Information About AMMONIA

Ammonia is the only one of the original refrigerants which are able to stand up to the onslaught from the halocarbons. It has been used for decades in industrial refrigeration plants and its continued popularity throughout the CFC era amply demonstrates its unique benefits in cold and chilled storage applications. It has no ozone depletion potential and no global warming potential. Its energy efficiency is at last as good as, and in most applications better than, R22.

There are, however, a number of drawbacks. The high compressor discharge temperature restricts the use of single-stage compression to evaporating temperatures above -10°C, unless screw compressors are utilized. Ammonia is not compatible with conventional lubricants and is highly corrosive to copper. It cannot therefore be used with hermetic or semi-hermetic compressors unless aluminium windings are used, and leakage from shaft seals is difficult to eliminate. A Japanese manufacturer claims to have overcome the shaft seal problem by using an air-tight can between the motor’s rotor and stator. No seal is needed and it said to be possible to completely prevent leakage of ammonia.

Traditionally, cold and chilled store applications using ammonia have been designed as flooded systems. A surge drum of liquid ammonia is reduced in temperature by the compressor evaporating the vapor from the top of the drum. This low-temperature liquid ammonia is then pumped to the blower units. More recently, the development of ammonia-soluble lubricants now allows fully automated operation and direct expansion evaporators. These will be very similar to R22 systems, although pipe work and materials will be predominantly mild steel, stainless steel and, to a lesser extent, aluminum.

It is important to note the difference between the meaning of the terms ‘soluble’ and ‘miscible’ in the context of ammonia compatible lubricants:

· Soluble refers to the ability of ammonia gas to dissolve in liquid oil.
· Miscible refers to the ability of liquid ammonia to mix completely with liquid oil.

Ammonia-soluble oils offer particular advantages in respect of refrigeration plant operating costs. The coefficient of performance of refrigeration systems is improved due to the increased heat transfer coefficient of evaporators running continuously in clean condition with no oil or wax films. Liquid ammonia and these oils are miscible so that in the evaporator the mixture has a viscosity of the same order as liquid ammonia itself. This means that there is no longer an oil pour point in the evaporator. The advantage of this type of oil becomes greater the lower the evaporating temperature of the system. The vapor pressure is low, helping to minimize oil carry over, the lubrication properties of suitably formulated products is excellent and the life is expected to be as long as the best synthetic non-soluble products currently in use. Lower the temperature, the greater the improvement.

As with synthetic oils used for HFCs it should be noted that these oils may have a tendency to absorb water from the atmosphere if the containers are left open and these should therefore be kept sealed.

The ammonia industry has an excellent opportunity to increase its market share and to grow into a major industrial activity. It is apparent that user industries are on the threshold of making major policy decisions and they need to be persuaded to consider ammonia as their preferred refrigerant. The question is ‘When and how quickly will the ammonia refrigeration industry change into a major global industrial player in the market sectors which have been lost to halocarbons?’ There is an urgent need to embark on a sophisticated strategic plan for the promotion and wider acceptance of ammonia technology as a valid commercial, and environmentally superior, alternative to halocarbons.

It must be recognized, however, that there are three major obstacles.

1. The halocarbon chemical industry has fought a highly successful marketing campaign for many years and will not easily relinquish market share.
2. Any large-scale return to ammonia will be hampered by an acute skills shortage among refrigeration engineers. Ammonia conversion courses for halocarbon engineers are expensive, time consuming and intellectually demanding. So far very few have made the change.
3. Finally, there are the safety issues. Ammonia is both toxic and flammable and must be kept away from people and products.

Standard defines ammonia as a type of refrigerant, that is to say both toxic and mildly flammable. The following restrictions are also applicable to other refrigerants, that is to say non-toxic, mildly flammable refrigerants such as R32 and R152A.
1. Where the system is located in an occupied space where the number of people is not restricted the refrigerant charge shall not exceed 10 kg.
2. Where the density of occupancy is lower than one person per 10 m2 of floor area, the refrigerant charge shall not exceed 50 kg.
3. Where the high-pressure side is located in a plant room or in the open air there shall be no restriction of refrigerant charge provided the refrigerating system does not extend to rooms where the density of occupancy is greater than one person per 10m2 Floor area.
4. For indirect systems utilizing secondary refrigerants, there shall be no restriction of charge except as required by local planning and building regulations.


There is no doubt that ammonia will remain the ‘best’ industrial refrigerant for the foreseeable future, particularly because it has a zero ODP. It is worthwhile to provide more information on ammonia at this point.

Ammonia or R717 is produced by combining free nitrogen and hydrogen under high pressure and temperature in the presence of a catalyst. The process most commonly used is the Haber-Bosch method. The molecular mass of ammonia is 17.03, while that for R22 is 86.47.

The nitrogen component is inert in the combustion reaction and account for the limited flammability of ammonia. Ammonia’s high lower limit of flammability and low heat of combustion substantially reduce its combustion/explosion hazards. Ammonia/air flammable by spark ignition at concentration of 16-27% by volume in air. However oil carried by ammonia lowers this level considerably, so that a figure of 4% by volume in air is considered the practical safe limit to prevent explosion.

Industrial-grade anhydrous ammonia is the most economically abundant and efficient heat-transfer medium available for industrial refrigeration. Its pungent odor provides an extremely effective self-alarming and leak-detecting characteristic.

One of the advantages of R12 compared with R717 is the relatively low condensing pressure. However, since, the only CFC refrigerant with unrestricted use is R22, this advantage is lost.

In virtually all refrigeration systems, the use of pressure vessels involves the risk of the vessel reputing, regardless of the fluid it contains, whether it be ammonia, a CFC or even air. In fact the nature of the risk presented by the fluid can only be secondary to the mechanical risk. However, it is obvious that the more regroups standards applied to vessels, pipework and plant for ammonia, compared with CFC, systems make an ammonia systems inherently more safe. Better reliability and lower maintenance costs for ammonia systems result from the use of: steel rather than copper pipework; welding rather than brazing for jointing; bolted flanges rather than flares connectors; and measures to prevent the ingress of impurities such as dirt, moisture and metallic particles, which adversely affect the refrigerant and oil. Furthermore, the management of oil in ammonia systems is simpler than that for CFC systems.

However, any malfunctioning system will always result in damage to the product or failure of the process, if prompt intervention is not made. Preventative maintenance, regular testing and continuous inspections. Either by operating or maintenance staff or by means of tele-monitoring, are essential to prevent breakdown, whatever the refrigerant being used.

Finally, here are some advantages and disadvantages of ammonia as a refrigerant:

1. Zero ODP and low GWP values
2. High latent thermal energy per unit mass
3. Large enthalpy difference per unit volume
4. High COP
5. Good heat-transfer characteristics caused by the high thermal conductivity, high latent thermal energy, low viscosity and low liquid density compared with the CFCs and HCFCs
6. Low molecular weight, M = 17.03, provides another advantage of low pressure-drop through compressor valves and ports - the disadvantage is the high value of k compared with those for CFCs and HCFCs
7. High compression ratio compared with that for most CFCs
8. Low purchase price and low maintenance costs
9. Toxicity and unpleasant smell
10. Leakage’s easy to detect.

It is useful to draw some comparisons between R717 and R22 at this juncture when considering point 5 above:

Characteristic Ratio R717/R22
Specific heat (liquid and vapour) 4:1
Latent thermal energy (Lv) 6:1
Thermal conductivity 5.5:1
Viscosity 0.8:1
Liquid density 0.5:1