AMMONIA R717 (NH3)

Ammonia is excellent refrigerant which is in use in the past 130 years mostly for larger cooling capacities in refrigerating systems in industries. Its advantages are:

ODP = 0, GWP < 1
Excellent thermodynamic characteristics: small molecule mass, large latent heat, large vapor density and excellent for heat transfer.
High critical temperature (132°C) which enables high values for energy efficiency cycles at high condensing temperatures.
In vapor condition it is easier then the air.
Its smell causes attention before danger arrives.
Low price.

Negative ammonia sides are: it is toxic, flammable in concentration in the air from 15.5 to 28%, it is not compatible with copper, and because bigger adiabatic exponent, temperatures on the discharge side are higher comparing with other refrigerants.

Ammonia refrigerating systems are liable to legal regulations and standards because of the safety of the people, but these exist for other refrigerants as well. If these regulations and standards are applied in practice, and also a good training for the personal in maintaining provided, a danger from ammonia usage does not exist. It is the best refrigerant in the cases where it can be used which a fact is shown from the practice in the past 130 years. Incidents and fatal consequences from usage of ammonia refrigerating systems in the Balkan region it is almost none, although the level of liability to the regulations is not the case as in the developed countries. Because of superior ammonia advantages, today there is big effort for spreading its appliance in the fields where HFCs are dominant. Because the only obstacle is safety reason, major goal of today development is how to decrease the charge (quantity) of ammonia in refrigerating systems. Regarding that, it should be avoid large reservoirs with liquid ammonia, as well as large pump systems. Already introduced in practice are plate heat exchangers, also "dry" evaporators with thermal expansion valves, but here remains a problem with the lubricating oil.

One of the ways for decreasing the ammonia charging is appliance of secondary coolants. With that the presence of the ammonia is limited only in machine room, and the secondary coolants circulate in the spaces where the cooling is occurred. Beside traditional secondary coolants (water, mixture with glycol, calcium-chloride, and sodium-chloride) on the market appeared new coolant: potassium-acetate with better characteristics for heat transfer. Pretty attractive results are achieved during the appliance of CO2 as secondary coolant.

In order to decrease potential places for ammonia leakage, it goes to new concept for compact constructions of refrigerating units, fully sealed and tested in factories, and most commonly with charging less than 50 kg of ammonia. On the market already there are present water chillers, so the last few years in European countries are installed a large number of air conditioning systems with ammonia, in commercial and public objects too. It is expected a huge expansion of these applications in next period because with increasing the volume of production, the prices of these units will fall. In the large industrial systems where there is a need for low temperatures (-30 to -50 °C) new concept is already applied with cascade refrigerating systems with NH3/CO2. Here the ammonia charging is also limited only in the machine room (high cascade), and in the equipment and the spaces where the cooling is taking part is CO2 (low cascade) which is harmless.

Also, the cascade concept will probably have its expansion in the application in the supermarkets where HFC (and HCFC) refrigerants with large charging were dominant so far and where great leakages in atmosphere are appeared.