Rajan Rajendran: “CO2 can offer comparable system efficiency.”

The use of HC-744 (CO2) in compressors has gotten yet another boost with the announcement by Emerson Climate Technologies that it has launched Copeland Scroll® compressors designed for use with the refrigerant. Applications are for low-temperature sub-critical cascade systems.

Emerson’s announcement said the company is working with U.S. OEMs who serve the supermarket refrigeration industry to test R-744 systems. The announcement also noted the interest in R-744 as a refrigeration refrigerant in Europe because of global warming issues concerning HFCs and tougher regulations than in the United States.

“As a global company, we’ve kept a close watch on the use of CO2 as a refrigerant in refrigeration applications,” said Rajan Rajendran, director of applications engineering for Emerson Climate Technologies’ Refrigeration Division. “For all applications, we think the answer to minimizing environmental impact is still the use of high-efficiency equipment and the reduction of refrigerant leaks.

“CO2 can offer comparable system efficiency when applied in a subcritical cascade refrigeration cycle, which can be applied in supermarket applications.”

The product line was launched in Europe to positive feedback, the company said. The product has received UL approval in the U.S. and the company is shipping samples and sharing product information with OEMs. “The Copeland scroll compressor is hermetically sealed, eliminating possible leak points found in reciprocating compressors, such as gaskets and bolted joints,” Rajendran said. “This reduces the potential for direct refrigerant leaks. The compressor’s strong steel shell allows these compressors to withstand the high pressures associated with CO2 systems.

“The subcritical cascade system is one where the CO2 compressor compresses the gas to a higher pressure, that is, pressures similar to those encountered with R-410A,” he explained. “The high-pressure, high-temperature gas condenses to a liquid in a condenser. The condensing temperature is close to the standard medium-temperature application values in refrigeration. Then the gas is fed to an expansion valve, exactly like any vapor-compression refrigeration cycle-based systems.”

He differentiated this approach from the secondary-loop technology that uses CO2 in conjunction with another refrigerant. “In secondary coolant systems, where CO2 is used as a coolant, the CO2 is a liquid under high pressure that is pumped through the system. There is no phase change and there are no compressors involved in the CO2 portion of the system.”

In a cascade system, it is typical for two refrigerants to be used. For example, the ammonia refrigeration sector has parlayed CO2 with ammonia, in part to reduce the amount of ammonia on site.

Regarding how the Emerson CO2 scrolls might be used in subcritical, low-temperature applications, Rajendran said, “Typically an HFC like R-404A is used. But other HFCs like R-134a, R-410A, etc., could also be used.”

For more information, visit www.emersonclimate.com.

Publication date:06/02/2008