US tests increase RTU efficiency by 25%
USA: System improvements and a switch to a lower GWP refrigerant are said to have brought 25% efficiency gains to a standard R410A rooftop air conditioning unit.
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.