With a worldwide phase-down of high GWP HFC refrigerants now appearing to be inevitable, the main air conditioning refrigerant R410A, with its GWP of 2088, is coming under increasing pressure.
The Japanese air conditioning manufacturers, lead by Daikin, have so far backed R32, a single component refrigerant with a GWP of just 677. Many developing countries are being encouraged to make the leap straight from R22 to R32, with remarkable effect. Daikin claims 6.5 million R32 air conditioner sales in 48 countries up to the end of 2015.
Also at stake is the need to find a refrigerant that will work efficiently in high ambient environments.
So, while, R32 has stolen a significant lead, it does have disadvantages, one being its high discharge temperature. As a result, a dozen new alternative blends have appeared, many claiming a more close capacity match to R410A, reduced energy consumption benefits and lower discharge temperatures.
One of the leading competitors to R32 is Chemours’ DR-55, a refrigerant pending official ASHRAE approval as R452B. According to Chemours, the new gas, which it will market as Opteon XL55, has a very similar GWP to R32 but with better efficiency, lower discharge temperatures and a lower flammability. In tests, DR-55 is also said to have exhibited better performance than both R410A and R32 when used as a drop-in in an R410A system.
Purdue conference paper
In a paper presented at this month’s International Compressor Engineering Conference at Purdue University, Indiana, Daikin authors Shigeharu Taira, Tomoatsu Minamida, Tomoyuki Haikawa and Fumio Ohta revealed the results of the Japanese manufacturers own performance evaluation of R32 and DR-55.
Despite selecting R32 from among the candidates a few years ago, the authors admit the need to continue comparing it to new candidates in search for an even better choice.
While DR-55 is not actually named as the lower GWP refrigerant blend in the paper, the authors reveal that the “mystery” blend is a mixture of R32/R125/R1234yf (67/7/26) – the same formula as DR-55.
The performance evaluation, which included cooling operation tests in high ambients, found that the COP of R32 was superior to DR-55 because of its better latent heat characteristic. In particular, the test are said to show that as condensing temperature increases such as in high ambient temperature operation, the COP of R32 is even more significant.
The tests were carried out in a mini-split type air-conditioner system with a nominal cooling capacity of 7.1kW.
“From the above, we consider that R32 is still the best refrigerant at present,” say the authors. ‘However, we will continue investigation in search for a better refrigerant.”
The authors say that Daikin chose R32 because its GWP is a third that of R410A, the required refrigerant charge is smaller, it has excellent thermophysical properties to achieve better performance in reversible heat-pumps.
“We judged at that time it was the best refrigerant among the candidate refrigerants from the viewpoint of safety, economy, and environment,” the authors say.
As a single component refrigerant, Daikin argues that there is no issues with glide or fractionation and R32 is easy to manage, in charge and recharge processes. It is also attractive from the viewpoints of recovery and recycling.
R32, DR-55 and all the other blends currently under consideration are A2L “mildly flammable” refrigerants. Chemours claims that DR-55 exhibits lower burning velocity than R32 and its own earlier drop-in tests are said to have shown that DR-55 has better efficiency and lower discharge temperatures than R32.
High ambient split-system tests conducted by the US government’s Oak Ridge National Laboratory (ORNL) appear to back-up Daikin’s findings. In tests carried out on four R410A alternatives, including R32 and DR-55, ORNL observed that R32 was the only refrigerant that showed consistently better capacity and efficiency than R410A. However, ORNL also pointed to the negative aspect of R32’s high discharge temperature.
Previous comparative tests by air conditioning manufacturer Trane have also shown R32 to have better capacity and efficiencies than DR-55.