What is it?
Carbon dioxide (CO2) is everywhere in nature, but it’s not widely known that it can be used in refrigeration systems. Calling CO2, designated “R-744” as a refrigerant, an emerging technology may be a bit of a stretch. It was originally patented as a refrigerant in 1850; however, it fell out of use with the development of synthetic refrigerants. In recent years, CO2 has become increasingly popular again as a refrigerant with an increased focus on environmental safety and ozone depletion.
How does it work?
CO2 is used in vapor compression refrigeration systems similar to any refrigerant. When compared to other refrigerants, CO2 has a lower critical point, the point at which a phase change from liquid to vapor occurs. This means it operates less efficiently in applications like air conditioning or commercial refrigeration systems for grocery stores, but better at low temperatures.
What are the most appropriate applications?
Due to its low critical point, CO2 is best suited for low-temperature applications. The most popular and effective application is in multiple stage (cascading) refrigeration systems where temperatures below -40ºF are required, usually for industrial applications. Cascading refrigeration systems have a high temperature and low-temperature component, and when CO2 is used as the low-temperature refrigerant, it can operate at its best efficiency.
What are the savings?
In low-temperature applications below -40ºF, savings for cascading systems using CO2 as the low-side refrigerant are close to 6% over standard systems using ammonia refrigerant. There typically aren’t savings for refrigeration systems operating at higher temperatures, but CO2 is increasingly used for non-energy reasons.
What are the non-energy benefits?
The global warming potential (GWP) of CO2 is 1, while the GWP of R-22 is close to 1,800, making CO2 a much more environmentally friendly option than synthetic refrigerants. CO2 is also less toxic than ammonia refrigerant in the case of a leak and is safer to distribute throughout a facility (although care should be taken in enclosed spaces).
What is the cost?
CO2 systems operate at a higher pressure and require special equipment, so costs are higher than standard systems. But, the technology and equipment are readily available.
What kinds of incentives/programs are available?
This technology is evaluated in custom programs and will most commonly be considered for industrial new construction applications.