2017 Tech Report Nov-Dec

TECHNICAL REPORT

THE

REFRIGERATING ENGINEERS & TECHNICIANS ASSOCIATION | NOVEMBER/DECEMBER 2017

COMING TO A NEIGHBORHOOD NEAR YOU Over the past several years CO2 has begun to reemerge as an alternative refrigerant to both traditional halocarbons and is considered for use in a particular application: • its normal operating “There are several draw-backs to CO2 that must be taken into

pressures are higher than most common refrigerants; • it has a low critical point compared to other common refrigerants—87.76ºF (31ºC); • it has a high triple point compared to other common refrigerants— -69.8ºF (-56.6ºC); and • it is heavier than air, so it tends to concentrate in occupied areas and displace air, so it is an inhalation hazard. As the CO2 refrigeration system technology has evolved, a number of different system types have developed. The most common in industrial applications is the cascade

ammonia. CO2, like ammonia, is a natural—green—refrigerant. Being a natural refrigerant means that it occurs in, and is extracted from air or other naturally occurring sources. CO2 and ammonia are both components of air, they both are part of organic decay, and they are both found in living plants and animals. CO2 or R744, has some advantages as a refrigerant. It is available at a reasonable cost. Because it is more dense than other refrigerants, less volume has to be moved through the system for an equivalent mass flow—less cubic feet per minute (CFM) for the same pounds per minute flow rate.

account when CO2 is considered for use in a particular application.”

CO2 has a better BTU capacity per pound than the halocarbon refrigerants. Only ammonia has a lower ozone depletion potential (ODP) and global warming potential (GWP) numbers. R744 has no fire hazard potential, is non-toxic, and non-reactive. While there is no perfect refrigerant, CO2 is a good refrigerant by most measures. There are several draw-backs to CO2 that must be taken into account when CO2

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