Danfoss ejectors gain traction

Global component giant Danfoss continues to promote its CTM multi-ejector, which won the 2017 AHR Expo Innovation Award in the refrigeration category.

Working with a parallel compressor in a transcritical CO₂ system, the ejector saves between 10% and 20% on energy consumption (depending on the ambient temperature) compared to a conventional booster transcritical system, said James Knudsen, segment manager, food retail for Danfoss, who spoke to R744.com at the FMI Energy & Store Development Conference in late September.

The multi-ejector contains up to six ejectors of varying sizes, allowing it to modulate to different ejectors depending on load demands.

“The ejector is where most of our conversations start because it expands the [geographical] range [of transcritical systems],” he said, referring to the ability of the ejector to improve the efficiency of a transcritical system in a warmer climate, where it is more prone to operate in supercritical mode.

To date, the unit, which can serve as a gas or liquid ejector, is commercially available only as a gas ejector.

A Sprouts Farmers Market store in Woodstock, Ga., that opened in June became the first U.S. store to operate a transcritical system (from Hillphoenix) equipped with the Danfoss ejector. “Everything’s running fine,” reported Knudsen, adding that the transcritical system’s energy consumption is being studied.

Other U.S. food retailers are asking about the ejector, particularly for southern locations, he said. “And all OEMs have samples in their labs.”

In Europe, where transcritical systems are far more prevalent, about 150 stores are employing transcritical systems with the ejector, added Knudsen.

Knudsen delved into the way the ejector operates. In receiving CO₂ emanating from the gas cooler, “[an ejector] acts as an expansion valve,” he said. Knudsen added that in lower temperature subcritical operation, “it’s two-phase because there’s liquid and gas coming off the gas cooler.”

The ejector receives gas from the medium-temperature suction line and diverts it to a receiver where it combines with flash gas. “The flash gas is at a higher pressure so you can compress it using less energy,” he explained. “That’s where the energy savings comes from.” The combined gases go to the parallel compressor – “a lower-energy compressor.”

The ejector, he added, is “just a pressure pump – you can use it anywhere you need a pump.” As a liquid ejector, it diverts liquid from a flooded evaporator that might otherwise make it back to a compressor.