ASHRAE Journal - March 2021 - 37

ROUNDTABLE

temperatures, along with overall system design compatibility when compared to R-410A system designs are also
a consideration.
The technology barriers to designing a nonﬂammable
R-410A solution are many, and they have to do with the
performance characteristics desired versus the ﬂuid
properties available. When looking at ﬂuid choice, ﬂammability is one element of consideration, but it not the
only consideration. As mentioned previously, refrigerant
stability, materials of compatibility, overall environmental
impact and total system cost are other factors included in
ﬂuid selection. OEMs evaluate all of these factors closely
and make determinations based on the total picture and
what will serve their customers and market best for the
lifetime the equipment is expected to deliver.
Can any of these alternatives (R-32 and R-454B) be used to retroﬁt existing R-410A equipment?
Kujak: No! Under no circumstances should these ﬂammable refrigerants (ASHRAE Class 2L, 2 or 3) be used to
retroﬁt existing R-410A equipment. Serious safety situation could result. Much marketing of primarily R-32 and
to a lesser extent R-454B and their potential beneﬁts has
led to inquiries to retroﬁt installed R-410A equipment.
On the other hand, R-466A potentially could be used
as engineered retroﬁt for some R-410A products since
R-466A is nonﬂammable (ASHRAE Class 1). This will
be an interesting opportunity to watch and see how it
develops for existing R-410A equipment.
Are these current alternatives (R-32 & R-454B) considered a
long-term low GWP solution?
Johnston: Yes. Because of R-32's availability, low cost and
excellent performance, it is already used in large quantities in R-410A and most alternative low GWP blends. Given
R-410A's wide use today, we know R-410A, and therefore
R-32, will be in the service chain for several years to come
as high GWP HFCs are phased down gradually.
Kujak: No. Both R-32 (GWP 675) and R-454B (GWP
466) will be adopted to replace R-410A as interim GWP
steps until phasedown regulations push them out of use.
Much debate is occurring how long the adoption window will last, but it is estimated to be the 2030 to 2036
time frame before other lower GWP refrigerants will be
needed to meet the regulations. Refrigerant research
and innovation are underway on lower GWP alternatives
to allow the transition from <750 GWP alternatives to
more long-term sustainable GWP limits, with <300 GWP
as a possible target.

What about using natural refrigerants as a replacement for
R-410A applications?
Johnston: Natural refrigerants, for example R-290 (propane) with its A3 classiﬁcation, are being used in small systems in very small charge quantities in residential refrigeration applications. As mentioned above, each refrigerant
must be evaluated for each application in a variety of
characteristics. The difﬁculty then for application of A3
refrigerants into larger capacity systems, which are the
norm in residential and commercial buildings, is that due
to the larger charge sizes necessary, the much lower (about
10 times) ﬂammable concentration limits and much lower
minimum ignition energy (MIE), it is much more difﬁcult to apply such A3 refrigerants. For consideration of
other natural refrigerants, characteristics such as toxicity
(R-717) or pressure (R-744) either mean they can'tt be used
in human comfort applications due to current building
codes (R-717) or major system designs and efﬁciency can
be problematic (R-744). Ammonia, hydrocarbons and CO2
have not been widely pursued in this segment due to toxicity, safety and energy efﬁciency issues.
Kujak: Product standards are allowing higher charges
of hydrocarbons, and both R-600a (isobutane) and
R-290 (propane) are being used in small portable refrigeration and air-conditioning products. Hydrocarbons
are higher efﬁciency than their ﬂuorinated alternatives,
but their high combustibility restricts their use to small,
hermetically sealed multi-circuit products.
Carbon dioxide (R-744) is thermodynamically too
low in efﬁciency to be given much consideration in
this space other than in applications without efﬁciency
restrictions. Ammonia (R-717) is not considered a possible alternative in applications requiring direct refrigerant expansion.
It is expected that product fragmentation will occur in
the R-410A space with hydrocarbon being used in small
hermetically sealed portable room air conditioner (RAC)
products. Some large charge products will migrate to
other available technological architecture, like chillers
or other indirect refrigerant products.

References

1. Myhre, G, D. Shindell, F-M Bréon, Collins,
W, et al. 2013. " Anthropogenic and natural
radiative forcing. " In: Climate Change 2013: The
Physical Science Basis. Contribution of Working Group I
to the Fifth Assessment Report of the Intergovernmental
Panel on Climate Change. Cambridge and New York:
Cambridge University Press.
MARCH 2021

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