are very energy-conscious.
In October 2015, hoping to improve the performance and efficiencies of the location’s refrigeration systems, Roche Bros. installed two Trillium Series Condensers in its Westwood store. Prior to the installation, Eversource, the electric utility company serving Westwood, commissioned an independent study of the energy savings to be achieved through the units. Based on the results, Eversource provided a generous incentive to Roche Bros. for the installation of the Trillium Series Condensers. The following report provides the details of this installation and describes the benefits that have been achieved.
THE BAC TRILLIUM SERIES CONDENSER
At its heart, the Trillium Series Condenser is an air-cooled system that rejects its heat to ambient air drawn by fans across condenser coils (heat exchangers). The Trillium Series Condenser is unique in that its older-style horizontal condenser coils have been replaced with vertically mounted aluminum microchannel coils that provide greater heat rejection with a lower refrigerant charge. Its evaporative cooling media have been mounted to the outside of the heat exchangers. Under high ambient conditions, water flowing across the media evaporates into the condenser air, thereby lowering its temperature and increasing heat rejection.
To minimize water use, water that is not evaporated is recirculated over the pads and then flushed to drain at the end of each day. With no standing water, chemical/biological treatment is not required. Trillium Series Condensers also run in its dry mode the majority of the year, only using water when the ambient temperature rises above a predetermined set point. This minimizes water consumption. Low-efficiency fan motors typically found in air-cooled condensers have been replaced with high-efficiency, ultra-quiet electronically commutated (EC) fan motors with integral variable-speed drives. This can reduce fan energy use significantly, depending on the ambient conditions.
Additional energy savings are achieved as the refrigeration systems are now able to run under lower head pressures during upper ambient conditions. Finally, Trillium Series Condensers are durable, lightweight, easy to support, and mostly recyclable.
The refrigeration at Roche Bros. Westwood is provided by three rack systems with a combined capacity of 125 ton. Prior to the retrofit, these were connected to three air-cooled condensers.
On hot summer days, these systems often suffered from insufficient cooling capacity, elevated head pressures, and increased energy usage. To minimize these problems, water sprinklers were placed under the condensers. This greatly increased water and sewage costs.
Eversource commissioned Boyko Engineering of Gorham, Maine, to study the proposed retrofit. The study projected annual savings of 232,093 kWh and 35.6 kW at a total project price of $155,825. Eversource provided a rebate incentive of $75,000, leaving Roche to pay the remaining $80,825. While the projected payback was 2.17 years, since the condensers were in need of replacement, the actual payback was about one year.
The installation began in September of 2015 and was completed in approximately four days with the original condensers being replaced by two Trillium Series Condensers. The retrofit process was greatly simplified by the fact that the units have a vertical coil configuration so they required a minimal amount of space. As a result, the existing supporting steel was more than adequate.
The first two days of work were spent running the refrigerant piping, power wiring, and control wiring to the area where the Trillium Series Condensers would reside. With cold weather approaching, Roche held off on bringing water to the units until April 2016. Because of the preparation work, it was only necessary to shut down each refrigeration system for approximately two hours. When the installation was complete, several more days were spent modifying the controls and tweaking their operation.
After five months of winter operation, Christopher Rasys, director of facilities, Roche Bros, observed that on the warmest days, the condensing temperature of the refrigerant has typically been within 2°F of ambient. By comparison, the original air-cooled systems typically ran 15°-20° above ambient. Compressor manufacturers’ data suggest that this 20° reduction will lower compressor energy use by about 20 percent while substantially increasing cooling capacity. Additional energy savings are being achieved as a result of the standard-efficiency condenser fans being replaced by high-efficiency EC fans. Since the EC fans have integral variable frequency drives (VFDs), their speed is reduced as the ambient temperature falls. Also, additional savings are realized. While the original three air-cooled condensers were connected to three 15-A breakers, the two Trillium Series Condensers only required one such breaker. Other than at peak ambient, the fans typically run at a reduced speed and draw very little power.
Rasys points to the substantial benefits Roche Bros. has achieved by upgrading to Trillium condensers. “This is the third store we’ve converted,” Rasys said. “In the other two, by comparison to air-cooled condensers, we experienced improved upper ambient performance and more efficient refrigeration system operation. Because of this, we decided to retrofit the condensers at
Westwood. Over the first five months of operation, we’ve been very pleased.”
Ivon Louis-Letang, program manager of energy efficiency at Eversource, noted Trillium Series Condensers are helping the utility to achieve the comprehensive savings goals. “They are providing cost-effective refrigeration energy savings, which, until recently, has been difficult to achieve. This is important to our food store customers and of great benefit to our program.”
Content courtesy of Marc Sandofsky, partner, RetroCoolEnergy Services Inc., on behalf of Baltimore Aircoil Co. Inc. Contact him at 508-545-1176 or firstname.lastname@example.org.
Publication date: 10/10/2016