ASHRAE Journal - September 2013 - 83

Column RefRigeRation applications
Andy Pearson

Itchy Foes?

the mix makes the compounds generally more reactive
than their fluoroalkane (that is, saturated) equivalents.
This means that they do not last as long in the atmoBy andy peaRson, ph.d., c.eng., MeMBeR ashRae
sphere which, in last month’s terms is “a good thing,” but
that they are flammable, clearly “a bad thing.” Just how
Last month’s column looked at good things
flammable is a subject of great and detailed debate. The
and bad things; now we turn our attention
most commonly proposed substances occupy a grey area
to a family of refrigerants that transcends
between the completely inert and the highly combustible.
In fairness, it must be said that traditional refrigerthat discussion and causes deeply divided
ants containing hydrogen, such as R-22 and R-134a also
opinions to emerge on many fronts—the
occupy this grey area. They happen to lie on one side of
fluorinated alkenes, more commonly
the flammability fence and the HFOs lie on the other
known as HFOs.
side. The exact location of the borderline is a question of
Even the adopted name of this family has generated
opinion and much debate. It is not a clear-cut scientific
polarized reactions. Opponents have dismissed it as “a
fact but depends on factors such as pressure and temmarketing stunt.” These chemicals contain hydrogen, flu- perature and even leads to such philosophical questions
orine and carbon so they are obviously HFCs, aka f-gases,
as “what is a flame?” and “what is a spark?” A lot of addiwhich are currently the subject of restrictive legislation
tional work, including fresh insights and new underaround the world. Furthermore, the “O” in the name is
standing, is required to enable us to determine how to
potentially misleading since they don’t contain oxygen.
deal with the reactivity of HFOs in the myriad applicaProponents point out calmly and often that “O” stands
tions of the refrigeration and heat pump world.
for “olefin” (pronounced oalyfin), a term currently used
The world of refrigerants became more complicated
by the International Union of Pure and
when we decided that in addition to having
Is it a bird, is it a plane…?
Applied Chemistry to describe any molgases that were nonflammable and nonecule that contains a carbon-to-carbon
toxic we also wanted them to have no effect
“double bond.” Molecules with these types
on the ozone layer and not cause global
of bonds are called “unsaturated” because,
warming. At the same time systems are to
like a half-damp sponge, it is possible for
be “cost-effective” (usually a synonym for
them to absorb more elements by adding
“as cheap as possible”) but also must use
them to either end of one of the double
minimal energy. Now we are contemplatbonds, turning it into a single bond.
ing the addition of further constraints—for
However, the adoption of the new family name has
example “no persistent effect on the local environment”
historical precedent. All synthetic refrigerants were
or “no toxic products of combustion.” It is clear none of the
simply known as “halocarbons” until it became necesproposed working fluids for refrigerating and heat pump
sary in the 1980s to discriminate between those consystems satisfy all of these criteria, and the prospect of findtaining only chlorine, fluorine and carbon, those also
ing something that satisfies them all is nonexistent.
containing hydrogen, and those without any chlorine.
The answer to this riddle, therefore, lies in the realms
Unfortunately, the new name, HFO, is not perfect. What of the economists, legislation-writers and accountants,
about unsaturated fluorocarbon compounds that don’t
not the chemists and engineers. We need a method of
contain hydrogen? What about those, like ethylene and
assessing relative merits of different options, taking all
propylene that only contain hydrogen and carbon—are
relevant factors into account. As cheap as possible is
they hydroolefins or just olefins? And furthermore, to
a good measure, but the key question is “what is poshyphenate or not to hyphenate?
sible?” or, to be more exact, “what is permissible?”
This unusual family of molecules is not new. They have
been familiar to chemists for decades (under the name
Andy Pearson, Ph.D., C.Eng., is group engineering director at Star Refrigeration in
Glasgow, U.K.
fluoroalkenes). The addition of the double bond into
Septem ber 2013

ashrae.org

ASHRAE JouRnAl

ASHRAE Journal - September 2013

Table of Contents for the Digital Edition of ASHRAE Journal - September 2013