R717 Ammonia as a refrigerant

Ammonia has a reputation in the conventional refrigeration industry as being dangerous

History of ammonia in the refrigeration industry

Ammonia (NH3 or R717) is the refrigerant that was first used in cold steam engines around 1870. More than 100 years ago, it has been used as a refrigerant in large-scale refrigeration and industrial plants.

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 plant).

The ozone depletion potential (ODP) of ammonia is 0. Thus, ammonia is considered to be relatively environmentally friendly.

The low molar mass of NH3 in relation to air means that gaseous refrigerant from a refrigeration system rises very quickly in the room and can be brought out of the room via an exhaust fan.

In the stratosphere, the lifetime of NH3 is about seven to fourteen days. Thus it is considered very short-lived.

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

Refrigeration systems with a lower evaporation temperature than -33 ° C thus work in the vacuum range. Thus, all leaks on the suction side lead to the entry of air and humidity into the refrigeration system.

At water (moisture input) NH3 has a high affinity. 1 kg of water can theoretically dissolve up to 7 kg NH3; it produces ammonium hydroxide (sal ammoniac). The redissolution of NH3 is an exothermic process. The solution heats up strongly.

An NH3 plant with high water content reduces the performance. Here it is advisable to install a NH3 drying plant (also on loan).

As a general rule, systems operating in the vacuum range should be equipped with an automatic air vent. This ensures that foreign gases are permanently removed from the refrigeration system.

Another important issue with NH3 refrigeration systems is the refrigeration oil.

In contrast to freons, NH3 does not combine with the oils used as standard, which results in a fundamentally different oil return.

Furthermore, NH3 plants must always be constructed of steel or stainless steel, since NH3 copper and z. B. attacks bronze and destroyed. Thus, manufacturers and their products for NH3 refrigeration systems are usually completely different from conventional freon or carbon dioxide (CO2) refrigeration systems.

BUT

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

In my opinion, the fear is completely unfounded!

How dangerous is NH3?

Previously, ammonia pharyngeal ampoules were used to rescue people from fainting; nowadays it is used to treat, for example, borderline patients.

While countless people around the world fetch their breakfast eggs from the chicken coop without being deterred by the undisputedly strong ammonia odor of such a facility, NH3 is considered a health risk in industrial engine rooms.

NH3 is rather harmless compared to CO2.

The perception threshold of NH3 for humans is 1-3 ppm and is so low that one has already long since fled before a health-threatening condition occurs.

CO2, on the other hand, does not smell. It is heavier than air, settles in the lungs when inhaled, stays there and can no longer be coughed off. An asphyxiation is almost inevitable.

For newly built refrigeration systems with NH3, you can smell almost nothing!

For NH3 refrigeration systems, high safety requirements set by current standards and directives apply. As a result, an accident case can be almost ruled out.

Only during system filling or servicing a small amount of toxic ammonia can escape. A trained refrigeration technician protects himself through deliberate, proven work steps and personal protective equipment (PPE).

It remains to be considered that NH3 is flammable. It ignites at a concentration in the air between 15% and 28%.

The complete shutdown of a system but takes place at a concentration of about 30,000 ppm, ie about 3%.

However, the ignition temperature is very high at 650 ° C and the combustion must be permanently maintained by a backup fire.

Nevertheless, a high concentration of NH3 in closed rooms must be avoided! This is achieved by installing a ventilation system in accordance with regulations and standards. This would ensure that the deliberate operation of a NH3 system, the risk of fire can be almost excluded.

Cost check

From the point of view of overall costs, NH3 refrigeration systems perform particularly well with their low operating costs compared to R134a and R404A.

Even compared to the meanwhile banned refrigerant R22 NH3 is clearly better - primarily due to the low energy consumption.

Due to the extraordinarily high enthalpy difference of NH3 (about 6 times higher than R22) and a comparatively low circulating mass flow, NH3 has by far the best values.

This means that NH3 has the largest cooling capacity per kg of refrigerant.

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

In addition, NH3 is by far the cheapest in comparison to all other refrigerants.