A new store in Europe will be the second retail location in the world to install a transcritical CO2 (R744) system that uses an integrated pressure-exchanger device to improve the efficiency of the system.
The device, known as the PX (pressure exchanger) G1300, is made by Energy Recovery, a San Leandro, California (U.S.)-based manufacturer of pressure-exchanger devices for several industries.
The PX G1300 will also be employed by Vallarta Supermarkets, a California (U.S.) chain with more than 50 locations, as a retrofit of an existing transcritical CO2 system in a store located in Indio, California.
Both installations will take place in 2022.
This update on Energy Recovery’s plans was provided by Joseph Marchetti, its Product Manager, CO2 Refrigeration, and Satyaki Das, its Director of Product Development, during a webinar at the ATMO World Summit on March 30. The event was organized by ATMOsphere (formerly shecco), publisher of R744.com.
“We are working with an OEM who has a presence in the North American and European markets to do a new system installation with the PX in a supermarket in Europe,” said Marchetti. “The planned installation is the middle of 2022.” The installation at the Vallarta store is scheduled to take place “in the next several months,” he added.
Energy Recovery is also working with “a number of parties” in the commercial refrigeration industry to integrate the PX G1300 device in current transcritical CO2 store installations, Marchetti said. Das added that the company is partnering with refrigeration OEMs to develop “the best possible configuration” for the device in a transcritical CO2 system.
Energy Recovery announced plans to install its pressure-exchanger device in transcritical CO2 refrigeration systems in June of 2021.
By reducing the load on compressors, the device can improve the efficiency of transcritical CO2 systems, particularly in warm ambient climates, where the systems otherwise could experience lower efficiencies as they enter transcritical mode. In addition to cutting energy costs, the devices can extend the life of compressors, Marchetti said.
According to Marchetti, the PX G1300 device can boost the COP of a transcritical CO2 system by 10% at 80°F (27°C) ambient conditions, with a gas cooler temperature at 90°F (32°C), and a capacity of 400MBH/34.1TR (120kW). Given the efficiency gains, the PX device is priced to deliver a “two-to-three year payback for the end user,” said Das, adding that he expects the device to last for at least 25 years – the lifespan of the devices installed in the desalination application.
The PX device can currently accommodate capacities of 205–409MBH/17.1–42.7TR (60–150kW), and pressures up to 2,030psig (140bar). “It is feasible to go much larger [in capacity] by banking PX’s together,” said Marchetti. “Or in a single housing, we can deliver up to 10 times [the capacity] fairly easily.” Thus the company sees opportunities for the device to be used in industrial transcritical CO2 applications.
Over the past 30 years Energy Recovery has installed thousands of its pressure-exchanger devices in the desalination industry, its largest sector. The device can recover up to 60% of otherwise wasted energy in the seawater reverse osmosis (SWRO) desalination process, improving the efficiency of the process, according to the company.
How it works
In the ATMO World Summit webinar, Marchetti explained how the CO2 PX G1300 device from Energy Recovery is able to improve the efficiency of the system.
In brief, the device harnesses the high-pressure CO2 fluid (liquid, gas or supercritical) coming from the gas cooler to increase the pressure of low-pressure suction gas coming from the evaporator and flash gas coming from the receiver. It then returns the now higher pressure gas to the gas cooler instead of to the compressors, reducing the work required of the compressors. This reduces energy costs and lengthens the life of the compressors, reducing Capex costs, said Marchetti.
The system requires a separate commercially available lift device to bring low-pressure gas to the PX device, and another lift device to bring high-pressure gas from the PX device to the gas cooler, each lift device contributing 2-3bar (29–43.5psig) of additional pressure to overcome line losses.
At the same time, the high-pressure fluid from the gas cooler exits the PX device as a low-pressure CO2 liquid/gas mixture, moving onto the receiver where the flash gas recirculates to the PX while the liquid is piped to the cooling load (evaporators).
Currently, a separate controller is used to control an electric motor in the PX device, thereby managing the rotational speed of the rotor the forms the core of the device. The controller, which also oversees the two lift devices, is linked to the transcritical CO2 system’s host controller; ultimately, Energy Recovery wants its controller algorithm to be part of the overall system controller.
By improving the efficiency of the lift devices, Energy Recovery expects to improve the overall efficiency of the PX system. For example, in the 400MBH system at 80°F ambient temperature, lift devices operating at 50% efficiency would enable a COP improvement of 19% rather than 10%, Marchetti said. Energy Recovery designed a similar pressure pump for its desalination application.
The PX G1300 device reduces the work done by compressors in a way similar to that of a parallel compressor. The PX G1300 also competes with other components designed to improve the efficiency of transcritical CO2 systems, such as ejectors and adiabatic gas coolers.
“We are working with an OEM who has a presence in the North American and European markets.”Joseph Marchetti, Energy Recovery
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