06 October 2017
Ed Whinyates of Stonegrove Refrigeration Services separates the fact from the fiction when it comes to choosing ammonia as your next refrigerant.
Ammonia refrigerant (also known as R717 and its chemical formula NH3) has been used as a refrigerant in industrial applications for more than 150 years. It offers a number of significant environmental and operational benefits with zero direct global warming potential (GWP) and zero ozone depleting potential (ODP).
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When talking about ammonia as a refrigerant it can be a divisive subject, mainly due to perceptions about safety. Rather than overlook or dismiss these perceptions it is better to acknowledge and offer sensible and proven facts to alleviate concerns.
Ammonia’s very nature probably makes it the safest refrigerant to operate. Due to its acute toxicity, safety forms a major part in design and operation of refrigeration systems that contain ammonia. Despite these hazards ammonia has an excellent safety record when installed and maintained correctly. Installers of ammonia refrigeration systems are legally required to conform to strict regulations including but not limited to the Provision and Use of Work Equipment Regulations 1998 (PUWER), the Pressure Equipment Regulations 1999 (PER), the Pressure Systems Safety Regulations 2000 (PSSR) and the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). There is also easily accessible guidance from specialist bodies like the Institute of Refrigeration.
Serious incidents involving ammonia are thankfully rare, however on the very few occasions when they do occur it is normally an accident rather than system failure. The design of ammonia systems has advanced to a point where smaller refrigerant charges are required for maximum performance. (Note; The refrigerant charge refers to the amount of refrigerant contained within a sealed pressure system). For example, using ammonia as a primary refrigerant with food-safe glycol as the secondary refrigerant - so charge of ammonia is very low and is contained within the plant room. This in turn means a greatly reduced chance of serious injury should an accident occur.
With its distinctive odour in minute quantities ammonia can be quickly and easily detected. Coupled with a comprehensive leak detection and monitoring system as well as strict maintenance regimes with specialist trained engineers, any potential issues can be both prevented and quickly dealt with.
Outside of the safe design and installation of ammonia equipment, there are other safety mechanisms in place including clear documented emergency procedures/risk assessments. In and around the plant room there are alarms, wind-socks, respiratory and protective equipment, room ventilation, warm water showers and eye wash, as well as the expected first aid access.
An ammonia installation offers far more benefits than just the aforementioned safety features.
Ammonia refrigeration is the most cost-effective and energy efficient method of processing and storing frozen and chilled foods. As a refrigerant, ammonia offers distinct advantages over other commonly used industrial refrigerants. It is environmentally compatible so does not deplete the ozone layer or contribute to global warming. Because of its zero GWP it will not have to be replaced with any alternative refrigerants – unlike a lot of current HFC refrigerants that are being phased out.
Ammonia installations tend to be slightly more expensive due to for example the requirement for steel piping and the additional safety devises. However, ammonia has superior thermodynamic qualities so as result uses less electricity and lower energy costs. Reduced operating costs in turn lead to a far quicker pay-back on capital outlay. The properties of ammonia make it perfect for refrigeration use. With ammonia having a greater cooling capacity than other refrigerants the system does not need to work as hard.
The technological advantages of ammonia systems include volumetric efficiency, built in safety features such as leak detection, floats on oil within the system to make it easy to reclaim the oil as part of planned maintenance. it requires only small-dimensioned piping and throttle cross sections, and typically the compressors are smaller – all of which benefit installations.
Ammonia itself is also an inexpensive and abundant refrigerant, so the cost to charge a system is far less per kg than HFCs.
Ammonia is suitable for use in a temperature range from -50°C to +10°C. Because of this it is primarily used in industrial refrigeration applications for perishable goods storage and distribution centres, food processing plants, food manufacturing, dairies and breweries, as well as other non-food applications like ice rinks and water chillers.
Having passed the test of time over more than a century as one of the best choices for industrial applications, ammonia is now receiving attention in areas of application where before it would not have been considered. The commercial refrigerant landscape is changing, so much so that some in the commercial refrigeration industry are looking at new ways to use ammonia as a refrigerant.
The key to ammonia’s accepted use is that it be used in a safe, well-designed system, and maintained to the highest standards.
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