R717 Ammonia as a Refrigerant

History of Ammonia in the Refrigeration Industry

Ammonia (NH₃ or R717) is the refrigerant that was first used in vapor compression machines around 1870. It has thus been used in large-scale refrigeration and industrial systems for more than 100 years.

Key Data

NH₃ has the lowest TEWI (Total Equivalent Warming Impact = direct greenhouse effect of the refrigerant as well as indirect greenhouse effect due to the energy consumption of the system).

The ozone depletion potential (ODP) of ammonia is 0, making it relatively environmentally friendly.

Due to the low molar mass of NH₃ compared to air, gaseous refrigerant escaping from a refrigeration system rises quickly in the room and can be vented out through a fan near the ceiling.

In the stratosphere, the lifetime of NH₃ is about seven to fourteen days, classifying it as a short-lived substance.

The evaporation temperature of NH₃ is approximately -33°C (at atmospheric pressure).

Refrigeration systems with an evaporation temperature lower than -33°C operate in a vacuum. As a result, any leaks on the suction side will allow air and moisture to enter the refrigeration system.

NH₃ has a strong affinity for water (moisture entry). One kilogram of water can theoretically dissolve up to 7 kilograms of NH₃, resulting in ammonium hydroxide (ammonia water). Dissolving NH₃ is an exothermic process, which heats the solution significantly.

An NH₃ system with high water content experiences a loss in performance. In such cases, it is recommended to install an NH₃ drying system (even on loan).

Systems operating in a vacuum should generally be equipped with an automatic air purger to continuously remove non-condensable gases from the refrigeration system.

Another important point in NH₃ refrigeration systems is the compressor oil.

Unlike freons, NH₃ does not mix with standard oils, resulting in a fundamentally different oil return process.

Furthermore, NH₃ systems must be made of steel or stainless steel because NH₃ attacks and destroys copper and, for example, bronze. As a result, manufacturers and products for NH₃ refrigeration systems are often different from those for conventional freon or CO₂ refrigeration systems.

But:

In the conventional refrigeration industry, NH₃ has a reputation for being dangerous! Is this a prejudice?

In my opinion, this fear is completely unfounded!

How dangerous is NH₃?

In the past, ammonia smelling salts were used to revive unconscious people. Today, it is used, for example, to treat patients with borderline personality disorder.

While countless people around the world collect their breakfast eggs from chicken coops without being deterred by the strong ammonia smell, NH₃ is considered a health risk in industrial machine rooms.

In fact, NH₃ is comparatively less dangerous than CO₂.

The human detection threshold for NH₃ is 1–3 ppm, which is so low that people would flee long before a harmful concentration is reached.

CO₂, on the other hand, has no odor. It is heavier than air, settles in the lungs upon inhalation, and cannot be coughed out. Suffocation is almost inevitable.

In newly built NH₃ refrigeration systems, you can hardly smell anything!

NH₃ refrigeration systems are subject to high safety requirements set by current standards and regulations, making an emergency scenario nearly impossible.

Only during system filling or maintenance can a small amount of toxic ammonia escape. A trained refrigeration technician protects themselves through deliberate, practiced procedures and personal protective equipment (PPE).

It is important to remember that NH₃ is flammable. It ignites at concentrations between 15% and 28% in air.

However, the complete shutdown of a system occurs at a concentration of approximately 30,000 ppm, or about 3%.

The ignition temperature of NH₃ is very high at 650°C, and combustion must be maintained by an external flame.

Nevertheless, high concentrations of NH₃ in enclosed spaces must be avoided! This is achieved by installing a ventilation system in accordance with regulations and standards. As a result, the risk of a fire can be almost entirely eliminated when operating an NH₃ system with care.

Cost Check

In terms of total costs, NH₃ refrigeration systems perform particularly well compared to R134a and R404A, due to their low operating costs.

Even in comparison to the now-banned refrigerant R22, NH₃ is clearly superior, primarily due to its low energy consumption.

With NH₃’s exceptionally high enthalpy difference (approximately six times higher than R22) and relatively low circulating mass flow, NH₃ achieves by far the best values.

This means that NH₃ provides the highest cooling capacity per kilogram of refrigerant.

Thus, NH₃ refrigeration systems achieve high COP values (Coefficient of Performance) compared to other refrigerants.

Additionally, NH₃ is by far the most cost-effective refrigerant compared to all others.

Conclusion

From an economic perspective and in terms of environmental friendliness, NH₃ is the ideal refrigerant.

Its toxicity should not be a deterrent, as, after all, sniffing a bit of NH₃ clears the sinuses.

R. Desens