Ammonia (NH3) is a well-known refrigerant, particularly applicable in large, industrial plants where its advantages can be fully utilized without compromising safety.
Ammonia is renowned for its favorable thermodynamic properties. In a wide range of applications, it outperforms synthetic refrigerants. However, it has a number of drawbacks that have so far prevented the use of ammonia for commercial applications, e.g. material compatibility, toxicity, and flammability.
Ammonia is a highly efficient refrigerant, with a theoretical efficiency slightly higher than that of R134a or propane. In practice, there is evidence that ammonia systems perform even better than in theory.
Due to the toxicity and flammability of ammonia, installations using ammonia are governed by national regulations. Even with strict regulation in place to secure safety in operation, there is pressure on ammonia installations to reduce charge levels, especially when situated in populated areas.
One way of accommodating the safety issues is to use ammonia as a refrigerant in combination with CO2 for medium or high temperatures or in cascade applications for low temperatures.
Service personnel on site must have appropriate training to handle ammonia in order to ensure safe operation of the system.
Ammonia is a natural refrigerant. It has zero ODP and zero GWP. In combination with its efficiency, it is one of the most environmentally friendly refrigerants.
The operating pressures of ammonia are comparable to those of other common refrigerants (HFCs and HCs) and it has a relatively high normal boiling point (–33.3 °C). Ammonia has high volumetric capacity, so ammonia pipe lines are smaller than HFC pipe lines. It should be noted, however, that when ammonia is used for suction lines, the lines are larger compared to those of CO2.
Ammonia is compatible with all common materials except copper and brass. This means that only welded steel pipes can be used. Furthermore, it is necessary to use either semi hermetic compressors or hermetic compressors with special motor coatings or aluminium motor wires.
Ammonia is not miscible with common oils. In addition, ammonia is lighter than oil, which makes oil return systems fairly simple.
Ammonia is an inexpensive and abundantly available refrigerant. Ammonia installations, however, tend to be relatively expensive due to the requirement for steel tubing, semi hermetic compressors, and the installation of a number of safety devices, such as gas detectors.
Today ammonia is primarily used in industrial refrigeration applications:
• Distribution cold stores
• Freezing tunnels
• Food processing plants (slaughterhouses, ice cream factories, etc.)
• Fish trawlers
These applications are high capacity charges however, there are on-going efforts to develop low-charge ammonia systems in order to take further advantage of the beneficial thermodynamic and environmental properties of ammonia. Some of the efforts undertaken by Danfoss and research partners are to develop low-charge systems with new, advanced control algorithms, further development of ammonia-optimised heat exchangers, DX systems and new cascade systems with CO2.
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