By Andrew Perks
Although I was unable to visit the IIR conference in Ohrid this year, I have received the technical papers discussing the drive to bring ammonia into the market previously dominated by the hydrocarbon refrigerants.
It is always educational and thought-provoking to reflect on other players in the industry in the Northern Hemisphere, specifically the papers from Andy Pearson of Star, and Pega Hrnjak of the University of Illinois. The following are some interesting observations and conclusions noted:
The history of ammonia goes back to 1834, but over this period, due to its toxicity and potential flammability, it has gone in and out of fashion. Throughout the 20th century ammonia remained a common refrigerant for industrial applications (food factories, warehouses, chemical processes and other large refrigeration applications), but due to component constraints it was hardly ever used in other markets.
With the introduction of R22 and R502 fluorocarbons more specifically suited to industrial applications, ammonia came under threat and looked like it would fade out of use in the 1960s as CO2 did in the 1950s. But the superior efficiency and ease of use of ammonia meant that it did not completely disappear. In the late 1980s it was recognised that in order to combat climate change CFCs and then HCFCs had to be replaced with green refrigerants. Ammonia was well known in the industrial market as it has no Global Warming Potential (GWP) or Ozone Depletion Potential (ODP), so it began to make inroads into a variety of new refrigeration applications throughout many parts of the world. This has resulted in some very innovative solutions.
Without a doubt, the ammonia industry is changing – reducing risks, modernising, and moving towards more compact systems with lower refrigerant charges.
Several methods are being investigated including central plant systems but also those with DX evaporators, plate heat exchangers, or individual package systems spread throughout the site, using condensing units/evaporator assemblies at the service points. These can be flooded or DX. Based on this design concept the ammonia charge can easily be reduced by 75% and, compared to a traditional pumped system, further reductions are feasible. There are three charge levels being investigated: Ultra-low charge < 50 g/kW, Low charge < 0.5kg/kW and Regular charge < 5 kg/kW. These are very low charges by current standards in South Africa.
These charges should be compared to the charge of other A2L refrigerants based on flammability, with additional emphasis on the B2L nature of ammonia. Based on specific system charges in the range of 20-50g/kW, ULC chillers for systems with capacity per unit or circuits of 50-100kW could be sufficient for a variety of current needs and equipment size. Setting a low industry acceptable charge would further incentivise work on extremely low charged chillers to reduce ammonia volumes to make them accepted as a real competitor for chiller applications.
In California, any ammonia installation is subject to rigorous inspection and operating procedures if the charge of ammonia in a system exceeds 500lb (220kg). This is not possible with a central plant using a pumped system, but by breaking the total installation into individual low charge modules it is easy to keep each module below the threshold limit. This will enable ammonia to be considered for installations which previously would not tolerate the risk of toxic consequences of leakage.
In this respect the majority of success stories have been where the end-user was actively involved in the construction decisions and took a “whole-life” approach.
This is an issue in markets where the person who pays for the construction is not the same as the person who has to budget for the operation, maintenance and replacement of the system. With the current issues concerning power and water availability around the world, operational costs are becoming a major factor.
Capital cost for the installation of an ammonia system remains a very significant factor compared to the cheaper HFO plants resulting in these less efficient cheaper plants being purchased. The expected life span of an HFO plant is said to be around 10 years, but for an ammonia system 30 years can be expected. Obviously with proper maintenance and care these figures can be extended. With the latest trends, new refrigerants are arriving on the market virtually every year. Who knows how long the most fashionable refrigerant will still be available, but you can rest assured ammonia – in whatever guise – will still be there?
However, if it is not possible to engineer innovative designs and significant cost reductions in the manufacturing and deployment of ammonia and CO2 systems then there is a risk that the ground which has been gained in new areas of installation will be lost to cheaper HFO plants. In some instances, an ammonia plant has a payback period of two years against other refrigerants. From there, it’s all money in the bank.
Overseas, ammonia will continue to be the preferred refrigerant for industrial systems in jurisdictions where its use is permitted. Countries which have in recent years moved away from ammonia for industrial applications due to the safety concerns related to large site installed systems can benefit greatly from the new designs of low charge, high efficiency systems that are being developed. This should also bring about a significant increase in the use of ammonia in developing economies.
Safety is always an important consideration, and both ammonia and CO2 have developed an excellent safety record, totally compatible with the fluorocarbon sector, over the last 30 years. There is a very good understanding of what it takes to design a safe system and how that level of security can be maintained. With the exception of the toxicity of ammonia in direct systems, safety should not, in most cases, be a reason for rejecting ammonia systems as they can be designed to be as safe as any other system.