Refrigeration is a Gas
Throughout most of the history of commercial refrigeration, the industry has primarily relied on synthetic refrigerants. But beginning in 1987, the Montreal Protocol set out a pattern for identifying and then attempting to regulate and eventually curtail the use of these substances that were found to be environmentally harmful. One, in particular, that was the most widely used refrigerant at the time (R12, Freon-12 or Freon for short), was found to be a threat to the ozone layer which protects life from the harmful effects of the sun’s ultraviolet radiation, and even more so a contributor to global warming.
The class of refrigerants based on chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) that includes R-12 and R-22 among others have been on a path toward the discontinuation of their use since a timeline was established by the Montreal Protocol. That timeline calls for the complete elimination of CFC and HCFCs by the end of this decade.
The common ingredient in both CFC and HCFC refrigerants is chlorine. Although the chlorine in these compounds is detrimental to the ozone layer, its effect (indicated by its ozone depletion potential or ODP) is of otherwise lower impact on the environment (apart from the ozone layer) than that of other commercially used synthetic refrigerants. Global warming potential (GWP) is of critical environmental consequence and many of these other refrigerants have significantly higher GWP numbers than that of CFC/HCFCs.
Following Montreal, Kyoto and more recently Paris, international agreements have built upon that initial effort to more substantially reduce and eliminate synthetic refrigerants. As part of this movement away from CHCs and HCFCs, another class of refrigerants, HFCs such as R134a were widely adopted. But HFCs were also found to be environmentally harmful as well.
International agreements have not been the only factor in the move away from synthetic refrigerants. Government regulation has played a significant part domestically in changing the industry. Here in the US, these include the Clean Air Act along with an alphabet soup of acronyms like EPA/SNAP, DOE, CARB and others. In Europe, EU F-gas regulations are yet another example. Regardless of where these regulations have been put in place however, the effect upon the industry has been profound.
Although the industry has responded with the search for environmentally safe synthetic alternatives, one of the most popular solution so far has been to initially limit the volume of these substances used such as through an approach called secondary loop systems, and then later through the eventual elimination of them entirely from the use by replacing them with natural refrigerants. This has resulted initially in glycol refrigeration systems which use a secondary loop approach. This approach limits the synthetic refrigerant to a small space where most of the refrigeration equipment in a store is housed.
Heat is transferred from the display cases and walk-ins to that part of the system through chilled loop piping that carries a propylene glycol solution which is a food-safe, environmentally friendly material.
More recently, with the arrival in the industry of carbon dioxide (CO2) first as another type of secondary fluid for low-temperature applications such as for frozen food door cases and walk-in freezers, and then later on as both a medium and low-temperature refrigerant through the development of