NFPA Journal - May/June 2017 - 90

BOSTON 2017

Conference & Expo

"The reality is there are only so many chemical compounds
that actually work as refrigerants," said Bill Walter, an engineering fellow at United Technologies and a member of the
board of directors at the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), which
publishes refrigerant safety codes. "Every time we cross one of
these thresholds, we leave a bunch of chemicals behind and
the ones that are left present new challenges."
In February, researchers at the National Institute of Standards and Technology (NIST) completed a multiyear study to
identify the best new refrigerant candidates to replace HFCs
in air conditioning applications. All 27 fluids it tested with low

HFCs has been under consideration for nearly a decade,
and for much of that time the refrigeration industry has
been working on developing refrigerants with lower global
warming impact, Walter said. Europe has been aggressively
replacing HFC refrigerants for years to curb its global
warming impact, and the EPA, through its Significant New
Alternatives Policy program, has been investigating and listing acceptable alternatives for a few years.
While the final refrigerant substitutes for most applications
are still up for debate, two main groups-hydrocarbons such
as propane, isobutane, and propylene, and a group of synthetic
chemicals called hydrofluoroolefins, or HFOs-are the leading
contenders. (Carbon Dioxide [CO2] is
also being used in some instances but
its effectiveness is limited in warm
climates). The rub is, current model
codes now severely restrict the use of
both HFOs and hydrocarbons due to
flammability concerns.
Propane, a highly flammable
substance, is a very energy-efficient
refrigerant with a low environmental
impact. Some in the food industry
see propane as a potential savior
that "could effectively eliminate EPA
compliance concerns for the foreseeable future," according to Emerson
Climate Technologies, a commercial
HVAC consulting firm.
HFOs, meanwhile, are slightly flammable and very efficient
synthetic refrigerants with much lower global warming potential than HFCs. HFOs could be used in a variety of refrigerant
applications, from chillers, commercial and household refrigeration, a variety of air-conditioning units, and more.
In terms of flammability, propane and HFOs differ significantly. Although some HFOs are flammable, "they have
a very high lower flammable limit, so it takes a lot to leak
before they ignite-and when they do burn they don't give
off a lot of heat and tend to burn very slowly," Walter said.
"These are all desirable qualities if you have to use a flammable chemical." The properties are so unique that ASHRAE
created a relatively new flammability classification called 2L
to accommodate them.
ASHRAE's refrigerant safety rating system is based on toxicity and flammability-nontoxic refrigerants are class A, and
toxic refrigerants are class B; the numbers 1, 2, and 3 following
the class indicate levels of flammability, from nonflammable
(1), lower flammability (2), to higher flammability (3). The new
2L classification is reserved for chemicals like HFOs that are
mildly flammable, but have much lower flame propagation
speeds than regular class 2 refrigerants.
Model codes have not yet been updated to recognize the
new 2L class, so HFOs are still considered A2 refrigerants
by regulators, Walter said. Propane, a hydrocarbon also used
in gas grills, is listed as A3, the highest flammability rating.
Current codes severely limit the charge size-the amount of
refrigerant used in a system-for both A2 and A3 refrigerants,

"THERE ARE ONLY SO MANY

CHEMICAL COMPOUNDS
THAT ACTUALLY WORK AS
REFRIGERANTS. EVERY TIME
WE CROSS ONE OF THESE
THRESHOLDS, WE LEAVE A
BUNCH OF CHEMICALS BEHIND
AND THE ONES THAT ARE LEFT
PRESENT NEW CHALLENGES. "

climate impact are at least slightly flammable. "The takeaway
is there is no perfect, easy replacement for current refrigerants," NIST chemical engineer Mark McLinden said. "Going
into the study, we thought surely there has to be something
else. Turns out, not so much. So it was a bit surprising, a bit
disappointing."
Unless a unicorn-like chemical refrigerant with ideal properties-efficient, chemically stable, nontoxic, nonflammable,
and environmentally friendly-is suddenly found, something
will have to give, possibly certain restrictions on the use of
flammable refrigerants.
Code-making panels from groups including ASHRAE and
Underwriters Laboratories (UL), which both set safety standards for refrigerants and the equipment that use them, are
considering increases to the amounts and types of flammable
refrigerants that can be used in systems, opening the door to
a future in which billions of appliances, from air-conditioning
units to industrial HVAC systems to household refrigerators,
will contain substances that burn.
"This is coming, and it's coming quickly so it's important to
get this in front of the fire protection community," said Walter,
who is cohosting an education session on the topic at the 2017
NFPA Conference & Expo. "We don't want anyone to be surprised when the code change proposals come through."

Promising, concerning alternatives
While the official global HFC phase-out effort is relatively
new, the world is not starting from scratch. Phasing down

90 | NFPA JOURNAL * M A Y / J U N E 2 0 1 7

Table of Contents for the Digital Edition of NFPA Journal - May/June 2017