The tests were carried out by the Oak Ridge National Laboratory (ORNL) and manufacturer Trane as part of the US Department of Energy’s effort to support the transition to lower-GWP refrigerants while simultaneously improving system efficiency.
The project is said to have initially focused on cost-effective RTU efficiency increases using R410A. This included an exhaustive search for more efficient components and system concepts for improving the mechanical design.
The lab prototype achieved a 20% efficiency gain, still using R410A. With the same lab prototype, the team later achieved an additional 5% efficiency gain by replacing R410A with the lower-GWP refrigerant DR-55.
Developed by Chemours, DR-55 has been provisionally assigned the ASHRAE number R452B. A blend of R32, R125 and R1234yf, DR-55 has a GWP of 675. It has also been said to exhibit lower discharge temperatures and a lower flammability than its rival R32. However, like R32, it is a “mildly flammable” A2L refrigerant.
The Trane/ORNL tests showed DR-55 providing a 5% boost in RTU efficiency compared to R410A. Similar improvements were reported by fellow US manufacturer Lennox when testing the new refrigerant in a 17.6kW rooftop unit last year.