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Honeywell’s N41 – a blast from the past

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?

Honeywell’s announcement at the end of June of Solstice N41, a potential non-flammable, lower GWP replacement for R410A, caused quite a stir.

Until now, R32 has been the only acceptable lower GWP alternative for small splits but that refrigerant’s “mild” flammability makes it unsuitable for VRF systems. And, it also has to be said that, rightly or wrongly, any degree of flammability is a source of concern for some engineers.

The Cooling Post’s exclusive story regarding the components of Honeywell’s new refrigerant and its likely GWP of 733 created equal interest. 

It had previously largely been accepted that man-made HFC or HFO refrigerants with a GWP less than 1000 would be flammable to some degree. Now here is a refrigerant with a GWP estimated to be around 733 that is non-flammable.

Honeywell’s Solstice N41, or R466A, is expected to provide a lower GWP non-flammable alternative to R410A

Interestingly, the new refrigerant, given the provisional ASHRAE number of R466A, still contains the two constituents of R410A – R32 and R125 – but with the addition of a large slug of something called CF3I, also known as trifluoroiodomethane or trifluoromethyl iodide.

A fire suppressant with a GWP of just 0.4, CF3I is also being considered as a replacement for halon 1301 in unoccupied areas. It also seen as a potential medical propellant, is a seriously good foam blowing agent, an alternative to SF6 and is used as an etching gas in the production of semiconductors.

Despite its very low GWP, CF3I does, however, have a small ozone depletion potential, but more of that later.


For most in the refrigeration and air conditioning industry this will have been the first time that they have ever come across this gas but it has a history as a potential refrigerant replacement dating back at least 30 years. As far as refrigerants are concerned it has previously been researched and tested in various blends to replace CFCs and HCFCs, and, in some cases, HFCs.

Back in the early 1990s in the US, Jon Nimitz and Lance Lankford formed a now defunct company the Ikon Corporation in Albuquerque, New Mexico, and began patenting a number of blends of HFCs and CF3I. Known as iodofluorocarbons (IFCs), these were all described as non-flammable, “essentially zero” ozone-depletion potential, low GWP and exhibiting high performance. Importantly, to a large extent they were also seen as “drop-ins”.

Tests were carried out in association with NASA and the US Environmental Protection Agency on three refrigerants, Ikon A, Ikon B and Ikon C.

The most important was probably Ikon A, a near-drop-in replacement for R12, R500 and R134a. Fully miscible with mineral oil, it was a near-azeotropic blend of R152a and CF3I. Its temperature glide was said to be about 0.10-0.15K, making it suitable for critically flooded evaporators.

The inclusion of R152a, a low GWP gas, but largely overlooked due to its A2 flammability, helped Ikon A achieve a GWP of just 30. 

It was tested in automotive air conditioners with good results and in an R12 reefer unit for two years with, it was reported at the time, no indications of incompatibility or refrigerant decomposition.

With a superior cooling capacity and energy efficiency to both R12 and R134a, the fact that it was never commercialised is probably down to timing and cost. By the end of the 90s when Ikon A was still undergoing tests, many manufacturers were already committed to R134a. In addition iodine, a major component of CF3I, is a relatively expensive material and large sources of supply were, and are, limited.

Also, a report at the time states that, from the point of view of car manufacturers, Ikon A’s efficiency was expected to only result in a small saving in fuel consumption, but that “the relatively high leak rates of automotive air conditioning systems make an inexpensive refrigerant such as R134a more desirable for these systems”. Little were they to know that, just a few years later, R134a would be supplanted in new cars by an even more expensive replacement in R1234yf, or that the cost of R134a, in Europe at least, would go through the roof.

In the meantime, CF3I was seemingly forgotten until 2006 and the introduction of the MAC directive. This European edict demanded that automotive manufacturers switch to a refrigerants with a GWP below 150. So, goodbye R134a with its GWP of 1430.

Chemical companies scrabbled to be first with yet another new non-flammable refrigerant alternative. Many toyed with the newly developed, “fourth generation” HFOs. One of these, R123yf, would eventually become the generally accepted industry standard, but there were initial concerns regarding that refrigerant’s “mild flammability” – a characteristic that would later meet heavy criticism from German car manufacturers.

Initially, however, Honeywell had worked on a non-flammable blend which twinned R1234yf with our old friend CF3I. The inclusion of 30% CF3I in the blend made it non-flammable. Honeywell was also thought to be looking at a blend of R32 and CF3I at this time as well.

The 1234yf/CF3I blend was known by Honeywell as Fluid H, and, jokingly, as Preparation H by its competitors.

Initial tests were encouraging. Fluid H demonstrated lower leak rates than R134a and performance evaluations were described as “promising” especially in optimised systems. Being non-flammable, aftermarket service procedures were expected to be no different than those with R134a.

However, by the end of 2007, Honeywell had abandoned Fluid H to concentrate on the single substance R1234yf as the replacement for R134a.

There was speculation that Fluid H had stability problems, and that the assessment panels of the Montreal Protocol had raised environmental and health concerns about the toxic and ozone-depleting characteristics of CF3I.

It is true that tests on small furry animals had detected that CF3I has a relatively low cardiac sensitisation threshold, although cardiac sensitisation is a characteristic of many hydrocarbons and halocarbons.

Also, while iodinated organic compounds are in general more reactive, more toxic, and less stable, scientists maintain that the presence of fluorine in CF3I provides greater stability and decreased toxicity.

Honeywell points out that CF3I is classified A1 – non toxic and non flammable – by ASHRAE. In terms of its ODP, Honeywell stresses that CF3I has a short atmospheric lifetime and a theoretical ODP value of 0.008 based on the most recent atmospheric research.

The main drawback for Honeywell’s new refrigerant could be the cost. The iodine component makes CF3I relatively expensive and sources are limited. However, while cost may have been an obstacle in years gone by, the new HFOs are far from cheap and, in Europe at least, the phase down of HFCs have seen enormous price increases on established refrigerants.

With hindsight, you could argue that had Jon Nimitz’s Ikon A R152a/CF3I blend been originally adopted as a replacement for R12 in car air conditioning, there would have been no need for a MAC directive or a further change away from R134a, or worries, in Germany at least, about the flammability of R1234yf.

Perhaps this time, Honeywell’s adoption of CF3I will lead to its wider use and the development of other lower GWP, non-flammable refrigerant blends.

Related stories:

Secret of Honeywell’s new refrigerant27 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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