Energy Recovery, Inc., a San Leandro, California (U.S.)-based manufacturer of pressure-exchanger devices, is “very close” to marketing a pressure exchanger designed to significantly improve the efficiency of transcritical CO2 (R744) refrigeration systems in high-ambient-temperature locations.

The transcritical CO2 pressure exchanger device, model PX G1300, uses high-pressure gas from the gas cooler to boost the pressure of low-pressure flash bypass gas, explained K.C. Chen, vice president of engineering for Energy Recovery. The now higher pressure gas can then be channeled back to the gas cooler rather than to the medium-temperature compressor, thereby saving energy.

Energy Recovery has determined that the PX G1300 can boost the efficiency (COP) of a standard transcritical CO2 system by up to 50% at 90°F (32.2°C).

The device consists of only four pieces, a rotor and three stators containing an array of channels arranged around the axis of the rotor.

With the design of the system in place, the company is in “the early stages of engagement” with potential commercial partners – CO2 refrigeration OEMs,” said Chen. “We are very close to going to market.” He added that the PX G1300 will be “competitively priced.”

Energy Recovery has marketed its pressure exchanger technology over the past 30 years in the desalination industry. The device can recover up to 60% of otherwise wasted energy in the seawater reverse osmosis (SWRO) desalination process, noted Chen.

Approached by national lab

Energy Recovery decided to develop the refrigeration application after being approached by Oak Ridge National Laboratory, which had done research into using a pressure exchanger to improve the efficiency of a CO2 refrigeration system.

Chen describes the PX G1300 as “almost like a revolving door” facilitating a direct pressure-to-pressure exchange of energy, with a high pressure stream elevating the pressure of a low-pressure stream. “And you can adjust how fast the door turns to accommodate different cooling capacities,” he said.

At the same time, high-pressure gas is also allowed to become low-pressure coolant channeled to the liquid receiver.

The PX G1300 would be an alternative to existing technologies that enhance the efficiency of transcritical CO2 systems in warm climates, such as an ejector or a parallel compressor. According to Efficient Energy, ejector technology typically manages “less than 200psi (14bar) of pressure differential boost,” while the PX G1300 “is able to manage an unlimited differential boost as required by the system, and therefore continues to perform as temperatures rise.”

Chen said that the PX G1300, by reducing energy use on transcritical CO2 refrigeration, “aligns with our ESG [environmental, social and governance] initiative completely.” Energy Recovery’s inaugural ESG report was recently shortlisted for “Best 1st Time Sustainability Report” by Corporate Register Reporting Awards, along with eight other corporations.

The PX G1300 works “almost like a revolving door.”

K.C. Chen, Energy Recovery