With modern shifts in the regulatory environment and strident steps being taken to reduce global warming and ozone depletion, refrigeration manufacturers have been working towards utilizing refrigerants with low global warming potential (GWP) and ozone depletion potential (ODP). Foremost among these “green” refrigerants are hydrocarbons (HC’s) and carbon dioxide (CO2), which have been experiencing a surge of use around the world. Understanding why these refrigerants are currently popular, and in particular why HC’s have become the refrigerant of choice in the modern world over CO2, requires taking a look at both the history of their use and how they are being used today.
History of CO2 and HC’s as Refrigerants
Belying their resurgence as green refrigerants today, both CO2 and HC’s have a long history of use as refrigerants. Although CO2 had begun to be experimented with as a refrigerant around the mid 19th century, the first compressor designed around utilizing it wasn’t introduced until 1886 by Franz Windhauzen. Most of the refrigeration units at that time were utilizing either ammonia or Sulphur dioxide, which were extremely noxious chemicals that had also caused explosions in failing systems. Ammonia based systems were also highly inefficient, and more expensive, further increasing the appeal of transitioning to CO2. CO2, on the other hand, was inexpensive, non-toxic, and non-flammable, which led to its use in a variety of different refrigeration applications. Particularly, systems that used small-sized compressors, such as food storage in kitchens, restaurants, on ships, and in hospitals were ideal for CO2 based refrigeration units. As designs continued to develop, use of CO2 outside of food storage began to be seen, with units commonly used for comfort systems in hotels, theaters, and restaurants.
Competing alongside CO2 and ammonia based refrigeration systems, HC based systems were in use throughout the early 20th century as well. HC’s were first used as refrigerants as early as 1867, and remained in use on a limited level until the introduction of chlorofluorocarbon (CFC) refrigerants in the 1930’s. A number of different constraints limited the use of HC’s at their early inception, and continued to limit their use until relatively recently. Primarily, HC’s flammability and volatility were higher than other refrigerants at the time, and there were technological limitations allowing for the safe widespread implementation of HC based devices.
The environmental impact of commonly used refrigerants today, such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), along with regulatory changes limiting or eliminating their use, has resulted in a resurgence of interest and use in HC refrigerants. There are a number of different HC’s in use as refrigerants, including propane, butane, propylene, cyclopropane, isobutene, and dimethyl ether. These substances consist primarily of hydrogen and carbon, are naturally occurring substances, and can be produced as byproducts of distillation. This makes them widely available and inexpensive for use as refrigerants.
However, the most appealing aspect of utilizing HC’s as refrigerants is their effect on the environment; they have zero ODP and very low GWP. Despite their low toxicity, and low environmental impact, until recently the use of HC’s as refrigerants was limited due to their flammability. However, with proper handling and within a closed system HC’s have been proven to be a safe alternative to HFC’s and other environmentally unfriendly refrigerants. Additionally, HC’s have been shown to be more efficient than less environmentally friendly refrigerants when used as a drop-in replacement in certain systems.
The use of HC’s as a replacement to environmentally damaging refrigerants is a positive direction for both consumers and the environment. HC’s cost less, are less toxic to both humans and the environment, and operate more efficiently than other systems. Other countries throughout the world have already begun transitioning to HC based systems, with India and China in particular beginning to widely use HC’s in domestic refrigerators. As more countries continue to adopt HC’s, the efficiency of refrigeration units, from large double or single door refrigerators to small countertop coolers, will rise while the environmental impact will continue to decrease.
 William S. Bodinus, “The Rise and Fall of Carbon Dioxide Systems,” ASHRAE Journal April, 1999: 37.