ASHRAE® Long Island

American Society of Heating, Refrigerating and Air Conditioning Engineers
ASHRAE Long Island Chapter 006

C T T C

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