REFRIGERANTS
The green credentials of modern ammonia systems
Ammonia is efficient, cost-effective and has outstanding green credentials. Now, developments in technology and manufacturing are addressing its one downside as Kevin Glass, managing director of Bitzer UK, explains.
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mmonia is arguably one of the greenest refrigerants available. Due to its thermodynamic properties, it is highly energy efficient, requiring the lowest energy input of any refrigerant to produce a given refrigerating effect.
In economic terms, not only are ammonia systems efficient and cost less to run, but the refrigerant itself is relatively inexpensive, even in the high purity grade required for use in refrigeration. Given the large charges required by some industrial systems, this can translate into substantial savings over synthetic refrigerants. In environmental terms, ammonia has impeccable credentials. Both the ozone depletion potential and global warming potential of ammonia is zero. This, combined with its inherent efficiency, means it has the lowest total equivalent warming impact (TEWI) of any refrigerant (where TEWI is the sum of the direct and indirect effects of an ammonia system on global warming over its lifetime).
Although ammonia is made through industrial processes for use in refrigeration, as the substance occurs in nature it is considered a natural refrigerant. Ammonia is part of Earth’s nitrogen cycle and is produced in soil as a result of decomposition of organic matter. This contrasts with synthetic fluorinated refrigerants, which are entirely man-made and do not occur naturally in Earth’s ecosystems.
For all these reasons, ammonia has been used in industrial refrigeration for more than a century. While there have been many changes in refrigerants used in smaller commercial refrigeration and air conditioning over this time, due mainly to growing understanding of their impact on the environment, ammonia has remained the
14 June 2019
industry’s mainstay for industrial applications. Against these valuable upsides, ammonia has two well-known and important downsides – it is flammable in certain concentrations under certain conditions, and it is toxic. In terms of flammability, it is considered relatively low-risk due to its chemical affinity to moisture in the air. This gives it an advantage over hydrocarbon refrigerants, such as propane, which have a much higher flammability rating.
Ammonia’s chief Achilles heel is its toxicity. The risk is mitigated to a degree by two factors: ammonia’s distinctive, pungent smell is detectable at concentrations well below those considered to be harmful. This so-called ‘self-alarming’ property is not shared by other potentially hazardous refrigerants. Secondly, ammonia is lighter than air. In the event of a leak, therefore, it tends to rise and dissipate in the atmosphere. This contrasts with other common refrigerants which are generally heavier than air, and therefore tend to collect in depressions and may pose an asphyxiation risk.
Recent advances in technology, system design and manufacturing processes have addressed these potential risks associated with use of ammonia and open the way to safer application in future.
For example, due to the nature of industrial refrigeration applications, ammonia systems have traditionally often been designed and built as one-offs and assembled on site. This approach inevitably incurs additional risk due to the less-than-ideal conditions often encountered.
The recent move towards the production of complete ammonia systems in pristine factory-controlled conditions eliminates the vagaries and rough-and-tumble
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