Why ammonia in industrial refrigeration?
Ammonia offers a wealth of benefits for industrial refrigeration
Ammonia was used for refrigeration in 1876, for the first time in a vapour compression machine by Carl Von Linde. Other refrigerants like CO2, SO2 also were commonly used till 1920s.
Development of CFC’s (Chlorofluorocarbons) in USA, in 1920s swung the pendulum in favour of these refrigerants, as compared to all other refrigerants used in those days, CFC’s were considered harmless and extremely stable chemicals. The consequences to the outer environment of massive releases of refrigerant could not be foreseen in those days. “CFC” refrigerants were promoted as safety refrigerants, resulting in an accelerating demand and CFC’s success. These refrigerants became known as God sent and man-made chemicals.
Due to success of CFC’s, Ammonia came under heavy pressure, but held its position, especially in large industrial installations and food preservation.
In 1980’s the harmful effects of CFC refrigerants became apparent and it was generally accepted that the CFC refrigerants are contributing to depletion of ozone layer and to global warming, finally resulting in Montreal protocol (1989) where almost all countries agreed to phase out CFC’s in a time bound program.
In view of seriousness of damage to atmosphere and resulting dangers due to CFC/ HCFC emissions as also due to global warming effects, the revisions in Montreal protocol (1990), 1992(Copenhagen) and 1998 Kyoto Japan demanded accelerated phase out schedule. Even HCFC’s are also to be phased out and Europe has taken the lead.
Many countries in Europe have stopped use of HCFC refrigerants, and new refrigerants as well as well-tried and trusted refrigerants like Ammonia and Carbon Dioxide are being considered for various new applications as well.
Ammonia has a number of benefits, which has been proven by many decades of application of ammonia refrigeration systems.
1. Energy efficiency
Ammonia is one of the most efficient applications out there, with the application range from high to low temperatures. With the ever increasing focus on energy consumption, ammonia systems are a safe and sustainable choice for the future. Typically a flooded ammonia system would be 15-20 % more efficient than a DX R404A counterpart. Recent developments of NH3 and CO2 combination contributed to increase the efficiency further. NH3/CO2 cascaded is extremely efficient for low and very low temperature applications (below -40’C), while NH3/CO2 brine systems are around 20% more efficient than traditional brines
Ammonia is the most environmentally friendly refrigerant. It belongs to the group of so called “natural” refrigerants, and it has both GWP (Global Warming Potential) and ODP (Ozone Depletion Potential) equal to zero.
Ammonia is a toxic refrigerant, and it is also flammable at certain concentrations. That is why it has to be handled with care, and all ammonia systems have to be designed with safety in mind. At the same time, unlike most other refrigerants, it has a characteristic odor that can be detected by humans even at very low concentrations. That gives a warning sign even in case of minor ammonia leakages. In case it is necessary to reduce ammonia charge, combination of ammonia and CO2 (as cascade or as brine) could be a good and efficient option.
4. Smaller pipe sizes
In both vapour and liquid phase ammonia requires smaller pipe diameters than most chemical refrigerants.
5. Better heat transfer
Ammonia has better heat transfer properties than most of chemical refrigerants and therefore allow for the use of equipment with a smaller heat transfer area. Thereby plant construction cost will be lower. But as these properties also benefit the thermodynamic efficiency in the system, it also reduces the operating costs of the system.
6. Refrigerant price
In many countries the cost of ammonia (per kg) is considerably lower than the cost of HFCs. This advantage is even multiplied by the fact that ammonia has a lower density in liquid phase. Furthermore as any leakage of ammonia will be detected very quickly due to the odour, hence any potential loss of refrigerant will also be lower.
Ammonia is not a universal refrigerant, and mainly suitable for industrial and heavy commercial applications. Ammonia’s toxicity, flammability and material compatibility have to be taken in to account. At the same time, there is a huge global population of ammonia systems where those challenges are successfully dealt with.