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Concerns persist over R466A compatibility

USA: New tests on R466A, Honeywell’s long-awaited non-flammable lower GWP alternative air conditioning refrigerant, are said to have shown comparable performance to R410A but have again raised material compatibility concerns.  

First announced by Honeywell in June 2018, R466A is a blend of R32 and R125 – the two components of R410A – with the addition of 39.5% of trifluoroiodomethane, better known as CF3I or R13I1. Despite the initial market enthusiasm, more than three years on, R466A has still not been adopted by any OEM in a production model. And this is despite Honeywell insisting that R466A has undergone “extensive analysis” by OEMs and leading compressor manufacturers. 

The latest tests by the University of California, Davis, Western Cooling Efficiency Center (WCEC), evaluated its performance in a Trane Foundation rooftop unit. The results were described as “very successful” displaying similar capacity and COP across a wide range of outdoor air conditions. 

However, the UC Davis tests again question its material compatibility, stating that it represented a viable alternative to R410A “if the compatibility issues with certain metals can be mitigated through the use of alternative materials and appropriate additives”.

UC Davis refers to “documented concerns” around the chemical stability of the R-13I1 component which, they say, “reacts with zinc causing the molecule to break down”.

Honeywell has previously countered such claims, telling the Cooling Post that the stability and shelf-life can be addressed with standard measures practiced in the industry.


The latest tests were carried out on a new 15-ton Trane Foundation model, brought in to replace an existing 15-ton Trane R22 model on the roof of one of the UC Davis campus buildings. The RTU was initially charged with R466A and an unspecified oil additive, which the UC Davis researchers said was “to avoid compatibility issues” with R466A.

The additive used in the tests was said to have been developed by Trane Technologies specifically to improve the compatibility of R13I1 with system materials. The Trane Foundation unit was a production packaged R410A RTU, where the R410A had been recovered and replaced with R466A.

The system with R466A was monitored from July 13 to August 29, 2021. It was then replaced with R410A and monitored through to September 29. There was no charge optimisation performed for either refrigerant. In both cases, the system was charged with the nameplate quantity of 14.6lbs, which was recommended for R410A.

A previous study, by WCEC, found that a refrigerant charge optimisation for R466A required minor adjustments to the thermal expansion valve and a 7% increase in refrigerant weight compared to R410A to compensate for differences in refrigerant liquid densities. This project looked at the worst-case scenario for a drop-in replacement, where no charge optimisation was performed and the charge was simply based on manufacturer recommendations for R410A. 

The tests

In the tests, R466A appeared to deliver slightly higher capacity than R410A as outdoor temperatures increased, but, in general, the capacity differences between the two refrigerants were within the margin of error of the measurements. 

Power draw tests showed R466A to have a slightly steeper profile with lower power draw at lower outdoor air temperatures and higher power draw at higher outdoor air temperatures. However, the UC Davis engineers recognised that this increase in power draw could be attributed to the lack of a charge optimisation with R466A. In terms of COP, the refrigerants showed very similar across all outdoor air temperature conditions.

The average subcooling during the measurement period was 9.0°F for R466A and 4.1°F for R410A

Related stories:

Trane to conduct field trials on R466A29 June 2021
USA: Honeywell and Trane are to conduct field tests on Trane rooftop units with R466A – Honeywell’s long-awaited non-flammable alternative refrigerant to R410A. Read more…

Honeywell partners with Sporlan on R466A refrigerant – 19 September 2019
USA: The Sporlan Division of controls and components manufacturer Parker Hannifin has given the thumbs up to R466A, Honeywell’s yet to be introduced low GWP, non-flammable replacement for R410A. Read more…

Honeywell joins forces with Sanhua on R466A – 14 August 2019
USA: Honeywell has joined forces with Sanhua, the Chinese air conditioning and refrigeration controls and components manufacturer, to commercialise the use of R466A, Honeywell’s lower GWP R410A replacement refrigerant. Read more…

Midea opts for Honeywell’s A1 aircon refrigerant R466A – 26 June 2019
USA/CHINA: Chinese manufacturer Midea is looking to use Solstice N41 (R466A), Honeywell’s new non-flammable, lower GWP refrigerant, in all its VRF and chiller systems. Read more…

Promising results for R466A in VRF air con tests – 10 January 2019
USA: Toshiba Carrier is said to have described R466A, Honeywell’s new non-flammable R410A replacement, as “promising” after initial performance testing in a VRF air conditioning system. Read more…

R466A has close performance to R410A – 14 October 2018
GERMANY: Solstice N41, Honeywell’s new non-flammable lower GWP refrigerant, is said to have performance characteristics close to R410A. Read more…

Honeywell’s N41 – a blast from the past – 24 August 2018
CF3I is, seemingly, the unknown quantity in Solstice N41, Honeywell’s new R410A replacement refrigerant. But the records show that far from being new to the refrigerants business, it has been considered as a component in replacements for CFCs, HCFCs as well as HFCs in tests dating back at least 30 years. Could the earlier adoption of CF3I have saved the industry a number of system changes along the way? Read more…

Secret of Honeywell’s new refrigerant – 27 June 2018
USA: Honeywell’s development of a non-flammable low GWP alternative to R410A has created huge interest, but what’s in it? The Cooling Post may have the answer. Read more…

Honeywell announces R410A breakthrough – 26 June 2018
USA: Honeywell has announced the development of a new lower GWP non-flammable alternative to R410A in stationary air conditioning systems. Read more…

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