Arkansas HVACR NewsMagazine November 2025

HVACR NewsMagazine November 2025

Tech News

other hand, CO2 is an A1 refrigerant with a GWP of 1, but its operating pressures are very high. Despite those challenges, plenty of facilities successfully use these refrigerants. Several organizations offer training on these systems, and compressors that can handle the unique challenges of R-290 and CO2 already exist. Just as Copeland optimized their scroll compressors for R-32 and R-454B, they've designed scroll compressors for R-290 and subcritical CO2 (as well as semi-hermetic compressors for subcritical and transcritical CO2). R-290 scrolls sold in the United States come in vertical and horizontal varieties. Vertical scrolls for R-290 can be used in medium temp, extended medium-temp, and low-temp refrigeration. Horizontal scrolls are made for medium-temp and low-temp applications. The table below shows horizontal scrolls for A2Ls and R-290: R-290 Scroll Compressors

and vapor in its circuit, and it's common in low-temp refrigeration. Supercritical CO2 exceeds a temperature and pressure called the critical point, at which the temperature and pressure decouple, and is more common in medium-temp CO2 systems. Copeland's ZO scroll series is for low-temp subcritical CO2 systems, and their ZO(D) series specifically refers to their digital scrolls. Again, the CO2 only changes between liquid and vapor. In a booster system with medium temp and low-temp refrigeration, the subcritical CO2 will be compressed and discharged into the medium-temp circuit with CO2 from the medium-temp evaporators and bypass valve (shown below).

Credit: Copeland

In a hybrid cascade system with HFCs, the discharge CO2 goes to a heat exchanger that gives off some of that heat to the medium temp HFC circuit.

Credit: Copeland

CO2 Scroll Compressors

CO2 refrigeration is a unique beast, so I'll leave you with THIS tech tip if you want to learn more about it, but the main thing you need to know is that you may deal with subcritical or supercritical operation (or both). Subcritical CO2 only changes between liquid