Ammonia, the “New Thing” in Refrigerants?

“Tomorrow was created yesterday” penned British author John le Carre’ confirming the old saying that “History repeats itself”.  The HVAC industry is seeing the technologies of yesterday presented as new and what was once considered old-school, is now seen as the future. Consider, for example, the resurgence of ammonia as a refrigerant.

The Global Cold Chain Alliance, a non-profit organization that advocates for companies involved in the temperature-controlled food industry, had an article on their website entitled “Ammonia: The Refrigerant of the Future”.  A similar article in the NEWS noted that ammonia-based refrigerants “remain on the list of possible refrigerants of the future.”  Apparently, ammonia is the “new thing” in refrigerants, maybe “the next best thing”.

Articles describing the energy-efficient and environmentally-friendly future of ammonia refrigeration are interesting if for no other reason than the fact that ammonia is actually not new. In fact, as a refrigerant, ammonia is quite old having been used in the first air conditioning system ever invented back in 1903. Ammonia slipped out of the spotlight as the commercial refrigeration and home air conditioning industries became two different markets in the mid-1950’s. Today, with new laws governing synthetic refrigerants in air conditioning units, ammonia is back in the discussion.

Regulatory oversight established by the United States’ acceptance of the Montreal Protocol is reducing the use of, and in the case of R22, the production of many CFC’s, HCFC’s, and other synthetic refrigerants. These regulations have dramatically shifted the HVACR industry away from common refrigerants like R12 and R22 towards refrigerants with lower Ozone Depleting Potential (ODP) and Global Warming Potential (GWP) ratings including R134a and R410a. R134a and R410a are both abundant, energy efficient, and perfectly legal and safe to use in commercial HVAC systems. Although there is no phase-out plan for these refrigerants, a recent EPA program suggests that a phase-out may be in the works. In September of 2016, the EPA announced that beginning in 2024, R134a and R410a can no longer be used in new chillers. The HVAC industry suspects something is coming and is now researching the next safe refrigerant. Ammonia may be what they’re looking for.

Ammonia (R717) brings a lot to the table as a refrigerant. Ammonia is widely used today in large industrial and commercial refrigeration systems because of its excellent thermodynamic properties including being 3% – 10% more efficient than R22 and R134a.  Furthermore, the ASHRAE 2013 Handbook–Fundamentals, Chapter 29, Table 8 lists ammonia systems as having a higher theoretical Coefficient of Performance (COP) than other common refrigerants. From a cost standpoint, refrigerant grade ammonia is inexpensive at about $1 per pound compared to $4 per pound for R410a. There is an interesting article in the NEWS comparing the cost and system performance of R-134a chillers and ammonia chillers, with ammonia getting high marks for overall efficiency and applicability in large industrial facilities.

As a natural refrigerant, federal regulators are encouraged by ammonia’s growing popularity because both the GWP and ODP rating of ammonia are zero. That means ammonia has no effect on the ozone layer or global warming. In comparison, the GWP of the now-phased-out R22 is 1,760, environmentally friendly R134a is 1,300, but ammonia (R717) is 0. Ammonia is so safe to the environment that when it needs to be emptied from a cooling system, it is typically discharged directly to the atmosphere without the need of a reclaim machine required for CFC’s and HCFC’s.

There are some downsides to using ammonia as a refrigerant, but regulatory maturation and improving technology are likely to reduce the impact of these negative qualities. Ammonia in large quantities is toxic to humans and is classified as an “extremely hazardous substance” by the EPA. However, ammonia’s sharp odor is itself a protective feature because even in very diluted concentrations, people who smell ammonia quickly move away from the source to avoid the respiratory irritation. So although ammonia is toxic, ammonia leaks can be detected rapidly and the leak can be repaired before major damage occurs. Ammonia is also flammable in high concentrations, but the American Society of Heating, Refrigerating and Air-Conditioning Engineers’ (ASHRAE) position document Ammonia as a Refrigerant notes that ammonia “is difficult to ignite and will not support combustion after the ignition source is withdrawn.”  This is not to diminish the dangers of concentrated ammonia as there have been injuries and fatalities related to ammonia explosions. But, like every chemical used in the HVAC industry, risk can be mitigated with proper use and correct safety planning.

Finally, there is a cost downside to ammonia. Although refrigerant grade ammonia itself is cheaper than other common refrigerants, the piping systems through which ammonia can flow are not the same as standard HVAC systems. Whereas most commercial HVAC systems use copper pipe as the refrigerant circuit, ammonia chemically reacts with copper and corrodes the inner pipe wall leading to leaks or pipe failure. As a result, ammonia cooling systems must be built with aluminum or stainless steel pipes that are much more expensive than standard copper piping.

With all of these factors taken into account, however, the outlook for increased ammonia use as a commercial refrigerant is high. ASHRAE’s position paper closes with their goal to “[e]ncourage the broad use of ammonia in traditional and new applications.”

So it seems the adage was right. Tomorrow’s HVAC technology really was created yesterday and the HVAC industry is seeing this in ammonia’s resurgence as a viable alternative to synthetic refrigerants.

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