In 2015, Whole Foods contracted Unison Energy to implement a custom combined heat and power (CHP) system that could operate as a microgrid during utility outages. Roof-mounted to save space, this CHP system features two 160 kW reciprocating natural gas engines that cover over 85% of store energy needs and continue to operate even during grid failures, preventing costly food spoilage.
Moreover, the CHP system has proven to be an effective solution for running the store’s CO2 refrigeration system. CO2 is increasingly used for refrigeration because other chemicals are hazardous to the environment if a leak occurs. However, CO2 systems do require colder ambient temperatures — otherwise, they become less efficient and consume enormous amounts of power. Unison designed the Whole Foods CHP system to utilize the waste heat with a lithium bromide absorption chiller, which sends chilled water to the CO2 refrigeration system to keep it at its most efficient operating point.
The resulting system has an energy consumption rate of about 1.3 kWh/MBH, making it one of the most energy-efficient natural refrigerant systems that any Whole Foods has installed to date, according to a 2017 study. What’s more, this innovative solution for refrigeration earned a patent (Patent No. 9709302). The CHP system also integrates with the HVAC so that waste energy can heat water used in the store and the brewery.
Unison Energy worked closely with Whole Foods to ensure the project was a success not just for the store, but for the community as well. Because this Whole Foods location is surrounded by high-end apartments, it was critical that the store took steps to avoid noise complaints from the neighbors. Unison Energy installed sound enclosures that kept the system’s operating noise at just 55 db, a noise level that allows for normal conversation while standing right next to the equipment.
Tristam Coffin, Director of Sustainability and Facilities for Whole Foods Market, noted that using cogeneration to power the natural refrigerant-based system offers not just energy efficiency and “overall reduced consumption,” but also helps “sustain operations for the folks that are intending to sell broccoli in the stores,” even if the grid goes down. Thanks to Unison Energy, this Whole Foods location now has a resilient, efficient, and sustainable energy solution.