Transcritical CO2 (R744) industrial condensing units made by U.S. manufacturer M&M Carnot have been found to use almost 53% less energy than R448A-based systems in three U.S. locations.
This calculation is based on data provided by Clark Andrews, Director of Business Development, M&M Carnot, and Larry Gilliland, Vice-President of SubZero Constructors, during a presentation at the ATMOsphere (ATMO) America Summit 2023 on natural refrigerants. The conference took place June 12–13 in Washington, D.C., and was organized by ATMOsphere, publisher of R744.com.
M&M Carnot, which was acquired by Johnson Controls in June 2023, introduced its Aquilon DS CO2 condensing units in 2021 – one of the few CO2 condensing units offered in the U.S. Aquilon DS is a line of plug-and-play units with capacities between 10 and 85TR (35.1 and 298.9kW) at -40 to 40°F (-40 to 4.44°C) SST (saturated suction temperature). It features a high-pressure design with heat recovery along with a PLC-based control system.
Andrews and Gilliland presented a comparison of performance between Aquilon DS condensing units and R448A condensing units in three U.S. cities: San Diego, California, Kissimmee, Florida, and Indianapolis, Indiana. All test units were at different capacities: 100TR (351.6kW), 75TR (263.7kW) and 125TR (439.6kW), respectively.
The annual energy savings of the CO2 units compared to the R448A units were found to be 374,718kWh, 438,458kWh and 382,421kWh, for San Diego, Kissimmee, and Indianapolis, respectively. This represented a 53% energy savings overall.
Average annual operating costs – including energy, maintenance and other costs – for all locations were reduced up to 48% with the CO2 condensing units, said Gilliland, adding that life cycle cost over a 20-year period is reduced by at least 21%.
As a result, the premium on the R744 condensing units could be paid back within 2.5 to 6.4 years depending on different locations and capacities, noted Andrews.
Andrews noted that the Aquilon DS system would comply with regulations in California, such as Title 24 and new GWP restrictions. Tital24 is urging all energy users in California to make use of the most efficient appliances. For cold storage facilities, this could include eliminating the high head pressure of 70°C (158°F) for traditional refrigeration systems, and using the transcritical CO2 system’s 60°C (140°F), said Gilliland.
“Another main driver to use this system is the carbon restriction implemented for high-GWP refrigerants in California,” he added.
Barriers and Challenges
Andrews and Gilliland pointed out some challenges still affecting the uptake of CO2 systems.
For example, Andrews acknowledged that end users compare the initial higher cost of CO2 systems with that of synthetic condensing units without looking at the long-term benefits of CO2. This approach is disadvantageous from both economic and environmental perspectives.
He also noted that the CO2 condensing unit “is a little bit challenging to implement in places where there is high wet-bulb temperature, and we are working on it to eliminate this barrier.”
Andrews also agreed that “it is harder to find maintenance and installation manpower.” To address that, M&M Carnot has been training service technicians. “At first, service technicians were a little bit skeptical [of CO2] because of its high pressure, but after safe testing at 120bar [1,740.45psi] for 24 hours, all technicians realized that it is a safe and robust system,“ he explained.
“Equally, the growth of nationwide networks of transcritical CO2-trained service technicians will ease the maintenance service soon,” he added.
Another issue is that fewer and heavier rooftop condensing units present challenges for structural engineers.
M&M Carnot plans to increase the standard size range of transcritical CO2 condensing units, test transcritical CO2 units as air source heat pumps and use the Logix supervisory system to network multiple condenser units.
“The growth of nationwide networks of transcritical CO2-trained service technicians will ease the maintenance service soon”Clark Andrews, Director of Business Development, M&M Carnot