Refrigerants and the future
In May 2018, thirty years after the Montreal Protocol which united 197 nations in the quest to heal the ozone hole, scientists discovered a new source of ozone-depleting refrigerants being emitted into the atmosphere with the apparent origin being eastern Asia.
Since the treaty, which included a ban on trichlorofluoromethane (CFC-11), levels of the chemical had been falling steadily, but that decline suddenly slowed down by 50 per cent. Initial thoughts were that some rogue organisations had resumed its manufacture.
However, it didn’t take too long to track down the culprits. Within a week of discovering the pollution, researchers find that much of it is arising from recycling refrigerators by independent repair shops in China. But that isn’t the only problem. CFC-11 is also being manufactured illicitly in China for the production of polyurethane insulation.
It’s a big deal. The ozone layer reduces the flux of ultraviolet radiation reaching the earth’s surface protecting us from skin cancer, eye cataracts and other problems.
So what is the connection between refrigerants and the ozone layer? Are the refrigerants in use today safer? And what of the future – are even safer refrigerants under development? And what do we do about legacy refrigerants that continue to harm the environment?
A brief history of refrigerants
The history of refrigeration based on the compression and expansion of gasses dates back to the late 18thcentury. In the early days just about any gas that could be compressed into a liquid was used. While refrigerants with higher masses transferred more heat, those with lower masses required less energy to compress. Unfortunately it turned out that the most efficient refrigerants tended to be highly toxic or inflammable. The main ones were ammonia (NH3), sulphur dioxide (SO2) and methyl chloride (CH3Cl)
Chlorofluorocarbons make an appearance
Needless to say, there were many safety issues which led chemists to design alternatives, though some, such as ammonia, still find application. They came up with a class of chemicals called chlorofluorocarbons (CFCs) which are hydrocarbons containing chlorine and fluorine. CFCs are non-toxic and non-flammable. Although they have a relatively high mass, they can easily be compressed to a liquid and transfer a high quantity of heat as they evaporate. Thus, CFCs are, in many ways, the perfect refrigerant. They also found multifarious uses as solvents, propellants, foam blowing agents, and fire extinguishers.
Ozone hole appears over the Antarctic
CFCs are highly inert, so they hang around in the environment. One of the few things that break them down is ultraviolet radiation, which leads to a substantial environmental problem. When CFCs are released into the atmosphere, they eventually reach the stratosphere. Here they are broken down by ultraviolet radiation from the sun, releasing chlorine radicals. The chlorine reacts with ozone (O3) in the ozone layer to produce oxygen (O2), but the reaction generates more chlorine radicals which go on to break down more ozone. In fact, a single chlorine atom destroys on average 100,000 ozone molecules.
Ozone depletion was discovered by the British Antarctic Survey teamin 1985, and within two years the first Montreal Protocol mentioned in the introduction was signed with the aim of protecting the ozone layer. As a result, the use of CFCs was phased out.
As a replacement for CFCs, chemists developed two alternative refrigerant classes: hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). These have similar refrigerant properties to CFC, with the advantage they do not react with ultraviolet radiation to produce chlorine radicals, so they don’t destroy the ozone layer. Also, they are less inert than CFCs and break down photochemically before they reach the stratosphere.
Although significantly more expensive to produce than CFCs, for a while they appeared to offer an excellent solution, but then an entirely different problem came to light.
Although HCFCs and HFCs don’t damage the ozone layer, they are potent greenhouse gasses and play a significant role in climate change. This also applies to CFCs. Although their atmospheric concentrations are low, their contribution to climate change is high.
The impact of gasses on climate change depends on their global warming potential (GWP), which is a combination of their ability to trap heat and their persistence in the atmosphere. The GWP of the common greenhouse gas carbon dioxide (CO2)is standardised as 1 (GWP = 1). By comparison, the GWP of CFC-12 is 10,200; and the GWP of HCFC-22 is 1,760.
As a result of this, revisions to the Montreal Protocol now call for phasing out of HCFC-R22 by 2020 and a complete ban on all HCFCs by 2030.
Climate-friendly alternative refrigerants
A wide range of alternative climate-friendly refrigerants exist and are available, though currently there is no universal solution. Different kinds of products and different operating conditions require different refrigerants. A problem, however, is that many of them suffer from the same problems as those we describe in the introduction: they are toxic, inflammable, or both.
Ammonia is one of these. Although it was one of the original refrigerants, it has never fallen entirely out of use; it is used extensively in a variety of situations from air conditioning to food preservation. Although toxic, this is mitigated by its pungent odour that is apparent well before toxic levels are reached. With a GWP of zero, its use is likely to continue into the future.
By definition,it has a GWP of 1, and it’s characteristics make it useful for cooling intense heat loads such as servers used in bitcoin mining and similar applications. Special equipment is required to deal with the high pressures involved, but its use as a refrigerant for specialist applications is likely to continue into the future.
One class of refrigerants that is receiving considerable attention is Hydrofluoroolefins (HFOs). These are unsaturated organic molecules containing carbon, hydrogen and fluorine. They have zero potential for damaging the ozone layer, and their GWPs are relatively low – just 0.1 per cent of HCFCs. Unlike HCFCs and CFCs, when released in the atmosphere HFOs are unstable with typical lifetimes of 10 to 22 days. While some HFOs are inflammable, which may limit their use in specific applications, most are non-flammable.
Are HFOs the panacea of refrigerants for the future?
So, are HFOs the perfect future refrigerants? An extensive Study on the environmental and health effects of HFO refrigerants published in December 2017 comes up with mainly positive conclusions.
The report identifies HFOs such as HFO-1234yf that are currently in use and those such as HFO-1336mzz that are likely to be used in the future. Although these have short lifetimes once released into the atmosphere, their breakdown products may be potentially damaging. Typically these include trifluoroacetic acid (TFA), hydrofluoric acid (HF), hydrochloric acid (HCl), formic acid and carbon dioxide. However, there is no evidence currently of their adverse environmental impact. Similarly, so far no health hazards associated with HFOs for workers have been identified.
Refrigerants have gone through a long journey and some, such as ammonia first introduced over 150 years ago, continue to be used today and will be into the future. While there are legacy problems with CFCs such as we mentioned initially, these have solutions, and the ozone hole is healing.
HFO’s might not turn out to be the panacea they seem today, but on current evidence,their long-term future appears guaranteed. We consider the way forward a 3 step approach from HFO with Low GWP, Low flammability and natural gases and manufacturers looking at heat Pump systems with zero GWP systems.
With Natural refrigerants and innovative technologies DPAC UK has developed an innovative product/technology for the green cooling sector. As a member DPAC UK supports the Green Cooling Initiative in its efforts to promote natural refrigerants, innovative technological products and protect the environment, resources and the climate.
This article is written by Simon Lamberton-Pine of DPAC UK Ltd
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