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Retro-Refrigerants -
What's Old is New
It is hard for many today to
imagine a time when comfort
cooling was not considered a
basic amenity, not a luxury
or an extravagance. Yet, it
was not until the 1920’s to
1930’s that comfort cooling
became more readily
available for the masses.
Even until the mid to late
1950’s air conditioning for
the home was not the norm
and, when installed, usually
comprised one or two window
mounted or through the wall
units. Air conditioning in
automobiles was, in those
rare cases where it was
provided, generally in the
form of an “add-on” with the
evaporator unit sitting
between the transmission
hump (remember them) and the
bottom of the dashboard.
Fast-forward to the present,
when comfort cooling is the
norm. If a home doesn’t have
central A/C, it probably has
a combination of window
units and/or mini-splits to
keep the occupants at a
comfortable temperature
while they go about their
business. What could
possibly be wrong with this
picture? Only that we are
now being told that we are
smothering mother earth in a
blanket of ozone depleting,
global-warming inducing
gases which are going to do
result in our demise some
day. We are told that our
leaking air conditioning
systems are the source of
this blanket and that we
have to change our ways.
Whether or not one is in
agreement with the
global-warming/ozone
depletion scenario (as
opposed to a cyclical
occurrence based on
naturally occurring events)
one has no choice but to
agree that governmental
limits are in place which
determine what refrigerants
we can and will be able to
use now and for the future.
What is one to do? Certainly
giving up our accustomed
comfort levels will never
fly, human nature being what
it is, so alternatives must
be found. The good news?
There already exists several
“natural” refrigerants, one
of which is R-717. That’s
right, Ammonia! NH3 .
Anhydrous ammonia, to be
precise, 99.98% pure ammonia
(not to be confused with its
cousin, household cleaner
ammonia, which is a 10%
ammonia solution in water).
It turns out that not only
does ammonia have a 130-150
year (depending on which
side of the Atlantic Ocean
one resides) history of use
in refrigeration but it is
about as “natural” a
refrigerant that one can
find. Consisting of a
molecular amalgam of
hydrogen and nitrogen, not
only is ammonia considered
to have Zero Ozone Depletion
Potential (ODP) and Zero
Global Warming Potential
(GWP) but, if it is released
into the atmosphere it has a
life cycle of approximately
one week, whereupon it
breaks down into its
constituent parts. Some of
the nitrogen so liberated
may even find its way back
into mother earth, providing
nutrient for local flora. It
seems to be a veritable
environmental bonanza. What
else can one say about
ammonia? It turns out it is
more thermally efficient,
thus generally permitting
smaller tubing, requiring
less system charge and, due
to lower mass flow rate,
uses less power to pump the
required amount of
refrigerant around to
achieve rated cooling.
One might ask oneself why we
ever got away from using
ammonia in the first place.
In fact, much of the heavy
duty, large scale cooling
plants have been using
ammonia all these years
because of the many positive
attributes. However, use in
small equipment for
residential use waned with
the development of the
earlier noted halogen based
refrigerants we have
embraced, which eliminated
concerns about ammonia’s
odor and toxicity.
Ironically, it is ammonia’s
odor which, in many ways,
makes it less problematic
than odorless non-toxic
refrigerants which are still
capable of displacing
breath-able oxygen, and
causing death by
asphyxiation. Since the
level at which one can smell
ammonia is about 5 parts per
million (ppm) and the level
of toxicity is about 300
ppm, in case of an ammonia
leak, there exists a better
chance of knowing about it
with sufficient warning to
evacuate the area. Ammonia,
being a lighter than air
gas, tends to rise (without
getting trapped in “pockets”
as some other refrigerants
do) which tends to dilute
the concentrations of
ammonia and keep it below
the toxic level. It has been
estimated that at one time,
there was as much Halocarbon
refrigerant in the
atmosphere (from leaking
systems) as was contained in
all the systems from which
it escaped. In that case,
being odorless was not a
positive point.
Apart from the odor and
toxicity, what else
precluded the widespread use
of ammonia for smaller
cooling installations? There
are a few other negative
characteristics, none of
which are complete “show
stoppers”, but still
significant enough to
require additional
consideration during the
design process. Ammonia has
a tendency to be absorbed
into any porous material.
While this would appear to
be a major concern, the fact
that the food processing
industry has experienced a
long time success with
ammonia refrigeration
indicates that with proper
precautions it need not be a
deterrent. As noted earlier,
with an ammonia based
system, everyone in the area
is a leak detector,
resulting in early detection
of any leakage issues.
Ammonia is not compatible
with copper or any copper
alloy. This requires the
use, generally, of steel
tubing. Since the size of
tubing is generally smaller
due to the thermal
efficiency of the ammonia,
and steel tubing is
generally cheaper than
copper, this alone is a
benefit that results in
lighter, smaller, less
expensive coil assemblies.
Of more con-cern is the use
of ammonia with
semi-hermetic compressors,
requiring the use of
aluminum conductors for the
windings and electrical
conductors, and compatible
lubricants. While the
anhydrous ammonia has little
water content, prolonging
the interior condition of
tubing, extra care must be
taken to insure that
external corrosion does not
take place under the
insulation on connecting
piping. As any exposed
sections would have a
tendency for external
condensation, which could
find its way under the
insulated covering, some
program of preventative
maintenance is required
(both visual and
ultra-sonic) for larger
systems. Without long runs
of external piping, smaller
cooling units would not be
expected to encounter this
problem to a significant
degree. While considered
flammable, within narrow
ranges of ammonia/air
mixtures, ammonia generally
will not burn unless in the
presence of an external
flame, minimizing the
possibility of explosive
occurrences. Last but not
least, there is the issue of
regulation. The use and
storage of ammonia are
subject (at least in the
workplace) to numerous OSHA
regulations. While an
additional consideration,
the existence of these
regulations provides a
clear-cut path to
compliance, removing some of
the ambiguity that sometimes
accompanies the
implementation of different
technology. With no negative
characteristics without
solutions, and the positive
attributes associated with
ammonia one might expect to
see an increase in its use,
displacing the more
conventional, but
“environmental unfriendly”
refrigerants normally used
in smaller comfort cooling
systems. Since ammonia’s
closest “natural
refrigerant” competition is
carbon dioxide which is
presently under attack by
the various environmental
enforcers, ammonia may have
another 150 years or more to
go before it is displaced as
a refrigerant.
Don Kane,
P.E.
CTTC
Chair
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