The development of larger CO2 compressors, and various energy-efficiency improving technologies, has seen R744 technology make huge inroads into industrial refrigeration in the last few years, but is the technology ready to be crowned king of what is traditionally considered the domain of ammonia?
Managing Director of Isentra, Daniel Clark, thinks that CO2 has “some key advantages over ammonia” for industrial refrigeration, and believes that “transcritical CO2 systems will overlap much more deeply into the traditional ammonia space than HFC systems ever did.”
U.K.-based Isentra manufactures CO2 heat pumps and refrigeration equipment. However, in an article posted on LinkedIn, Clark stresses that he is very much a fan of ammonia refrigeration, and that Isentra would not rule out building ammonia solutions at some point.
“There is no such thing as a perfect refrigerant,” Clark stressed. “For ammonia, its principal drawbacks are its toxicity and flammability.”
In the U.K., ammonia systems have to comply with the Dangerous Substances & Explosive Atmosphere Regulations (DSEAR). The implications of having to comply with DSEAR, and other similar regulations around the world, adds “significantly to the first cost and then the lifecycle cost of an ammonia installation,” Clark argues. The operational responsibilities of ammonia systems also imposes a “burden” on end users to manage health and safety systems and procedures, he added.
With regards to low-charge ammonia systems, Clark said “A well-designed low-charge ammonia system in a direct application will be very efficient.” However, “low-charge ammonia glycol chillers will certainly struggle to beat the efficiency of a direct transcritical CO2 system, especially in more northern geography.”
“Transcritical CO2 systems will overlap much more deeply into the traditional ammonia space than HFC systems ever did.”Daniel Clark
CO2 ready to be crowned king?
So, is CO2 the best option for industrial applications going forward? Well, it’s not that simple, according to Clark. “There is no such thing as the perfect refrigerant,” he said.
“CO2, of course, has its own drawbacks too. The standout disadvantage is cooling capacity in high ambient temperatures. When CO2 systems go transcritical in ambient temperatures over circa 25°C, capacity can drop off significantly.”
However, In later years there has been a lot of research and development done to improve and counteract this drop in CO2 refrigeration efficiency. Clark has most faith in parallel compression, which reduces compression ratio of the flash gas leaving the low-pressure receiver.
“Transcritical CO2 will sit in the space vacated by HFC refrigerants at the smaller end of industrial refrigeration applications, and it will become more prevalent in mid-sized applications often served by smaller ammonia systems,” Clark opined. “This is an increasingly common market development driven by cost, risk and the available option to maintain simpler and efficient direct cooling with higher charge applications.”
However, “for the time being at least, the transcritical side of the CO2 system is limited to reciprocating piston compressors,” Clark said. “This is where ammonia has the ultimate capacity advantage when allied with the massive swept volume capacities that screw compressors and multi-cylinder reciprocating compressors can provide.”
“Ammonia will therefore go unchallenged in the upper capacity echelons of the industrial refrigeration sector, or certainly until someone develops a transcritical compressor that squares up. I feel this is some way off.”
In other words, there is room for both CO2 and ammonia, according to Clark. “It’s a matter of playing each of them to their advantages.”
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